Periodicity

Seite 1

The Periodic Table

Groups: The vertical columns in the Periodic Table

Periods: The horizontal rows in the Periodic Table

Blocks:

S-block: The s-block consists of elements in Group 1 and Group 2. The highest energy electron of an element in the s-block is in an s orbital.

P-block: The p-block consists of elements in Groups 3 to 8. The highest energy electron of an element in the p-block is in a p orbital

D-block: The d subshell is being filled for an element in the d block

Seite 2

Atomic Radii

Types of Atomic Radii

Covalent radius: Half the distance between the nuclei when two atoms of that element are covalently bonded together in a homonuclear diatomic molecule

Van der Waals radius: Half of the distance between the closest approach of two non-bonded atoms of a given element

The covalent radius will always be smaller than the Van der Waals radius.

Trends in Atomic Radii

In general:

Decrease across period

Increasing number of protons → Increasing nuclear charge

Electrons feel stronger attractive force of nucleus → Pulled towards the nucleus → Smaller radius

Increase down the group

Electrons are being added to new quantum shell → Placed further away from nucleus → Larger radius

Electrons experience shielding by lower energy electrons → Less attracted to nucleus → Larger radius

Seite 3

Melting and Boiling Points

Element with giant lattice structure have high melting and boiling temperatures.

Elements with simple molecular structure have low melting and boiling temperatures

Seite 4

First Ionisation Energies

First ionisation energy: The first ionisation energy of an element is the energy required to remove an electron from each atom in one mole of atoms in gaseous atoms

In general:

Increase across the period

Increasing number of protons → Increasing nuclear charge → Electrons are lower in energy → More energy needed to remove them → Higher first ionisation energy

Decrease down the group

Electrons added to new quantum shell → New shell has higher energy and electrons are more shielded by lower electrons → Higher energy electrons → Less energy needed for removal → Lower first ionisation energy

However, there are some anomalies:

Ionisation energy of Group 3 element is less than that of Group 2 element

Example: Ionisation energy of beryllium is greater than that of boron

Orbital energies

Outer electron of boron is in p orbital

Outer electron of beryllium is in s orbital

Therefore, outer electron of boron is higher in energy → Easier to remove than outer electron of beryllium → Lower ionisation energy than beryllium

Shielding

Outer electron of boron experiences shielding from two inner electrons subshells

Outer electron of beryllium experiences shielding from only one inner electron subshell

Therefore, outer electron of beryllium is lower in energy→ Electron on beryllium feels more attractive force of nucleus → Beryllium has higher ionisation energy

Ionisation energy of Group 6 element is less than that of Group 5 element

Example: Ionisation energy of nitrogen is greater than that of oxygen

Paired electrons

Presence of two electrons in one orbital increases electron-electron repulsion → Electrons will be higher in energy

First electron removed from oxygen comes from a pair → Higher in energy → Requires less energy to remove than unpaired outer electron of nitrogen