atoms and subatomic particles -...
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Atoms and Subatomic Particles
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Atoms and Subatomic Particles
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What are atoms made of?
What is the size of one atom in nanometres (nm)?
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What particles are atoms made of?
protons neutrons electrons
Atoms are made up of three smaller, or subatomic, particles:
The electrons are spread out
around the edge of the atom.
They orbit the nucleus in layers
called shells (energy levels).
The protons and neutrons exist in a
dense core at the centre of the atom.
This is called the nucleus.
The radius of a nucleus is less
than 1/10,000 of that of the atom.
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particle relative mass relative chargeproton
neutron
electron
There are two properties of protons, neutrons
and electrons that are especially important:
relative mass
relative electrical charge.
The atoms of an element contain equal numbers of protons and electrons and so have no overall charge.
-1almost 0
01
+11
Mass and electrical charge
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Properties of subatomic particles
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Discovering atomic structure
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Summary: atomic structure
The nucleus is:
made up of protons and neutrons
positively charged because of the
protons
dense because it contains most of the
mass of the atom in a tiny space.
Electrons are:
very small and light, and negatively charged
able to be lost or gained in chemical reactions
found thinly spread around the outside of the nucleus,
orbiting in layers called shells (energy levels).
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Atoms and Subatomic Particles
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How many protons?
Each element has a definite and fixed number of 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 the 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.
If the number of protons changes, then the atom becomes
a different element.
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sodium
iron
tin
fluorine
The atomic number (proton number)
What are the atomic (proton) numbers of these elements?
11
26
50
9
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What is 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.
1413aluminium
43lithium
01hydrogen
neutronsprotonsatoms mass number
27
71
It is the larger of the two numbers shown
in most periodic tables.
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mass number = number of protons + number of neutrons
What is the mass number?
What is the mass number of these atoms?
3227
3529
22
59
64
4
cobalt
copper
helium
neutronsprotonsatoms mass number
iodine
germanium
53
32
74
41 73
127
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Building a nucleus
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What are the missing numbers?
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Sodium (Na) can form an Na+ ion.
11 protons
12 neutrons
10 electrons
Na+ has a charge of +1 because it has lost one electron,
and has one more proton than electrons.
How many protons, electrons and neutrons does Na+ have?
Use the tile from the periodic table below to help you.
Charged particles: ions
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Atoms and Subatomic Particles
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Introduction to electron shells
A Danish scientist called Niels Bohr suggested that electrons
orbit the nucleus in fixed energy levels called shells.
The arrangement
of electrons can be
written from the
lowest energy level
to the highest.
1st shell holdsa maximum of
2 electrons
2nd shell holds
a maximum of
8 electrons
3rd shell holds
a maximum of
8 electrons
Each shell has a maximum number of electrons that it is able
to hold. Electrons fill the shells nearest the nucleus first.
This electron arrangement of this
atom is written as 2,8,8.
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How are electrons arranged?
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Calculating electron arrangement
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Atoms and Subatomic Particles
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Glossary
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True or false?
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Multiple-choice quiz