Download KS4 The atom

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
recently have special
microscopes been invented
that can “see” them.
Water
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Elements – different types of atom
• Elements are the simplest
substances. There are
about 100 different
elements. Two of John
Daltons ideas were:
– Elements contain different
types of atom.
– Each element has only one
type of atom.
O
S
N
Fe
K
C
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Atoms – How Small?
N
• Atoms are about 1/100,000,000 cm
across. They are small.
X 3,000,000,000
• To make an atom the size of a football
we would have to magnify it to around
3,000,000,000 times its normal size
• If we magnified the size of a football by
the same amount it would stretch from
the UK to the USA!
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Even Smaller Particles!
• For some time people thought atoms were
the smallest particles and that they could
not be broken into anything smaller.
• We now know that atoms are themselves
made from even smaller and simpler
particles.
• These particles are
– Protons
– Neutrons
– Electrons
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How Are the Particles Arranged?
• Protons, neutrons and electrons are
NOT evenly distributed in atoms.
• The protons and neutrons exist in a
dense core called the nucleus.
• Around the outside are very thinly
spread electrons.
• These electrons exist in layers
called shells.
The Nucleus
a dense core of
protons and
neutrons
containing
nearly all the
mass of the
atom
‘Shells’ of electrons
electrons are really very very tiny
so the atom is mostly empty
space.
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Properties of Sub-atomic Particles
• There are two properties of sub-atomic
particles that are especially important:
– Mass
– Electrical charge
Particle
Protons
Neutrons
Electrons
Charge Relative Mass
+1
1
0
1
-1
0.0005
Element atoms contain equal numbers of protons and
electrons and so have no overall charge
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Atomic Number
• The atom of any particular element always
contains the same number of protons. E.g.
– Hydrogen atoms always contain 1 proton
– Carbon atoms always contain 6 protons
– Magnesium atoms always contain 12 protons
12
• The number of protons in an atom is known
as its atomic number.
• It is the smaller of two numbers shown in
most periodic tables
C
6
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How Many Protons?
• Note that any element has a definite and
fixed number of protons.
• If we change the number of protons in an
atom then this changes that atom into 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
or nuclear reactors.
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Mass Number
• The mass of each atom results almost entirely
from the number of protons and neutrons that
are present. (Remember that electrons have a
relatively tiny mass).
• The sum of the number of protons and
neutrons in an atom is the mass number.
Atom
Protons
Neutrons Mass Number
Hydrogen
1
0
1
Lithium
3
4
7
Aluminium
13
14
27
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How Many Neutrons 2
• It is not strictly true to say that elements
consist of one type of atom.
• Whilst atoms of a given element always
have the same number of protons, they
may have different numbers of neutrons.
• Atoms that differ in this way are called
isotopes.
Remember: The number of
protons defines
the element
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How Many Neutrons 3
• Isotopes are virtually identical in their chemical
reactions. (There may be slight differences in
speeds of reaction).
• 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.
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Isotopes: Carbon
• Natural samples of elements are often a
mixture of isotopes. About 1% of natural
carbon is carbon-13.
12
6
13
C
99%
6
6
6
1%
Protons
Electrons
Neutrons
6
C
6
6
7
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Isotopes: Hydrogen
• Hydrogen exists as 3 isotopes although
Hydrogen-1 makes up the vast majority of the
naturally occurring element.
1
1
H
Protons
Electrons
Neutrons
Hydrogen
2
1
H
Protons
Electrons
Neutrons
(Deuterium)
3
1
H
Protons
Electrons
Neutrons
(Tritium)
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Isotopes: Chlorine
• About 75% of natural chlorine is 35Cl the rest is
37Cl.
37
35
Cl
17
Protons
Electrons
Neutrons
17
17
18
75%
Cl
17
25%
Protons
Electrons
Neutrons
17
17
20
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Activity
Isotopes of Oxygen
16
• Almost all of natural oxygen is
but
about 0.2% is 18O.
• Produce a Table showing the particles
in each isotope.
16O
Oxygen-16
O
8
Oxygen-18
Protons
8
Protons
8
Electrons
8
Electrons
8
Neutrons
8
Neutrons
10
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Isotopes and Relative Atomic Mass
• Many natural elements are a mixture of
isotopes.
• This means that when we react atoms of an
element we are using a mixture of atoms with
different mass numbers.
• The relative atomic mass given in the
periodic table takes account of this.
E.g.. For 100 atoms of chlorine:
Mass of 75 atoms of Chlorine 35: 75 x 35 =2625
Mass of 25 atoms of Chlorine 37: 25 x 37 =925
Total
= 3550
Average (divide by 100)
= 35.5
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Activity
Drag the statements at the top onto the correct
side of the table
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Activity
Drag the statements at the top onto the correct
side of the table
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Summary: The atom so far!
The nucleus.
• Dense: contains nearly all the mass of the
atom in a tiny space.
• Made up of protons and neutrons.
• Has a positive charge because of the protons.
The electrons.
• Exist thinly spread around the outside of the
atom.
• Very small and light.
• Negatively charged.
• Exist in layers called shells.
• Can be lost or gained in chemical reactions.
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How Are Electrons Arranged?
• Electrons are not evenly spread.
• The exist in layers known as shells.
• The arrangement of electrons in these shells is
often called the electron configuration.
1st Shell
2nd Shell
3rd Shell
4th Shell
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How Many Electrons per Shell?
• Each shell has a maximum number of
electrons that it can hold.
The maximum
1st Shell: 2 electrons
2nd Shell: 8 electrons
3rd Shell: 8 electrons
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Which Shells Do Electrons go into?
• Opposites attract.
• Protons are + and electrons are – charged.
• Electrons will occupy the shells nearest the
nucleus unless these shells are already full.
1st Shell: Fills this first
2nd Shell: Fill this next
3rd Shell: And so on
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Working Out Electron Arrangements
1. How many electrons do the element atoms
have? (This will equal the atomic number).
2. Keeping track of the total used, feed them into
the shells working outwards until you have used
them all up.
Drawing neat
diagrams helps you
keep track!
1st Shell: Fills this first
2nd Shell: Fill this next
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The Electrons in Carbon
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The Electrons in Neon
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The Electrons in Silicon
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Electrons in Phosphorus
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The Electrons in Argon
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The Electrons in Sodium
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The Electrons in Fluorine
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The Electrons in Aluminium
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The Electrons in Nitrogen
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The Electrons in Sulfur
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The Electrons in Oxygen
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The Electrons in Chlorine
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The Electrons in Magnesium
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Ions and Electron Structures
1. Ions are atoms that have either extra
electrons added or electrons removed. e.g.
Atoms
Protons
Electrons
Lose 1 electron
1+ ion
Gain 1 electron
Protons
Electrons
So in ions the
number of
electrons no
longer equals the
number
1- ion
Protons
Electrons
of protons
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Positive Ions
•
These are ions formed by the atom losing one or
more electrons.
Lost 1 e-
•
•
•
+
They are called cations. This is because during
electrolysis
(Or
It is nearly they move towards the cathode.
Ions usually
always they are Lost
because
“pussytive”!).
have
2 e2+
metal
OUTER
atoms
that on the ions is equal to theelectron
The
charge
number of
lose
electrons
that the atom
has lost. shells that
Lost 3 e
electrons
3+
are either
completely
In equations the charge is usually shown
above
2+or).else
full
and to the right of the symbol. (E.g. Mg
empty
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The Electrons in a Sodium Ion
In the sodium atom
Atomic number = number of protons
Number of electrons = 11
Na
23
= 11 Na
11
Na+
Bye!
Electron
lost
Electron arrangement:
2.8.1 (Incomplete Shell)
Electron arrangement:
2.8 (Full Shells)
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The Electrons in a Magnesium Ion
In the magnesium atom
Atomic number = number of protons
Number of electrons = 12
24
= 12 Mg
12
Bye!
Mg2+
Mg
Bye!
Electron arrangement =
2.8.2 (Incomplete shell)
2 electrons
lost
Electron arrangement
2.8 (Full Shells)
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Activity
The Lithium Ion
•How many electrons?
3
•How many electrons in the first shell?
2
•How many electrons in the second shell?
1
What electron arrangement?
7
Li
3
2.1
1st Shell = 2: full
2nd Shell = 1: not full
How many electrons to lose?
1
Li
Li+
New electron arrangement?
Include a diagram
Bye!
2.(0)
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Activity
The Boron Ion
•How many electrons?
5
•How many electrons in the first shell?
2
•How many electrons in the second shell?
3
What electron arrangement?
11
B
5
2.3
1st Shell = 2: full
2nd Shell = 3: not full
How many electrons to lose?
New electron arrangement?
Bye!
Bye!
3
BB3+
Bye!
2.(0)
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Negative Ions.
•
These are ions formed by the atom gaining one
or more electrons.
Gain 1 e
•
They are called anions. This is because during
It is nearly
Ions usually
electrolysis
they
move
towards
the
anode.
always
have
non-metal
OUTER
The
charge
number of
atoms
that on the ions is equal to theelectron
gain
electrons
that the atom has gained.shells that
Gain 3 eelectrons
3are either
completely
In equations the charge is usually shown
above
2- or
and to the right of the symbol. (E.g.. Ofull
). else
empty
Gain 2 e
•
•
-
2-
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The Electrons in a Sulphide Ion.
In the sulphur atom
Atomic number = number of protons
Number of electrons = 16
32
S
= 16
16
S2-
S
2 electrons
gained
Electron arrangement:
2.8.6 (incomplete shell)
Electron arrangement
2.8.8 (Full shells)
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The Electrons in a Fluoride Ion.
In the fluorine atom
Atomic number = number of protons
Number of electrons = 9
19
=9
F
9
F2-
F
1 electron
gained
Electron arrangement:
2.8.7 (incomplete shell)
Electron arrangement
2.8.8 (Full shells)
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Activity
The Oxide Ion
8
•How many electrons?
•How many electrons in the first shell?
2
•How many electrons in the second shell?
6
What electron arrangement?
16
O
8
2.6
1st Shell = 2: full
2nd Shell = 6: not full
How many electrons to gain?
2
OO2-
New electron arrangement?
2.8
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Drag the words at the top to their correct
places in the sentences.
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Word check
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1. Which of the following is not a subatomic particle?
A.
B.
C.
D.
Proton.
Isotope.
Neutron.
Electron.
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2. The element Cobalt has a relative atomic
mass of 59 and an atomic number of 27.
Which of these is a true statement about
each neutral cobalt atom?
A.
B.
C.
D.
It contains 59 neutrons.
It contains 27 electrons.
It contains 32 protons.
It contains equal numbers of neutrons and
electrons.
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3. The Periodic Table displays iron as shown
below. This indicates that Fe atoms:
56
A.
B.
C.
D.
Fe
contain 56 neutrons.
26
contain 30 electrons.
contain 26 protons.
contains more protons than neutrons.
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4. Bromine consists of a mixture of two
isotopes: Bromine-79 and Bromine-81
• Which of the following is true:
80
Br
A.
B.
C.
D.
35
Both isotopes contain 35 protons.
Bromine 79 contains 46 neutrons.
Bromine 81 contains 44 neutrons.
Bromine-81 is more reactive than bromine79.
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5. Natural boron consists of approx. 20%
boron-10 and 80% boron-11.
• What will the relative atomic mass of natural
boron will be?
?
A.
B.
C.
D.
10.0
11.0
10.5
10.8
B
5
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6. Which answer best describes the shell
arrangement of the electrons in a sodium
atom?
23
Na
11
A.
B.
C.
D.
2,8,1.
2,2,7.
2,8,8,3.
2,8,8,1.
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7. Which answer best describes the shell
arrangement of the electrons in an
oxygen atom?
16
O
A.
B.
C.
D.
2,8,6.
2,8,8.
2,8.
2,6.
8
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8. Which of these elements will have
electron shells that are either full or
empty (i.e. not partially full)?
A
14
N
B
7
C
40
Ca
20
40
Ar
18
D
27
Al
13
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9. Which answer best describes the shell
arrangement of the electrons in an
oxide ion O2-?
16
O
A.
B.
C.
D.
2,8,6.
2,8,8.
2,8.
2,6.
8
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