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1.1 Atomic structure

The Structure of the Atom
Mass Spectrometry
Electronic Structure
Ionisation Energies

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a) Protons, neutrons and electrons

Atoms are made up of three fundamental particles: protons, neutrons and electrons.

Protons and neutrons are found in the nucleus and are collectively called nucleons.
Electrons orbit the nucleus in a similar way to that in which planets orbit a…

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Not all atoms of the same element have equal numbers of neutrons this may vary slightly.
The sum of the number of protons and neutrons in the nucleus of an atom is called its mass
number. It is represented by the symbol A.

The mass number is the sum of…

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c) Relative atomic mass

The mass of an atom is measured in atomic mass units, where one unit is 12th of the mass of
one atom of carbon12.

The relative isotopic mass of an isotope is the ratio of the mass of one atom of that
isotope to 1/12th of…

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Eg The relative molecular mass of CO2 is 12.0 + 16.0 + 16.0 = 44.0

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The mass spectrometer is an instrument used for measuring the masses of atoms and
molecules. It can also be used to measure the relative abundance of different isotopes and to
predict the structure of more complex molecules.

1. How the mass spectrometer works

The workings of the mass…

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The degree of deflection depends on the mass and the charge the greater the mass, the less
the deflection, and the greater the charge, the greater the deflection. It can be shown that the
deflection is inversely proportional to the m/e ratio.

In most cases, however, the charge is +1,…

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2. Calculating relative atomic masses

The relative atomic mass can be calculated by the formula:
(perentage abundance of each isotope x mass of each isotope)

eg Using the mass spectrum of neon above:

ram = (90 x 20 + 10 x 22)/100 = 20.2

All relative atomic masses have…

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i) Energy levels

Electrons do not orbit the nucleus randomly they occupy certain fixed energy levels. Each
atom has its own unique set of energy levels, which are difficult to calculate but which
depend on the number of protons and electrons in the atom.

Energy levels in an…

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An sorbital in the second energy level is a 2s orbital, etc

porbitals: these are shaped like a 3D figure of eight. They exist in groups of three:

Every energy level except the first level contains three porbitals. Each porbital in the same
energy level has the same energy but…


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