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Page 1

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Atomic structure
All material things are made from atoms. There are just over one hundred different types of
atom, called elements. Atoms can join together in millions of different combinations to
make all the substances on Earth and beyond.

Structure of the atom
Every atom is made…

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Section of the periodic table showing elements ascending by atomic number


The chemical symbol for carbon
The full chemical symbol for an element shows its mass number at the top and atomic
number at the bottom. Here is the full symbol for an isotope of carbon, carbon-12 or 12…

Page 3

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Isotopes of chlorine
Chlorine atoms contain 17 protons and 17 electrons. About 75 per cent of chlorine atoms
have 18 neutrons, while about 25 per cent have 20 neutrons.

Isotopes of chlorine

Isotope Protons Electrons Neutrons

17 17 35 - 17 = 18

17 17 37 - 17 = 20…

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Arrangement of electrons in a lithium atom

Arrangement of electrons in a carbon atom
A calcium atom has 20 electrons. Two are in the first energy shell, and eight in the second
energy shell, eight in the third energy shell and two in the fourth energy shell.

Electronic structure

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The electronic configuration for lithium is written as 2.1 (showing that lithium atoms have
three electrons, two in the first shell and one in the second shell).
The table describes the electronic structures of four more elements.

Electronic structures of elements

Element Numeric Electrons Periodic
format table group

F 2.7…

Page 6

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The periodic table
There are more than 100 different elements. The periodic table is a chart showing all the
elements arranged in a particular way. The vertical columns in the periodic table are called
groups. Each group contains elements that have similar properties.

The modern periodic table
The periodic table…

Page 7

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Positively charged sodium and aluminium ions

Negatively charged oxide and chloride ions

How many charges?
There is a quick way to work out what the charge on an ion should be:
The number of charges on an ion formed by a metalis equal to the group number of the

Page 8

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There is a strong electrostaticforce of attraction between these oppositely charged ions,
called an ionic bond . The animation shows ionic bonds being formed in sodium chloride,
magnesium oxide and calcium chloride.

The alkali metals
The group 1 elements are placed in the vertical column on the left hand side…

Page 9

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Metal + water metal hydroxide + hydrogen
For example, here are the equations for the reaction of sodium with water:
sodium + water sodium hydroxide + hydrogen 2Na + 2H2O
2NaOH + H
2(the 2s in front
of Na, H2O and NaOH are for balancing)
The reactivity of the alkali…

Page 10

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The melting points show a pattern, or trend, down the group. It is therefore possible to
predict that the melting point of rubidium is between 29°C and 63°C (it is actually 39°C). The
same can be done with other physical properties, such as the densities of rubidium and
caesium, for…


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