1. Atomic Number and Mass Number
The Atom
Atomic Number and Mass Number
Isotopes

2. JJ Thomson Plum-Pudding Model Cathode Ray Tube

3. Rutherford
Discovered atom is mostly empty space since most particles went through the foil.
A few particles bounced back which meant there must be a nucleus.

4. Bohr

5. Atomic Theory Atoms are building blocks of elements
Similar atoms in each element
Different from atoms of other elements
Two or more different atoms bond in simple ratios to form compounds

6. LecturePLUS Timberlake
Subatomic Particles
Particle Symbol Charge Relative
Mass
Electron e
Proton p
Neutron n
LecturePLUS Timberlake

7. Location of Subatomic Particles

8. Atomic Number
Counts the number of
protons
in an atom

9. Atomic Number on the Periodic Table11 Na
Atomic Number
Symbol
LecturePLUS Timberlake

10. All atoms of an element have the same number of protons11 Na
11 protons
Sodium
LecturePLUS Timberlake

11. LecturePLUS Timberlake
Learning Check
State the number of protons for atoms of each of the following:
A. Nitrogen
1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons 2) 16 protons 3) 6 protons
C. Barium
1) 137 protons 2) 81 protons 3) 56 protons
LecturePLUS Timberlake

12. LecturePLUS Timberlake
Number of Electrons
An atom is neutral
The net charge is zero
Number of protons = Number of electrons
Unless it is an ion.
LecturePLUS Timberlake

13. LecturePLUS Timberlake
Mass Number
Counts the number of
protons and neutrons
in an atom
LecturePLUS Timberlake

14. LecturePLUS Timberlake
Atomic Symbols
Show the mass number and atomic number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11
LecturePLUS Timberlake

15. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl
chlorine chlorine - 37

16. LecturePLUS Timberlake
Atomic Mass Na
22.99
Listed on the periodic table
Gives the mass of “average” atom of each element compared to 12C
Average atom based on all the isotopes and their abundance %
Atomic mass is not a whole number
LecturePLUS Timberlake

17. Calculating Average Atomic Mass
Percent(%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
(mass isotope1)(%) + (mass isotope 2)(%) +…

18. Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg = 24.0 amu %
25Mg = amu %
26Mg = amu %
Atomic mass (average mass) Mg = 24.3 amu Mg
24.3
LecturePLUS Timberlake

19. LecturePLUS Timberlake
Learning Check
Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the average atomic mass of gallium?
LecturePLUS Timberlake

20. Solution Atomic mass Ga = 69.7 amu 68.9 amu x 60.2 = 41.5 amu for 69Ga
100 +
Ga-71
70.9 amu x = amu for 71Ga
Atomic mass Ga = amu