How Many Electrons
• The atoms of any element have an equal
number of protons and electrons.
Atom
Protons
Neutrons Electrons
Helium
2
2
2
Copper
29
35
29
Cobalt
27
32
27
Iodine
53
74
53
Germanium
32
41
32
..and so
overall
charge
equals
zero
Activity
How Many Electrons
• Fill in the blank columns
Atom
Protons Neutrons Electrons
Boron
5
6
Potassium
19
20
Chromium
24
28
Mercury
80
121
Argon
18
22
Atomic
number
Mass
Number
5
19
5
19
11
39
24
80
18
24
80
18
52
201
40
Note – atomic number is defined as the number of protons
rather than electrons because atoms can lose (or gain)
electrons but do not normally lose protons
Activity
Drag the statements at the top onto the correct
side of the table
Activity
Drag the statements at the top onto the correct
side of the table
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
Working Out Electron Arrangements
1. How many electrons do the element atoms
have? (This will equal the atomic number).
2. Draw 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
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
Happiness is…………………. A full outer shell
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
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
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!
Electron arrangement =
2.8.2 (Incomplete shell)
2 electrons
lost
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
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?
New electron arrangement?
Bye!
Bye!
3
2.(0)
BB3+
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
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-
The Electrons in a Sulphide Ion.
In the sulphur atom
Atomic number = number of protons
Number of electrons = 16
32
= 16
S2-
S
2 electrons
gained
Electron arrangement:
2.8.6 (incomplete shell)
Electron arrangement
2.8.8 (Full shells)
S
16
The Electrons in a Fluoride Ion.
In the fluorine atom
Atomic number = number of protons
Number of electrons = 9
19
=9
F
F2-
F
1 electron
gained
Electron arrangement:
2.8.7 (incomplete shell)
Electron arrangement
2.8.8 (Full shells)
9
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
Drag the words at the top to their correct
places in the sentences.
Word check
1. Which of the following is not a subatomic particle?
A.
B.
C.
D.
Proton.
Isotope.
Neutron.
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.
B.
C.
D.
It contains 59 neutrons.
It contains 27 electrons.
It contains 32 protons.
It contains equal numbers of neutrons and
electrons.
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.
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.
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
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.
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
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
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