CHEM 1 Revision

Basically, a recap of all the things covered in the first Chemistry Unit - Atoms and Bonding - for the AQA GCSE exam board.

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  • Created by: L Lawliet
  • Created on: 25-02-12 16:10
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CHEM 1 Revision - Structure and
Bonding (Unit 1)
1. Atoms and elements
A substance that is made of only one type of atom is called an element. There are about 115
different elements.
Structure - Atoms have a small central nucleus made of positive particles called protons and
neutral particles called neutrons. Around the nucleus there are negative electrons. In an atom,
the number of protons is equal to the number of electrons, because the overall charge of an
atom is always neutral.
Elements - These are substances that cannot be broken down into simpler substances. They
contain only one type of atom.
Atomic number - This is the number of protons in an atom. The atomic number determines the
chemical nature of each atom.
Periodic Table - This is arranged in order of atomic number. Vertical columns are called groups
and horizontal rows are called periods. Elements are in the same group if they have the same
number of outer electrons.
Atomic Mass - This is the number of protons + number of neutrons in the atom.
Isotopes - These are atoms with the same number of protons but a different number of
electrons. Isotopes have the same chemical properties but different physical properties
because the isotopes of an element all have the same number of protons and same outer
number of electrons in the atom.
Atoms are mostly empty space. They are extremely small. The nucleus is denser than any other
part of the atom.
Particles Mass Column
Protons 1 +1
Electrons 1/2000 -1
Neutrons 1 0
The reason the electrons does not collapse into the protons is because electrons can only be in
certain shells; they cannot ever be in any other place.

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Radioactivity - If an element is unstable, it can collapse to make itself stable. When this process
emits radiation waves, it is called radiation or radioactivity.
Structure - An atom has several shells, in which only a certain number of electrons in each. The
first shell contains 2 electrons maximum, the second shell contains 8 electrons maximum and the
third shell contains 8 electrons maximum.
Chemical reactions can neither create nor destroy atoms.
Ionisation Energies - An atom with a charge is called an ion.…read more

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Compounds
Compounds are made of more type of atom which are bonded together. The different atoms in
a compound are in a definite fixed ratio. They are substances in which two or more elements are
combined in fixed proportions by mass.
The chemical formula shows the number and type of atoms that are bonded to make the
compound. No atoms are gained or lost during a chemical reaction, so we can write balanced
equations showing the atoms involved.
4.…read more

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In a metal, the metal cations are arranged in a close packed lattice surrounded by a sea of
mobile, delocalised, valence electrons. The strong electrostatic attraction between the positive
metal cations and the sea of mobile, delocalised, valence electrons is called a metallic bond.
Metallic bonding is the bonding of a pure metal by releasing each atom's electron, resulting in a
series of qualities. In a metallic bond, the electrons move.
6. Properties of Metals
Metals are shiny.…read more

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Non-metal atoms gain electrons to form negative ions (also known as anions). These non-metal
anions often have noble gas configurations of electrons. Non-metal ions are usually negatively
charged.
The strong electrostatic attraction between positive ions and negative ions is called an ionic
bond.
This diagram is a dot and cross diagram. Note how the two excess electrons in the example of
MgO moves from the Mg atom to the O2 atom forming an ionic bond.
The [ ] shows that it is an ion.…read more

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Ionic compounds have high melting points and boiling points because a lot of energy is needed
to pull the ions in the lattice apart.
Ionic compounds cannot conduct as solids because the ions are not free to move in a solid lattice.
If the ionic compound is melted/molten or dissolved in water, the ions are free to move and so
the ionic compound will conduct electricity because the ions carry a charge.
8.…read more

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