Edexcel AS Chemistry - Chapter 1.3 Atomic Structure and the periodic table

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Chapter 1.3
A mass spectrometer finds the relative atomic mass of an atom.
The sample must be in a The vapour is bombarded with high The ions are
gaseous state. The sample is energy electrons which collide with accelerated by an
injected into the mass the atoms of the sample. They electric field.
spectrometer and is first knock out electrons to form positive
vaporised. ions (cations +1).
The strength of the magnetic field The ions enter a uniform magnetic
They pass through
is steadily increased. At any field, which deflects them. The
a velocity sector,
particular setting only ions of one amount they are deflected depends
which makes
particular mass: charge ratio will on the mass and charge on the ion.
them all travel at
pass through and be detected, The heavier the ions, the less they are
the same velocity.
others will be deflected too much deflected. Ions with a smaller charge
or too less to pass through. are deflected less.
Ionisation energy ­ The amount of energy needed to remove an electron from an atom.
It's an endothermic process.
The first ionisation energy is a measure of how tightly or loosely the outer electron is attracted to
the positive nucleus. The less tightly it is bound, the, more easily it is removed, and the more
reactive it is.
To calculate the total energy to remove the first and second electron, you have to add the first and
second ionisation energies together.
Shell Subshells Orbital Maximum number of electrons
1 1s s 2
p 6
2 2s 2p
d 10
3 3s 3p 3d
f 14
4 4s 4p 4d 4f

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Elements in the same group have the same number of electrons in their outer shell.
Elements in the same period have the same number of electron shells. E.g. elements in period 1
have one shell; those in period 2 have 2 shells etc.
Elements in the s block have outer electrons in the s subshells; those in the p block have outer
electrons in p subshells etc.
s-block elements ­ Group 1 and group 2 elements.
- The outermost electrons are in the s subshells.…read more

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The atomic radius generally decreases across a period ­ As you go across a period, the effective
nuclear charge increases as the number of protons in the nucleus increases. The number of electrons
also increases, but the outer electrons are all in the same shell, so they are attracted more strongly
to the nucleus, thus reducing the atomic radius across a period.
The atomic radius generally increases down a group ­ The outer electrons enter new energy levels
passing down a group.…read more


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