Periodicity - Properties

Periodicity - Properties

The repeating pattern of physical and chemical properties shown by different periods

Physical Properties

1.Atomic radii

– decreases as you go across a period because protons are added to the nucleus so increasing the attraction between the nucleus and the electrons

- increases as you go down a group because a further energy level is added increasing radii

2.Ionic radius

- increases as you down a group because of the extra energy level/shell

- cations are smaller than the parent atom as one less shell AND ionic radius decreases across a period as the same # of electrons but an increased # of protons so increased attraction

- anions are larger than the parent atom as more electrons AND decrease across a period as the # of protons increases

3.Ionisation Energy

– decreases as you go down a group as electrons are further from the nucleus

4.Electronegativity

- increases across a period as atomic size decreases

- decreases down a group as atomic size increases

5.Melting Points

- depends on the intermolecular and intramolecular bonding

- Group I – melting point decreases going down the group as atoms get larger and metallic bands get weaker

- Group VII – melting point increases going down the group as Van der WAal’s forces between molecules increase

- Period 3 – increase to Si, then decrease to Ar

Chemical Properties

• Change from metals to metalloids to non-metals across a period. Metal oxides tend to be basic (AL is amphoteric)

Non-metal oxides tend to be acidic:

• Group I– reactive metals, good reducing agents, reactivity increases going down the group as the outer shell electrons are easier to remove.

- readily react with water

2Na

2K

-readily react with Cl2 and Br2 to form ionic salts

2K

• Group VII – good oxidizing agents, reactivity decreases down the group

-the higher halogen gas can remove halide ions from solution

or

• Halide ions can be detected and identified by adding : AgCl – White

AgBr – Cream

AbI - yellow