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Chapter 5
Atomic Structure
5.1
Classification of elements into metals, nonmetals and semi-metals
5.2
Atoms
5.3
Structure of an atom
5.4
Atomic number and mass number
5.5
Isotopes
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5.6
Relative isotopic mass and relative atomic
mass
5.7
Arrangement of electrons in atoms
Key terms
Progress check
Summary
Concept map
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5.1 Classification of elements into
metals, non-metals and semi-metals
Classifying elements into metals and non-metals
An important way of classifying elements is to
group them into metals and non-metals based
on their physical properties.
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What are the differences in
physical properties between
metals and non-metals?
5.1 Classification of elements into metals, non-metals
and semi-metals
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Differences in physical properties between metals and
non-metals
Metals are usually shiny when freshly cut.
They are silvery white in colour, with only a few
exceptions.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Iron
Lead
Zinc
Silver Calcium
Tin Magnesium Aluminium Copper Gold
Figure 5.1 Most metals are silvery white in colour.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Solid non-metals usually have a dull appearance.
Unlike metals, they show a variety of colours.
Learning tip
White phosphorus usually appears yellow because of
the presence of impurities.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Figure 5.2 Non-metals show a variety of colours.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Property
State at room
temperature and
pressure
Appearance
Melting point and
boiling point
Metals
Non-metals
solids (except
mercury)
gases or solids
(except bromine)
shiny
usually dull in
appearance
usually high
usually low (some
non-metals like
diamond and
graphite have a high
melting point and a
high boiling point)
Table 5.1 Some typical differences in physical properties of metals and
non-metals.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Property
Hardness and
strength
Malleability and
ductility
Density
Thermal
conductivity and
electrical
conductivity
Metals
Non-metals
hard and strong
brittle
malleable and
ductile
not malleable and
not ductile
usually high
low
good conductors
of heat and
electricity
poor conductors of
heat and nonconductors of
electricity (except
graphite)
Table 5.1 Some typical differences in physical properties of metals and
non-metals.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Exceptions
Sodium
a metal but so soft that it can be easily cut with
a knife
a low melting point (below 100°C)
its density is so low that it floats on water
Carbon (in the form of graphite)
a non-metal but a good conductor of electricity
shiny and has a very high melting point
(3730°C)
5.1 Classification of elements into metals, non-metals
and semi-metals
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Learning tip
We should note that:
mercury is the only liquid metal
bromine is the only liquid non-metal
5.1 Classification of elements into metals, non-metals
and semi-metals
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Classifying an element according to its physical
properties
What is the physical state of the element at room conditions?
gas
liquid
non-metal
solid
What is its colour?
silvery
mercury
(metal)
Figure 5.3 A flow chart
showing how to classify an
element as a metal or a
non-metal.
Does it conduct electricity?
yes
reddish brown
bromine
(non-metal)
no
Is it brittle?
yes
no
graphite (non-metal)
metal
5.1 Classification of elements into metals, non-metals
and semi-metals
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non-metal
Elements with properties of both metals and nonmetals — the semi-metals
A few elements, called semi-metals (or
metalloids), have properties of both metals
and non-metals.
Examples: boron and silicon
Think about
5.1 Classification of elements into metals, non-metals
and semi-metals
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Example 5.1
Figure 5.4 Two examples of semi-metals — boron and silicon.
Concept check
5.1 Classification of elements into metals, non-metals
and semi-metals
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Semi-metals are usually brittle, shiny solids.
When they are heated or slightly impure, they
conduct electricity quite well. They are
semi-conductors.
Figure 5.5 Silicon is used to make computer chips.
5.1 Classification of elements into metals, non-metals
and semi-metals
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Key point
Elements can be classified into ________,
metals
non-metals and _____________
semi-metals based on their
___________
physical properties.
Activity 5.1
Class practice 5.1
5.1 Classification of elements into metals, non-metals
and semi-metals
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5.2 Atoms
What are atoms?
Everything consists of a basic type of particles
called atoms.
Key point
atom is the smallest part of an element
An ________
which has the chemical properties of that element.
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Example: Copper
a copper atom is the smallest particle that has
the chemical properties of copper
copper atom
Figure 5.6 A copper wire consists of trillions of copper atoms.
(1 trillion = 1 000 000 000 000, i.e. 1 × 1012)
5.2 Atoms
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Relationship between elements and atoms
An element contains only one kind of atoms.
silver atom
silver ring
gold atom
gold ring
Figure 5.7 Silver consists of only silver atoms while gold consists of
only gold atoms.
5.2 Atoms
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Some elements exist as small particles formed
from atoms.
For example, hydrogen exists as particles formed
from hydrogen atoms.
each hydrogen particle
consists of two hydrogen
atoms
hydrogen gas
Figure 5.8 A gas jar of hydrogen gas.
5.2 Atoms
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Learning tip
The hydrogen particle formed from two hydrogen
atoms is known as a hydrogen molecule. More about
‘molecules’ will be discussed in Chapter 8.
Key point
element is a substance that is made up of
An ________
only one kind of atoms.
Different elements have different properties
because they consist of different kinds of atoms.
5.2 Atoms
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Size and mass of an atom
Atoms are very tiny particles.
Atom
10−24
volume
(cm3)
10−30
Raindrop Basketball
10−3
103
10−20 10−10
1
1010
1020
Earth
1016
1030
Figure 5.9 The range of volumes (in cm3) from atoms to Planet Earth.
mass
(g)
10−30
10−20 10−10 1 1010
10−23
Atom
1020
1030
1027
102
10−3
Raindrop Basketball Earth
Figure 5.10 The range of masses (in g) from atoms to Planet Earth.
5.2 Atoms
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Atoms of different elements have different sizes
and masses.
Gold atoms are larger and heavier than copper
atoms.
We can represent atoms as small spheres of
different sizes.
hydrogen oxygen carbon copper gold
potassium
Figure 5.11 Scale models of atoms of hydrogen, oxygen, carbon, copper,
gold and potassium.
5.2 Atoms
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Key point
Atoms of different elements have different sizes
and masses.
5.2 Atoms
Class practice 5.2
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Symbols for elements and atoms
Symbols for elements
Chemical symbols are symbols which represent
the names of elements.
These symbols are universally accepted and
can help chemists from different parts of the
world communicate more effectively.
5.2 Atoms
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Chemical
symbol
Element
Chemical
symbol
Aluminium
Argon
Calcium
Carbon
Chlorine
Copper
Hydrogen
Al
Ar
Ca
C
Cl
Cu
H
Magnesium
Nitrogen
Oxygen
Phosphorous
Potassium
Silicon
Sodium
Mg
N
O
P
K
Si
Na
Iron
Lead
Fe
Pb
Sulphur
Zinc
S
Zn
Element
Table 5.2 Chemical symbols of some common elements.
5.2 Atoms
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Each chemical symbol shown in the table
consists of one or two letters.
Some chemical symbols have letters from their
English names e.g. Argon Ar, Carbon C,
Magnesium Mg and Silicon Si.
5.2 Atoms
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Other chemical symbols come from their Latin
names.
copper (Cu) from Latin word Cuprum
iron (Fe) from Latin word Ferrum
lead (Pb) from Latin word Plumbum
potassium (K) from Latin word Kalium
sodium (Na) from Latin word Natrium
5.2 Atoms
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Symbols for atoms
Chemical symbols of some elements are also the
atomic symbols for their atoms.
Thus, the letter C is the chemical symbol for the
element carbon, but also the atomic symbol for
a carbon atom.
Class practice 5.3
5.2 Atoms
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5.3 Structure of an atom
Figure 5.12 About 100 years ago, scientists still believed that atoms were
‘solid’ indivisible spheres.
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What are atoms made up of?
Atoms are made up of three fundamental
subatomic particles:
Protons
Neutrons
Electrons
The centre of an atom is a very tiny and extremely
dense region called nucleus.
5.3 Structure of an atom
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The nucleus contains protons and neutrons
packed tightly together.
A proton and a neutron have about the same
mass.
Protons are positively charged but neutrons
have no charge.
The nucleus is hence positively charged.
5.3 Structure of an atom
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Figure 5.13 Imagine there is a pea in the centre of this stadium. The
nucleus would be about the size of this pea if the atom would be about the
size of the stadium.
Learning tip
The football stadium is not spherical in shape. This
only gives an approximate idea of the relative sizes of
an atom and a nucleus.
5.3 Structure of an atom
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An atom is mostly empty space, occupied by
electrons.
Electrons are negatively charged. They are very
much lighter in mass than protons and neutrons
in the nucleus.
Electrons move very fast around the nucleus.
5.3 Structure of an atom
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positively charged
proton
neutron
nucleus containing
protons and neutrons
three-dimensional
diagram
negatively charged
electrons moving
around the nucleus
two-dimensional
diagram
Figure 5.14 A simple model for the structure of an atom.
Animation (Structure of an atom)
5.3 Structure of an atom
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Key point
Atoms are made up of protons, neutrons and
protons (positively charged) and
electrons. The ________
neutrons (neutral) are concentrated in the very
_________
electrons (negatively charged)
tiny nucleus. The _________
move around the nucleus.
5.3 Structure of an atom
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More about protons, neutrons and electrons
Subatomic
Symbol
particle
Mass (in g)
Proton
p
Neutron
n
1.6725 × 10–24
1.6748 × 10–24
Electron
e–
9.109 × 10–28
Electric
charge
Relative
(relative to
mass
that on a
proton)
1
+1
1
Negligible
1
(
)
1837
Table 5.3 Data on the three fundamental subatomic particles.
5.3 Structure of an atom
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0
–1
Building up different atoms from protons, neutrons
and electrons
The hydrogen atom is the simplest of all atoms.
Each hydrogen atom has one proton and no
neutron in the nucleus. It has one electron moving
around the nucleus.
The next simplest one is the helium atom. Each
helium atom has two protons and two neutrons in
the nucleus. It has two electrons moving around
the nucleus.
5.3 Structure of an atom
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Learning tip
We refer to the most common type of hydrogen and
helium atoms here.
5.3 Structure of an atom
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neutron
electron
proton
nucleus
hydrogen atom
helium atom
Figure 5.15 Simplified diagrams that represent the structures of a hydrogen
atom and a helium atom respectively.
5.3 Structure of an atom
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Atom
Symbol
Hydrogen (氫)
Helium (氦)
Lithium (鋰)
Beryllium (鈹)
Boron (硼)
Carbon (碳)
Nitrogen (氮)
Oxygen (氧)
Fluorine (氟)
Neon (氖)
H
He
Li
Be
B
C
N
O
F
Ne
Number of
protons neutrons electrons
1
2
3
4
5
6
7
8
9
10
0
2
4
5
6
6
7
8
10
10
1
2
3
4
5
6
7
8
9
10
Table 5.4 Number of protons, neutrons and electrons in the atoms of the
first 20 elements.
5.3 Structure of an atom
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Atom
Symbol
Sodium (鈉)
Magnesium (鎂)
Na
Mg
Aluminium (鋁)
Silicon (硅)
Phosphorus (磷)
Sulphur (硫)
Chlorine (氯)
Al
Si
P
S
Cl
Ar
K
Ca
Argon (氬)
Potassium (鉀)
Calcium (鈣)
Number of
protons neutrons electrons
11
12
11
12
12
12
13
14
15
16
17
18
19
20
14
14
16
16
18
22
20
20
13
14
15
16
17
18
19
20
Table 5.4 Number of protons, neutrons and electrons in the atoms of the
first 20 elements.
5.3 Structure of an atom
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Learning tip
The number of neutrons stated in the table refers to
the number of neutrons found in the most common
type of atoms of the elements.
5.3 Structure of an atom
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Atoms being electrically neutral
Although an atom contains electrically charged
particles, the atom itself has no overall charge, i.e.
an atom is electrically neutral.
In an atom, the number of protons is equal to
the number of electrons.
Class practice 5.4
5.3 Structure of an atom
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5.4 Atomic number and mass number
Atomic number
The atomic number (symbol: Z) of an atom is
the number of protons in the atom.
For example, a silver atom contains 47
protons.
∴ the atomic number of silver is 47.
Each element has its own unique atomic number.
Key point
Atomic number of an atom
= number of protons in the atom
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Mass number
The mass of an atom is nearly all due to protons
and neutrons.
For this reason, mass number (symbol: A) of an
atom is the sum of the numbers of protons and
neutrons in the atom.
For example, a sodium atom (with 11 protons
and 12 neutrons) has a mass number of
11+12 = 23.
5.4 Atomic number and mass number
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Key point
Mass number of an atom
= sum of number of protons and number of
neutrons in the atom
The atomic number (Z) and mass number (A) of
an atom are usually shown in a full atomic
symbol as follows:
mass number = number of
proton + number of neutron
A
Z
X
Example
atomic
symbol
atomic number = number of
proton = number of
electrons of an atom
mass number
4
atomic number
2
He
Problem-solving strategy 5.1
Class practice 5.5
5.4 Atomic number and mass number
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5.5 Isotopes
What are isotopes?
All atoms of the same element have the same
number of protons (i.e. same atomic number).
However, atoms of the same element may have
different numbers of neutrons (i.e. different mass
number).
Key point
Isotopes are different atoms of the same element,
with the same number of protons but different
numbers of neutrons.
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Example: hydrogen
1
Three isotopes of hydrogen: 1
2
,1
H H
Isotope
3
, 1
H
Number of
proton(s)
electron(s)
neutron(s)
1
1
0
2
1
1
1
1
3
1
1
1
2
1
1
H
H
H
Table 5.5 Number of protons, electrons and neutrons in the three isotopes
of hydrogen.
5.5 Isotopes
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Learning tip
The three isotopes of hydrogen have special
names – protium ( 11H ), deuterium ( 21H ) and tritium
( 31H ).
5.5 Isotopes
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Relative abundance of isotopes
In most cases, one of the isotopes is more
abundant than the others in nature. The relative
abundance of an isotope refers to the proportion
of that particular isotope of an element in nature.
Atom
1
1
Relative abundance
of isotopes in
nature (%)
99.984
1
1
2
3
0.016
very small percentage
Atomic
Mass
Symbol
number number
Hydrogen
1
1
2
1
3
1
H
H
H
Table 5.6 Isotopes of some elements in nature.
5.5 Isotopes
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Atom
Carbon
Oxygen
Sodium
Chlorine
6
6
6
8
8
8
11
17
12
13
14
16
17
18
23
35
Relative abundance
of isotopes in
nature (%)
98.892
1.108
very small percentage
99.76
0.04
0.20
100
75.4
17
37
24.6
Atomic
Mass
Symbol
number number
12
6
13
6
14
6
16
8
17
8
18
8
23
11
35
17
37
17
C
C
C
O
O
O
Na
Cl
Cl
Table 5.6 Isotopes of some elements in nature.
Class practice 5.6
5.5 Isotopes
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Comparing properties of different isotopes
Isotopes of the same element have the same
number of protons and electrons in their atoms.
Therefore, they have the same chemical
properties.
However, they have different numbers of
neutrons, so they have different masses and
hence slightly different physical properties.
5.5 Isotopes
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5.6 Relative isotopic mass and relative
atomic mass
The mass of one hydrogen atom is
0.000 000 000 000 000 000 000 001 673 g
Figure 5.16 An atom is very light in mass.
Is there any simpler way
express the mass of an atom?
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to
Carbon-12 as standard
Scientists expressed the mass of an atom relative
to a reference standard
They chose a carbon-12 (12C) isotope, which
has six protons and six neutrons, to be the
standard atom.
Then they took the mass of one carbon-12 atom
as exactly 12.00 units (atomic mass unit,
a.m.u.).
5.6 Relative isotopic mass and relative atomic mass
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The masses of all other atoms are compared
with this reference standard to give their relative
masses.
magnesium
atom
carbon atom
helium atom
(a)
(b)
Figure 5.17
(a) This magnesium atom has the same mass as two 12C atoms. The
relative mass of this magnesium atom is thus 12 × 2 = 24.
(b) Three helium atoms have the same mass as one 12C atom. The relative
mass of a helium atom is thus 12 ×
1
= 4.
3
5.6 Relative isotopic mass and relative atomic mass
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Relative isotopic mass
By comparing the mass of one isotope of an
element with the reference standard, we obtain
the relative isotopic mass (also known as
isotopic mass) of that particular isotope of the
element.
On the 12C = 12.00 scale, the relative masses of
a proton and a neutron are both very close to 1.
The relative mass of an electron is nearly 0.
5.6 Relative isotopic mass and relative atomic mass
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Relative isotopic mass is a relative value. It
carries no unit.
Key point
Relative isotopic mass ≈ mass number
Relative atomic mass
There is only one relative atomic mass for an
element.
5.6 Relative isotopic mass and relative atomic mass
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The relative atomic mass of an element is
determined by:
the relative isotopic mass and
the relative abundance
of each naturally occurring isotope of the
element.
The relative atomic mass of an element is the
weighted average of the relative isotopic
masses of all the naturally occurring isotopes of
that element on the 12C = 12.00 scale.
Relative atomic mass is also a relative value. It
carries no unit.
Concept check
5.6 Relative isotopic mass and relative atomic mass
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Key point
Relative atomic mass
= a% × MA + b% × MB + c% × MC
where a%, b%, c% = relative abundances of
isotopes A, B and C respectively
MA, MB, MC = relative isotopic masses of isotopes A,
B and C respectively.
Example 5.2
Example 5.3
5.6 Relative isotopic mass and relative atomic mass
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Class practice 5.7
5.7 Arrangement of electrons in atoms
Electronic arrangement
Niels Bohr, a Danish scientist, suggested that
the electrons in an atom move in orbits
(electron shells) surrounding the nucleus of
the atom.
Figure 5.18 Niels Bohr
(1885–1962)
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first shell – a maximum of 2
electrons
nucleus
second shell – a maximum of 8
electrons
third shell – a maximum of 18
electrons
fourth shell – a maximum of
32 electrons
Figure 5.19 Electrons in an atom move in electron shells surrounding
the nucleus.
5.7 Arrangement of electrons in atoms
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Learning tip
If n is the shell number, the maximum number of
electrons a shell can hold is 2n2. For example, the
second shell (n = 2) can hold a maximum of 2 × 22 =
8 electrons.
The way in which electrons are arranged in
different electron shells is called electronic
arrangement (or electronic configuration).
5.7 Arrangement of electrons in atoms
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Rules for finding electronic arrangement
1. Find the atomic number of the element. This is
equal to the number of protons, and hence the
number of electrons present in an atom of the
element.
2. Place electrons into the electron shells one by
one, starting from the innermost shell. When a
certain shell is ‘full’, any remaining electrons
would go into the next outer shell and so on, until
all are placed.
5.7 Arrangement of electrons in atoms
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Ways of representing electronic arrangement
Electronic arrangement by numbering
The number of electrons is listed, starting from
the first shell (innermost shell). The numerals
are separated by commas.
2, 8, 1
Number of
1st 2nd 3rd
electrons in:
shell shell shell
Figure 5.20 Representing the electronic arrangement of a sodium
atom by numbering.
5.7 Arrangement of electrons in atoms
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Element
Symbol
Atomic
No. of
no.
electrons
No. of electrons in
electron shells
1st
2nd
3rd
4th
Electronic
arrangement
Hydrogen
H
1
1
1
1
Helium
He
2
2
2
2
Lithium
Li
3
3
2
1
2, 1
Beryllium
Be
4
4
2
2
2, 2
Boron
B
5
5
2
3
2, 3
Carbon
C
6
6
2
4
2, 4
Nitrogen
N
7
7
2
5
2, 5
Oxygen
O
8
8
2
6
2, 6
Fluorine
F
9
9
2
7
2, 7
Neon
Ne
10
10
2
8
2, 8
Table 5.7 The electronic arrangements of the elements with atomic numbers
1-20 represented by numbering.
5.7 Arrangement of electrons in atoms
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Element
Symbol
Atomic
No. of
no.
electrons
No. of electrons in
electron shells
1st
2nd
3rd
4th
Electronic
arrangement
Sodium
Na
11
11
2
8
1
2, 8, 1
Magnesium
Mg
12
12
2
8
2
2, 8, 2
Aluminium
Al
13
13
2
8
3
2, 8, 3
Silicon
Si
14
14
2
8
4
2, 8, 4
Phosphorus
P
15
15
2
8
5
2, 8, 5
Sulphur
S
16
16
2
8
6
2, 8, 6
Chlorine
Cl
17
17
2
8
7
2, 8, 7
Argon
Ar
18
18
2
8
8
2, 8, 8
Potassium
K
19
19
2
8
8
1
2, 8, 8, 1
Calcium
Ca
20
20
2
8
8
2
2, 8, 8, 2
Table 5.7 The electronic arrangements of the elements with atomic numbers
1-20 represented by numbering.
5.7 Arrangement of electrons in atoms
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Note that for potassium and calcium, the
electronic arrangements are not the same as
expected (i.e. 2, 8, 9 for K; 2, 8, 10 for Ca).
Electronic arrangement by electron diagram
The nucleus is often represented by the
symbol of the atom.
Electrons are shown by dots or crosses.
5.7 Arrangement of electrons in atoms
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hydrogen
1
sodium
2, 8, 1
oxygen
2, 6
lithium
2, 1
silicon
2, 8, 4
Figure 5.21 Electron diagrams of atoms of some elements.
potassium
2, 8, 8, 1
Key point
The way in which electrons are arranged in
different shells is called electronic arrangement.
Skill corner 5.1
5.7 Arrangement of electrons in atoms
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Class practice 5.8
Key terms
1.
2.
3.
4.
5.
6.
7.
8.
9.
atom 原子
atomic number 原子序
chemical symbol 化學符號
electron 電子
electron diagram 電子結構圖
electron shell 電子層 (電子殼)
electronic arrangement/electronic
configuration 電子排佈/電子組態
isotope 同位素
mass number 質量數
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10.
11.
12.
13.
14.
15.
16.
17.
18.
metal 金屬
nucleus 原子核
neutron 中子
non-metal 非金屬
proton 質子
relative atomic mass 相對原子質量
relative isotopic mass 相對同位素質量
semi-metal/metalloid 半金屬/類金屬
subatomic particle 次原子粒子
Key terms
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Progress check
1. How do we classify elements into metals,
semi-metals and non-metals based on their
physical properties?
2. What is an atom?
3. What is the relationship between element and
atom?
4. What are the chemical symbols for common
elements?
5. What are the three fundamental subatomic
particles that make up an atom?
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6. What are the relative charges and the relative
masses of a proton, a neutron and an electron?
7. What is the meaning of atomic number?
8. What is the meaning of mass number?
9. How do we interpret and use symbols such as
23
11 Na ?
10. How can we deduce the numbers of protons,
neutrons and electrons in atoms with given atomic
numbers and mass numbers?
11. What is the meaning of isotopes?
12. What is the meaning of relative isotopic mass?
Progress check
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13. What is the meaning of relative atomic mass?
14. How can we calculate the relative atomic mass of
an element?
15. How can we represent the electronic
arrangements of atoms by numbering?
16. How can we represent the electronic
arrangements of atoms using electron diagrams?
Progress check
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Summary
5.1 Classification of elements into metals, nonmetals and semi-metals
1.
2.
Elements can be classified into metals,
non-metals and semi-metals.
All metals conduct electricity. All non-metals
(except carbon in the form of graphite) do not
conduct electricity. To tell whether an element is
a metal or non-metal, a simple but effective way
is to test whether it conducts electricity.
(Refer to Table 5.1 for some typical differences
in physical properties between metals and nonmetals.)
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5.2 Atoms
3.
An atom is the smallest part of an element
which has the chemical properties of that
element.
4.
An element is a substance that is made up of
only one kind of atoms. Different elements
have different properties because they consist
of different kinds of atoms.
Summary
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5.
Atoms of different elements have different
sizes and masses.
6.
Chemists use chemical symbols to represent
elements. Chemical symbols of most elements
come from their English names.
(Refer to Table 5.2 for chemical symbols of
some elements.)
Summary
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5.3 Structure of an atom
7. (a) An atom consists of three types of subatomic
particles — protons, neutrons and electrons.
7. (b)
Subatomic particle
Relative mass
Relative charge
Proton (p)
1
+1
Neutron (n)
1
0
Electron
(e–)
negligible (
1
)
1837
Summary
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–1
7. (c) An atom has a very small and extremely dense
centre called nucleus. The protons and
neutrons are in the nucleus.
7. (d) Electrons move around the nucleus at a very
high speed.
7. (e) An atom is electrically neutral.
5.4 Atomic number and mass number
8.
Atomic number of an atom = number of protons
in the atom
Summary
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9.
Mass number of an atom = number of protons +
number of neutrons in the atom.
10.
Full atomic symbol
mass number = number of
proton + number of neutron
A
Z
X
Example
atomic
symbol
mass number
4
atomic number
2
atomic number =
number of proton =
number of electrons of an
atom
Summary
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He
5.5 Isotopes
11.
Isotopes are different atoms of the same
element, with the same number of protons (and
electrons) but different numbers of neutrons.
Different isotopes of the same element have
the same chemical properties but slightly
different physical properties.
5.6 Relative isotopic mass and relative atomic
mass
12.
Relative isotopic mass ≈ mass number
Summary
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13.
Relative atomic mass of an element = weighted
average of the relative isotopic masses of all
the naturally occurring isotopes of that element
on the 12C = 12.00 scale.
5.7 Arrangement of electrons in atoms
14.
The way in which electrons are arranged in
different electron shells is called electronic
arrangement.
(Refer to Table 5.7.)
Summary
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Concept map
Gas
Liquid
Solid
Electricity
can
conduct
Metal
Semi-metal
Non-metal
exist as
can be
classified
as
Element
can be
represented
by
the smallest
part is
ATOM
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Chemical
symbol
ATOM
consists of
Nucleus
Electrons
same
number
as
Electrons
contains
Protons
move around
the nucleus in
Neutrons
Electron
shells
sum of numbers of protons
and neutrons in an atom
Atomic
_______
number
Mass
_______
number
Concept map
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ATOM
different
atoms of
the same
element
Isotopes
weighted
average of
masses of
all isotopes
mass of
isotope
Relative
isotopic
mass
Concept map
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Relative
atomic
mass