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© Boardworks Ltd 20071 of 47
© Boardworks Ltd 20072 of 47
Chapter 2
Atomic
Structure
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2.1 Atoms and
Elements
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16-09-2021
Thursday
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1 Atoms are made up of three
different particles:
• protons, which are positively charged
• neutrons, which have no charge
• electrons, which are negatively charged.
The negatively charged particles are arranged in different shells
(energy levels) around the nucleus of the atom. The particles
with a negligible mass are the electrons. All atoms of the same
element contain the same number of protons and neutrons.
Atoms of the same element with different numbers of neutrons
are known as isotopes.
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2 a 3
b 4
c 7
d
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The electrons in an atom are arranged in a series of shells
around the central nucleus. These shells are also called
energy levels. In an atom, the shell closest / nearest to the
nucleus fills first, then the next shell, and so on. There
is room for:
• up to two electrons in the first shell
• up to eight electrons in the second shell
• up to eight electrons in the third shell.
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The elements in the Periodic Table are organized in the
same way as the electrons fill the shells. Shells fill from left
to right across the rows of the Periodic Table.
• The first shell fills up first, from hydrogen to helium.
• The second shell fills next, from lithium to neon.
• Eight electrons go into the third shell, from sodium to
argon.
• Then the fourth shell starts to fill, from potassium.
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4 a Mg (magnesium)
b F (fluorine)
c K (potassium)
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5 a boron / 2,3
b phosphorus / 2,8,5
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b one (the atoms of element B)
c B and C
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d 3
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8 a 38
b 53
c 78
d 137 – 55 = 82
e Isotopes are different atoms of the same
element that have the same proton
number but different nucleon numbers.
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9 a B
b E
c A and C
d B and D
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10 a 2 protons, 2 neutrons, +2
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10 b The gold atoms are packed together in a
regular arrangement (lattice) / in layers / the
atoms can only vibrate about fixed positions.
c This suggests that the atoms were largely empty
space through which the α-particles passed.
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d These α-particles had made direct hits on
the nuclei of the gold atoms. They are
repelled backwards because the nucleus of
the atom is positively charged and so are the
α-particles.
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b The chemical properties of isotopes of the same element
are the same because the number and arrangement of
electrons in the isotopes are the same / the atoms of the
isotopes all have the same number of outer electrons.
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