Cardiovascular System Notes

BIO 301
Human Physiology
Cardiovascular system

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The Cardiovascular System:

• consists of the heart plus all the blood vessels
• transports blood to all parts of the body in two 'circulations': pulmonary (lungs) & systemic (the rest of the body)

Heart:

• hollow, muscular organ
• 4 chambers: 2 atria (right & left) & 2 ventricles (right & left)

Blood returning from the systemic (body) circulation enters the right atrium (via the inferior & superior vena cavas). From there, blood flows into the right ventricle, which then pumps blood to the lungs (via the pulmonary artery). Blood returning from the lungs enters the left atrium (via pulmonary veins), then the left ventricle. The left ventricle then pumps blood to the rest of the body (systemic circulation) via the aorta.

 
Cardiovascular system
 
Heart anatomy and function
 

Path of a red blood cell
 

Heart walls - 3 distinct layers:

1 - endocardium - innermost layer; epithelial tissue that lines the entire circulatory system 2 - myocardium - thickest layer; consists of cardiac muscle 3 - epicardium - thin, external membrane around the heart

Cardiac muscle tissue:

• striated (see photo below; consists of sarcomeres just like skeletal muscle)
• cells contain numerous mitochondria (up to 40% of cell volume)
• adjacent cells join end-to-end at structures called intercalated discs

Intercalated discs contain two types of specialized junctions:

• desmosomes (which act like rivets & hold the cells tightly together) and
• gap junctions (which permit action potentials to easily spread from one cardiac muscle cell to adjacent cells).

http://en.wikipedia.org/wiki/Gap_junctions

Cardiac muscle tissue forms 2 functional syncytia or units:

• the atria being one &
• the ventricles the other.

Because of the presence of gap junctions, if any cell is stimulated within a syncytium, then the impulse will spread to all cells. In other words, the 2 atria always function as a unit & the 2 ventricles always function as a unit. However, there are no gap junctions between atrial & ventricular contractile cells. In addition, the atria & ventricles are separated by the electrically nonconductive tissue that surrounds the valves. So, as will be discussed later, a special conducting system is needed to permit transmission of impulses from the atria to the ventricles. In cardiac muscle, there are two types of cells:

• contractile cells &
• autorhythmic (or automatic) cells.

Contractile cells, of course, contract when stimulated. Autorhythmic cells, on the other hand, are self-stimulating & contract without any external stimulation. The action potentials that occur in these two types of cells are a bit different:
On the left is the action potential of an autorhythmic cell; on the right, the action potential of a contractile cell. Autorhythmic cells exhibit PACEMAKER POTENTIALS. Depolarization is due to the inward diffusion of calcium (not sodium as in nerve cell membranes). Depolarization begins when:

• the slow calcium channels open (4),
• then concludes (quickly) when the fast calcium channels open (0).
• Repolarization is due to the outward diffusion of potassium (3).

Used with permission: http://mail.bris.ac.uk/~pydml/CVS/Heart/Cells/Electrics/APpmr.htm In Contractile cells:

• depolarization is very rapid & is due to the inward diffusion of sodium (0).
• repolarization begins with a slow outward diffusion of potassium, but that is largely offset by the slow inward diffusion of calcium (1 & 2). So, repolarization begins with a plateau phase. Then, potassium diffuses out much more rapidly as the calcium channels close (3), and the membrane potential quickly reaches the 'resting' potential (4).

Used with permission: http://mail.bris.ac.uk/~pydml/CVS/Heart/Cells/Electrics/APpmr.htm

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Most of the muscle cells in the heart are contractile cells. The autorhythmic cells are located in these areas:

• Sinoatrial (SA), or sinus, node
• Atrioventricular (AV) node
• Atrioventricular (AV) bundle (also sometimes called the bundle of His)
• Right & left bundle branches
• Purkinje fibers

Various automatic cells have different 'rhythms': SA node - 60 - 100 per minute (usually 70 - 80 per minute)
AV node & AV bundle - 40 - 60 per minute
Bundle branches & Purkinje fibers - 20 - 40 per minute
SA node = has the highest or fastest rhythm &, therefore, sets the pace or rate of contraction for the entire heart. As a result, the SA node is commonly referred to as the PACEMAKER.
 
Spread of cardiac excitation (check this animation: Conducting System of the Heart):

• Begins at the SA node & quickly spreads through both atria
• Also travels through the heart's 'conducting system' (AV node > AV bundle > bundle branches > Purkinje fibers) through the ventricles
• For efficient pumping:
• The atria should contract (& finish contracting) before the ventricles contract. This occurs because of AV nodal delay (that is, the impulse travels rather slowly through the AV node & this permits the atria to complete contraction before the ventricles begin contraction).
• The atria should contract as a unit, & the ventricles should contract as a unit. This occurs because the impulse spreads so rapidly that all myocardial cells in the atria and ventricles, respectively, contract at about the same time. The impulse spreads rapidly through the ventricles because of the conducting system.

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Refractory period of contractile cells:

• Lasts about 250 msec (almost as long as contraction period)

The long refractory period means that cardiac muscle cannot be restimulated until contraction is almost over & this makes summation (& tetanus) of cardiac muscle impossible. This is a valuable protective mechanism because pumping requires alternate periods of contraction & relaxation; prolonged tetanus would prove fatal.

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Electrocardiogram (ECG) = record of spread of electrical activity through the heart
P wave = caused by atrial depolarization
QRS complex = caused by ventricular depolarization
T wave = caused by ventricular repolarization
ECG = useful in diagnosing abnormal heart rates, arrhythmias, & damage of heart muscle

Electrocardiogram

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Coronary artery disease (CAD) is a condition in which plaque builds up inside the coronary arteries that supply heart muscle with oxygen-rich blood. Plaque is made up of fat, cholesterol, calcium, and other substances found in the blood. When plaque builds up in the arteries, the condition is called atherosclerosis. Plaque narrows the arteries and reduces blood flow to your heart muscle. It also makes it more likely that blood clots will form and partially or completely block blood flow. When coronary arteries are narrowed or blocked, oxygen-rich blood can't reach the heart muscle. This can cause angina or a heart attack. Angina is chest pain or discomfort that occurs when not enough blood flows to an area of heart muscle. A heart attack occurs when blood flow to an area of heart muscle is completely blocked. This prevents oxygen-rich blood from reaching that area of heart muscle and causes it to die. Without quick treatment, a heart attack can lead to serious problems and even death. Over time, CAD can weaken heart muscle and lead to heart failure and arrhythmias. Heart failure is a condition in which your heart can't pump enough blood throughout your body. Arrhythmias are problems with the speed or rhythm of your heartbeat. CAD is the most common type of heart disease. It's the leading cause of death in the United States for both men and women. Lifestyle changes, medicines, and/or medical procedures can effectively prevent or treat CAD in most people (Source: NHLBI).

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Heart Valves:

• Atrioventricular (AV) valves - prevent backflow of blood from ventricles to atria during ventricular systole (contraction)
• Tricuspid valve - located between right atrium & right ventricle
• Mitral valve - located between left atrium & left ventricle

• Semilunar valves - prevent backflow of blood from arteries (pulmonary artery & the aorta) to ventricles during ventricular diastole (relaxation)
• Aortic valve - located between left ventricle & the aorta
• Pulmonary valve - located between right ventricle & the pulmonary artery (trunk)

All valves consist of connective tissue (not cardiac muscle tissue) and, therefore, open & close passively. Valves open & close in response to changes in pressure:

• AV valves - open when pressure in the atria is greater than pressure in the ventricles (i.e., during ventricular diastole) & closed when pressure in the ventricles is greater than pressure in the atria (i.e., during ventricular systole)

• Semilunar valves - open when pressure in the ventricles is greater than pressure in the arteries (i.e., during ventricular systole) and closed when pressure in the pulmonary trunk & aorta is greater than pressure in the ventricles (i.e., during ventricular diastole)

 
 
Heart valves & function

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Cross-section of a healthy heart, including the four heart valves. The blue arrow shows the direction in which oxygen-poor blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body.

Heart valve disease is a condition in which one or more heart valves don't work properly, making the heart work harder and affecting its ability to pump blood. Malfunctioning heart valves can create two basic problems: (1) Regurgitation, or backflow, occurs when a valve doesn’t close tightly. Blood leaks back into the chamber rather than flowing forward through the heart or into an artery. Backflow is most often due to prolapse (the flaps of the valve flop or bulge back into an upper heart chamber during a heartbeat). (2) Stenosis occurs when the flaps of a valve thicken, stiffen, or fuse together. This prevents the heart valve from fully opening, and not enough blood flows through the valve. You can be born with heart valve disease (congenital) or you can acquire it later in life. Although a valve may be normal at first, disease can cause problems to develop over time. Many people have heart valve defects or disease, but don't have symptoms. For some people, the condition will stay largely the same over their lifetime and not cause any problems. For other people, the condition can worsen slowly over time until symptoms develop. If not treated, advanced heart valve disease can cause heart failure, stroke, blood clots, or sudden death due to cardiac arrest. Lifestyle changes and medicines can relieve many of the symptoms and problems linked to heart valve disease, and can also lower the risk of developing a life-threatening condition, such as stroke or sudden cardiac arrest. Eventually, however, faulty heart valves may have to be repaired or replaced (Source: NHLBI).

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Mechanical Events of the Cardiac Cycle:     (also check www-medlib.med.utah.edu/kw/pharm/hyper_heart1.html and McGraw-Hill.com)

• the cardiac cycle has two phases: systole (contraction) & diastole (relaxation)
• 'Electrical' events are correlated with the 'mechanical' events:
• P wave = atrial depolarization = atrial systole
• QRS complex = ventricular depolarization = ventricular systole (& atrial diastole occurs at the same time)
• T wave = ventricular repolarization = ventricular diastole
• What happens in the heart during each 'mechanical' event:
• Atrial systole (labeled AC below):
• no heart sounds (because no heart valves are opening or closing)
• a slight increase in ventricular volume because blood from the atria is pumped into the ventricles
• Ventricular systole:
• the first heart sound (lub) (labeled S1 below) - this sound is generated by the closing of the AV valves (& this occurs because increasing pressure in the ventricles causes the AV valves to close)

• initially there is no change in ventricular volume (called the period of isometric contraction) because ventricular pressure must build to a certain level before the semilunar valves can be forced open & blood ejected. Once that pressure is achieved, & the semilunar valves do open, ventricular volume drops rapidly as blood is ejected.
• Ventricular diastole:
• the second heart sound (dub) (labeled S2 below) - this sound is generated by the closing of the semilunar valves (& this occurs because pressure in the pulmonary trunk & aorta is now greater than in the ventricles & blood in those vessels moves back toward the area of lower pressure which closes the valves)
• ventricular volume increases rapidly (period of rapid inflow) - this occurs because blood that accumulated in the atria during ventricular systole (when the AV valves were closed) now forces open the AV valves (because the pressure in the atria is now greater than the pressure in the ventricles). & flows quickly into the ventricles. After this 'rapid inflow', ventricular volume continues to increase, but at a slower rate (the period of diastasis). This increase in volume occurs as blood returning to the heart via the veins largely flows through the atria & into the ventricles.

Used with permission: http://mail.bris.ac.uk/~pydml/CVS/Heart/Whole/CardCyc/CCprvo.htm
 




Human heart

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Cardiac output:

• volume of blood pumped by each ventricle
• equals heart rate (beats per minute) times stroke volume (milliliters of blood pumped per beat)
• typically about 5,500 milliliters (or 5.5 liters) per minute (which is about equal to total blood volume; so, each ventricle pumps the equivalent of total blood volume each minute under resting conditions) BUT maximum may be as high as 25 - 35 liters per minute

Cardiac reserve:

• the difference between cardiac output at rest & the maximum volume of blood the heart is capable of pumping per minute
• permits cardiac output to increase dramatically during periods of physical activity

What factors permit variation in cardiac output?

• Changes in heart rate:
• Parasympathetic stimulation - reduces heart rate
• Sympathetic stimulation - increases heart rate

Effect of parasympathetic stimulation on the heart:
Increased parasympathetic stimulation > release of acetylcholine at the SA node > increased permeability of SA node cell membranes to potassium > 'hyperpolarized' membrane > fewer action potentials (and, therefore, fewer contractions) per minute

a = sympathetic stimulation, b = normal heart rate, & c = parasympathetic stimulation

Effect of sympathetic stimulation on the heart:
Increased sympathetic stimulation > release of norepinephrine at SA node > decreased permeability of SA node cell membranes to potassium > membrane potential becomes less negative (closer to threshold) > more action potentials (and more contractions) per minute

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Regulation of Stroke Volume:

• intrinsic control ==> related to amount of venous return (amount of blood returning to the heart through the veins)
• extrinsic control ==> related to amount of sympathetic stimulation

Intrinsic control:

• Increased end-diastolic volume = increased strength of cardiac contraction = increased stroke volume
• This increase in strength of contraction due to an increase in end-diastolic volume (the volume of blood in the heart just before the ventricles begin to contract) is called the Frank-Starling law of the heart:

• Increased end-diastolic volume = increased stretching of of cardiac muscle = increased strength of contraction = increased stroke volume

Source: http://www.sci.sdsu.edu/Faculty/Paul.Paolini/ppp/lecture21/sld006.htm Extrinsic control:

• Increased sympathetic stimulation > increased strength of contraction of cardiac muscle
• Mechanism = sympathetic stimulation > release of norepinephrine > increased permeability of muscle cell membranes to calcium > calcium diffuses in > more cross-bridges are activated > stronger contraction

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Flow rate through blood vessels

• directly proportional to the pressure gradient
• inversely proportional to vascular resistance

Flow = Difference in pressure/resistance Pressure Gradient = difference in pressure between beginning & end of vessel (pressure = force exerted by blood against vessel wall & measured in millimeters of mercury)
Resistance:

• hindrance to blood flow through a vessel caused by friction between blood & vessel walls
• major determinant = vessel diameter (or radius)
• is inversely proportional to radius to the fourth power (so, for example, doubling the radius of a vessel decreases the resistance 16 times which, in turn, increases flow through the vessel 16 times)

Source: http://www.oucom.ohiou.edu/CVPhysiology/H003.htm

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Arteries:

• serve as passageways for blood from heart to tissues
• act as pressure reservoirs because the elastic walls collapse inward during ventricular diastole (when there is less blood in the arteries):

• blood pressure averages 120 mm Hg during systole (systolic pressure) & 80 mm Hg during diastole (diastolic pressure) (& the difference between systolic & diastolic pressures is called the pulse pressure)

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Arterioles:

• distribute cardiac output among systemic organs (whose needs vary over time)
• Resistance (&, therefore, blood flow) varies as a result of VASODILATION & VASOCONSTRICTION
• Factors that influence radius of arterioles:
• intrinsic (or local) control
• extrinsic control

Intrinsic (local) control:

• changes within a tissue that alter the radius of blood vessels & adjust blood flow
• especially important in skeletal muscles, the heart, & the brain
• increased blood flow in an active tissue results from active hyperemia:

Increased tissue (metabolic) activity > increases levels of carbon dioxide & acid in the tissue & decreases levels of oxygen > these changes in the concentrations of acid, CO2, & O2 cause smooth muscle in the walls of the arterioles to relax & this, in turn, causes vasodilation of the arterioles > vasodilation reduces resistance with the vessel &, as a result, blood flow through the vessel increases So, blood flow increases when a tissue (e.g., skeletal muscle) becomes more active & the increased blood flow delivers the needed oxygen & nutrients.
 
Extrinsic control occurs via:

• sympathetic division of the Autonomic Nervous System
• parasympathetic division of the Autonomic Nervous System

The sympathetic division innervates blood vessels throughout the body while the parasympathetic division innervates blood vessels of the external genitals. Varying degrees of stimulation of these two divisions, therefore, can influence arterioles (& blood flow) throughout the body.

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Capillaries

Capillaries:

• site of exchange of materials between blood & tissues
• exchange may occur by simple diffusion
• diffusion enhanced by:
• thin capillary walls (just one cell thick)
• narrow capillaries (so the red blood cells & plasma are close to the walls)
• large numbers (the human body has 10 - 40 billion capillaries!) which translates into a tremendous amount of surface area through which exchange can occur
• relatively slow flow of blood (providing more time for exchange to occur)
• exchange also occurs through pores (located between the cells the form the capillary walls), by vesicular transport (e.g., pinocytosis), & by bulk flow

BULK FLOW:

• protein-free plasma filters out of capillaries, mixes with surrounding interstitial fluid, & is then reabsorbed. Plasma filters out at the arteriole end of capillaries because hydrostatic (blood) pressure (an outward force) exceeds osmotic pressure (an inward force). At the venous end of capillaries, the filtrate tends to move back in because osmotic pressure now exceeds hydrostatic pressure (check this animation at mcgraw-hill.com).
• because the outward force at the arteriole end exceeds the inward force at the venous end, more plasma filters out than moves back in to the capillaries. So, fluid tends to accumulate in the tissues. The lymph vessels pick up this fluid & transport it back to the blood.

BULK FLOW:

1 - not very important in exchange (much more exchange occurs by way of diffusion) 2 - important in regulating the 'distribution' of fluids between the plasma & interstitial fluid (which is important in maintaining normal blood pressure)

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Veins:

• serve as low-resistance passageways to return blood from the tissues to the heart
• serve as a BLOOD RESERVOIR (under resting conditions nearly two-thirds of all your blood in located in the veins) &, therefore, the veins are important in permitting changes in stroke volume

Cardiovascular System Notes

Cardiovascular System Notes in Physiology

Notes on the Cardiovascular System:

Veins and arteries differ in structure

• Left ventricle is thickest because it squeezes the hardest to get blood thoughout the body.

2 types of circulation:

• Pulmonary circulation (involves lung only)
• Systemic circulation (blood leaving the LV dispersed throughout body, and comes back to RA)

Systole-when ventricles are contracted, and atria relaxed and filling with blood (duration is 0.3 second)
Diastole—when ventricles are relaxing and filling, atria are contracting. (duration is 0.5 seconds)

Each complete heartbeat is less than one second (because normal resting is 70bpm)

Three different kinds of heart cells

• Pacemaker cells
  • Autorhythmic myocardia (cause excitation/contraction rhythmically)
  • Found in various heart regions, but typically in the nodes of the heart
    • Sinoatrial node SA node—roof of right atrium
    • Atrioventricular AV node—found at floor of right atrium
      •  (node is cluster of pacemaker cells)
  • Set the pace in terms of heartbeat. SA node starts the signal, sending to AV node, which sends to conduction myofiber

• Conduction myofibers
  • Found in Atrioventricular bundle (Bundle of His) fibers run down between right and left ventricles and throughout the ventricles. Now these fibers are called Purkinje fibers. Purkinje fibers allows signals to be spread/conducted to various parts of the heart

• Contractile Myocardium
  • Actual contractile cells. Millions of cells in the ventricles and atrial walls that contract at same time to perform a heartbeat.

Heart EKG Technique


Three applications of Calmodulin:

1. Calcium calmodulin—promotes Exocytosis
2. Calcium calmodulin in smooth muscle--Activates myosin light chain kinases
1. Small protein associated with myosin head
3. Calcium calmodulin in growth hormone—activates phosphodiesterase
1. Turns cyclic amp (cAMP) into AMP.
2.  GH opposes glucagon because decrease in cAMP decreases glucagon.

Cardiac Output

Cardio Output = Heart Rate x Stroke Volume

• The amount of blood the heart pumps in a minute.
• Can vary dramatically depending on activity level.
• At resting 5L per min.
• After exercise (close to aerobic capacity) can be 25 Liters/min.

  Heart Rate: Number of beats per minute.
  
  
  
  Stroke Volume: The amount of blood pumped per heart beat.
  

Brief notes on Venous Return

Cardiac Blood Flow

Definition of high blood pressure (hypertension)

What is hypotension?

 

Other Cardiovascular System Topics

Atheriosclerosis

What is Ischemia?

What is Syncope?

Cause of Edema

alkali earth metals

7.5. The reaction of s-block metals and oxygen & their oxide (O^2-) chemistry

The oxides and hydroxides are white ionic solids.

• The reaction of Group 1 metals with oxygen (a redox reaction)
• Group 1 metals: 4M_(s) + O_2(g) ==> 2M₂O_(s)    (M = Li, Na, K, Rb, Cs)
  • shows the formation of the 'simple' oxide expected from their position in the periodic table when the element is heated or burned in air.
  • Oxidation state changes: M is 0 to +1, Oxygen is 0 to -2 in the oxide ion O^2-.
    • ionically: 4M_(s) + O_2(g) ==> 2(M⁺)₂O^2-_(s)
      • the metal is oxidised (0 to +1), electron loss, increase in oxidation state
      • oxygen molecules are reduced (0 to -2), electron gain, decrease in oxidation state
  • The oxides are soluble in water forming the strongly alkaline hydroxide:
    • M₂O_(s) + H₂O_(l) ==> 2MOH_(aq)
    • ionically: (M⁺)₂O^2-_(s) + H₂O_(l) ==> 2M⁺_(aq)  +  2OH^-_(aq) (not a redox change)
      • This is an acid-base reaction, the O^2- ion is a strong Bronsted-Lowry base and accepts a proton from water (acting as the Bronsted-Lowry acid).
  • Unfortunately, except for lithium (an anomaly), 'higher' oxides can be formed e.g.
  • 2M_(s) + O_2(g) ==> M₂O_2(s)  [redox change, M (0 to +1), O (0 to -1)]
    • shows the formation of the yellow-orange peroxide by Na, K, Rb and Cs
    • each oxygen is in the -1 oxidation state in the peroxide ion O₂^2- 
    • they readily hydrolyse with water forming hydrogen peroxide
      • M₂O_2(s) + 2H₂O_(l) ==> 2MOH_(aq) + H₂O_2(aq)  (not a redox change)
  • M_(s) + O_2(g) ==> MO_2(s)  shows the formation of the 'superoxide' by K, Rb and Cs
    • oxidation number changes are M from 0 to +1 as expected, but on average each oxygen changes from 0 to  -¹/₂  in the superoxide ion O₂^- 
    • 2MO_2(s) + 2H₂O_(l) ==> 2MOH_(aq) + H₂O_2(aq) + O_2(g)  (redox change)
    • oxidation state changes: M and H no change (+1), four O's change from  -¹/₂  in superoxide ions to two of -1 in the peroxide molecule and two at zero in the oxygen molecule.
      • This is a case of disproportionation where the oxidation state of an element gives a higher and lower state product from the same 'original species'.
• The simple oxides readily dissolve in acids and are neutralised to form salts.
  • M₂O_(s) + 2HCl_(aq) ==> 2MCl_(aq) + H₂O_(l)   (M = Li, Na, K, Rb, Cs)
    • to give the soluble chloride salt
    • ionically: (M⁺)₂O^2-_(s) + 2H⁺_(aq) ==> 2M⁺_(aq) + H₂O_(l)  (not a redox change)
      • Acid-base reaction, acid donates proton the oxide ion base, applies to all four examples.
      • The chloride Cl^-, nitrate NO₃^- and sulphate SO₄^2- are spectator ions.
  • M₂O_(s) + 2HNO_3(aq) ==> 2MNO_3(aq) + H₂O_(l) to give the soluble nitrate salt
  • M₂O_(s) + H₂SO_4(aq) ==> M₂SO_4(aq) + H₂O_(l) to give the soluble sulphate salt
  • M₂O_(s) + 2CH₃COOH_(aq) ==> 2CH₃COOM_(aq) + H₂O_(l) to give the soluble ethanoate salt

• The reaction of Group 2 metals with oxygen (a redox reaction)
• Group 2 metals:  2M_(s) + O_2(g) ==> 2MO_(s)    (M = Be, Mg, Ca, Sr, Ba)
  • shows the formation of the oxide expected from their position in the periodic table when the element is heated or burned in air. Oxidation state changes: M from 0 to +2, and oxygen from 0 to -2.
  • The oxide, apart from beryllium, is slightly soluble in water forming the alkaline hydroxide, which increases in strength of basic character down the group.
    • MO_(s) + H₂O_(l) ==> M(OH)_2(s/aq)   (not a redox change, M = Be, Mg, Ca, Sr, Ba)
      • ionically: M²⁺O^2-_(s) + H₂O_(l) ==> M(OH)_2(s/aq)
        • if the hydroxide is soluble: M²⁺O^2-_(s) + H₂O_(l) ==> M²⁺_(aq) + 2OH^-_(aq)
        • Bronsted-Lowry acid-base reaction, the oxide base accepts proton from the water.
        • The mixture of magnesium hydroxide and water is sometimes called milk of magnesia.
        • The formation of calcium hydroxide (slaked lime) when water is added to calcium oxide (quicklime) is very exothermic!
        • The pH of the resulting solution ranges from ~pH 10 to ~pH 13 for Mg(OH)₂ to Ba(OH)₂
    • All the oxides are basic and readily neutralised by acids (not a redox change).
      • MO_(s) + 2HCl_(aq) ==> MCl_2(aq) + H₂O_(l)   (M = Be, Mg, Ca, Sr, Ba)
        • to give the soluble chloride salt
        • ionically: M²⁺O^2-_(s) + 2H⁺_(aq) ==> M²⁺_(aq) + H₂O_(l) 
        • This applies to all four acid reactions examples in this section, acid proton donation to the oxide ion base.
        • In each case the chloride Cl^-, nitrate NO₃^- and sulphate SO₄^2- are spectator ions.
    • MO_(s) + 2HNO_3(aq) ==> M(NO₃)_2(aq) + H₂O_(l)   (M = Be, Mg, Ca, Sr, Ba)
      • to give the soluble nitrate salt
    • MO_(s) + H₂SO_4(aq) ==> MSO_4(aq/s) + H₂O_(l)    (M = Be, Mg, Ca, Sr, Ba)
      • to form the sulphate salt (soluble => insoluble)
      • but reaction increasingly slower for calcium oxide ==> barium oxide as the sulphate becomes less insoluble.
    • MO_(s) + 2CH₃COOH_(aq) ==> (CH₃COO)₂M_(aq) + H₂O_(l)  (M = Be, Mg, Ca, Sr, Ba)
      • to give the ethanoate salt
    • Beryllium oxide BeO is amphoteric (another Be Gp 2 anomaly) and dissolves in strong bases like sodium hydroxide.
      • The equation below shows the formation of a hydroxo beryllate complex ion (not a redox change).
      • BeO_(s) + 2NaOH_(aq) + H₂O_(l) ==> Na₂[Be(OH)₄]_(aq) (beryllate salt)
      • ionically: Be²⁺O^2-_(s) + 2OH^-_(aq)  + H₂O_(l) ==> [Be(OH)₄]^2-_(aq)  

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7.6. Reaction of s-block metals and water & their hydroxide (OH^-) chemistry

The oxides and hydroxides are usually white ionic solids.

• The reaction of group 1 metals with water (a redox reaction)
• Group 1 metal hydroxide formation
  • 2M_(s) + 2H₂O_(l) ==> 2M⁺OH^-_(aq) + H_2(g)   (M = Li, Na, K, Rb, Cs)
  • shows the formation of the alkaline metal hydroxide and hydrogen.
    • Oxidation state changes: M from 0 to +1, one H per water remains unchanged in oxidation number and one changes from +1 to 0 in H₂.
  • M = Li (slow at first), Na (fast), K (faster - may ignite hydrogen to give a lilac coloured flame* from hot potassium atoms), Rb, Cs, Fr (very explosive) i.e. the reactivity increases down the group.
    • The reactivity trend is explained in section 7.4
    • * 2H_2(g) + O_2(g) ==> 2H₂O_(l)  i.e. the chemistry of the lit splint pop!
  • The hydroxides, MOH, are white ionic solids, all very soluble (except  LiOH), strong bases, getting stronger down the group.
    • All Group 1 hydroxides are soluble in water giving strongly alkaline solutions,
    • and their aqueous solutions readily neutralised by acids (not a redox change) e.g.
    • MOH_(aq) + HCl_(aq) ==> MCl_(aq) + H₂O_(l)   (M = Li, Na, K, Rb, Cs)
      • to give the soluble chloride salt*
      • ionically: OH^-_(aq) + H⁺_(aq) ==> H₂O_(l)  
      • an acid-base reaction, same for all four examples in this section
    • MOH_(aq) + HNO_3(aq) ==> MNO_3(aq) + H₂O_(l)   (M = Li, Na, K, Rb, Cs)
      • to give the soluble nitrate salt
    • 2MOH_(aq) + H₂SO_4(aq) ==> M₂SO_4(aq) + 2H₂O_(l)   (M = Li, Na, K, Rb, Cs)
      • to give the soluble sulphate salt
    • MOH_(aq) + CH₃COOH_(aq) ==> CH₃COOM_(aq) + H₂O_(l)   (M = Li, Na, K, Rb, Cs)
      • to give the soluble ethanoate salt CH₃COO^-M⁺
    • * The hydroxide solutions are readily titrated with standardised hydrochloric acid (burette) using phenolphthalein indicator, the colour change is from pink to colourless.

• The reaction of group 1 metals with water (a redox reaction)
• Group 2 metal hydroxide formation
  • M_(s) + 2H₂O_(l) ==> M(OH)_2(aq/s) + H_2(g)    (M = Mg, Ca, Sr, Ba)
  • shows the formation of the hydroxide and hydrogen with cold water.
  • ionically: M_(s) + 2H₂O_(l) ==> M²⁺_(aq) + 2OH^-_(aq) + H_2(g)
  • oxidation number changes, M is 0 to +2, for one H per water it changes from +1 to 0 in H₂.
  • M = Be (no reaction, anomalous), Mg (very slow reaction), Ca, Sr, Ba (fast to very fast).
    • i.e. the reactivity increases down the group.
    • The reactivity trend for Group 2, and its explanation, are similar to that above for the Group 1 Alkali Metals.
    • The reactivity trend for s-block metals is explained below
    • Magnesium hydroxide and calcium hydroxide (limewater) are sparingly soluble, but the solubility increases down the group, so barium hydroxide is moderately soluble.
    • As previously mentioned, a mixture of magnesium oxide/hydroxide and water is sometimes called milk of magnesia and the saturated aqueous solution of calcium hydroxide is called limewater.
• If the metal is heated in steam the oxide is formed:
  • e.g. Mg_(s) + H₂O_(g) ==> MgO_(s) + H_2(g) 
    • NOT an experiment you would do with Alkali Metals! but beryllium gives little reaction.
  • The oxide is formed because the hydroxide is thermally unstable at higher temperatures
    •   M(OH)_2(s) ==> MO_(s) + H₂O_(g)    (M = Be, Mg, Ca, Sr, Ba)
• REACTIVITY TREND THEORY: The Group 1/2 metal gets more reactive down the group because ...
  • When an alkali metal atom reacts, it loses an electron to form a singly positively charged ion.
    • e.g. Na ==> Na⁺ + e^-
    • in terms of electrons 2.8.1 ==> 2.8 and so forming a stable ion with a noble gas electron arrangement.
  • As you go down the group from one element down to the next the atomic radius gets bigger due to an extra filled electron shell as you go down from one period to the next one.
  • This means the outer electron is further and further from the nucleus.
  • This also means the outer electron is also shielded by the extra full electron shell of negative charge.
  • Due to this shielding the effective nuclear charge on the external electron is ~ +1 (~ proton number - number of noble gas inner core electrons).
  • Further more, the effective nuclear charge of ~+1 is acting over a larger 'surface area' as the atomic radius increases.
  • Therefore both of these factors combine to make the outer electron less and less strongly held by the positive nucleus as the atomic number increases (down the group).
  • So, the outer electron is more easily lost, and the M⁺ ion more easily formed, and so the element is more reactive as you go down the group - best seen in the laboratory with their reaction with water.
  • The reactivity argument mainly comes down to increasingly lower ionisation energy down the group (i.e. ease of ion formation) and a similar argument applies to the Group 2 metals, but two electrons are removed to form the cation.
  • The enthalpy change in forming the hydrated cation from the solid metal does not appear to be as important here.
    • At a more advanced and detailed level, this change can be theoretically split into the
    • enthalpies of (i) atomisation, (ii) ionisation, (iii) hydration of gaseous ion ... (BUT not here!).
  • The reactivity trend is also paralleled by the increasingly negative half-cell potential (E^θ_M/M+ and E^θ_M/M2+) down groups, 1 and 2 i.e. increasing potential to acts as a reducing agent - an electron donor.
  • As with water, the reaction of a group 1/2 metal with oxygen or halogens gets more vigorous as you descend the group.
• All the hydroxides are basic with increasing strength down the group and readily neutralised by acids (not redox reactions). Magnesium hydroxide is sparingly soluble in water but the solubility increases down the group.
  • M(OH)_2(aq/s) + 2HCl_(aq) ==> MCl_2(aq) + 2H₂O_(l)    (M = Be, Mg, Ca, Sr, Ba)
    • to give the soluble chloride salt*
    • all base (OH^-) ... acid (H⁺) reactions
    • ionically if soluble the reaction is: OH^-_(aq) + H⁺_(aq) ==> H₂O_(l)  
    • ionically if insoluble: M²⁺(OH^-)_2(s) + 2H⁺_(aq) ==> M²⁺_(aq) + 2H₂O_(l)
  • M(OH)_2(aq/s) + 2HNO_3(aq) ==> M(NO₃)_2(aq) + 2H₂O_(l)    (M = Be, Mg, Ca, Sr, Ba)  
    • to give the soluble nitrate salt
  • M(OH)_2(aq/s) + H₂SO_4(aq) ==> M₂SO_4(aq/s) + 2H₂O_(l)    (M = Be, Mg, Ca, Sr, Ba)  
    • to give the sulphate salt
  • M(OH)_2(aq/s) + 2CH₃COOH_(aq) ==> (CH₃COO)₂M_(aq) + 2H₂O_(l)    (M = Be, Mg, Ca, Sr, Ba)  
    • to give the ethanoate salt
  • * Saturated calcium hydroxide solution (limewater) can be titrated with standardised hydrochloric acid (burette, low molarity) to determine its solubility. You normally use phenolphthalein indicator and the end-point colour change is from pink to colourless.
• The Group 2 hydroxides, M(OH)₂, get more soluble down the group:
  • If the hydroxide more or less insoluble (e.g. for Be and Mg), they can be made by adding excess sodium/potassium hydroxide solution to a solution of a soluble salt of a Group 2 metal e.g. three 'double decompositions' are shown below ...
    • (i) calcium chloride + sodium hydroxide ==> sodium chloride + calcium hydroxide
      • CaCl_2(aq) + 2NaOH_(aq) ==> 2NaCl_(aq) + Ca(OH)_2(s) 
    • (ii) magnesium sulphate + potassium hydroxide ==> potassium sulphate + magnesium hydroxide
      • MgSO_4(aq) + 2KOH_(aq) ==> K₂SO_4(aq) + Mg(OH)_2(s) 
    • (iii) beryllium nitrate + sodium hydroxide ==> sodium nitrate + beryllium hydroxide
      • Be(NO₃)_2(aq) + 2NaOH_(aq) ==> 2NaNO_3(aq) + Be(OH)_2(s) 
    • or ionically: M²⁺_(aq) + 2OH^-_(aq) ==> M(OH)_2(s) for any Group 2 metal M
    • All the hydroxides are white powders or white gelatinous precipitates.
• Beryllium hydroxide is amphoteric (an anomaly in the group), because apart from the reactions above, it dissolves in strong alkalis like sodium hydroxide to form a hydroxo-complex ion salts called 'beryllates' e.g.
  • Be(OH)_2(s) + 2NaOH_(aq) ==> Na₂[Be(OH)₄]_(aq)  (not a redox change)
  • ionically: Be(OH)_2(s) + 2OH^-_(aq) ==> [Be(OH)₄]^2-_(aq) showing formation of a complex ion
• For the reaction of Group 1 and 2 hydroxides with carbon dioxide to form the carbonates and hydrogen carbonates, see section 7.9
• For the thermal decomposition of nitrates see section 7.11
• See also VOLUMETRIC TITRATION QUESTIONS involving acids and group1 /2 alkaline hydroxides

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7.7. The reaction of s-block metals with acids

• Group 1 metals are far too reactive to contemplate adding them to acids in a school laboratory!
• Group 2 metals, apart from beryllium (another anomaly), readily react with acids, with increasing vigour down the group (explanation in section 7.4). A redox reaction to form the soluble chloride salt.
  • M_(s) + 2HCl_(aq) ==> MCl_2(aq) + H_2(g)   (M = Mg, Ca, Sr, Ba)
    • ionically for all four examples: M_(s) + 2H⁺_(aq) ==> M²⁺_(aq) + H_2(g) 
    • oxidation state changes: one M at (0) and two H's at (+1) ==> one M (+2) and two H's at (0)
      • the metal is oxidised, electron loss, increase in oxidation state
      • hydrogen ions are reduced, electron gain, decrease in oxidation state
  • M_(s) + 2HNO_3(aq) ==> M(NO₃)_2(aq) + H_2(g)
    • to form the soluble nitrate salt
    • Looks ok in principle, and does this with Mg and very dilute nitric acid, but rarely this simple, the nitrate(V) ion can get reduced to nasty brown nitrogen(IV) oxide gas (nitrogen dioxide, NO₂) and other products, NO gas?, NO₂^- ion?
  • M_(s) + H₂SO_4(aq) ==> MSO_{4(aq/ s)} + H_2(g)
    • to form soluble ==> insoluble sulphate salt
    • The reaction from magnesium to barium becomes increasingly slower as the sulphate becomes less soluble, it coats the metal, inhibiting the reaction.
  • M_(s) + 2CH₃COOH_(aq) ==> (CH₃COO)₂M_(aq) + H_2(g)  to form soluble ethanoate salt
    • This reaction is much slower than the previous three because ethanoic acid is a weak acid (about 2% ionised, so the fizzing appears a lot less vigorous than the other three acids using solutions of similar molarity).
• In aqueous solutions the metal cations formed are hydrated to aqa-complex ions.
  • not quite the simple isolated ions Mⁿ⁺_(aq) which we use in most equations for brevity.
  • e.g. [M(H₂O)₆]ⁿ⁺_(aq) where n=1 for Gp 1 and n=2 for group 2.
    • There may be several layers of water molecules around the ion, so the six is not the whole story, but is typical for the number of 'nearest neighbours', albeit weakly dative covalently bonded water molecules in this case.
    • The six is called the co-ordination number and each water molecule (or anything else attached to the central metal ion) is called a ligand. 
    • The shape of such an ion is 'octahedral' and its simplified structure is shown above on the right. The middle 'blob' is the metal ion and the six outer 'blobs' are the water molecules.
    • (I will replace with proper diagrams later) 
    • However lithium and beryllium are anomalous (M = Li n = 1, or Be n = 2), because of electronic quantum level restrictions, they can have a maximum co-ordination number of four, so their aqueous cations should be written as [M(H₂O)₄]ⁿ⁺_(aq) which has a tetrahedral shape (shown on the left).
• As described above, The soluble groups 1/2 salt solutions contain the hydrated cations derived from the metal:
  • tetra-aqua cations [Li(H₂O)₄]⁺(aq) and [Be(H₂O)₄]²⁺(aq)
  • or the hexa-aqua ions [M(H₂O)₆]⁺(aq) M = Na, K etc. for Group 1
  • and [M(H₂O)₆]²⁺(aq) where M = Mg, Ca etc. for Group 2
  • The tetraaqua beryllium ion and the hexaaqua magnesium ions generate a slight acidity in their salt solutions due to the significant polarising power of the ions (Be²⁺ very small and double charged, Mg²⁺ double charged) e.g.
  • for beryllium: [Be(H₂O)₄]²⁺(aq) + H₂O(l) [Be(H₂O)₃(OH)]⁺(aq) + H₃O⁺(aq) 
  • or magnesium: [Mg(H₂O)₆]²⁺(aq) + H₂O(l) [Mg(H₂O)₅(OH)]⁺(aq) + H₃O⁺(aq) 

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7.8. The reaction of s-block metals with chlorine & halide (X^-) salts

The salts are white or colourless crystalline solids

• Group 1 metals readily react with halogens (a redox reaction)  
  • e.g. heating the metal in chlorine will cause it to burn forming the chloride
  • 2M_(s) + Cl_2(g) ==> 2MCl_(s)  (redox reaction, M = Li, Na, K, Rb, Cs)
    • Oxidation state changes: M from 0 to +1, X = F, Cl, Br & I from 0 to -1
    • The salt products, M⁺X^-, are white-colourless crystalline ionic solids that dissolve in water to give neutral solutions of about pH 7. The crystalline solids have high melting and boiling points.
    • The solids do not conduct electricity (no mobile ions or electrons) but will conduct and undergo electrolysis when molten or dissolved in water when ions are free to move to electrodes.
  • The halogen is in the -1 oxidation state in the halide ion X^- 
  • The halides of groups 1-2 are important raw materials e.g.
    • sodium chloride ==> sodium hydroxide from rock salt by electrolysis of aqueous solution
    • potassium bromide/iodide ==> elemental bromine/iodine from seawater by oxidation
    • calcium chloride ==> calcium metal by electrolysis of molten chloride
• Group 2 metals (except Be) readily react on heating with halogens (a redox reaction)   
  • e.g. heating in chlorine the chloride is formed
  • M_(s) + Cl_2(g) ==> MCl_2(s)    (M = Mg, Ca, Sr, Ba)
    • Oxidation state changes: M from 0 to +2, X = F, Cl, Br & I from 0 to -1
    • The salt products, M²⁺(X^-)₂,  are similar in properties to the Group 1 M⁺X^- compounds.
    • However, beryllium chloride has a polymeric covalent structure, due to the high polarising influence of beryllium in its +2 oxidation state and the smaller difference in electronegativity between Be-Cl compared to chlorine and the other group 1 and 2 metals.