AQA GCSE Chemistry Unit 2 - Key Points for C2

HideShow resource information
  • Created by: chaitz
  • Created on: 12-06-13 18:03
Preview of AQA GCSE Chemistry Unit 2 - Key Points for C2

First 427 words of the document:

AQA Chemistry Unit 2 ­ Key Points
1.1 Chemical bonding
Elements react together to form compounds by gaining or losing electrons or by sharing
The elements in Group 1 react with the elements in Group 7. As they react, atoms of Group
1 elements can each lose one electron to gain the stable electronic structure of a noble gas.
This electron can be given to an atom from Group 7, which then also achieves the stable
electronic structure of a noble gas.
1.2 Ionic Bonding
Ionic compounds are held together by strong forces of attraction between the oppositely
charged ions. This is called ionic bonding.
Besides the elements in Groups 1 and 7, other elements that can form ionic compounds
include those from Groups 2 and 6.
1.3 Formulae of ionic compounds
The charges on the ions in an ionic compound always cancel each other out.
The formula of an ionic compound shows the ratio of ions present in the compound.
Sometimes we need brackets to show the ratio of ions in a compound, e.g. magnesium
hydroxide, Mg(OH)2.
1.4 Covalent bonding
Covalent bonds are formed when atoms share pairs of electrons.
Many substances containing covalent bonds consist of simple molecules, but some have
giant covalent structures.
1.5 Metals
The atoms in metals are closely packed together and arranged in regular layers.
We can think of metallic bonding as positively charged metal ions, which are held together by
electrons from the outermost shell of each metal atom. These delocalized electrons are free to
move throughout the giant metallic lattice. (higher)
2.1 Giant ionic structures
It takes a lot of energy to break the many strong ionic bonds which hold a giant ionic lattice
together. So ionic compounds have high melting points. They are all solids at room
Ionic compounds will conduct electricity when we melt them or dissolve them in water.
That's because their ions can then move freely around and can carry charge through the
2.2 Simple molecules
Substances made up of simple molecules have low melting points and boiling points.
The forces between simple molecules are weak. These weak intermolecular forces explain why
substances made of simple molecules have low melting points and boiling points. (higher)
Simple molecules have no overall charge, so they cannot carry electrical charge. Therefore
substances made of simple molecules do not conduct electricity.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Giant covalent structures
Some covalently bonded substances
have giant structures. These substances have high melting points and boiling points.
Graphite contains giant layers of covalently bonded carbon atoms. However, there are no
covalent bonds between the layers. This means they can slide over each other, making
graphite soft and slippery. The atoms in diamond have a different structure and cannot slide
like this. So diamond is a very hard substance.
Graphite can conduct electricity because of the delocalized electrons along its layers.…read more

Page 3

Preview of page 3

Here's a taster:

We can calculate empirical formulae given the masses or percentage composition of elements
present. (higher)
3.4 Equations and calculations
Balanced symbol equations tell us the number of moles of substances involved in a chemical
We can use balanced symbol equations to calculate the masses of reactants and products in a
chemical reaction. (higher)
3.5 The yield of a chemical reaction
The yield of a chemical reaction describes how much product is made.…read more

Page 4

Preview of page 4

Here's a taster:

The effect of temperature
Reactions happen more quickly as the temperature increases.
Increasing the temperature increases the rate of reaction because particles collide more
frequently and more energetically. More of the collisions results in a reaction because a
higher proportion of particles have energy greater than the activation energy.
4.4 The effect of concentration or pressure
Increasing the concentration of reactants in solutions increases the frequency of collisions
between particles, and so increases the rate of reaction.…read more

Page 5

Preview of page 5

Here's a taster:

An alkali is a soluble hydroxide. Alkalis produce OH- ions when we add them to water.
We can use the pH scale to show how acidic or alkaline a solution is.
5.2 Making salts from metals or bases
When we react an acid with a base a neutralisation reaction occurs.
The reaction between an acid and a base produces a salt and water.
Salts can also be made by reacting suitable metal with an acid. This reaction produces
hydrogen gas as well as a salt.…read more

Page 6

Preview of page 6


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »