C2.1 Structure and

bonding

Key words

Atoms

Elements

Periodic table

Compounds

Chemical bonding

Electrons

Ions

Electronic structure

Alkali metals

Ionic compounds

Halogens

Giant structure

Electrostatic forces

Lattice

Ionic bonding

Covalent bonds

Macromolecules

Giant structures

•To write formulae for ionic compounds from given symbols and ionic

charges

to represent the electronic structure of the ions in sodium chloride,

magnesium oxide and calcium chloride in the following forms:

You should be able to:

for sodium ion (Na+)

You should be able to:

•to represent the covalent bonds in molecules such as water,

ammonia, hydrogen, hydrogen chloride, chlorine, methane and

oxygen and in giant structures such as diamond and silicon

dioxide in the following forms:

You should be able to:

•To represent the bonding in metals in the following form:

a) Compounds are substances in which atoms of two or more elements are

chemically combined.

b) Chemical bonding involves either transferring or sharing electrons in

the highest occupied energy levels (shells) of atoms in order to achieve the

electronic structure of a noble gas.

TOTTERDOWN

c) When atoms form chemical bonds by transferring electrons, they form

ions. Atoms that lose electrons become positively charged ions. Atoms that

gain electrons become negatively charged ions. Ions have the electronic

structure of a noble gas (Group 0).

Element Symbol Group Charge

PotassiumK 1 1+

Magnesium2+

Lithium 1

Ba 2+

Aluminium

Na 1 1+

ChlorideCl-

BromideBr- 1-

FlourideF-

OxideO2-

SulfideS2-

Element Symbol Group Charge

PotassiumK 1 1+

MagnesiumMg 2 2+

Lithium Li 1 1+

BariumBa 2 2+

Aluminium Al 3 3+

SodiumNa 1 1+

ChlorideCl- 7 1-

BromideBr- 7 1-

FlourideF- 7 1-

OxideO2- 6 2-

SulfideS2- 6 2-

d) The elements in Group 1 of the periodic table, the alkali metals, all react with

non-metal elements to form ionic compounds in which the metal ion has a

single positive charge.

Sodium transfers an electron (to chlorine) and so becomes positively charged

Chlorine gains an electron so becomes positively charged

e) The elements in Group 7 of the periodic table, the halogens, all

react with the alkali metals to form ionic compounds in which the

halide ions have a single negative charge.

Mg + 2F → MgF2

The ratio of ions is:

Mg 2+ : F1+

1: 2

So the formula of the compound is MgF2

Fluoride F- Oxide O 2- Carbonate

CO32-

Phosphate

PO43-

Lithium Li+

Barium Ba 2+

Copper Cu2+

Aluminium Al3+

Complete the following table with the formula of each compound

formed.

You do not need to remember the charges on the ions – these are

given in the data sheet

Br- OH- NO3- SO4

2-

K+

Mg 2+

Fe 3+

f) An ionic compound is a giant structure of ions. Ionic

compounds are held together by strong electrostatic forces

of attraction between oppositely charged ions. These

forces act in all directions in the lattice and this is called

ionic bonding.

g) When atoms share pairs of electrons, they form covalent

bonds. These bonds between atoms are

strong. Some covalently bonded substances consist of

simple molecules such as H2, Cl2, O2, HCl, O,

NH3 and CH4.

Others have giant covalent structures (macromolecules), such as

diamond and silicon dioxide.

The giant structure of

diamond The giant

structure of silicon

Property Ionic Covalent

Melting point High

Solubility soluble in water doesn’t usually

mix with water

Electrical

conductivity

high low

h) Metals consist of giant structures of atoms

arranged in a regular pattern.

The atoms in metals are closely packed

together and arranged in regular layers.

This means they can form crystals.

i) The electrons in the highest occupied energy levels (outer shell) of

metal atoms are delocalised and so free to move through the whole

structure. This corresponds to a structure of positive ions with electrons

between the ions holding them together by strong electrostatic

attractions. (HT)

Why do atoms bond?

They want to have a full outer electron shell.

This is why oxygen that we breathe in is O2, chlorine gas is

Cl2 etc…

METAL NON-METAL

METAL

NON-METAL

What type of bond?

metallic ionic

ionic covalent

What are the properties of the different

types of chemical bond?

IONIC METALLIC COVALENT COVALENT

Type of

structure

Are ions

present?

Are delocalised

electrons

present?

How strong is

the chemical

bond?

High/Low

melting point?

Conductor of

electricity?

What are the properties of the different

types of chemical bond?

IONIC METALLIC COVALENT COVALENT

Type of

structure giant giant GiantSimple

molecules

Are ions

present? yes yes no no

Are delocalised

electrons

present?no yes no (except

in graphite)no

How strong is

the chemical

bond?strong strong

very

strong

very

strongHigh/Low

melting point? high high very high low

Conductor of

electricity?

when molten/

in solution yes no (except

graphite)no

Ionic bonds

Make sure you know how to draw the electrons on a diagram to

show both atoms and ions

Don’t forget to add the charge when drawing diagrams of ions!

(Use a square bracket and write the charge top right).

Remember – ions have a full outer shell.

What is an ionic bond?

Why do ionic substances have high melting points?

Why can ionic substances conduct electricity when they are

molten or in solution, but not when they are solid?

Covalent bonds

What is this compound?

Why do giant covalent substances such as diamond or carbon

have very high melting points?

Why do simple covalent bonds have lower melting points?

Small molecules Giant covalent structure

Put these in the correct place:

Methane CH4 Silicon dioxide SiO2 Diamond C Ammonia NH3

Small molecules Giant covalent structure

Methane CH4

Silicon dioxide SiO2

Ammonia NH3

Diamond C

Put these in the correct place:

Sodium Chloride

Magnesium oxide

Calcium Chloride

Hydrogen Sulfide

Iron (II) chloride

Iron (III) chloride

Sodium Sulfide

Sodium Sulfate

Calcium Hydroxide

Magnesium Nitrate

Sodium carbonate

Calcium sulfate

Write the correct formula for these compounds

Sodium Chloride NaCl

Magnesium oxide MgO

Calcium Chloride

Hydrogen Sulfide

Iron (II) chloride

Iron (III) chloride

Sodium Sulfide

Sodium Sulfate Na2SO4

Calcium Hydroxide Ca(OH) 2

Magnesium Nitrate Mg(NO3) 2

Sodium carbonate Na2CO3

Calcium sulfate CaSO

Write the correct formula for these compounds

H2 gas insoluble no

S8 solid insoluble no

H2O liquid n/a low

CO2 gas slightly soluble no

C25H52 solid insoluble no

C12H22O11 solid Insoluble no

What’s the link?

Giant Covalent Structures

What is an ionic bond?

Li Li

What’s missing?

Giant Ionic Structures

Oppositely charged ions are

attracted to each other.

This attraction forms a strong

ionic bond.

The charge on a ion acts in

all directions.

The ions arrange themselves

into a lattice structure,

involving huge numbers of

ions, which is why they are

named giant structures.

Because of this, an electric current can be passed

through the solution.

The same is true when ionic substances are molten.

When an ionic

substance

dissolves, the

ions break out of

their lattice

structure and are

free to move

about and carry

a charge.

When atoms share electrons, they are

held together very tightly. This is a

covalent bond.

Example – Hydrogen:

H H

x

H Hx

Hydrogen atoms Hydrogen molecule

H2

You are very likely to get a question about why giant

covalent substances (like diamond or silicon dioxide –

sand) have very high melting points.

Lots (thousands,

millions!) of atoms

joined together by

covalent bonds

• very strong bonds

• lots of bonds to be broken

• need a huge amount of

energy/heat to break the bonds

• therefore a very high melting

point

Simple covalent substances

(molecules)

Molecules: a small number of atoms covalently

bonded.

They have very different properties to giant

covalent substances.

Simple molecules all have low melting and

boiling points.

Why?

H Hx

The covalent bonds are very

strong, so the atoms are held

together tightly.

But, the individual molecules

are separate from each

other.

There is a force of attraction between individual molecules

(called the intermolecular force). This is weak, and only

a small amount of energy is needed to overcome it.

H H

Cl Cl

STRONG

covalent bond

WEAK

intermolecular

force When a molecular substance

melts/boils, it is the intermolecular

forces that are overcome.

The covalent bonds are not broken.

Finally, metallic bonds

• outer shell electrons delocalise (come away from the atom) and are

free to move

• forming a ‘sea of electrons’ and leaving positive metal ions

• the attraction between negative electrons and the positive ions

holds the metal together – the electrons act like glue

• the metal ions are held tightly in neat rows that can slide over each

other