OCR A-Level Chemistry: Chapter 7 - Periodicity

Dmitri Mendeleev

Increasing atomic mass

Groups

Periods

The sub shells of n energy level fill up.

The removal of one or more electrons from an atom.

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

Greater distance between the nucleus and outer electrons, the attraction is lower.

More protons creates a greater attraction between the nucleus and the outer electrons.

Inner shell electrons repel outer shell electrons, called shielding. This reduces the attraction between the nucleus and the outer electrons.

More electrons shells so the outer electrons are further away and there is a greater shielding effect.

The number of protons in the nucleus increases so nuclear charge increases causing atomic radius to decrease, whilst shielding stays the same.

There are less electrons so the nuclear attraction on the remaining electrons will be greater.

The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.

Moving down to a closer shell, as these electrons are closer so experience a greater nuclear attraction.

The number of electrons in the outer shell, the group of the element in the periodic table and thus the identity of the element.

Atomic radius increases,
More inner shells so shielding increases,
Nuclear attraction on outer electrons decreases,
First ionisation energy decreases.

Nuclear charge increases,
Same shell: similar shielding,
Nuclear attraction increases,
Atomic radius decreases,
First ionisation energy increases.

The new electron enters the 2p sub shell, which is slightly further away from the nucleus than the 2s sub shell.

Nitrogen’s electrons in the 2p sub shell are unpaired so oxygen’s 8th electron is paired, causing repulsion and a lower ionisation energy.

Nuclear charge increases,
Nuclear attraction increases,
Atomic radius decreases.

Each atom donates an outer shell electron, which becomes delocalised. This creates cations.

Strong electrostatic attraction between the fixed cations and the delocalised electrons.

Strong metallic bonds
High electrical conductivity
High melting and boiling points

Number of delocalised electrons per atom and charge on cation increase, so stronger electrostatic attraction.

Forms a giant covalent lattice, where each atom is covalently bonded to four others.

High melting and boiling points
Insoluble in almost all solvents
Do not conduct (except for graphite and graphene)

Covalent bonds holding it together are too strong to be broken by interaction with solvents.

All four outer shell electrons are involved in covalent bonding.

Weak induced dipole-dipole forces between molecules are easy to break.