1. Atomic Number and Mass Number
Chapter 4
The Atom
Atomic Number and Mass Number
Isotopes

2. LecturePLUS Timberlake

3. LecturePLUS Timberlake
Thomson

4. LecturePLUS Timberlake
Rutherford

5. LecturePLUS Timberlake
Bohr

6. Quantum Model/Wave Model/ Current Model
LecturePLUS Timberlake
Quantum Model/Wave Model/ Current Model

7. Subatomic Particles Particle Symbol Charge Relative Mass
Proton p amu
Neutron n amu
Electron e amu
Atomic Mass Unit (AMU)
1 AMU = 1/12 the mass of Carbon-12 atom (approx x kg)

8. Width of the nucleus
10-13cm
Width of an atom
10-8 cm

9. I. Atomic Structure Atomic Number: Number of protons in an atom
Atomic number identifies the type of element
Example: Iron - ________ - _______
Atomic #
26 (26 protons)

10. All atoms of an element have the same number of protons11 Na
26.1
Atomic #
11 protons
Symbol
Sodium
Atomic
mass

11. 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

12. LecturePLUS Timberlake
Atomic Charge: (Charge of the whole atom)
The total charge of an atom is is ALWAYS neutral/0
What is the charge of a sodium atom?
Example: Cobalt (Co) - __27 p______ and _27 e-
Atomic # also equals number of electrons in an ATOM
Number of protons = number of electrons in an ATOM

13. LecturePLUS Timberlake
Learning Check 2
If a Magnesium atom has 12 protons how many electrons does it have?
An Aluminum atom has 13 protons, how many electrons does it have?

14. Mass Number: # of protons + # of neutrons
Example: Helium has 2 protons and 2 neutrons so the
mass number is 4
Beryllium has 4 protons and 5 neutrons what is the
mass number?

15. Calculating Parts of an atom
LecturePLUS Timberlake
Calculating Parts of an atom
Look at Bromine on the periodic table.
How many protons?
35 from atomic #
How many electrons
How many neutrons?
Mass – atomic number
= 44.9 – round to nearest whole #
45 neutrons

16. LecturePLUS Timberlake
Parts of an atom
How many protons, neutrons, and electrons in Iron?

17. II. Isotopes An isotope is a different version of the same element.
Apples come in different varieties- golden delicious, granny
smith, gala, etc. These varieties have different sizes and colors.
Atoms are the same, the varieties of an atom are isotopes.
An isotope is a different version of the same element.
Isotopes are atoms of the same element (same # of protons) that have different numbers of neutrons and therefore different mass.

18. III. Isotopes Isotopic Notation:
Shows the mass of an atom along with element symbol
Mass # 4 5
Example: 94 Be ______ p; _______ n; _______ e- 4
Atomic #
Example: C – ____ p: ____ n; ____ e 6 8 6
Mass #

19. II. Isotopes 1 1
11H 1 2
21H 1 1 2 3
31H

20. III. Isotopes Atomic # = 34 Mass # = 79 7934 Se
Example: Find the number of neutrons in an atom of Se-79
Atomic # = 34
Mass # = 79
7934 Se
# of n = Mass # - Atomic #
= 79 – 34 = 45 n
Example: Find the number of neutrons in an atom of Se-80
Atomic # = 34
Mass # = 80
8034 Se
# of n = Mass # - Atomic #
= 80 – 34 = 46 n

21. Learning Check 7 6 6 6 #P _______ _______ _______
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.
12C C 14C
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______

22. Solution 7 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___
12C C 14C
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___

23. Learning Check 4 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
An atom has 10 protons and 10 neutrons.
Its atomic number is
Its mass number is
The element is

24. IV. Calculating Atomic Mass
The mass found on your period table is NOT the mass of a single atom of that element. That number is the atomic mass which is the average of the isotopes and their abundance for that element. (ex. – C’s atomic mass is )
Atomic Mass:
the average mass of the naturally occurring isotopes based on each of the isotopes’ abundance and mass number

25. IV. Atomic Masses
How to find the atomic mass: Carbon has two naturally occurring stable isotopes . Most carbon atoms % are C-12, while the remaining 1.108% are C-13. What is the atomic mass of carbon?
(Count sig. figs. ONLY for percents! Then add and round to the place with least number of sig. figs)
Divide by 100
Step 1: Convert % to decimal # and multiply the decimal by its mass number
(0.9889)
(12 amu)
= amu
( )
(13 amu)
= amu
Step 2: Add the masses of isotopes
11.87 amu amu =
12.01 amu

26. IV. Atomic Masses
92.21% of Si is found to be amu, 4.70% is found to be amu, and the remaining 3.09% is found to be Calculated the atomic mass of carbon
27.98 amu (0.9221) = amu
28.98 amu (0.0470) = 1.36 amu
29.97 amu (0.0309) = amu
25.80 amu amu amu = amu

27. 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

28. IV. Ions An atom that has gained or lost one or more electrons.
# of protons does not equal # of electrons
Example
23 11 Na 1+
Atomic # # of protons
Mass # # of neutrons
Ion Charge # of electrons

29. LecturePLUS Timberlake
IV. Ions
Anion: An atom that has gained electron(s). Negatively charged (two n’s for negative)
Cation: An atom that has lost electron(s). Positively charged

30. LecturePLUS Timberlake
Examples
7Li ____p ____n ____e _________
31P ____p ____n ____e _________
79Se ____p ____n ____e _________
19F ____p ____n ____e _________