Download Isotopes - Debra Daniels` Chemistry

Isotopes
Subatomic Particles
• # protons = atomic number
Carbon - atomic number 6; # of protons 6
• # electrons (neutral atom) = # protons
Carbon - # protons 6 = # electrons 6
• # neutrons = mass number – atomic number
Carbon-12
6 neutrons = 12 (mass number) – 6 (atomic
number)
ATOMS OF THE 1ST TEN ATOMS
NAME
SYMBOL
ATOMIC #
p+
n0
MASS #
e-
Hydrogen
H
He
Li
Be
B
C
N
O
F
Ne
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
0
2
4
5
6
6
7
8
10
10
1
4
7
9
11
12
14
16
19
20
1
2
3
4
5
6
7
8
9
10
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
or Na-23
or Na-24
Isotope: two or more atoms having the same
number of protons but different
numbers of neutrons
• Every Cl atom has 17 protons, w/o
exception, but not every Cl atom has 18
neutrons.
– Atoms with the same # of protons but
contain different #s of neutrons are called
isotopes.
• Since isotopes of an element have different
#s of neutrons they have different masses
• Isotopes are chemically alike because they
have identical numbers of protons and
electrons
– It’s the electrons and protons that are
responsible for chemical behavior
• Isotopes can be noted using hyphen
notation (Cl-35 vs. Cl-37) or (Chlorine – 35
vs. Chlorine – 37)
– element symbol hyphen mass number
– element name hyphen mass number
Hydrogen Isotopes
Nuclide
Protium
#p+ #n0 # e1
0
1
at. #
1
mass number (#p+ and #n0)
1
(1 + 0)
Deuterium 1
1
1
1
2
(1 + 1)
Tritium
2
1
1
3
(1 + 2)
1
Hydrogen Isotopes
1
1
H
2
1
H
3
1
H
9
Write the hyphen notations for the following:
Average Atomic Mass
• This is the mass that is on the periodic table.
• It is a weighted average of the masses of all
the isotopes of a particular element.
• Atomic mass = (mass isotope 1)(% abundance)
+ (mass isotope 2)(% abundance) +.....
• This is what is located on the periodic table
Practice
1. Naturally occurring chlorine is 75.53% chlorine35 and 24.47% chlorine-37. What is the average
atomic mass?
Ans. (0.7553)(35) + (0.2447)(37) =
1. The element Neon consists of three isotopes with
masses 19.99, 20.99, and 21.99 amus. These
three isotopes are present in nature to the
extent of 90.51%, 0.27%, and 9.22% respectively.
Calculate the atomic mass of neon.
Isotopes of Neon
Isotopes
% in
Nature
Atomic
Number
Atomic
Mass
(amu)
1 atom
Mass
Number
Average
Atomic
Mass
(amu)
Ne-20
90.51%
10
19.99244
amu
20
20.183
amu
Ne-21
0.27%
10
20.99395
amu
21
Ne-22
9.22%
10
21.99138
amu
22
3. The element silver exists in nature as two
isotopes Ag-107 and Ag-109. The accepted
atomic mass of silver is 107.87amu. What
isotope is more abundant?
4. Calculate the average atomic mass of an
element given the following information:
• Nitrogen-15 is 30% abundant
• Nitrogen-13 is 20% abundant
• Nitrogen-14 is 50% abundant