Periodicity

HL and SL

3.1 The periodic tableThe periodic table is a list of all the elements in order of increasing atomic number.

Elements are placed vertically in GROUPS according to the number of electrons in their outer energy level. These groups are numbered 1 – 7 and 0.

All the elements in the same group have similar chemical properties as they have the same number of electrons in their outer energy level.

The number of electrons in the outer energy level is the same as the group number.

There is a gap between groups 2 and 3 for the TRANSITION ELEMENTS.

The elements are arranged horizontally in PERIODS.

The periods are number 1 – 7 and the period number indicates the number of energy levels containing electrons.

H and He are in period 1 so have 1 energy level containing electrons.

Li to Ne are in period 2 so have 2 energy levels containing electrons etc.

You should be able to locate an element in the periodic table from its electron arrangement alone.

On a blank copy of the Periodic Table indicate the position of the elements A to J (not their actual symbols).

A: 2 B: 2, 1

C: 2, 8, 2 D: 2, 8, 5

E: 2, 6 F: 2, 3

G: 2, 8 H: 2, 8, 8, 1

I: 2, 8, 7 J: 2, 8, 4

3.2 Physical Properties

Important definitions:

FIRST IONISATION ENERGY – Energy required to remove one electron from an atom of an element to form a gaseous ion with a 1+ charge.

ELECTRONEGATIVITY – The ability of an atom to pull electron density from a covalent bond to itself.

Now try the ‘Physical Properties’ exercise.

3.3 Chemical Properties

• Elements of group 1 with water and with chlorine

• Halogens with halide ions (halogen displacements)

• Oxides of period 3

Watch the video clip and use it to write down information on group 1 elements.

For fun: Rubidium and caesium

Brainiac style

The video clip shows the reaction of sodium with chlorine gas to make sodium chloride as a white crystalline solid.

2Na(s) + Cl2(g) 2NaCl(s)

The other members of the group react in a similar fashion to form white crystalline chlorides. The vigour of the reaction again increases down the group. Lithium burns in chlorine with a red flame and potassium with a lilac flame.

Explain the reactivity trend using Bohr’s model of the atom.

Watch the video clip and use it to write down information on group 7 elements.

Key idea: a more reactive halogen displaces a less reactive halogen from one of its compounds.

Reactions of Period 3 Elements

The solid elements (Na to S) all burn in air or oxygen when ignited.

Video clips over the next few slides show some of the reactions.

Sodium with oxygen

Sodium burns with a yellow flame forming the oxide.

2Na(s) + ½O2(g) Na2O(s)

Magnesium to Phosphorus with OxygenMagnesium, aluminium, silicon and phosphorus burn when ignited, emitting a very bright white light and white smoke of the oxides. The reactions are all exothermic.

Mg(s) + ½O2(g) MgO(s)

2Al(s) + 1½O2(g) Al2O3(s)

Si(s) + O2(g) SiO2(s)

P4(s) + 5O2(g) P4O10(s)

This clip shows magnesium and oxygen

Sulphur with oxygen

Sulphur burns with a blue flame, but much less vigorously than the previous elements, to form the pungent, colourless gas sulphur dioxide.

S(s) + O2(g) SO2(g)

Tabulate the melting points of the oxides of sodium to sulphur and use these values to deduce the structure and bonding of these oxides.

Na2O

Tm / K bonding structure

MgO

Al2O3

P4O10

SiO2

SO2

1548

3125

2345

1883

573

200

ionic

ionic

ionic-covalentcovalent

covalent

covalent

lattice

lattice

lattice

macromolecular

molecular

molecular

Reactions of oxides of group 3 with water:

Sodium oxide dissolves to form a strongly alkaline solution.

Na2O(s) + H2O(l) 2NaOH(aq)

sodium

magnesium

Magnesium oxide is also soluble in water. It dissolves to form a weakly alkaline solution of magnesium hydroxide.

MgO(s) + H2O(l) Mg(OH)2(aq)

aluminium

Aluminium oxide is insoluble in water.

However, aluminium oxide is described as AMPHOTERIC as it will react with both acids and bases.

silicon

Silicon dioxide is insoluble in water.

However, silicon dioxide is considered to be an acidic oxide.

phosphorus

Phosphorus(V) oxide dissolves readily in water to form a weakly acidic solution.

P4O10(s) + 6H2O(l) 4H3PO4(aq)

sulphur

Sulphur dioxide dissolves in water to form a solution of sulphurous acid (a weak acid).

SO2(g) + H2O(l) H2SO3(aq)

Sulphur trioxide dissolves in water to form a solution of sulphuric acid (a strong acid).

SO3(g) + H2O(l) H2SO4(aq)

The highest oxide of chlorine (Cl2O7) also dissolves in water to from an acidic oxide.

Complete the table below:

Formula of oxide

Na2O

Structure and bonding

Ionic lattice

Nature of oxide

Strong alkali