AQA Chemistry 2 Key Points

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C2: Chemistry
C2 1.1: Chemical Bonding.
Elements react together to form compounds by gaining or losing electrons, or by sharing electrons.
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.
C2 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.
C2 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 atoms present in the compound.
Sometimes we need brackets to show the ratio of ions in a compound, e.g. magnesium hydroxide, Mg(OH)2.
C2 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
C2 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.
C2 2.1: Giant Ionic Structures.
It takes a lot of energy to break the many strong ionic bonds which hold the giant ionic lattice together. So
ionic compounds have high melting points. They are all solids at room temperature.
Ionic compounds will conduct electricity when we melt them or dissolve them in water. That's because their
ions can move freely around and carry charge through the liquid.
C2 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.
Simple molecules have no overall charge, so they cannot carry electrical charge. Therefore substances
made from simple molecules do not conduct electricity.

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C2 2.3: 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 overreach 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
Graphite can conduct electricity because of the delocalized electrons along its layers.…read more

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The relative atomic masses of the elements in a compound and its formula can be used to work out its
percentage composition.
We can calculate empirical formulae given the masses or percentage composition of elements present.
C2 3.4: Equations and Calculations.
Balanced symbol equations tell us the number of moles of substances involved in a chemical reaction.
We can use balanced symbol equations to calculate the masses of reactants and products in a
chemical reaction.
C2 3.5: The Yield of a Chemical Reaction.…read more

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The rate of a chemical reaction increases if the surface area of any solid reactants is increased. This
increases the frequency of collisions between reacting particles.
C2 4.3: 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 result in a reaction because a higher proportion of particles
have energy greater than the activation energy.
C2 4.4: The Effect of Concentration or Pressure.…read more

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Endothermic changes can be used in instant cold packs for sports injuries.
C2 5.1: Acids and Alkalis.
Acids are substances which produce H+ ions when we add them to water.
Bases are substances that neutralise acids.
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.
C2 5.2: Making Salts from Metals or Bases.…read more

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Hydrogen is used to make, margarine.
Sodium hydroxide is used to make, bleach, paper and soap.
C2 5.8: Electroplating.
We can electroplate objects to improve their appearance, protect their surface, and to use smaller
amounts of precious metals.
The object to be electroplated is made the negative electrode in an electrolysis cell. The plating metal is
made the positive electrode. The electrolyte contains ions of the plating metal.…read more


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