Additional Science Chemistry Revision

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  • Created on: 08-04-14 13:20
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Chemistry:
{Forming ions, ionic compounds, giant ionic compounds, covalent bonds in simple and macro
molecules, properties of simple molecules, properties of macromolecules, metals, polymers,
nanoscience, atomic structure and isotopes, relative formula mass, paper and gas
chromatography, chemical calculations, reacting mass calculations, reaction yields, rates of
reaction, energy changes, acids and alkalis, making salts, making soluble and insoluble salts,
using electricity, useful substances from electrolysis and electrolysis products}
Forming ions:
An ion is formed when an atom loses or gains one or more electrons.
Positive ions:
Metal atoms and hydrogen atoms loses
electrons to form positive ions. For
example, a sodium atom loses its outer
electron to form a sodium ion, Na+.
Negative ion:
Non-metal atoms gain electrons to form
negative ions. For example, a chlorine
atom gains one outer electron to form a
chloride ion, Cl-.
Patterns in the periodic table:
Remember:
The number of charges on positive ions is the same as the group number of the
element.
The number of charges on negative ions is 8 minus the group number of the element.
Group 1 2 3 5 6 7
Charge On Ion + 2+ 3+ 3- 2- -
Ionic Compounds:

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Ionic compounds contain positive and negative ions, formed when atoms transfer electrons.
Group 1 elements (the alkali metals)
The elements in group 1 are metals which react with non0metal elements to form ionic
compound to produce ions with 1+ charge. Lithium, sodium and potassium are in group 1.
Group 7 elements (the halogens)
The elements in group 7 are non-metals which react with metal elements to form ionic
compounds to produce ions with 1- charge. Chlorine, bromine and iodine are in group 7.…read more

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Covalent bonds:
A covalent bond is a shared pair of electrons. It forms
between two non-metal atoms. Covalent bonds are
strong.
Representing covalent bonds:
A covalent bond can be shown in another way: H-H (where the straight line is the bond).
Representing simple molecules:
Hydrogen exists as simple molecules. A simple molecule contains only a few atoms joined
together by covalent bonds. The diagrams show
the bonding in other simple molecules.…read more

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Low melting and boiling points
Substances that exist as simple molecules, such as oxygen (O2):
Have relatively low melting points and boiling points.
Tend to be gases or liquids at room temperature (but can be solid such as wax).
There are weak attractive forces between simple molecules, called intermolecular forces.
When the substance melts or boils:
The intermolecular forces are relatively easy to overcome or break.
The covalent bonds do not break.…read more

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Metals consist of giant structures of atoms packed together in a regular pattern or lattice.
This explains some of their properties. For example, metals can be bent and shaped because
layers of atoms can slide over each other. Metallic bonds are strong.
Conduction in metals
Delocalised electrons in metals are free to move through the structure. This is why metals
conduct heat and electricity.
Polymers:
Thermosoftening polymers
Thermosoftening polymers such as poly(ethane) and poly(propene) consist of individual, t
angled polymer chains.…read more

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Nanotubes are one example of nanoparticles. They are made of carbon and have a structure
similar to graphite layer rolled into a tube. Nanotubes are very strong and can conduct
electricity. They are used to strengthen tennis rackets and golf clubs. They may lead to the
development of new, faster computers.
Atomic structure and isotopes:
Name Of Particle Relative Mass
Proton 1
Neutron 1
Electron Very Small
Numbers
The mass number of an atom is the total number of protons and neutrons in an atom.…read more

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What is Paper Chromatography?
Artificial colourings may be added to food to improve its appearance. Paper chromatography
can be used to detect and identify artificial colours.
Carrying out paper chromatography
To set up paper chromatography:
Draw a pencil line near the bottom of the paper,
Ass spots of colourings to the line,
Put the paper into a chromatography tank with a solvent at the bottom and below the
line.…read more

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Chemical Calculations:
Percentage composition by mass
The atoms of each element in a compound contribute to the total mass of the compound. A
percentage composition is a measure of how much of a particular element is present in a
compound.…read more

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Rates of reaction
The rate of a reaction can be found by measuring: the amount of reaction used over time
and the amount of product made over time,
Colliding particles:
For a reaction to happen reactant particles must collide with each other and the collision
must have enough energy. The minimum amount of energy particles need to react is called
the activation energy. A successful collision has enough energy for a reaction to happen.…read more

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The pH Scale
The pH scale is a measure of the acidity or
alkaliinty of a solution. It goes from 0 to
14. Neutral solutions are pH 7. Incicators
are subtances that hve different colours,
dependsing on their pH. Universal
indicator solution or paer is often used to estimate the pH of a solution. The colour produced
by the indicator is matched to a colour chart, which is shows the pH for each colour.…read more

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