{getToc} $title={Table of Contents}
Atomic radii increase down a group (more electron shells, further from nucleus, less nuclear charge) and decrease across a period from left to right (greater nuclear charge but equal shielding effect).
All borohydrides are reducing agents. They reduce ‘down’ the oxidation ladder. However, NaBH4 is unable to reduce carboxylic acids, esters or amides (since it is not as powerful as LiAlH4).
There are several tests for ketones and aldehydes:
The reaction between Cl2 and NaOH is different depending on whether NaOH is hot or cold. For cold NaOH:
For hot concentrated NaOH:
Precipitate produced upon addition of dilute NaOH:
Precipitate produced upon addition of dilute NH3:
Tests for anions:
Tests for halides:
Stability of diatomic halides increases down the group (greater permanent dipole-permanent dipole interactions due to higher polarizability of the bigger electron clouds).
Summary of the properties of Group 17 halides (down the group):
Atomic Structures
Ionisation energies decrease down a group (less nuclear charge) and increase across a period from left to right (greater nuclear charge but equal shielding effect).Atomic radii increase down a group (more electron shells, further from nucleus, less nuclear charge) and decrease across a period from left to right (greater nuclear charge but equal shielding effect).
Chemical Bonding
Organic Chemistry (Miscellaneous)
Hot, acidified KMnO4 is used to directly oxidise alkenes to carbonyl compounds such as carboxylic acids (note oxidation ladder). Cold, dilute KMnO4 is used to form diols from alkenes.All borohydrides are reducing agents. They reduce ‘down’ the oxidation ladder. However, NaBH4 is unable to reduce carboxylic acids, esters or amides (since it is not as powerful as LiAlH4).
There are several tests for ketones and aldehydes:
The reaction between Cl2 and NaOH is different depending on whether NaOH is hot or cold. For cold NaOH:
For hot concentrated NaOH:
Tests for Metals and Ions
Flame test colours:Precipitate produced upon addition of dilute NaOH:
Precipitate produced upon addition of dilute NH3:
Tests for anions:
Tests for halides:
Ideal Gas and Gas Laws
Real gases are most ideal at high temperature and low pressure.
At r.t.p (20°C and 1 atm), 1 mole of a gas is equivalent to 24 dm3 of gas. At s.t.p (25°C and 1 atm), 1 mole of a gas is equivalent to 22.4 dm3 of gas.
ΔH of atomization of a compound refers to the energy taken to convert it into its constituent gaseous atoms.
Bond energy of a bond refers to the amount of energy needed to break the bond in the gas phase.
When Gibbs free energy < 0, forward reaction is thermodynamically spontaneous and when Gibbs free energy > 0, forward reaction is not thermodynamically spontaneous, while the backward reaction is. When Gibbs free energy = 0, reaction is at equilibrium.
Where k is temperature dependent but constant for a reaction at a constant temperature.
Half-life formula for a reaction is shown below:
In homogeneous catalysis, the catalyst is in the same phase (either liquid or gas) as the reactants. In heterogeneous catalysis, the catalyst is in a different phase (solid) from the reactants (usually liquid or gas).
Typically for equilibria questions, an ICE table needs to be drawn to figure out the concentrations of the reactants and products.
Equilibrium constants can only be affected by temperature since rate constant is affected by temperature.
For a reaction where there are more moles of products produced than reactants, lowering the pressure shifts the equilibrium to the left. When there are less moles of products produced than reactants, increasing the pressure shifts the equilibrium to the left.
For exothermic reactions, lowering the temperature does not always increase the rate of reaction because lowering temperature can also decrease the average kinetic energy of molecules. This also applies in the same way to pressure.
The anionic radius is bigger than the atomic radius, and decreases from P3- to S2- to Cl-.
First ionisation energies are also affected by inter-electron repulsion and removal of an electron further away from the nucleus (easier to remove 3p electron than 3s electron).
For Period 3 elements, melting and boiling point increases from Na to Si, decreases from Si to P, increases from P to S, and decreases from S to Ar.
Na, Mg and P react vigorously to form their oxides (for P, P4O6 or P4O10). Al reacts vigorously but reaction stops after its oxide coats the metal preventing further reaction. S reacts slowly to form SO2.
Oxides increase in melting and boiling point from Na to Mg, then decrease from Mg to S.
Na (strongly, reacts with water) and Mg (weakly, does not react with water) oxides are basic.
Al oxide is amphoteric (does not react with water).
Si (does not react with water), P (reacts with water) and S (SO3 reacts with water, SO2 dissolves to form sulphurous acid) oxides are acidic.
Na, Mg and Al react vigorously to form their chlorides. Si and P react slowly to form their chlorides (for P, PCl3 or PCl5).
Chlorides decrease in melting and boiling point from Na to Si, then increase from Si to P.
All hydrolyse or dissolve in water.
Reactivity of Group 2 metals mirrors their reducing power.
Mg reacts slowly with cold water while Ca, Sr and Ba react spontaneously.
For Group 2 metals, reactivity with oxygen increases from Mg to Ba. BeO and Be(OH)2 are acidic (they are covalent due to Be’s high charge density).
Solubility of Group 2 compounds with large anions (SO42-, CO32-, NO3-) decreases down the group. Solubility of Group 2 compounds with small anions (OH-, F-) increases down the group.
Going down Group 17, melting and boiling points increase, and volatility decreases.
Fluorine is a pale yellow gas, chlorine is a yellowish-green gas, bromine is a reddish-brown liquid, iodine is a dark violet solid (looks black).
Halogens are strong oxidising agents, but the oxidising power decreases down the group. They all react with hydrogen gas in the gaseous state to form hydrogen halides.
Adding AgNO3 to a compound containing a halide helps identify it. If the precipitate is white, the halide is Cl. If it is cream, the halide is Br. If it is yellow, the halide is I.
Summary of the properties of Group 2 metals (down the group):
At r.t.p (20°C and 1 atm), 1 mole of a gas is equivalent to 24 dm3 of gas. At s.t.p (25°C and 1 atm), 1 mole of a gas is equivalent to 22.4 dm3 of gas.
Chemical Thermodynamics
ΔH of atomization of an element refers to the energy taken to form one mole of gaseous atoms from the element:ΔH of atomization of a compound refers to the energy taken to convert it into its constituent gaseous atoms.
Bond energy of a bond refers to the amount of energy needed to break the bond in the gas phase.
When Gibbs free energy < 0, forward reaction is thermodynamically spontaneous and when Gibbs free energy > 0, forward reaction is not thermodynamically spontaneous, while the backward reaction is. When Gibbs free energy = 0, reaction is at equilibrium.
Reaction Kinetics
Rate law is shown below:Where k is temperature dependent but constant for a reaction at a constant temperature.
Half-life formula for a reaction is shown below:
In homogeneous catalysis, the catalyst is in the same phase (either liquid or gas) as the reactants. In heterogeneous catalysis, the catalyst is in a different phase (solid) from the reactants (usually liquid or gas).
Chemical Equilibria
When Kc > 1, product formation at equilibrium is favoured and vice versa.Typically for equilibria questions, an ICE table needs to be drawn to figure out the concentrations of the reactants and products.
Equilibrium constants can only be affected by temperature since rate constant is affected by temperature.
For a reaction where there are more moles of products produced than reactants, lowering the pressure shifts the equilibrium to the left. When there are less moles of products produced than reactants, increasing the pressure shifts the equilibrium to the left.
For exothermic reactions, lowering the temperature does not always increase the rate of reaction because lowering temperature can also decrease the average kinetic energy of molecules. This also applies in the same way to pressure.
Ionic Equilibria
The following formulae apply:Chemical Periodicity
The cationic radius is smaller than the atomic radius, and decreases from Na+ to Mg2+ to Al3+.The anionic radius is bigger than the atomic radius, and decreases from P3- to S2- to Cl-.
First ionisation energies are also affected by inter-electron repulsion and removal of an electron further away from the nucleus (easier to remove 3p electron than 3s electron).
For Period 3 elements, melting and boiling point increases from Na to Si, decreases from Si to P, increases from P to S, and decreases from S to Ar.
Na, Mg and P react vigorously to form their oxides (for P, P4O6 or P4O10). Al reacts vigorously but reaction stops after its oxide coats the metal preventing further reaction. S reacts slowly to form SO2.
Oxides increase in melting and boiling point from Na to Mg, then decrease from Mg to S.
Na (strongly, reacts with water) and Mg (weakly, does not react with water) oxides are basic.
Al oxide is amphoteric (does not react with water).
Si (does not react with water), P (reacts with water) and S (SO3 reacts with water, SO2 dissolves to form sulphurous acid) oxides are acidic.
Na, Mg and Al react vigorously to form their chlorides. Si and P react slowly to form their chlorides (for P, PCl3 or PCl5).
Chlorides decrease in melting and boiling point from Na to Si, then increase from Si to P.
All hydrolyse or dissolve in water.
Chemistry of Groups 2 and 17
As we move down the two groups:- There is an increase in atomic and ionic radii.
- First ionisation energy, electronegativity and electron affinity decrease.
- Metallic character increases.
Reactivity of Group 2 metals mirrors their reducing power.
Mg reacts slowly with cold water while Ca, Sr and Ba react spontaneously.
For Group 2 metals, reactivity with oxygen increases from Mg to Ba. BeO and Be(OH)2 are acidic (they are covalent due to Be’s high charge density).
Solubility of Group 2 compounds with large anions (SO42-, CO32-, NO3-) decreases down the group. Solubility of Group 2 compounds with small anions (OH-, F-) increases down the group.
Going down Group 17, melting and boiling points increase, and volatility decreases.
Fluorine is a pale yellow gas, chlorine is a yellowish-green gas, bromine is a reddish-brown liquid, iodine is a dark violet solid (looks black).
Halogens are strong oxidising agents, but the oxidising power decreases down the group. They all react with hydrogen gas in the gaseous state to form hydrogen halides.
Adding AgNO3 to a compound containing a halide helps identify it. If the precipitate is white, the halide is Cl. If it is cream, the halide is Br. If it is yellow, the halide is I.
Summary of the properties of Group 2 metals (down the group):