S3.1 The Periodic Table

What is a ligand?

Species that gives a pair of electrons to form coordinate covalent bonds

What is a coordinate covalent bond?

A bond between two atoms in which one atom donates a lone pair of electrons to form the bond

What is the Crystal field theory?

Properties of complex ions are caused by the splitting of the d-orbitals into 2 sets of diff energies .

How does the crystal field theory work ?

Splitting occurs when ligands approach central metal ion; causing repu’lsion between the lone pairs of electrons on the ligands and the electrons in the 5 d-orbitals of the central ion

Periodicity

Properties repeat periodically

Effective nuclear charge down group and across periods

Down group = decreases

Across periods = increases

What is effective nuclear charge?

Basically how strong the nucleus is attracting elections

Why does Li have a higher effective nuclear charge than Fr?

Li-only two electrons between valence e and nucleus but Fr has 86 so it has higher shielding.

Way does effective nuclear charge increase along periods?

Valence e= being added to same energy level → shielding decreases

Atomic radius down a group?

Increases

Because adding e- to higher energy levels so electrons have spread out so radius gets larger.

Atomic radius across a period

Decreases

Because e- are added to same energy level not higher energy level, so nucleus pulls valence electrons closer to itself so radius decreases

Ionic radius

Metals will lose electrons to become positive ions, smaller ionic radius

Non metals will gain electrons> negative , larger ionic radius

When gaining electron, ionic radius

Increases because repulsion with added electron and electrons already there makes atom spread

When losing electron, ionic radius…

Decreases less repulsion, lost valence electron

What is ionisation energy?

Amount of energy required to remove an electron from an atom

Trend of ionization energy

Across period increases=> metals lose electrons easily , non metals are the gainers

Down group decreases => increased shielding> further away from nucleus

Electron affinity

1 mole of electron added to a gaseous atom to form a negative ion (‘how much atoms like electrons’)

Trends for electron affinity

Across periods, increases because non metals want to gain electrons

Down groups, decreases because of shielding

Electronegativity

The ability of an atom to attract electrons towards itself in a covalent bond

Trends for electronegativity

Across periods, increases

Down group, decreases

Most =fluorine Least=caesium

Melting point trend in Group 1

Decreases as you go down=> atomic radius is larger, atoms are further apart so easier to break apart

Melting point down groups 17

Increases because dispersion forces increase

Group 1

Most reactive on table

Reactivity increases going down=> increasing atomic radius and decreasing ionisation energy

Low density

Group 17

Diatomic

Reactive + reactivity increases down group=> increasing atomic radius down

Found as gases

Coloured + reacts with group 1=> halide ions Cl- pale green, I- dark purple, Br- brown

ionic character trends

Decreases across period

Acidic character trends across period 3 oxides

Basic → Amphoteric(both) → Acidic

Na2O, MgO =basic Al2O3 = amphoteric SiO2 and so on = acidic