1. KS4 Chemistry
Comparing Bonding

2. Comparing bonding Bonding and structure Melting and boiling point
Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities

3. Types of bonding
There are three ways in which atoms can chemically bond. In each case, electrons are involved in different ways.
ionic bonding – electrons are transferred from metal to non-metal atoms to form positive and negative ions. These oppositely-charged ions are attracted to each other.
covalent bonding – electrons are shared between non-metal atoms.
metallic bonding – electrons become delocalized and form a sea of free electrons, which attracts positive metal ions.

4. Predicting bonding

5. Bonding and structures
The type of bonding in a substance affects the structure of that substance.
Bonding
Type of structure
Particles in structure
State at room temperature
Ionic
Covalent
Metallic
giant ionic millions of ions solid
lattice
simple few atoms usually liquid or
molecular solid
giant covalent millions of solid
lattice atoms
giant metallic millions of ions solid (except
lattice mercury – liquid)

6. Bonding and properties
The bonding and structure of a substance affects the properties of that substance.
Different bonds require different amounts of energy to be broken – this affects properties such as melting and boiling point, solubility and hardness.
Different bonds involve electrons in different ways – this affects properties such as conductivity of electricity and heat.

7. How do properties differ?
How do the properties of substances differ according to the type of bonding they contain?

8. Comparing bonding Bonding and structure Melting and boiling point
Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities

9. Melting and boiling point: giant structures
Substances with giant structures generally have high melting and boiling points because all the atoms are strongly bonded together to form a continuous 3D lattice. A large amount of energy is needed to break these bonds. + -
strong covalent bonds holds atoms together
strong metallic bonds holds ions
together
strong ionic bonds holds ions together

10. Melting and boiling point: molecules
Simple molecular substances have low melting and boiling points because the forces that hold the molecules together are weak and easily broken.
weak bonds between molecules
strong bonds within molecules
In general, the larger the molecule, the higher the melting and boiling point.

11. Comparing bonding Bonding and structure Melting and boiling point
Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities

12. Conductivity – ionic substances
Ionic substances cannot conduct electricity when solid because the ions are bonded together in the lattice. + -
ions cannot move to carry a charge
When liquid (molten) or dissolved, however, the ions are able to break free of the lattice. + -
ions are able to move and carry a charge

13. Conductivity – covalent substances
Substances with covalent bonding do not conduct electricity because all the outer electrons are fixed in shells.
electrons unable to move and carry a charge
The exception is graphite, which has free electrons between layers of carbon atoms.

14. Conductivity – metals
Metals can conduct electricity because the sea of delocalized electrons between the metal ions are free to move anywhere in the structure.
sea of electrons
metal ions
electrons free to move and carry an electrical charge

15. Bonding and electrical conductivity

16. Comparing bonding Bonding and structure Melting and boiling point
Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities

17. Solubility
Substances with giant covalent or metallic structures generally do not dissolve easily in water or other solvents.
This is because dissolving involves breaking bonds, which needs lots of energy.
Many ionic substances dissolve in water because water molecules have a slight electrical charge and can attract the ions away from the lattice.
Simple molecular substances are usually insoluble in water but soluble in solvents such as petrol.

18. Strength
Substances with giant structures are generally hard because a large amount of energy is needed to break ionic, covalent and metallic bonds.
Ionic substances are hard but brittle – when a force is applied, ions with like-charges are brought together. These repulse each other and cause the lattice to shatter.
Covalent substances are hard but brittle – the covalent bonds do not bend but break when enough force is applied.
Graphite is slippery because the weak forces between layers of carbon atoms can easily be broken.
Metals are hard but malleable and ductile – the delocalized electrons allow the metallic bonds to move.

19. Density
The density of a substance depends on the type and strength of bonding and how the atoms/ions are arranged.
Giant substances, especially metals, are dense because the atoms/ions are tightly packed together.
strong bonds cause tight packing
Substances with simple molecular structures have lower densities. The weak forces between molecules cannot pull the molecules together tightly.
weak bonds cause loose packing

20. Bonding, structure and properties

21. Effect of structure on properties

22. Comparing bonding Bonding and structure Melting and boiling point
Contents
Comparing bonding
Bonding and structure
Melting and boiling point
Conductivity
Other properties
Summary activities

23. Glossary
 covalent bond – A strong bond between two atoms in which each atom shares one or more electrons with the other.
 delocalized – Electrons that are free to move throughout a structure. In metals, they form a ‘sea of electrons’.
 ionic bond – The strong electrostatic force of attraction between oppositely charged ions.
 giant structure – A structure containing millions of atoms or ions bonded together. The structure extends in three dimensions until all available atoms or ions are used up.
 lattice – A 3D structure of closely packed atoms or ions.
 metallic bonding – The strong attraction between positive metal ions and a sea of electrons.
 molecule – A simple structure containing two or more atoms covalently bonded together.

24. Anagrams

25. The effect of bonding on properties

26. Comparing bonding – team game

27. Multiple-choice quiz