1. Atomic Variation

2. Ions Variation in the number of electrons
Anion
Cation
gain of electrons
overall charge is negative
lose of electrons
overall charge is positive
11 protons
12 neutrons
11electrons
10 electrons
Sodium atom
Sodium ion 1+ Na 1− F

3. C C C Isotopes 12 6 13 6 14 6 Variation in the number of neutrons
Atoms that have the same number of protons but have a different masses
Ex: 3 isotopes of carbon: 12 6 C 13 6 C 14 6 C

4. X Isotope Notation A ±# Z Atomic Number Mass Number
the number of protons in an atom
Identifies element
Symbol: Z
Represents the total number of protons and neutrons in the nucleus (p+ + n0)
Symbol: A
Charge
Chemical Symbol
States whether electrons were gained or lost from the neutral atom
Helps indicate chemical bonding
Symbol: ± #
Short-hand abbreviation for the element name
Only first letter should be capital

6. Naming Isotopes
State the element name or symbol followed by a hyphen and the mass number
Ex: Carbon—14

7. Practice How many protons, neutrons and electrons are in Cobalt—59?
Write the isotope notation and name of an isotope that has 15 protons, 17 neutrons, and 18 electrons.
Write the isotope notation of an isotope that has 18 protons, 22 neutrons, and 18 electrons.

8. Atomic Mass Atomic Mass Unit
Mass of an atom in atomic mass units (amu)
Atomic Mass Unit
Mass exactly equal to 1/12 the mass of one carbon atom

9. Average Atomic Mass
the weighted average of all the naturally occurring isotopes of an element
Formula:
Average Atomic mass of
an element = (
% abundance of
Isotope #1 x
mass
Isotope #1 ) +
Isotope #2 …

10. Example 1
Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of amu. Ag-109 has a relative abundance of 48.18% and a mass of amu. Calculate the average atomic mass of silver.

11. Example 2
Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb. If the abundance of 85Rb is 72.2% with an atomic mass of amu and the abundance of 87Rb is 27.8% with an atomic mass of amu, what is the average atomic mass of rubidium? 85 37 87 37