Atomic Structure3.ppt.Atomic Structure11

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KS4 Chemistry
Atomic Structure

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Atomic Structure
Electron configuration
Summary activities
Isotopes
Introducing atoms
Atomic number and mass number
Contents

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Discovery of atomic structure

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Atoms – the building blocks
All substances are made from very tiny particles called atoms.
John Dalton had ideas about the
existence of atoms about 200 years
ago but only relatively recently have
special microscopes (called
electron microscopes) been
invented that can ‘see’ atoms.
The yellow blobs in this image are
individual gold atoms, as seen
through an electron microscope.

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Elements – different types of atom
Elements are the simplest substances. There are about
100 different elements.
Each element is made up of just one particular type of atom,
which is different to the atoms in any other element.
Copper is an
element made up of
copper atoms only.
Carbon is an
element made up of
carbon atoms only.

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How small is an atom?
Atoms are extremely small – they are about 0.00000001cm
wide.
N X3,000,000,000
If a football was enlarged
by the same amount it
would stretch from the
UK to the USA.
To make an atom the size of a football it would have to be
enlarged by about 3,000,000,000 times.

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The Amazing Atomic Zoom

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Inside an atom
Where are the electrons and nucleus found in an atom?

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Atomic Structure
Summary activities
Isotopes
Introducing atoms
Contents

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How heavy is an atom?
A single grain of sand contains millions of atoms of silicon
and oxygen.
Each atom must therefore have an extremely small mass.
millions of these atoms
join to form each tiny
grain of sand
Si
O
O

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Relative atomic mass
Atoms are so small that their mass is not measured in grams
but in atomic mass units.
Relative atomic mass = 12
C
The element carbon is the atom that the mass of all other
atoms is compared to. Carbon has a RAM of 12.
The atoms of each type of element have a relative atomic
mass (RAM).

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Relative atomic mass – examples
The lightest atom is hydrogen. It has 1
⁄12 the mass of carbon
and so has a RAM of 1.
Mg
Magnesium is twice as heavy as carbon. It has a RAM of 24.
H
H H H
H H
H
H
H
H H
H
H
H H H
H H
H
H
H
H H
H C
12 atoms x 1 = 1 atom x 12
C
C
Mg
1 atom x 24 = 2 atoms x 12

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Even smaller particles
For some time people thought that atoms were the smallest
particles and could not be broken into anything smaller.
proton
neutron
electron
Scientists now know that atoms are actually made from even
smaller subatomic particles. There are three types:

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Where are subatomic particles found?
Protons, neutrons and electrons are NOT evenly distributed in
an atom.
The electrons are
spread out around the
edge of the atom. They
orbit the nucleus in
layers called shells.
The protons and neutrons
exist in a dense core at the
centre of the atom. This is
called the nucleus.

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The atom: check it out!
Draw a labelled diagram of the atom showing the nucleus
and labelling protons, neutrons and electrons.
nucleus
neutron proton
electron

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Particle Mass Charge
proton 1 +1
neutron 1 0
electron almost 0 -1
Properties of subatomic particles
There are two properties of subatomic particles that are
especially important:
1. Mass
2. Electrical charge
The atoms of an element contain equal numbers of
protons and electrons and so have no overall charge.

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How many protons?
The atoms of any particular element always contain the same
number of protons. For example:
The number of protons in an atom
is known as its atomic number
or proton number.
It is the smaller of the two numbers
shown in most periodic tables.
 hydrogen atoms always contain 1 proton;
 carbon atoms always contain 6 protons;
 magnesium atoms always contain 12 protons,

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What’s the atomic number?
What are the atomic numbers of these elements?
11
sodium
26
iron
50
tin
9
fluorine

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More about atomic number
Each element has a definite and fixed number of protons. If
the number of protons changes, then the atom becomes a
different element.
Changes in the number of particles in the nucleus
(protons or neutrons) is very rare. It only takes place in
nuclear processes such as:
 radioactive decay;
 nuclear bombs;
 nuclear reactors.

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Atom Protons Neutrons Mass number
hydrogen 1 0 1
lithium 3 4 7
aluminium 13 14 27
Mass number
Electrons have a mass of almost zero, which means that the
mass of each atom results almost entirely from the number of
protons and neutrons in the nucleus.
The sum of the protons and neutrons in
an atom’s nucleus is the mass number.
It is the larger of the two numbers shown
in most periodic tables.

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127
What’s the mass number?
What is the mass number of these atoms?
73
59
64
4
Mass number = number of protons + number of neutrons
Atom Protons Neutrons Mass number
helium 2 2
copper 29 35
cobalt 27 32
iodine 53 74
germanium 32 41

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How many neutrons?
How many neutrons are there in these atoms?
Atom
Mass
number
Atomic
number
Number of
neutrons
helium 4 2
fluorine 19 9
strontium 88 38
zirconium 91 40
uranium 238 92
51
146
50
10
2
Number of neutrons = mass number - number of protons
= mass number - atomic number

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Building a nucleus

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Atomic Structure
Summary activities
Isotopes
Introducing atoms
Contents

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Atom Protons Neutrons Electrons
helium 2 2 2
copper 29 35 29
iodine 53 74 53
How many electrons?
Atoms have no overall electrical charge and are neutral.
This means atoms must have an equal number of
protons and electrons.
The number of electrons is therefore the same as
the atomic number.
Atomic number is defined as the number of protons rather
than the number of electrons because atoms can lose or
gain electrons but do not normally lose or gain protons.

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Atom Protons Neutrons Electrons Atomic
number
Mass
number
boron 5 6
potassium 19 20
chromium 24 28
mercury 80 121
argon 18 22
Calculating the number of electrons
5
19
18
24
80
5
19
18
24
80
11
39
40
52
201
What are the missing numbers?

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How are electrons arranged?
Electrons are not evenly spread but exist in layers
called shells.
3rd
shell
2nd
shell
1st
shell
The arrangement of electrons in these shells is often called
the electron configuration.
.

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How many electrons per shell?
Each shell has a maximum number of electrons that it can
hold. Electrons will fill the shells nearest the nucleus first.
3rd
shell holds
a maximum of
8 electrons
2nd
shell holds
a maximum of
8 electrons
1st
shell holds
a maximum of
2 electrons

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Calculating electron configurations

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Properties of the nucleus and electrons

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 Thinly spread around the outside
of the atom.
 Very small and light.
 Negatively charged.
 Found orbiting the nucleus in layers called shells.
 Able to be lost or gained in chemical reactions.
Summary: the atom so far
The nucleus is:
Electrons are:
 Dense – it contains nearly all the mass
of the atom in a tiny space.
 Made up of protons and neutrons.
 Positively charged because of the
protons.

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Atomic Structure
Summary activities
Isotopes
Introducing atoms
Contents

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What is an isotope?
Elements consist of one type of atom, but sometimes these
atoms can be slightly different.
mass number
is different
atomic number
is the same
Atoms that differ in this way are called isotopes.
Although atoms of the same element always have the same
number of protons, they may have different numbers of
neutrons.

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Properties of isotopes
The isotopes of an element are virtually identical in their
chemical reactions.
The uncharged neutrons make no difference to chemical
properties but do affect physical properties such as melting
point and density.
Natural samples of elements are
often a mixture of isotopes.
This is because they have the same number of protons and
the same number of electrons.

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Isotopes of carbon
Most naturally-occurring carbon exists as carbon-12, about
1% is carbon-13 and a much smaller amount is carbon-14.
6 protons
6 neutrons
7 electrons
6 protons
6 neutrons
8 electrons
6 protons
6 neutrons
6 electrons

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Isotopes of hydrogen
Hydrogen-1 makes up the vast majority of the naturally-
occurring element but two other isotopes exist.
hydrogen deuterium tritium
1 proton
0 neutrons
1 electron
1 proton
1 neutron
1 electron
1 proton
2 neutrons
1 electron

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Isotopes of chlorine
About 75% of naturally-occurring chlorine is chlorine-35 and
25% is chlorine-37.
17 protons
18 neutrons
17 electrons
17 protons
20 neutrons
17 electrons

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What are the
particle
numbers in
each isotope?
10
8
8
8
8
8
oxygen-16 oxygen-18
protons
neutrons
electrons
Isotopes of oxygen
Almost all of naturally-occurring oxygen is oxygen-16 but
about 0.2% is oxygen-18.

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Isotopes and RAM
Many elements are a mixture of isotopes. The RAM given in
the periodic table takes account of this.
For example, chlorine exists as two isotopes:
chlorine-35 (75%) and chlorine-37 (25%).
To calculate the RAM of a mixture of isotopes,
multiply the percentage of each isotope by its
atomic mass and add them together.
= (0.75 x 35) + (0.25 x 37)
= 26.25 + 9.25
= 35.5
RAM of chlorine = (75% x 35) + (25% x 37)

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Calculating RAM
Bromine contains 50.5% bromine-79 and 49.5% bromine-81.
= (0.505 x 79) + (0.495 x 81)
= 39.895 + 40.095
= 79.99
= 80 (the RAM is usually rounded
to the nearest whole number)
RAM of bromine = (50.5% x 79) + (49.5% x 81)
What is the RAM of naturally-occurring bromine?

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Summarizing atomic structure

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Atomic structure word check

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Atomic Structure
Summary activities
Isotopes
Introducing atoms
Contents

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Glossary (part 1)
atom – The smallest particle that can exist on its own.
atomic number – The number of protons in the nucleus
of an element, also known as the proton number.
electron – Negative particle that orbits the nucleus of an
atom.
element – Substance made up of only one type of atom.
isotopes – Different atoms of the same element. They have
the same number of protons and electrons, but a different
number of neutrons.

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Glossary (part 2)
nucleus – The dense positive centre of an atom, made up
of protons and neutrons.
neutron – A neutral particle, with a mass of 1. It is found in
the nucleus of an atom.
mass number – The number of protons and neutrons in
an atom.
proton – A positive particle, with a mass of 1. It is found in
the nucleus of an atom.
relative atomic mass (RAM) – The mass of an
element compared to the mass of 1
⁄12 of the mass of carbon-
12.

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Anagrams

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Atomic structure word search

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Properties of subatomic particles

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Multiple-choice quiz

Atomic Structure3.ppt.Atomic Structure11

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