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Relative Atomic Mass
The link between the mass of an element and the number of atoms it contains is the relative atomic
mass of the element.

The relative atomic mass of an element is the mass of its atom relative to carbon-12

The relative atomic mass scale is used to…

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Amount of substance is measure using a unit called the mole.

A mole of a substance is the amount of substance which contains as many formula units as there are
atoms in 12g of carbon.

One mole of atoms or molecules of any substance will have a mass in…

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Empirical and Molecular Formulas
The empirical formula gives just the smallest whole number ratio of atoms in a compound
The molecular formula gives the actual numbers of atoms in a molecule
The molecular formula is made up of a whole number of empirical units

E.g. a molecule has an empirical…

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The Atom
Atoms are made up of protons, neutrons and electrons

Electrons move around the nucleus in shells. These shells take up
most of the volume of an atom.

Most of the mass of the atom is concentrated in the nucleus.
The nucleus is where you find the protons…

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Atomic Models

Dalton's Theory ­ 1803

Formed the atomic theory, which stages that all matter is composed of tiny
indestructible particles called atoms that are all alike and have the same atomic weight.

Tomson's Theory ­ 1897

Discovered the electron and developed the plum pudding model of the atom


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Nuclear Reactions
Some isotopes of some elements are unstable. Their nuclei break down spontaneously, and they
are described as being radioactive. These isotopes are called radioisotopes. As these nuclei break
down, they emit rays and particles called emissions. This breakdown (or radioactive decay) occurs
of its own accord ­ it…

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Nuclear Equations
Alpha Decay

Involves the emission of alpha particles which helium nuclei.
The isotope produced by alpha decay will have a mass number four units lower and a
nuclear charge two units lower than the original atom
E.g. 238 234 4
U Th + He
92 90 2


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Nuclear Fusion
In a nuclear fusion reaction, two light atomic nuclei fuse together to form a single,
heavier nucleus of a new element. The process release enormous quantities of energy.

Fusion reactions only occur at very high temperatures, such as those found in the sun
and other stars. For two…

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Electronic Structure
Electrons move around the nucleus in shells (sometimes called energy levels)

Shells further from the nucleus have a greater energy level than shells closer to the

Shells can only hold so many electrons:

Electron Shell 1st 2nd 3rd 4th
Maximum No. 2 8 18 32
of electrons…


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