#electrons.bonding.structure

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Patterns in First Ionisation Energies

Across a Period

e.g. Li --> Ne

The First I.E. tend to gradually increase going across the period. This is due to the fact that all the elements in the period all have the same complete quantum shells. Therefore, they have similar electron shielding. 

However, the nuclear charges of the elements increase as each time one more proton is added to the nucleus. Therefore, there is an increase in the electrostatic forces of attraction and ionisation energy.

Down a Group

e.g. Li --> Na

There is a gradual decrease in First I.E. on going down a group. This is due to the increase in electron shielding and distance in atomic radius (the distance between outershell electron and the nucleus) outweighing the fact that there is an increase in nuclear charge.

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Shells & Orbitals

Each shell is divided into subshells/orbitals.

There are 4 subshells that we study:

's' subshell has 1 orbital

'p' subshell has 3 orbitals

'd' subshell has 5 orbitals

'f' subshell has 7 orbitals

N.B. Each orbital contains 2 electrons and the name of the subshells are in lowercase letters.

Atomic Orbitals

Definition: A region that can hold up to two electrons with opposite spins

Each orbital contains 2 electrons in opposite spin due to the repulsion of the same charge. The directions are up or down. 

Each orbital has their own shape:

Subshells

Subshells are not filled in a numerical order. Instead, they follow the following pattern:

The arrows represent the direction of following the pattern.

Electronic Configuration

the lowest available energy level is filled first

Each energy level must be full before the next is started

Each box must be filled in  completely in one direction before others are added to it in the opposite direction. 

Each orbital can only contain 2 electrons. 

Positive ions = remove electrons from highest energy level

Negative ions = add electrons to the highest energy levels

The 'blocks' in the periodic table for 's' 'p' & 'd' correspond with the last subshell filled.

e.g. Bromine's last subshell filled is 4p and so it belongs to the 'p' block.

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Ionization Energies

First Ionisation Energy

Definition: The amount of energy required to remove one outer shell electron from each one mole of a gaseous atom to form one mole of a cation in a gas state forming a +1 charge. 

Unit: kJ/mol

Successive Ionisation Energy

Definition: The amount of energy required to remove one outershell electron from a gaseous cation. 

N.B. The electrons are removed from the outermost to the innermost. Think peeling an onion: out to in.

The successive ionisation energy increases as the electrons being removed become closer to the nucleus. Therefore, the electrostatic forces of attraction increases and so more energy is needed to overcome them in order to remove the electron. 

Closer = Stronger electrostatic forces of attraction = More energy to overcome = Increased I.E.

When a new shell of electrons is started to be removed, the ionisation energy will dramatically increase due to the reduced electron shielding.

Electron shielding is when the electrons in the shells between the outermost shell and the nucleus cancel some of the positive charges from the protons in the nucleus.

Therefore, if there are less shells between the outershell and the nucleus, there are stronger forces of attraction between the nucleus and the outershell electrons.

New shell= Less electron shielding = Less electrons to cancel positive charge=  Stronger forces of attraction = More energy to overcome= Increased I.E.

When an atomic number increases, so will the nuclear charge of the atom. Therefore, there are stronger forces of attraction between the increased number of protons & electrons and more energy is needed to overcome it. Therefore the I.E. also increases.

Increased Nuclear Charge= More protons= Stronger forces of attraction = More energy needed to over come = Increased I.e