1. isotopes
AP Chem

2. Subatomic Particles
Protons and electrons are the only particles that have a charge.
Protons and neutrons have essentially the same mass.
The mass of an electron is so small we ignore it.
Table 2.1

3. Symbols of Elements
Elements are symbolized by one or two letters.

4. Atomic Number
All atoms of the same element have the same number of protons:
The atomic number (Z)

5. Atomic Mass
The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

6. Isotopes:
Atoms of the same element with different masses.
Isotopes have different numbers of neutrons. 11 6 C 12 6 C 13 6 C 14 6 C

7. Isotopes of Strontium Strontium-87 Strontium-90 Mass #? Mass number
# protons?
# neutrons?
# electrons?
Strontium-90
Mass #?
# protons?
# neutrons?
# electrons? 90 38
90-38=52 38
87-38 =49 87
38Sr 90
38Sr

8. Isotopes with a charge:
56 = atomic #
= 81 54
Book info about scientists and atom models!
137Ba+2
How many protons?
How many neutrons?
How many electrons? 56