1. 4.3 Distinguishing Among Atoms

2. Hydrogen 1 H 1.008 Element Name Atomic number Element Symbol
Avg. Atomic Mass

3. } A. Basic Structure + + proton (+) neutron (Ø) Nucleus electron (-)
electron cloud
neutron (Ø) } + +
Nucleus
Nucleus: smallest yet heaviest part of the atom

4. A. Atomic Number
Key Idea: Elements are different because they contain different numbers of protons.
Atomic # = # Protons
# electrons = # protons when atom is neutral

5. Hydrogen 1 H 1.008 Element Name Element Symbol Avg. Atomic Mass
Atomic number
# of protons
Element Symbol
Avg. Atomic Mass

6. B. Mass Number (atomic mass units = a.m.u)
Each proton has a mass value of 1 amu
Neutron = 1 amu
Electrons are so tiny their mass doesn’t count
Mass Number = total # of protons and neutrons.

7. C. Charge
In a neutral atom all of the positive protons are cancelled out by the negative electrons and the overall charge of an atom is zero.

8. Li D. Notation 1. Isotopic Notation 2. Mass Notation Charge
Lithium - 7
Mass # → 7 + Li
mass #
element name 3
Atomic # →

9. E. Example 109Ag Sulfur -31 Mass Number = # of protons + neutrons
Element
Atomic #
# Proton
Mass #
# of Neutrons
# of electrons
Sulfur -31
109Ag
Mass Number = # of protons + neutrons
# Neutrons = Mass Number - Protons

10. E. Example Sulfur -31 109Ag 16 16 31 16 + =31 15 16 47 47 47 + =109 62
Element
Atomic #
# Proton
Mass #
# of Neutrons
# of electrons
Sulfur -31
109Ag 16 16 31
=31 15 16 47 47
=109 62 47
109
Mass Number = # of protons + neutrons
# Neutrons = Mass Number - Protons

11. Isotope Notes
EQ: What is an isotope?

12. A. What is an isotope?
Isotope: an atom with a specific number of protons and neutrons
Atoms that are isotopes of each other have the same # of protons but differ in the # neutrons and therefore have different mass #’s
The number next to the isotope signifies the mass number

13. What is an isotope? 6 6 8 6 14 12 Example: Carbon Carbon-14 Carbon-12
Protons
Neutrons
Mass # 6 6 8 6 14 12