The Structure of the
Atom
The atom is composed of a
negative, positive and neutral
charge
Nucleus
The nucleus contains
protons which have a
positive charge. It also
contains neutrons which
have no charge
Electrons
They are very, very tiny so
the atom is mainly empty
space. Electrons have a
negative charge
Na
Shells
The first shell always
contains two electrons when
full whereas the other shells
have a maximum of eight
electrons
*Na being sodium with this
particular atomic structure.
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How atoms combine
Ionic bonding
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Scientists found that elements in Group 8 were very
non-reactive.
They also noticed that those in Groups 1,2,6 and 7 were
extremely reactive.
They also noticed that metallic substances had several
properties that were very different from other
elements.
They could not at first understand why.
Eventually they discovered that it had to do with
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WHY DO COMPOUNDS FORM IN THE FIRST
PLACE?
ELECTRON CONFIGURATIONS
and
STABILITY
3
ELECTRON CONFIGURATION AND
Scientists’ research showed
that in compounds, elements
will combine so that the
valence or outermost
electrons will have the same
electron configuration as the
nearest noble gas
(in Group 8)
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STABILITY
4
HOW CAN ELEMENTS COMBINE TO ACHIEVE THIS?
Once an atom gains one or more
electrons, it becomes a negatively charged
particle known as an ANION
An element can lose
electrons to another
element to have the
same electron
configuration as the
nearest noble gas.
Once an atom loses one
or more electrons, it
forms a positively
charged particle known
as a CATION.
There
are three
(3) ways
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An element can gain electrons from the
element it combines with to have the
same electron configuration as the
nearest noble gas.
An element can share
valence electrons
with another element
to have the same
electron
configuration as the
nearest noble gas.
5
WELL BE
ASKING
WHAT DOES
THIS MEAN?
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YOU MAY
6
AT SOME
EXAMPLES TO
UNDERSTAND THIS
CONCEPT MORE
FULLY
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LET’S TAKE A LOOK
7
Let’s take sodium as an example
Sodium’s atomic number
is Z=11. Its electron
configuration is
therefore 2,8,1
Neon’s atomic number
is Z=10. Its electron
configuration is 2,8. It
is the nearest noble gas
to sodium.
Sodium will combine with another element so that
it can change its electron configuration from 2,8,1
to 2,8. To do this, it must lose 1 electron and give it
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8 element with which it combines.
to the
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Let’s take chlorine as an example
Chlorine’s atomic
number is Z=17. Its
electron configuration is
therefore 2,8,7
Argon’s atomic number
is Z=18. Its electron
configuration is 2,8,8. It
is the nearest noble gas
to chlorine.
Chlorine will combine with another element so
that it can change its electron configuration from
2,8,7 to 2,8,8. To do this, it must gain 1 electron
from the
element with which it combines.
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Ionic bonding
 It only occurs between a metal and a non-metal
 It is formed from an attraction between positively charged
and negatively charged ions
 Ionic bonding involves the complete transfer of electrons
from one atom to another
 This means that elections will try to fill an empty shell of
an atom using the minimum amount of energy. So if there
are 7 in one outer shell and 1 in the other, the atom with
1 will lose its electron and the one with 7 will gain it
 Remember that when an atom loses an electron it
becomes positively charged [e.g. 1+] whereas the atom
which gains an electron becomes negatively charged
[e.g. 1-]
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Ionic bonding
example
e.g. Sodium chloride. Remember
to draw all the shells in an exam
unless it asks for just the outer
shell as it may lose you marks
Na
Cl
1+
Na
1-
Cl
OF SODIUM CHLORIDE
First, the sodium
atom loses one
electron to form
a positive sodium
ion. (cation)
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IONIC BONDING
Source: www.revisionworld.co.uk
In order to form
the compound
sodium chloride,
there are three
(3) steps.
Then the
chlorine atom
accepts the
electron from the
sodium atom to
form a negative
chloride ion
(anion).
Then the sodium
cation and
chloride anion
become attracted
to each due to
their different
12
charges, forming
an ionic bond
An ion is an atom or molecule
where the total number of
electrons is not equal to the
total number of protons,
giving it a net positive or
negative electrical charge.
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IONS DEFINED
13

What is an electron configuration?
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REVIEW – ELECTRON CONFIGURATIONS
Definition: Electron configuration is the arrangement
of electrons in an atom, molecule or other body.

How do we represent electron configurations?
By using Bohr-Rutherford diagrams
Or electron configuration notation
11 p
10 n
2,8,1
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REMEMBER – “CONTRAST” MEANS “LOOK AT THE DIFFERENCES”
Fluorine






Neon
Element symbol F
Group 17
Atomic Number Z = 9
Mass number A = 19
Electron configuration: 2,7
Bohr-Rutherford diagram
9p
10 n






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LET’S CONTRAST –FLOURINE AND NEON
Element symbol Ne
Group 18
Atomic Number Z = 10
Mass number A = 20
Electron configuration: 2,8
Bohr-Rutherford diagram
10 p
10 n
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Sodium






Neon
Element symbol Na

Group 1

Atomic Number Z = 11

Mass number A = 23

Electron configuration: 2,8,1
Bohr-Rutherford diagram 
11 p
12 n
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LET’S CONTRAST – SODIUM AND NEON
Element symbol Ne
Group 18
Atomic Number Z = 10
Mass number A = 20
Electron configuration: 2,8
Bohr-Rutherford diagram
10 p
10 n
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Remember –
“Compare” means
“Look at
Similarities

F and Ne have the
same number of
electron shells
Scientists found that when
elements from Group 1 and
Group 7 combine, they lose or
gain an electron to have the
same number of electrons as
the nearest Noble Gas.
i.e. F and Na form ions
that are ISOELECTRONIC with Ne
Differences




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COMPARE AND CONTRAST ALL 3 ELEMENTS
Different atomic numbers
(Z) and therefore protons
Different mass numbers
(A) and therefore different
neutrons
F needs to gain 1 electron
to have the same number
of electrons as Ne
Na needs to lose 1 electron
to have the same number
of electrons as Ne
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IN GENERAL

1.
2.
3.

To become ISOELECTRONIC with the
nearest Noble Gas (either
within the same Period or
the Period just above)
Group 1 elements lose 1 eGroup 2 elements lose 2 eGroup 3 elements lose 3 eThis only happens when
combining or reacting with
another element(s) from
Groups 15,16 or 17
Groups 15, 16 and 17

1.
2.
3.

To become ISOELECTRONIC with the
nearest Noble Gas (either
within the same Period or the
Period just above)
Group 15 elements gain 3 eGroup 16 elements gain 2 eGroup 17 elements gain 1 e-
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Groups 1, 2 and 3
This only happens when
combining or reacting with
another element(s) from
Groups 1,2 or 3
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