Download neutrons

Aims
Class work
6 September 2007
Mass Number
LO’s
• What is the mass number?
• What’s an isotope?
Write it down!!
© C Meyer
Page 50
Chemistry Unit 2 Sections
Structures
Structures
and bonding  and properties  How much?
3 of 7
© C Meyer
Aims
All
• Know the relative masses of sub
atomic particles
• Know what an isotope is
Most
• Work out the mass number of an
atom
Some
• Explain how isotopes are different
What have I learnt?
T/F Quiz – Back
• Atoms are charged particles
• Electrons are found in energy levels
• Electrons are found in shells
• Electrons have a negative charge
• Protons are in the nucleus of the atom
• Neutrons are found in shells around the
nucleus
• The atomic number is the number of
protons
What have I learnt?
• What does the structure of the atom look like?
• There are two properties of sub-atomic
particles that are especially important:
– Electrical charge (looked at before)
– Mass (Need to look at now)
Overall neutral
Particle
Protons
Neutrons
Electrons
Charge
+1
0
-1
Relative Mass
1
1
0.0005
• Mass of proton = mass of neutron (relative mass = 1)
• Ignore mass of electron
m5
What have I learnt?
Atomic/Proton Number
• The atom of any particular element
always contains the same number of
protons. E.g.
– Hydrogen atoms always contain 1 proton
– Carbon atoms always contain 6 protons
– Magnesium atoms always contain 12 protons
• The number of protons in an atom is
known as its atomic/proton number.
• It is the smaller of two numbers shown in
most periodic tables
12
C
6
Activity
How Many Protons?
• Here is some data about elements
taken from the Periodic Table.
• What is the atomic number of the
elements?
23
56
119
19
27
Na
Fe
Sn
F
Al
11
26
50
9
13
11
26
50
9
13
What have I learnt?
How Many Protons?
• Note elements have a definite and fixed
number of protons.
• Changing number of protons in atom
changes that atom into a different
element.
What is the mass number?
Mass Number – What is it?
• The mass of each atom comes almost entirely
from the number of protons and neutrons
that are present. (Remember that electrons
have a relatively tiny mass).
MASS NUMBER = Number of protons + number of neutrons
Atom
Protons
Neutrons Mass Number
Hydrogen
1
0
1
Lithium
3
4
7
Aluminium
13
14
27
m2
Activity
What is the mass number?
• In back - Calculate the mass number of
the atoms shown.
Atom
Protons
Neutrons
Mass Number
Helium
2
2
4
Copper
29
35
64
Cobalt
27
32
59
Iodine
53
74
127
Germanium
32
41
73
MASS NUMBER = Number of protons + number of neutrons
What is the mass number?
• Mass number = protons + neutrons
• It is the bigger of two numbers shown in
periodic table
12
C
6
• Atomic/proton number = protons.
• It is the smaller of two numbers shown in
periodic table
m1
Activity
What is the mass number?
• In back - Calculate the number of
neutrons in these atoms.
Number of Neutrons = mass number - atomic number
Atom
Mass
Atomic Number of
Number Number Neutrons
Helium
4
2
2
Fluorine
19
9
10
Strontium
88
38
50
Zirconium
91
40
51
Uranium
238
92
146
Activity
What have I learnt?
• In Front - Copy and 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
What’s an isotope?
• Natural samples of elements are often a
mixture of isotopes. About 1% of natural
carbon is carbon-13.
12
6
13
C
99%
1%
6
C
What’s the
difference?
6
6
6
Protons
Electrons
Neutrons
6
6
7
m1
What is relative mass?
ATOMS are just like the
Ford Fiesta
ISOTOPE
m2
Version1
There are different
versions of the FIESTA
Version 2
Version 3
SPEEDY
m3
We also have different
versions of the same
element’s atoms
WE CALL THEM
ISOTOPES
m1
The only difference between
the atoms in an isotope is
that they contain
different numbers of
NEUTRONS
What’s an isotope?
• It is not strictly true to say that
elements consist of one type of atom.
•Atoms in an element always have the same
number of protons but may have different
numbers of neutrons.
•Atoms like this are called isotopes.
Remember: The number of
protons defines
the element
Isotopes: Hydrogen
• Hydrogen exists as 3 isotopes although
Hydrogen-1 makes up the vast majority of the
naturally occurring element.
All can make water
1
1
H
Protons
Electrons
Neutrons
Hydrogen
2
1
H
Protons
Electrons
Neutrons
(Deuterium)
3
1
H
Protons
Electrons
Neutrons
(Tritium)
m4
Isotopes: Chlorine
• About 75% of natural chlorine is 35Cl the rest is
37Cl.
37
35
Cl
17
Protons
Electrons
Neutrons
17
17
18
75%
Cl
17
25%
How many
neutrons?
Protons
Electrons
Neutrons
17
17
20
Activity
Isotopes of Oxygen
• Almost all of natural oxygen is
but about 0.2% is 18O.
• Produce a Table showing the
particles in each isotope.
Oxygen-16
16O
16
O
8
Oxygen-18
Protons
8
Protons
8
Electrons
8
Electrons
8
Neutrons
8
Neutrons
10
What’s an isotope?
• Isotopes are virtually identical in their
chemical reactions as have same
number of protons and electrons.
• The uncharged neutrons only affect
physical properties such as melting
point and density.
What have I learnt?
•
•
•
Draw the electronic structure of
carbon 12 and carbon 14
Say how many protons, neutron
Draw up a table of similar properties
and differences
Same
Different
What have I learnt?
12
6
C
1%
99%
6
6
6
13
6
Protons
Electrons
Neutrons
C
6
6
7
Same
Same number electrons
Different
Different number neutrons
Same number protons
Same chemical properties
Same proton number
Different mass number
Different physical props
Homework
•
Section 2 test
What have I learnt?
The End