1. The Atom
SC1. Obtain, evaluate, and communicate information about the use of the modern atomic theory and periodic law to explain the characteristics of atoms and elements.
a. Evaluate merits and limitations of different models of the atom in relation to relative size, charge, and position of protons, neutrons, and electrons in the atom.
b. Construct an argument to support the claim that the proton (and not the neutron or electron) defines the element’s identity.
d. Construct an explanation that relates the relative abundance of isotopes of a particular element to the atomic mass of the element.
e. Construct an explanation of light emission and the movement of electrons to identify elements.

2. The History of the Atom You should be familiar with the findings of:
Democritus
Dalton
Thomson
Rutherford
Bohr
Schrödinger/Heisenberg
Chadwick

3. Subatomic Particles Particle Symbol Charge Relative Mass
Electron e (1/1836) amu
Proton p amu
Neutron n0 none amu

4. Location of Subatomic Particles
1 angstrom = m

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

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

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

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

9. Solution
State the number of protons for atoms of each of the following:
1. Nitrogen
B) 7 protons
2. Sulfur
B) 16 protons
3. Barium
C) 56 protons

10. Mass Number
Counts the number of
PROTONS and NEUTRONS
in an atom

11. Atomic Notation atomic number
Shows the mass number and/or atomic number
Gives the symbol or name of the element
mass number
Na sodium-23
atomic number 23 11

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

13. Subatomic Particles in Some Atoms
O P Zn
8 p p p+
8 n 16 n 35 n
8 e e e-

14. 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

15. Learning Check
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 _______ _______ _______

16. Solution
12C C C #p #n #e

17. Learning Check 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

18. Solution An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67

19. Learning Check
Write the atomic symbols for atoms with the following subatomic particles:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________

20. Solution B. 17p+, 20n, 17e- 37Cl 17 47 16O A. 8 p+, 8 n, 8 e- 8
C. 47p+, 60 n, 47 e- 107Ag 47

21. Atomic Mass on the Periodic Table11 Na
22.99
Atomic Number
Symbol
Atomic Mass

22. Atomic Mass
Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.
Measured in amu (atomic mass units)

23. Example of an Average Atomic Mass
Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine.
35 x =
35.5
37 x =

24. Learning Check
Magnesium has 3 stable isotopes: Mg-24 (78.99%), Mg-25 (10.00%), and Mg-26 (11.01%).
Determine the average atomic mass.

25. Learning Check
Copper has 2 naturally occurring isotopes. Cu-63 has an atomic mass of amu and an abundance of 69.15%.
Identify the second isotope.

26. Energy Levels
Electrons are found outside the nucleus in energy levels, or shells
There are a maximum of 7 shells
n is used to identify the shell
n=1 for 1st energy level, n=2 for 2nd, up to n=7 for 7th

27. Energy Levels
There is a limit to the number of electrons per energy level
Max number of e- = 2n2
2nd shell can have up to 8 e-
6th shell can have…?

28. Energy Levels
Energy levels increase in size and energy as the distance increases from the nucleus

29. Atomic Spectra
An important consequence of the energy level concept is the understanding of atomic spectra.
When substances are heated, the electrons are excited into unstable energy levels.
It takes a discrete amount of energy (quantum) for an electron to be “bumped up”
E=hf (or hν)

30. Atomic Spectra
The electrons immediately return to their more stable energy levels, called ground state, releasing the absorbed heat energy in the form of light.
Because each element’s atom has a unique distribution of electrons among the energy levels, the release of the energy is uniquely associated with that element, and can allow that element to be identified.

31. Atomic Spectra
Emission spectrum for H
Absorption spectrum for H

32. Atomic Spectra