Download Mass number

Isowhat?
Man, you trippin’ nephew.
Isotopes
If you change the It will affect the… And the result
number of…
will be a…
Protons
Electrons
Neutrons
If you change the It will affect the… And the result
number of…
will be a…
Protons
Identity of the
atom
Completely
different atom
Mass
Isotope
Electrons
Neutrons
What Are Isotopes?
• They are atoms of the same element that
have different numbers of neutrons.
It’s just a change in the
neutrizzle fo shizzle!!!
An Example
•
Hydrogen has 3 isotopes
–
There are 3 different “versions” of a hydrogen atom
1. 1 proton and 0 neutrons (mass number = 1)
2. 1 proton and 1 neutron (mass number = 2)
3. 1 proton and 2 neutrons (mass number = 3)
Note how the number of
protons never change!!!
Example: Magnesium
• Has 3 isotopes
# protons
# neutrons Mass
(amu’s)
%
abundance
Isotope 1
12
12
24
79%
Isotope 2
12
13
25
10%
Isotope 3
12
14
26
11%
% abundance??????
• Every isotope is found in nature in a fixed
percentage.
• In other words, 79% of the magnesium
atoms in any “scoop” of magnesium found
anywhere in the universe will be
magnesium atoms with 12 neutrons, 10% of
the atoms in the scoop will have 13
neutrons, and 11% will have 14 neutrons.
– These percentages are different for each
element…you just have to look them up to find
out what they are.
The Vocabulary Section
Terms associated with isotopes
A Few Important Terms
Ya Gotta Know
• Atomic number = the number of protons
– It’s the same as the element’s position on the
periodic table
– For example, carbon is the 6th element on the
table, so its atomic number is 6 which means it
has 6 protons (and 6 electrons if it’s a neutral
atom)
A Few Important Terms
You Gotta Know
• Atomic mass = the “weighted” average
mass of all the different isotopes of an atom
– This is the “weird” number on the periodic
table that usually has a bunch of places past the
decimal point
A Few Important Terms
You Gotta Know
• Mass number = # of protons + # of neutrons
– This one kind of makes sense because remember we
said the electrons essentially don’t have any mass
– This HAS to be a whole number!!!!!
– It has to be, because you can’t have part of a proton
or neutron
– Mass number is NOT given on the periodic table
O.K. nephew…try these
examples, then we can
chill
‘till the next episode…
Let’s Practice Those Terms…
1. What is the mass number of a carbon atom that
has 6 neutrons? 7 neutrons?
2. How many neutrons does a nitrogen atom have
if its mass number is 14?
3. How many neutrons does a chlorine atom have
if its mass number is 37?
4. What is the atomic number of neon?
Answers
1.
2.
3.
4.
12 and 13
7
19
10
A
ZX
Notation for Isotopes
A shorthand way to write isotopes
A Short Way to Write Isotopes
A
Z
X
“X” will be the
symbol of the
element
Problem #1
1. Write az X notation for an isotope that has
17 protons and 18 neutrons.
Problem #2
• Write azX notation for an isotope that has 19
protons and 21 neutrons.
Different Forms of
•
35 Cl
17
AX
Z
is the same as 35Cl17
• Might also see “Cl-35” or “chlorine-35”