1. The Structure of an Atom
Chapter 4

2. Dalton’s Atomic Theory
1. All elements are made up of tiny indivisible particles
2. Atoms of the same element are identical.
3. Atoms of different elements can mix to form compounds in simple whole # ratios
4. Chemical reactions occur when atoms are separated and rearrange.

3. How small is an atom?
IF YOU PLACED 100,000,000 COPPER ATOMS SIDE BY SIDE, THE LINE WOULD BE 1 cm LONG

4. J. J. Thompson (1897) discovered electrons
Electrons are negatively charged particles
Developed chocolate chip cookie model

5. Robert Millikan (1916)
Discovered the quantity of charge of an electron

6. Protons & Neutrons E. Goldstein (1886)– discovered protons
Protons are positively charged particles
James Chadwick (1932)– discovered neutrons
Neutrons are particles without a charge

7. Ernest Rutherford (1911)
Discovered the nucleus of an atom

8. Matter is mostly empty space

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

10. Atomic Structure Notes EQ: How do Atoms of the Same Element Differ?
II.

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

12. B. Mass (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
Atomic mass = total # of protons and neutrons

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

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

15. E. Atomic Number Atomic # = # Protons
# electrons = # protons when atom is neutral

16. F. 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

17. Isotope Notes
EQ: What is an isotope?

18. 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

19. What is an isotope? 6 6 8 6 14 12 3. Example: Carbon Carbon-14
Protons
Neutrons
Mass # 6 6 8 6 14 12

20. B. Average Atomic Mass Weighted average of all isotopes
The isotope that is the most abundant has the greatest effect on the Avg. Atomic mass
Avg. Atomic mass = ∑ (mass x abundance)

21. Ex 1: There are two isotopes of copper. Cu-63 and Cu-65
Ex 1: There are two isotopes of copper. Cu-63 and Cu-65. Which is the most abundant?
Cu-63 b/c the mass is closer to the avg. atomic mass

22. Ex 2: Calculate the atomic mass of an element with two isotopes.
Relative Abundance
Mass (amu)
19.91%
10.012
80.09%
11.009
x amu = amu
x amu = amu
← add
amu

23. EQ: How are ions and atoms different?
Ion Notes
EQ: How are ions and atoms different?

24. A. Definitions
Ion: When an atom gains or loses an electron, it has an imbalance of charge
Cation (+) = loses e- to become positive
Anion (-) = gains e- to become negative
In an ion, the number of protons do not equal the number of electrons

25. B. Examples
Element
Atomic #
Mass #
Protons
Neutrons
Electrons
O2- F-
Ca2+ 16 8 8 16 8 8 10 8 19 9 19 9 10 10 9 41 20 41 20 21 18 20

26. Unstable Nuclei

27. A. Normal Reactions
atoms rearrange, the elements do not change

28. B. Nuclear Reactions 14 14  C N + 6 7 -1
Radioactive decay- atom breaks apart spontaneously 14 14 C N  + 6 7 -1
*Note: Please fit all reactions in one line

30. B. Nuclear Reactions 9 4 12 1 Be n He C + + 4 6 2
Radioactive bombardment: Particle hits atom & it splits 9 4 12 1 Be n He C + + 4 6 2

32. C. Types of Radioactive Particles
Symbol
Composition
Penetrating Power
Alpha,  He
2 P & 2 N
Low
Beta,  
electron
100 x alpha
gamma, 0
EM waves
Very great 4 2 -1

33. Penetrating Power Alpha Beta Gamma

34. Penetrating Power

35. D. Miscellaneous Notation
1. Positron
2. Neutron e +1 1 n

36. E. Transmutation
1. Fission : a very heavy-mass nucleus splits to form two medium-mass (size) nuclei.

37. E. Transmutation
2. Fusion : two very light-mass nuclei combine to form heavier, more stable nuclei

38. F. Balancing Nuclear Equations
1. mass # & atomic #’s must add up the same on both sides of the equation 31 4 27 1 30 Al + He + H Si
____ 2 13 1 14 15

39. Example #1 14 14 C N ? + 6 7
14 + ? = 14
7 + ? = 6 -1 e -1

40. Example #2
230 4 Th ? He  + + 2 90
? = 230
226 88
? = 90
226 Ra 88

41. Example #3 4 27 30 Al + He Si + ? 2 13 14
= 30 + ? 1 1
= 14 + ? 1 1 p or H 1 1