1. Isotopes and Ions of Atoms
Unit 3.3

2. Mass of Atoms Nucleus- contains most of the mass of an atom
Protons & Neutrons contains most of an atom’s mass
Electrons- 1/2000th of the mass of a proton or neutron
Grams are not used to measure mass of atoms because atoms are too small
Amu is used instead
Amu = atomic mass unit
Mass of proton = mass of neutron = 1amu

3. Masses of Atoms Protons- determine the type of element the atom is
Atomic number- tells us the number of protons and located at the top of the periodic table
Average atomic mass-total number of protons & neutrons and is located underneath the name of the element
# of neutrons = mass # - atomic #

4. Masses of Atoms How many neutrons are in an atom of gold (Au)?

5. Answer: 118 Neutrons (197-79=118)

6. Masses of Atoms
Isotope- Atoms of the same element with different numbers of neutrons
To indicate the identity of an isotope, write the element name – mass #
Copper-34, Copper-35
Average atomic mass- a weighted average of the masses of the isotopes of an element
Example: Copper
Av. Atomic Mass: 63.55
Atomic Number: 29
Number of Neutrons: 34.55?

7. Charges of Atoms
Charges of atoms- indicates # of electrons gained or lost by an element
Ion- an element that is positively or negatively charged
Cation- ion with a positive charge- lost electrons
Ex: Na +, Ba 2+
Anion- ion with a negative charge- gained electrons
Ex: Cl -, O 2-
Ex. NaCl Sodium chloride, or table salt, when dissolved becomes Na+ and Cl- (ionization)