Download Topic 2.3 The Atom Electron Configuration

Assessment Objectives
 2.3.4 Deduce the electron arrangement for atoms
and ions up to Z = 20.
Key Terms
 Electron
 Electron Configuration
 Electron Shell
 Ion
 Cation
 Anion
References
 Textbook on moodle
Starter
 What are the symbols for the following elements:
 Sulphur
 Phosphorous
 Chlorine
 Aluminium
 Berilium
 Potassium
Starter Activity
Write the answers to the following in the
back of your book.
 Name 3 sub-atomic particles and write
down as much information about each
one as you can remember.
 What can you say about the numbers of
protons and electrons in an atom?
Assessment Objective
 2.3.4 Deduce the electron arrangement for atoms
and ions up to Z = 20.
History
 1913 - Danish physicist Niels Bohr realised
that the secret of atomic structure lay in its
discreteness, that energy could only be
absorbed or emitted at certain values.
The Bohr Model
Bohr realised that the
electrons could only be at
specific energy levels (or
states) around the atom.
Models of Atoms
 This property of atoms can be represented by a
number of models which helps us explain how
chemical reactions work.
 (HL students will learn about another one)
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
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
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
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
Electron
Shells
Electrons occupy shells around the nucleus of an atom.
Each shell can hold different numbers of electrons before
it is full.
1st shell can hold 2 electrons
2nd shell can hold 8 electrons
3rd shell can hold 8 electrons
4th shell can hold 18 electrons
The shells MUST be filled up
from the centre outwards.
The Electrons in Carbon
The Electrons in Neon
The Electrons in Silicon
Electrons in Phosphorus
The Electrons in Argon
The Electrons in Sodium
The Electrons in Fluorine
The Electrons in Aluminium
The Electrons in Nitrogen
The Electrons in Sulfur
The Electrons in Oxygen
The Electrons in Chlorine
The Electrons in Magnesium
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
of protons
1- ion
Protons
Electrons
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
Itelectrolysis
is nearly
Ions usually(Or
they move towards the cathode.
always metal
have
because
they
are
“pussytive”!).
Lost 2 e
atoms that lose
2+
OUTER
electrons

The charge on the ions is equal to
electrons that the atom
has lost.
Lost 3 e

3+
electron shells
that number
are either
the
completely full
or else empty
In equations the charge is usually shown above
and to the right of the symbol. (E.g. Mg2+ ).
of
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)
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! 2 electrons
lost
Electron arrangement = 2.8.2
(Incomplete shell)
Electron arrangement 2.8 (Full
Shells)
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 +
New electron arrangement? Include a
diagram
2.(0)
Bye!
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?
Bye!
Bye!
3
B3+
New electron arrangement?
2.(0)
Bye!
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
Ions usually
anode.
have
It is nearly
always
nonelectrolysis
they move towards
the
Gain 2 e
metal atoms
2that gain
electrons
The charge on the ions is equal to
electrons that the atom
Gain 3 e-

-
OUTER
electron shells
the
that number
are either
full
has gained.completely
or else empty
3-
In equations the charge is usually shown above
and to the right of the symbol. (E.g.. O2- ).
of
The Electrons in a Sulphide Ion.
In the sulphur atom
Atomic number = number of protons
Number of electrons = 16
32
= 16
S
16
S2-
S
2 electrons
gained
Electron arrangement: 2.8.6
(incomplete shell)
Electron arrangement 2.8.8 (Full
shells)
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)
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
O2New electron arrangement?
2.8
Activity
Drag the words at the top to their correct places
in the sentences
Activity
The following sentences are all mixed up. Drag and
drop the Words in red until they are in the correct places
Activity
Word Check
1.
Which of the following is not a sub-atomic
particle?
A. Proton.
B. Isotope.
C. Neutron.
D. Electron.
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. It contains 59 neutrons.
B. It contains 27 electrons.
C. It contains 32 protons.
D. It contains equal numbers of neutrons and
electrons.
3. The Periodic Table displays iron as shown
below. This indicates that Fe atoms:
A. contain 56 neutrons.
56
Fe
26
B. contain 30 electrons.
C. contain 26 protons.
D. contains more protons than neutrons.
4. Bromine consists of a mixture of two
isotopes: Bromine-79 and Bromine-81

Which of the following is true:
80
Br
A. Both isotopes contain 35 protons.
35
B. Bromine 79 contains 46 neutrons.
C. Bromine 81 contains 44 neutrons.
D. Bromine-81 is more reactive than bromine-
79.
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. 10.0
B. 11.0
C. 10.5
D. 10.8
B
5
6. Which answer best describes the shell
arrangement of the electrons in a sodium
atom?
23
Na
11
A. 2,8,1.
B. 2,2,7.
C. 2,8,8,3.
D. 2,8,8,1.
7.
Which answer best describes the shell
arrangement of the electrons in an oxygen
atom?
16
A. 2,8,6.
B. 2,8,8.
C. 2,8.
D. 2,6.
O
8
Which of these elements will have electron
shells that are either full or empty (i.e. not
partially full)?
8.
A
14
N
B
7
C
40
Ca
20
40
Ar
18
D
27
Al
13
9.
Which answer best describes the shell
arrangement of the electrons in an oxide ion
O2-?
16
A. 2,8,6.
B. 2,8,8.
C. 2,8.
D. 2,6.
O
8
Plenary
in
shells
around
the
Where do we find electrons in an atom?
nucleus
2,8,8,18
How many electrons fit into each shell?
What symbol do we use to show electrons?
X
How do we arrange the electrons in the shells?
in pairs
What do we notice about the
XX
all full
electrons shells of the noble gases?
Draw the electron configuration of chlorine
XX
X
X
X
X
X
X X
X X
X
X
X
X
Homework
 Memorise the symbols for the following elements.
 Silver (Ag)
 Tin (Sn)
 Iodine (I)
 Lead (Pb)
 Mercury (Hg)
 Gold (Au)