© Boardworks Ltd 2005 1 of 49 Atomic Structure Electron configuration Summary activities Isotopes...
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© Boardworks Ltd 2005 1 of 49 Atomic Structure Electron configuration Summary activities Isotop es Introducing atoms Atomic number and mass number Contents
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Transcript of © Boardworks Ltd 2005 1 of 49 Atomic Structure Electron configuration Summary activities Isotopes...
© Boardworks Ltd 20051 of 49
Atomic Structure
Electron configuration
Summary activities
Isotopes
Introducing atoms
Atomic number and mass number
Contents
© Boardworks Ltd 20052 of 49
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 sandSi
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 = 12C
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).
© Boardworks Ltd 20054 of 49
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.
HH H HH H
HH
HH HH
HH H HH H
HH
HH HH C
12 atoms x 1 = 1 atom x 12
CCMg
1 atom x 24 = 2 atoms x 12
© Boardworks Ltd 20055 of 49
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 numberor 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.
© Boardworks Ltd 200513 of 49
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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
© Boardworks Ltd 200515 of 49
Building a nucleus
