3.1.1 Periodicity: Module 3: Periodic Table and Energy: Chemistry OCR A A Level

How are the elements arranged in a periodic table?

They are arranged in the order of increasing atomic numbers.

What is a period on a periodic table?

The horizontal rows in the periodic table.

What is a group on a periodic table?

The vertical columns.

What is meant by periodicity?

The repeating trends in chemical and physical properties.

What change happens across each period?

Elements change from metals to non metals.

Define first ionisation energy.

The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions.

Write an equation for the first ionisation energy of magnesium.

Mg (g) → Mg+ (g) + e-

What are the factors that affect ionisation energy?

● Atomic radius

● Nuclear charge

● Electron shielding or screening

Why does first ionisation energy decrease between group 2 to 3?

Decrease between 2 to 3 because in group 3 the outermost electrons are in p orbitals whereas in group 2 they are in s orbital, so the electrons are easier to be removed.

Why does first ionisation energy decrease between group 5 to 6?

The decrease between 5 to 6 is due to the group 5 electrons in p orbital are single electrons and in group 6 the outermost electrons are spin paired, with some repulsion. Therefore the electrons are slightly easier to remove.

Does first ionisation increase or decrease between the end of one period and the start of next? Why?

Decrease:

● There is increase in atomic radius.

● Increase in electron shielding.

Does first ionisation increase or decrease down a group? Why?

Decrease:

● Shielding increases → weaker attraction

● Atomic radius increases → distance between the outer electrons and nucleus increases → weaker attraction

● Increase in number of protons is outweighed by increase in distance and shielding.

What are the properties of giant metallic lattices?

● High melting and boiling point

● Good electrical conductors

● Malleability

● Ductility

What is a ductile metal?

The metal can be made stretched. E.g, can be made into wires.

What is a malleable metal?

The metal can be shaped into different forms.

Describe the structure, forces and bonding in every element across period 2.

● Li & Be → giant metallic ; strong attraction between positive ions and delocalised electrons; metallic bonding.

● B & C → giant covalent ; strong forces between atoms; covalent.

● N2, O2, F2 & Ne → simple molecular; weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules.

Describe the structure, forces and bonding in every element across period 3.

● Na, Mg & Al → giant metallic; strong attraction between positive ions and delocalised electrons; metallic bonding

● Si → giant covalent; strong forces between atoms; covalent.

● P4, S8, Cl2 & Ar → simple molecular; weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules.