C2

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  • Created on: 17-04-11 14:07
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C2
Structure and Bonding
Atomic structure:
Atoms are made up of protons, neutrons and electrons.
Protons and electrons have equal and opposite electric charges. Protons
are positively charged, and electrons are negatively charged.
Atoms are arranged in the periodic table in order of their atomic
number.
Neutrons have no electric charge. They are neutral.
The arrangement of electrons in atoms
The electrons in an atom are arranged in energy levels or shells
Atoms with the same number of electrons in their outer shell belong in
the same group in the periodic table.
The number of electrons in the outer shell of an atom determines the
way that the atom behaves in chemical reactions.
Chemical Bonding:
Elements react to form compounds by gaining or by sharing electrons
The elements in Group 1 react with the elements in Group 7, because
Group 1 elements can lose an electron to gain a full outer shell
Ionic bonding:
Ionic compounds are held together by strong forces between the
oppositely charged ions.
Other elements that can form ionic compounds include those in Groups
2 and 6.
Covalent bonding:
Covalent bonds are formed when atoms share electrons.
Many substances containing covalent bonds consist of molecules, but
some have giant covalent structures.
Bonding in metals:
The atoms (or ions) in metals are arranged in regular layers.
The positive ions in metals are held together by electrons from the
outer shell of each metal atom. These delocalised electrons are free to
move throughout the metal lattice.

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Structures and properties:
Ionic compounds:
It takes a lot of energy to break the bonds which hold a giant ionic
lattice together. So ionic compounds have very high melting points ­
they are all solids at room temperature.
Ionic compounds will conduct electricity when we melt them or dissolve
them in water because their ions can then move freely.
Simple molecules:
Substances made up of simple molecules have low boiling and melting
points
The forces between simple molecules are small.…read more

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How much?
Mass Numbers:
The relative mass of protons and neutrins is 1
The mass number of an atom tells you the total number of protons and
neutrons in its nucleus.
Isotopes are atoms of the same element with different numbers of
neutrons.
Masses of atoms and moles:
We compare the masses of atoms by measuring them relative to atoms of
Carbon-12
We work out the relative formula mass of a compound from the relative
atomic masses of the elements in it.…read more

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Rates of reaction:
How fast?
Knowing and controlling the rate of chemical reactions is important in
living cells, in the laboratory and in industry.
We can measure the rate of a reaction by following the rate at which
reactants are used up. Alternatively, we can measure the rate at which
products are made.
Collision Theory:
The minimum amount of energy that particles must have in order to
react is called the activation energy.…read more

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Energy and reactions:
Exothermic and endothermic reactions:
Energy may be transferred to or from the reacting substances in a
hemical reaction.
A reaction where energy is transferred from the reacting substances is
called an exothermic reaction
A reaction where energy is transferred to the reacting substances is
called an endothermic reaction
Energy and reversible reactions:
In reversible reactions, one reaction is exothermic, and the other is
endothermic.…read more

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Electrolysis:
The basics:
Electrolysis is splitting up a substance using electricity
Ionic substances can be electrolysed when they are molten or in
solution.
In electrolysis, positive ions move to the cathode, and negative ions
move to the anode.
Changes at the electrodes:
In electrolysis, the ions move towards the oppositely charged
electrodes, where negative ions are oxidised, while positive ions are
reduced. These are called redox reactions.
When electrolysis happens in water, the less reactive the element is
usually produced at an electrode.…read more

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Acids, alkalis and salts:
Acids and alkalis:
Acids are substances that produce H+ ions in water
Bases neutralise acids
And alkali is a soluble base, which produces OH- iond when we add them
to water.
Acids are pH 0-6. Alkali are pH 8-14
Making salts from metals or bases:
Acid + Base = Salt + Water ­ This is a neutralisation reaction.
Salts can also be made by reacting a metal with an acid. This reaction
produces hydrogen gas as well as salt.…read more

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