As you go down each Group:

1. (Atomic radius increases)
2. First ionisation energy decreases
3. Electronegativity decreases

You need to be able to explain these properties in the exam.

Why does atomic radius increase?

This happens because as you go down a Group, the elements have more electrons and therefore, need more orbitals in which to store these electrons. These orbitals get filled up gradually by the usual method: "1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ etc etc...

These orbitals surround the nucleus. As you go down the Group, you get more orbitals surrounding the nucleus (remember, all the orbitals are 'stacked' on top of each other) and therefore, the size of the atom increases.

Also, the further an orbital gets from the nucleus, the larger it gets because of the decrease in nuclear attraction from the nucleus.

Why does first ionisation energy decrease?

This happens because as you go down the Group, the number of orbitals increases and they get further away from the nucleus. This decreases the nuclear attraction between the orbital and the nucleus so it makes it easier for another element to remove an electron from the outer orbital as the outer orbital is hardly attracted to the nucleus.

Also, another reason the first ionisation energy decreases is because, of the shielding effect. All orbitals are filled up with electrons and these electrons are constantly repelling each other. The further out an orbital is from the nucleus, the greater the shielding effect on it and the lower the nuclear charge. Therefore, it's easier to remove an electron.

Exam tip

Whenever you are asked a question about explaining ionisation energies, always include the following 3 points.

1. Distance from nucleus
2. Shielding effect
3. Proton:Electron Ratio

Why does electronegativity decrease?

The ability of an atom to attract the electrons in a bonding pair decreases as you go down the group decreases because the bonding orbitals are further from the nuclear charge and shielded by the inner shells.

A Redox reaction is a reaction in which Oxidation and Reduction take place at the same time. Originally Oxidation was defined as the gaining of oxygen by an element and Reduction as the loss of oxygen. However, now Oxidation is defined as the loss of Electrons and Reduction as the gain of electrons.

A simple way of remembering oxidation and reduction is OILRIG

Oxidation is loss of electrons

Reduction is gain of electrons

A reaction can only be regarded as a redox reaction if oxidation and reduction occurs simultaneously.

Oxidation can also be defined as an increase in Oxidation State.

Oxidation can loosely be described as a gain of oxygen atoms (not oxide ions), but only if the oxygen goes into a -II (or -I) oxidation state.

Oxidation can loosely be described as the loss of hydrogen atoms (not H⁺ ions), but only if the hydrogen was in a +I oxidation state.

At the end of this topic, you will know the following information about Group II elements:

1. Trends in properties
2. Reactions with oxygen, water and hydrochloric acid
3. Thermal decomposition of the carbonates
4. Uses of Group II compounds

The Group II elements are powerful reducing agents.

M(s) → M²⁺(aq) + 2 e^-

A reducing agent is the compound that gets oxidised in the reaction and, therefore, loses electrons.

M = Mg, Ca, Sr, Ba, etc: 'M' is used as the general symbol for a Group II element in this topic.

Another term for Group II elements are Alkaline Earth Metals

All Group II elements have 2 electrons in their outer shell. They generally lose these two outer-shell electrons in order to react and, by doing so, they form M²⁺ ions.

1. Chemical reactivity increases down Groups 1 and 2

Note that group II metals form mostly ionic compounds because the electronegativities are significantly lower than elements such as oxygen and chlorine. Beryllium has the highest electronegativity in Group II and, as you might predict, it forms the chloride with most covalent character.

Why does chemical reactivity increase?

This happens because the ionisation energy decreases. All chemical reactions take place due to the transfer of electrons. Ionisation energy is the energy required to remove one electron from each atom in a one mole sample of gaseous atoms to form one mole of gaseous unipositive atoms.

Therefore, if its easier to remove an electron, then it should mean the it will be easier to react.

Carbonates of group II metals decompose on heating to give carbon dioxide.

MCO₃ → MO + CO₂

This is used to convert chalk (calcium carbonate) to quicklime, calcium oxide. Quicklime can be used to make a simple mortar for building so historically lime kilns and small quarries were to be found all over the UK. When roasted with clay quicklime is used to make cement.

The CO₂ produced by this reaction is also used to manufacture Sodium Carbonate (the Solway process).

Quicklime reacts vigorously with water to form Calcium Hydroxide (slaked lime). This is a very exothermic reaction.

CaO + H₂O → Ca(OH)₂

Slaked lime can purchased in garden centres as a soil conditioner, farmers spread it on the land to reduce acidity.

• The Group 1 and 2 elements are powerful reducing agents.
• A reducing agent 'loses electrons'.
• Another term for Group 1 elements is Alkali Metals
• Another term for Group 2 elements is Alkaline Earth Metals
• All Group 1 elements have 1 electron in their outer shell.
• All Group 2 elements have 2 electrons in their outer shell.

Group 7 consists of highly reactive non-metals called halogens.

Some main properties of the first 4 elements in group 7 are listed below.

The boiling and melting points increase as you go down the group. This is because the strength of the van der Waals forces (the induced dipole-dipole interactions) increases since the atoms have more electrons as you descend the group. This trend is highlighted by the fact that the physical state of the halogens changes from gaseous (fluorine) to solid (iodine) down the group. Volatility decreases down the group, which is another way of saying that the boiling points increase.

As you go down group 7, the halogens become less reactive.

-Halogens are oxidising agents

-Halogen + electron → Halide Ion

• The Group 7 elements are powerful oxidising agents.
• An oxidising agent 'gains electrons'.
• Another term for Group 7 elements is Halogens
• Another term for the anions formed by Group 7 elements is Halides
• All Group 7 elements have 7 electrons in their outer shell.