BMAT chemistry knowledge

a collection of chemistry notes for section 2 of the BMAT

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  • Created on: 31-10-15 11:41
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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 of a nucleus consisting ofprotons and neutrons . The nucleus is
surrounded by electrons . Protons and electrons are oppositely charged. Neutrons have no
charge. This means the nucleus of an atom is always positively charged.
An atom has a neutraloverall charge because it has the same number of electrons as
Protons and neutrons have the same mass.
Electrons have such a small mass that this can
usually be taken as zero.
Comparing the charge and mass of electrons, protons and
Proton Neutron Electron
Charge +1 0 -1
Mass 1 1 0.0005 (almost zero)
The atomic number(also called the proton number) is the number of protons in an atom.
The mass number (also called the nucleon number) is the total number of protons and
neutrons in an atom.
The elements are arranged in the periodic table in ascending order of atomic number so it's
easy to find the name or symbol for an atom if you know the atomic number.
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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.…read more

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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
Energy shells
Electrons are arranged in different shells around the nucleus. The innermost shell - or lowest
energy shell - is filled first.…read more

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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
The electronic structure of an atom is a description of how the electrons are arranged. It can
be shown as numbers or as a diagram.
Electron configuration diagram for lithium
Take lithium for example.…read more

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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 Fluorine atoms have nine electrons. Two of Group 7
these fit into the first energy shell. The
remaining seven fit into the second energy
Ne 2.8 Neon atoms have ten electrons.…read more

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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 has eight main groups. For example, group 1 contains very reactive
metals such as sodium - Na - while group 7 contains very reactive non-metals such as
chlorine - Cl.…read more

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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
The number of charges on an ion formed by a n
on-metal is equal to the group number
minus eight
Hydrogen forms H+
Group Group Group Group Group Group Group Group
1 2 3…read more

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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 of the periodic
Group 1 of the periodic table
Lithium, sodium and potassium are the three group 1 elements you are likely to see at
school.…read more

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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 metals increases down the group. Lithium is the least reactive and
potassium is the most reactive of the three.…read more

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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 example.…read more


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