Bonding

Chemistry revision

There are two types of bonding you need to be

familiar with…

1.Covalent bonding

2.Ionic bonding

You will be re-visiting…

The structure of the atom.

Why atoms want to lose or gain electrons.

Which type of materials use covalent or ionic bonding.

The properties that covalent and ionic bonding give to the material.

You need to be able to…

Name the components of an atom.

Understand how many electrons are in each orbital.

Describe the charge on each sub atomic particle.

Understand what an isotope is.

To draw dot and cross diagrams.

To draw ionic formula diagrams.

To name compounds which use these types of bonding

Atoms contain three sub-atomic particles called protons, neutrons and electrons.

The protons and neutrons are found in the nucleus at the centre of the atom, and the electrons are arranged in shells around the nucleus.

The atom

The charge in an atom

• Atomic heaven is to be neutral!• Atoms will share or steal electrons so

they can to obtain the structure of the Group 0 or Noble elements.

• This group reacts with very little at all!• By sharing or stealing electrons the

atoms bond to become compounds and therefore neutral!

Particle Charge

Relative Mass

Protons +1 1

Neutrons

0 1

Electrons

-1 0.0005

• There are two properties of sub-atomic particles that are especially important:

MassMassElectrical Electrical chargecharge

So now we look at the Periodic Table…

12

C6

Atomic Number = the number of protons in the nucleus.It is the smaller number in the box.

Atomic Mass = the number of protons and neutrons in the nucleus.It is the larger number in the box.

Here is the element Carbon

From these two numbers we can work out the number of electrons this element should have.

Carbon can also be an isotope

Isotopes have the same number of protons but a different number of neutrons. So isotopes have the same atomic number but a different atomic mass.12

6 C or 146 C

Other famous isotopes are uranium and radium

Where are the electrons?

The electrons are located in orbitals or shells around the nucleus.

The innermost orbital will take up to two electrons only.

The next three orbitals will take a maximum of eight electrons each.

Covalent Bonding

• Covalent compounds are formed when non-metal atoms react together.

• As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms.

• The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells.

Boardworks – Covalent Bonding

Examples of covalent bonding

Simple covalent bonds:

Water H2O

Ammonia NH3

Methane CH4

Oxygen O2

Giant covalent structures:

Graphite

Diamond

Properties of covalent compounds

Small numbers of atoms in the molecules.

Low melting and boiling points.

Most are gases or liquids at room temperature.

They do not conduct electricity.

They tend to be insoluble in water.

Ionic bondingMost ionic compounds contain a metal and a non-metal.

When metals react they lose outer shell electrons to leave a full electron shell.

This produces a charged atom (ion) with a + charge.

When non-metals react with a metal they gain electrons to achieve a full electron shell.

© Boardworks Ltd 2003

Ions and electron structures

Metals lose electrons to form positive(+) ions called cations.

Non-metals gain electrons to form negative (–) ions called anions.

n+

n-

We know that the atoms lose or gain electrons to achieve full electron shells.

To understand more about how ionic compounds form we must look at what is happening to the outer shell electrons.

© Boardworks Ltd 2003

Formation of Sodium Chloride- the overall process.

ClNa

Na Cl

Sodium loses itsouter electron.Chlorine gains it.The result is both end up with full shells

Two oppositelycharged ionsare formed, which attract.Millions of such pairs form a giant lattice

© Boardworks Ltd 2003

Simpler electron diagrams

We can assume full inner electron shells. We can therefore sometimes shorten bonding diagrams by omitting to draw the inner electron shells.

Na Cl

Na Cl

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OMg

2.8.2. 2.6

Magnesium atom

Oxygen atom

Bonding in Magnesium Oxide

More than one electron may be transferred between atoms in ionic bonding.

Mg2+ O2-

2.82.8

Magnesium Oxide

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Sodium Fluoride

Sodium atom

Fluorineatom

Copy the diagram and draw another box showing the electron configuration in sodium fluoride.

Na+

2.82.8

FNa

2.8.1. 2.7

F-

© Boardworks Ltd 2003

More Complicated Formulae

• Ionic compounds may contain ions consisting of groups of atoms rather than a single atom.

• Here are some more complicated ions you may come across.

Atoms presentChargeFormulaIon

2-

1-

1+

2-

1-

CO32-

OH-

NH4+

SO42-

NO3-

carbonate

hydroxide

ammonium

sulphate

nitrate N O O O

OS OOO

N H H H H

O H

C O O O

Examples of ionic structures

Animation of NaCL

Properties of ionic compounds

Atoms are held very strongly together.

The compound has a regular structure.

Ions form giant structures.

Very high melting and boiling points.

Soluble in water.

Conducts electricity when dissolved.

OK, have a go at this quiz and check what you should

know

This is the structure of Argon

It’s electronic configuration is written

2,8,8Which group of the Periodic Table will it be found in?