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

2. 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

3. Subatomic Particles Particle Symbol Charge Relative Mass
Electron e
Proton p
Neutron n

4. Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus

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

6. Periodic Table Represents physical and chemical behavior of elements
Arranges elements by increasing atomic number
Repeats similar properties in columns known as chemical families or groups

7. Periodic Table 11 Na

8. Atomic Number on the Periodic Table11 Na
Atomic Number
Symbol

9. All atoms of an element have the same number of protons11 Na
11 protons
Sodium

10. Learning Check #1
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

11. Number of Electrons An atom is neutral The net charge is zero
Number of protons = Number of electrons
Atomic number = Number of electrons

12. Mass Number
Counts the number of
protons and neutrons
in an atom

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

14. 16 31 65 8 15 30 More Atomic Symbols O P Zn 8 p+ 15 p+ 30 p+
O P Zn
8 p p+ 30 p+
8 n 16 n 35 n
8 e e e-

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
chlorine chlorine - 37 Cl Cl

16. Learning Check #2
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______ C C C 6 6 6 6 7 8 6 6 6

17. Solution #2 6 6 6 12C 13C 14C #P __6___ _ 6___ ___6___
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___

18. Learning Check #3 An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) ) ) 65
B. Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) ) ) 67

19. Learning Check #4
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________ O 16 8 Cl 37 17 Ag
107 47

20. Learning Check #5 16 14 14 An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) ) ) 36 X X X

21. Masses of Atoms
A scale designed for atoms gives their small atomic masses in atomic mass units (amu)
An atom of 12C was assigned an exact mass of amu
Relative masses of all other atoms was determined by comparing each to the mass of 12C
An atom twice as heavy has a mass of amu. An atom half as heavy is 6.00 amu.

22. Na 22.99 Atomic Mass 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