Isotopes-Chapter 4 p.110-120
Atoms of the same element must have the same number of protons, and electrons must match the atomic number.
Example:
Hydrogen has 3 isotopes: protium deuterium tritium or H-1 or H-2 or H-3
1p+ 1e- 1p+ 1e- 1p+ 1e-
0n ) 1n ) 2n )
99.985% 0.015% not found abundant abundant in nature
All atoms of a certain element MUST have the same number of protons (& electrons) in order to be chemically alike. The one particle that may vary is the number of neutrons .
Isotopes are atoms of the same element having different numbers of neutrons. Isotopes are either found naturally as part of nature or can be produced in a laboratory. The mass number and percent abundance of the naturally-occurring isotopes are measured by a machine called the mass spectrometer, and the average atomic mass is calculated for the element. Average atomic mass is the mass found on the periodic table.
There are from 1 up to 46 isotopes of any given element. Some are naturally-occurring and some are lab-made. The lab-made isotopes are radioactive, with a half-life, and break down into other different elements as nuclear changes occur.
For example there are 40 known isotopes of silver, but only 2 occur in nature, while the other 38 are made in a lab. Here are the Bohr diagrams of the 2 natural isotopes: silver-107
47p+ 2 8 18 18 1e-
60n ) ) ) ) )
Ag-107 makes up 51.839% of all natural silver. silver-109
47p+ 2 8 18 18 1e-
62n ) ) ) ) )
Ag-109 makes up the remaining 48.161% of all silver atoms.
There are more than 3, 000 total isotopes of all 120+…. elements known.
Notation for Atoms and Isotopes
Silver-107 or Ag-107 always shows the mass number. You must have a periodic table to find the atomic number or electrons.

107
47
Ag shows the mass number above the atomic number, ALWAYS, as this is the conventional way.
You might see Ag 107
47
or 107 Ag
47
or
47
Ag 107 . These all show the mass number higher than the atomic number. They tell you the same thing. Since isotopes will vary in the number of neutrons, always pay attention to the given mass number before drawing features of an atom.
Uranium has 3 natural isotopes:
1) U-234 or
234
92
U makes up 0.0055%.
2) U-235 or
235
92
U makes up0.720%.
3) U-238 or
238
92
U makes up 99.2745%.
Seven laboratory-made isotopes of uranium have been observed.
For Tues.
Draw a Bohr diagram of the gold-200 isotope, draw cadmium-97, neptunium, sulfur, lead-203, and europium.
79p
+
2e- 8e- 18e- 32e- 18e- 1e-
200
79
Au 121n o
) ) ) ) ) )
48p
+
2e- 8e- 18e- 18e- 2e-
97
48
Cd 49n o ) ) ) ) )
93p
+
2e- 8e- 18e- 32e- 23e- 8e- 2e-
237
93
Np 144n o
) ) ) ) ) ) )
16p + 2e- 8e- 6e-
32
16
S 16n o
) ) )
82p
+
2e- 8e- 18e- 32e- 18e- 4e-
203
82
Pb 121n o
) ) ) ) ) )
63p
+
2e- 8e- 18e- 25e- 8e- 2e-
152
63
Eu 89n o
) ) ) ) ) )
For Wed.
19-33, p.113-119. (omit 23-24)