Group (Chemistry)

Key Stage 3

Meaning

A Group is a column on the Periodic Table with elements with the same number of electrons on the Outer Shell.

About Groups

Helium, in Group 0 is an exception to this rule as it has 2 electrons in its Outer Shell.

The elements are arranged groups of similar chemical properties.

Elements have similar chemical properties when they have the same number of electrons in the Outer Shell.

Trends within groups

The chemical properties of elements within a group are similar. However, the reactivity within a group changes as you move up or down the periods.

• Group 1: The Alkali Metals all react strongly with water. The reactivity increases as you go down the group.
• Group 2: The Alkali Earth Metals all react strongly with steam and acids. The reactivity increases as you go down the group.
• Group 7: The Halogens all act as bleaching agents and kill bacteria. The reactivity decreases as you go down the group.
• Group 0: The Noble Gases are all inert (unreactive).

The physical properties of elements within a group are similar. However, the property changes gradually as you move down the group.

Key Stage 4

Meaning

A Group is a column on the Periodic Table with elements with the same number of electrons on the Outer Shell.

About Groups

Helium, in Group 0 is an exception to this rule as it has 2 electrons in its Outer Shell.

The elements were oringally arranged groups of similar chemical properties.

It was later discovered that elements have similar chemical properties when they have the same number of electrons in their Outer Shells.

Trends within groups

The chemical properties of elements within a group are similar. However, the reactivity within a group changes as you move up or down the periods due to the number of Electron Shells.

Group 1: The Alkali Metal

Chemical Properties

Alkali Metals are all highly reactive and will oxidise quickly in the presence of Oxygen.

Alkali Metals all react strongly with water to produce metal hydroxides and Hydrogen gas.

Alkali Metals all produce strong alkalis.

In a chemical reaction the electron in the outer shell is lost. The reactivity increases as you go down the group because: The outer electron is further away from the nucleus with each additional electron shell making the force of attraction weaker. This makes it easier for an atom to lose it's outer electron. Even though the charge of the nucleus increases the outer electron is shielded from most of the positive charge of the nucleus by electrons in the inner shells.

Physical Properties

Alkali Metals have a low density compared to other metals.

Alkali Metals are all solid at room temperature but have a low melting point compared to other metals.

Alkali Metals are soft and can be easily cut.

Alkali Metals all appear shiny (before they oxidise).

Group 7: The Halogens

Chemical Properties

The reactivity of Halogens decreases as you go down the Periodic Table.

Halogens all react strongly as bleaching agents.

Halogens all produce acids when combined with Hydrogen.

Halogens are toxic to bacteria and are used in disinfectants.

In a chemical reaction an extra electron is added to the outer shell. The reactivity decreases as you go down the group because: The outer electrons are further away from the nucleus with each additional electron shell making the force of attraction weaker. This makes it less able to gain an extra electron. Even though the charge of the nucleus increases the outer electrons are shielded from most of the positive charge of the nucleus by electrons in the inner shells.

Physical Properties

The physical properties of Halogens changes significantly as you go down the Periodic Table:

• Fluorine - A yellow gas at room temperature.
• Chlorine - A green gas at room temperature.
• Bromine - A brown liquid at room temperature.
• Iodine - A purple solid at room temperature.
• Astatine -A dark purple solid at room temperature.

The density, melting point and boiling point all increase as you go down the Periodic Table.

Group 0: The Noble Gases

Chemical Properties

The Nobel Gases are all inert (unreactive) because they have a full outer shell.

Physical Properties

The Nobel Gases are all gases at room temperature.

The density and boiling point all increase as you go down the Periodic Table.