Transcript Atoms and Elements and Compounds, etc

All substances are made of atoms
All substances are made of very tiny particles called atoms.
Many substances are made up of different types of atoms.
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hydrogen and
oxygen atoms
carbon and
hydrogen atoms
iron, aluminium,
silicon, oxygen
and boron atoms
carbon, nitrogen,
hydrogen, oxygen
and sulphur atoms
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What is an element?
All substances are made of very tiny particles called atoms.
There are about one hundred substances that are made up
of just one type of atom. These are the elements.
carbon
helium
copper
The elements are the simplest substances in the universe.
The elements are the building blocks of all other substances.
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Atoms in elements
An element is a substance made up of only one type of atom.
Copper is an
element made up of
copper atoms only.
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Carbon is an
element made up of
carbon atoms only.
Helium is an
element made up of
helium atoms only.
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Atoms and molecules of elements
An element is a substance made up of only one type of atom.
In some elements, the atoms are joined in groups of two or
more. A particle containing atoms grouped in this way is
called a molecule.
Oxygen is an
element made up of
oxygen atoms only.
How many atoms
are there in an
oxygen molecule?
Other elements, that contain atoms joined in molecules are
hydrogen, nitrogen, chlorine and bromine.
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Symbols for molecules of elements
In some elements, the atoms are joined together and
form molecules. Combining the symbols of the atoms
in a molecule gives you the formula of the molecule.
What is the formula for the molecules in each element?
oxygen
nitrogen
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O2
N2
There are
groups of
two atoms
in each
molecule.
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What is a compound?
A compound is the substance produced when two or more
elements combine in a chemical reaction.
Two elements, hydrogen (H)
and oxygen (O), combine to
make the compound, water.
Which two elements combine
to make the compound
carbon dioxide?
A compound is always made up of two or more
different types of atom.
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Making a compound – carbon dioxide
A compound has very different properties to the elements
from which it is made.
elements
carbon
oxygen
combines
with
A black solid
which can be
used as a fuel.
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compound
carbon dioxide
to make
A colourless gas
which is essential
for life.
A colourless gas
which is used
to put out fires.
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Making a compound – water
What are the elements which make up water?
In what ways are the elements different to their compound?
elements
oxygen
hydrogen
combines
with
A colourless gas
which is used in
hot air balloons.
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compound
water
to make
A colourless gas
which is essential
for life.
A liquid which is
essential to our
lives and has many
different uses.
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Element or compound?
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How small is an atom?
Atoms are extremely small – they are about
0.00000001cm wide.
To make an atom the size of a football it would have
to be enlarged by about 3,000,000,000 times.
N
X3,000,000,000
If a football was
enlarged by the same
amount it would
stretch from the UK to
the USA.
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The Amazing Atomic Zoom
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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.
Scientists now know that atoms are actually made
from even smaller subatomic particles. There are
three types:
proton
neutron
electron
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Where are subatomic particles found?
Protons, neutrons and electrons are NOT evenly
distributed in an atom.
The protons and
neutrons exist in a dense
core at the centre of the
atom. This is called the
nucleus.
The electrons are
spread out around
the edge of the
atom. They orbit the
nucleus in layers
called shells.
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Properties of subatomic particles
There are two properties of subatomic particles
that are especially important:
1. Mass
2. Electrical charge
Particle
Mass
Charge
proton
1
+1
neutron
1
0
electron
almost 0
-1
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:
 hydrogen atoms always contain 1 proton;
 carbon atoms always contain 6 protons;
 magnesium atoms always contain 12 protons,
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.
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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.
Atom
Protons
hydrogen
1
lithium
3
aluminium
13
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Neutrons Mass number
0
1
4
7
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How many neutrons?
Number of neutrons = mass number - number of proton
= mass number - atomic number
How many neutrons are there in these atoms?
Atom
helium
Atomic
number
4
2
fluorine
19
9
strontium
88
38
zirconium
91
40
238
92
uranium
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Mass
number
Number of
neutrons
2
10
50
51
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How are electrons arranged?
Electrons are not evenly spread but exist in
layers called shells.
The arrangement of electrons in these shells is
often called the electron configuration.
1st shell
2nd shell
3rd shell
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Summary: the atom so far
The nucleus is:
 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.
Electrons are:
 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.
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What is an isotope?
Elements consist of one type of atom, but sometimes
these atoms can be slightly different.
Although atoms of the same element always have
the same number of protons, they may have different
numbers of neutrons.
Atoms that differ in this way are called isotopes.
mass
number is
different
atomic
number is the
same
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Properties of isotopes
The isotopes of an element are virtually identical
in their chemical reactions.
This is because they have the same number of
protons and the same number of electrons.
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.
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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.
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6 protons
6 protons
6 protons
6 neutrons
7 neutrons
8 neutrons
6 electrons
6 electrons
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
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1 proton
1 proton
1 proton
0 neutrons
1 neutron
2 neutrons
1 electron
1 electron
1 electron
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Summarizing atomic structure
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