Complete the worksheet on the structure of the

atom

review of atomic structure and bonding

• LEARNING GOAL – to review Y11 work on the structure of the atom and bonding

Types of bondingAtoms can be bonded in three different ways:

All types of bonding involve changes in the number of electrons in the outer shells of atoms.

Bonding occurs because atoms with incomplete outer electron shells are unstable. By forming bonds, atoms completely fill their outer shells and become stable.

Ionic bonding Metal and non-metal atoms

Covalent bonding Non-metal atoms only

Metallic bonding Metal atoms only

Ionic compoundsCompounds that contain ions are called ionic compounds. These compounds are usually formed by a reaction between a metal and a non-metal.

Both the metal and non-metal atoms have incomplete outer electron shells and so are unstable.

One or more electrons are transferred from each metal atom to each non-metal atom. The metal and the non-metal atoms end up with completely full outer shells and become very stable.

The positive and negative ions are strongly attracted to each other. This electrostatic

attraction is called an ionic bond.

Sodium chloride

Sodium chloride is an ionic compound formed by the reaction between the metal sodium and the non-metal chlorine.

During the reaction, one electron is transferred from each sodium atom to each chlorine atom.

sodiumNa

chlorineCl

sodium chlorideNaCl+

ClNaNa

Sodium chloride

Sodium has 1 electron in its outer shell. If it loses this electron, it will have no partially-filled shells.

Chlorine has 7 electrons in its outer shell. If it gains 1 electron, it will completely fill its outer shell.

2.8.1 2.8.7[2.8]+ [2.8.8]-

Cl

+ -

Sodium chloride

The positive sodium ions and the negative chloride ions are strongly attracted to each other and form an ionic bond.

Na

+

Cl

-

More complicated ionic bondingSodium chloride and magnesium oxide are simple ionic compounds. In each case, the metal and non-metal need to lose and gain the same number of electrons.

This is not always the case.

Na Na+Cl Cl-1 electron

Mg Mg2+ O2-O2 electrons

Sodium oxide

O2-O

Na+

Na+

Na1 electron per

atom

Na

Sodium (2.8.1) needs to lose 1 electron but oxygen (2.6) needs to gain 2 electrons. Therefore, two sodium atoms are required for each oxygen atom.

Magnesium chloride

1 electron for each atomMg Mg2+

Cl

Cl

Cl-

Cl-

Magnesium (2.8.2) needs to lose 2 electrons but chlorine (2.8.7) needs to gain 1 electron. Therefore, two chlorine atoms are required for each magnesium atom.

Covalent bondingWhen non-metal atoms react together, they need to gain electrons to fill their outer shell and become stable.

They can only do this if they share electrons with each other.

The atoms share electrons so there is a strong force that joins the atoms together. This is called a covalent bond.

HH incomplete outer shells

HHboth atoms have a full outer shell

Covalent bonding and elementsMany elements exist as molecules – two or more atoms joined by a covalent bond. Each atom has a full outer electron shell and is therefore stable.

Two ways to indicate a covalent bond are:

Only the outer shell of electrons is involved in covalent bonding. This means that the inner shells do not always have to be included in diagrams.

H H Cl

dot and cross diagram HHsolid line

H H––H H

O O Cl

O

Covalent bonding in oxygen

Oxygen (2.8.6) needs 2 more electrons to have a completely full outer shell.

O2 or O=O

To achieve this, it can share two electrons with another oxygen atom. This creates a double bond.

O OO

Covalent bonding in nitrogenNitrogen (2.8.5) needs 3 more electrons to have a completely full outer shell.

N2 or N≡N

It can share three electrons with another nitrogen atom to do this. This creates a triple bond.

NN NN

Covalent bonding in compounds

Covalent bonding can take place between atoms of different elements to create molecules of covalent compounds. These covalent bonds can be single, double or triple.Both hydrogen (1) and chlorine (2.8.7) need 1 more electron to fill their outer shell. By sharing one electron each, they can fill their outer shells and become stable.

HCl or H Cl

ClH

O

Covalent bonding in waterOxygen (2.6) needs 2 more electrons, but hydrogen (1)

only needs 1 more. How can these two elements be covalently bonded?The oxygen atom shares 1 electron with 1 hydrogen atom, and a second electron with another hydrogen atom.

H2O or H O H

H H

N

Covalent bonding in ammonia

N H

Electron configuration

Electrons needed

Ratio of atoms

How are nitrogen and hydrogen bonded in ammonia?

2.5 1

3 1

1 3

H

H

NH3 or H N H

H

H

C H

Electron configuration

Electrons needed

Ratio of atoms

Covalent bonding in methane

How are carbon and hydrogen bonded in methane?

2.4 1

4 1

1 4

CH4 or H C H

H

H

CH

H

H

H

More covalent bonding diagramsDraw a line diagram to show the bonding in:

1. hydrogen sulfide

3. ethane (C2H6)

2. carbon dioxide OO C

HH SS

H H

H

H

C HC

H