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Fundamental Chemistry (s,p,d,f,g,h orbitals (First shell only has the s…
Fundamental Chemistry
s,p,d,f,g,h orbitals
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• Third shells has the s, p and d subshells 2+6+10= 18 electrons
• Fourth shell has the s, p d, and f subshells 2+6+10+14=32 electrons
• Fifth shell has the s, p, d, f, and g subshells 2+6+10+14+18=50 electrons
• Sixth shell has the s, p, d, f, g, and h subshells 2+6+10+14+18+22= 72 electrons
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Metals on the left, non metals in the right
Metals - they conduct heat and electricity
Non-metals - poor conductors
Metalloids - characteristics of metals and non metals
Pauling scale
Across the period = increasing electronegativity
Down a group = Decreasing electronegativity
3 types of bonding
- ionic bonding = metal and non metal
- covalent bonding = 2 non metals = share electrons
- metallic bonding = metals
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VSEPR Theory
- Electron group around a central
- Stable when they are far apart as possible.
- Valence shell electron pair repulsion Theory
- Electron are negativity charge - most stable when they are separated as much as possible
- Resulting geometric arrangement allows us to predict shape and bond angles in the molecule.
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pH = power of hydrogen
- a measure of activity of dissolved hydrogens
- In solution hydrogen ions occur as a number of cations including protons (H+) and hydronium ions (H3O+)
- Pure water at 25c = the concentration of hydrogen ions (H+) equals the concentration of hydroxide ions (OH-)
- Neutral corresponds to a pH level of 7
- Solutions where concentration of H+ exceeds OH- have pH value lower than 7. = Acids
- Solutions where OH- exceeds H+ have a pH value greater than 7. = bases
pH is dependent on ionic activity
Weak and strong acids or bases do not refer to the pH value
- It describes how well an acid or base ionizes in solution
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Neutralisation is the basis of titration
- a pH indicator shows when the equivalent number of moles of a base have been added to an acid.
Nutralisation will not always give a solution with pH7
- Only the case with acid and base of similar strengths being reacted
- neutralsation with a strong acid and a wear base will give a weakly acidic salt and vice-versa
Bases
- Strong base hydrolyses completely raising the pH of the solution towards 14
- Arrhenius bases are water soluble and donate hydroxide ions (OH-)
- Alkalis are bases. Not all bases are alkalis
- Alkalis are Arrhenius bases and hydroxides of the alkali metals - sodium, potassium
- Strong bases: NaOH, KOH, Ca(OH)2
- Weak bases: NH3 (ammonia)
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Henderson-Hasselbalch equation
- Describes the derivation of pH as a measure of acidity in biological and chemical system
- Useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions
- Pka is -log(Ka)
Buffers:
- Aqueous solutions consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid
- Buffers mean that the pH of solution changes very little when a small amount of acid or base is added to it.
- Buffer solutions are used as a means of keeping pH at a early constant value in biochemical applications
- Buffers are in cells and blood to maitain physiological pH
- a weak acid and its salt or a weak base and its salt
Buffers
- When H+ added to solution equilibrium move to the left - as hydrogen ions are on left side of equilibrium equation
- OH- are added to solution, equilibrium move to the right (as hydrogen ions are removed)
- Some of the added acid or base is neutralised in shifting the equilibrium so pH changes by less than it would if the solution were not buffered.
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Buffers in biology
- Resistant to change in pH
- Ideal buffer for particular pH has a pKa equal to pH, since such solution has maximum buffer capacity
- Buffers needed to keep correct pH for enzymes to work
- A buffer of carbonic acid (H2CO3) and bicarbonate (HCO3-) is present in blood plasma - maintains a pH between 7.35-7.45