Download Science 9 - Ms. J Reed

Unit 1: Chemistry
Lesson 4: Drawing Atoms
Section: 2-3
By the end of the lesson you should be able to:
 Determine the difference between an atom
and an ion
 Draw Bohr Model Diagrams for the first 18
elements on the Periodic Table
 Use atomic structure to explain why elements
behave differently

Atoms are elements as you see them on the
Periodic Table: with equal amounts of p+ and
e◦ EX: sodium atom has 11 p+ and 11 e-

Ions are elements that have gained/lost
electrons and now have a charge
◦ EX: sodium ion has 1+ charge because it has lost 1
e-
State if the following are Atoms or Ions
Na
K
H+
Cl-
Ca
O2-
Ne
Be2+
Al
N3-
Anything with a charge is an ion, all the others
are atoms

To determine the number of electrons in an ion
you need to subtract the charge to the atomic
number
◦ EX: Calcium has an atomic number of 20 and a 2+
charge.......so, its ion has 20 - 2 = 18 electrons
◦ EX: Fluorine has an atomic number of 9 and a 1charge.......so, its ion has 9 – (-1) = 10 electrons
(remember subtracting a negative is like adding!)

Complete the worksheet “The Number Game with
Atoms and Ions”


Niels Bohr described how the electrons are
arranged in the shells around a nucleus in an
atom
His theory has 3 ideas:
1. Electrons move around the nucleus in shells
2. Each shell is a certain distance away from the nucleus
and can hold a definite number of electrons
3. After the shell closest to the nucleus is full, electrons
start filling the next shell

Draw a circle and put the symbol and number of
protons and neutrons inside of it
◦ Number of protons equals the atomic number
◦ Number of neutrons equals the atomic mass – the
number of protons
number of protons + number of neutrons = atomic mass
Mg
12p+
12no

Add the appropriate number of shells (this is
determined by the period number)
◦ EX: Magnesium is in the 3rd period so it will have 3
shells
Mg
c +
12p
12no
There are now 3
shells in total
1.
2.
3.
4.
5.
Maximum of 2 electrons in the first shell
Maximum of 8 electrons in the next 2 shells
Maximum of 18 electrons in the 4th shell
and all shells after that (we won’t be making
these!!)
Electrons occur in pairs
There must be 4 single electrons before the
electrons will occur in pairs



EX: Magnesium has 12 electrons (from atomic
number)
So, 2 electrons in the first shell, 8 in the second
and 2 in the last
Watch how the electrons are added (up, down,
side to side)
Mg
12p+
12no

Draw the Bohr diagram for Carbon

Draw the Bohr diagram for Potassium

Draw the Bohr diagram for Sulphur


Number of protons? 6 (same as the atomic number)
Number of neutrons? 6 (atomic mass = 12
Atomic mass - # protons = # neutrons
12 – 6 = 6
C
6 p+
6 no

Add the appropriate number of shells (this is
determined by the period number)
◦ EX: Carbon is in the 2nd period so it will have 2
shells
C
6 p+
6 no



Fill the electron shells
Carbon has 6 electrons (from atomic number)
So, 2 electrons in the first shell, 4 in the
second
C
6 p+
6 no


Number of protons? 19 (same as the atomic number)
Number of neutrons? 20 (atomic mass = 39
Atomic mass - # protons = # neutrons
39 – 19 = 20
K
19 p+
20 no

Add the appropriate number of shells (this is
determined by the period number)
◦ Potassium is in the 4th period so it will have 4 shells
K
19 p+
20 no



Fill the electron shells
Potassium has 19 electrons (from atomic
number)
So, 2 electrons in the first shell, 8 in the
second, 8 in the third and 1 in the fourth
K
19 p+
20 no


Number of protons? 16 (same as the atomic number)
Number of neutrons? atomic mass = 32
Atomic mass - # protons = # neutrons
32 – 16 = 16
S
16 p+
16 no

Add the appropriate number of shells (this is
determined by the period number)
◦ Sulphur is in the 3rd period so it will have 3 shells
S
16 p+
16 no



Fill the electron shells
Sulphur has 16 electrons (from atomic
number)
So, 2 electrons in the first shell, 8 in the
second, 6 in the third
S
16 p+
16 no





This is a fancy way of saying “outer shell
electrons”
If you are ever asked for the number of
valance electrons, they are just asking how
many electrons are found in the last,
outermost, shell only
EX: Carbon 4
Potassium 1
6
Sulphur

Complete the worksheet “Analyzing Bohr
Model Diagrams”


GOLDEN RULE: all atoms want a full outer
shell (it makes them more stable) – they will
gain/lose electrons to achieve this!
Thus, elements that have the same number of
valence electrons will behave the same way as
they need to gain/lose the same number of
electrons!

Why do sodium and cesium behave the same
way?

Why do oxygen and sulphur behave the same
way?

Why are the noble gases un-reactive (inert)?

Why is this statement true?
“All atoms are trying to become like their nearest
Noble Gas”

All atoms want full outer electron shells

All metals lose electrons

All non-metals gain electrons

Work on “Drawing Bohr model diagrams”
Choose to make one of the following elements
Helium, Lithium, Berylium, Boron, Carbon, Nitrogen, Oxygen
or Fluorine
Neutrons = white
chocolate chips
Protons = chocolate
chips
Electrons = sprinkles