1. Chapter 5: Atomic Theory: The Nuclear Model of the Atom
Chemistry 120
Chapter 5: Atomic Theory: The Nuclear Model of the Atom

2. Figure: 04-04
Title:
Dalton's Symbols for Elements
Caption:
Dalton symbolized each element using a circle with an inscribed marking.
Notes:
Dalton saw elements as solid spheres of matter called "atoms," so he used different circles to represent each element.

3. Fig. 5-CO, p. 123

4. Atomic Theory
Elements (matter) is composed of small, indivisible particles called atoms.
Atoms of a given element are identical in mass and behavior.
Atoms of different elements differ in mass and behavior.
Chemical combination of elements to make different substances occurs when atoms join together in small whole number ratios.
Chemical reactions only rearrange the way the atoms are combined; the atoms themselves are not changed

5. Figure: 05-01
Title:
Thomson Model of the Atom
Caption:
Atoms are pictured as spheres of positive charge. The small negative particles represent electrons.
Notes:
Thomson's subatomic model was flawed, but he did determine the relative charge to mass ratio of electrons and protons.

6. Law of Multiple Proportions (John Dalton)
When the same two elements combine to form more than one compound:
the ratios of the mass of one element in the first compound to its mass in the second compound, (as it combines with the same mass of the other element), can always be expressed as ratios of small whole numbers

7. Carbon combines with oxygen to form CO and CO2 .
Mass of Carbon(g)
Mass of Oxygen(g)
Ratio of O in CO2 to O in CO CO
12.01
16.00
CO2
32.00
2:1

8. Example of the Law of Multiple Proportions
That of nitrogen and oxygen forming three different compounds that contain different relative amounts of nitrogen and oxygen.
Mass of Nitrogen that
combines with 1 g of Oxygen
Compound A g
Compound B g
Compound C g

9. Example of the Law of Multiple Proportions continued
The ratios of the masses of nitrogen combining with 1 gram of oxygen in each pair of compound should be small whole integer number
A/B = 1.750/ = 2 for nitrogen
0.8750/0.8750= 1 for nitrogen, a ratio 2:1
B/C= / = 2 for nitrogen
0.4375/ = 1 for nitrogen, a ratio 2:1
A/C = 1.750/ = 4 for nitrogen
0.4375/0.4375= 1 for nitrogen, a ratio 4:1

10. Sub Atomic Particles

11. Figure: 05-02
Title:
Alpha-Scattering Experiment
Caption:
The diagram shows the deflection of alpha particles by a thin gold foil. Some particles rebounded backward.
Notes:
The results of this experiment showed that the volume of an atom is mostly empty space.

12. Figure: 05-03
Title:
Explanation of Alpha-Scattering
Caption:
(a) Powerful alpha particles should pass through a homogeneous "plum-pudding" gold atom. (b) Since positively-charged alpha particles are deflected, Rutherford reasoned correctly that a gold atom has a dense, positively-charged nucleus.
Notes:
Rutheford's observations were consistent with the atomic model in (b), an atom with a core of positive charge.

13. Figure: 05-04
Title:
Rutherford Model of the Atom
Caption:
Most of the mass of the atom is found in the nucleus. Note that the atoms and nuclei are not to scale, as the size of an atom is about 100,000 times larger than the size of the nucleus.
Notes:
The vast majority of the atom is empty space.

14. Figure: UN
Title:
Atomic Models
Caption:
In the evolving model of the atom, what does the question mark (?) represent in the 2000 model?
Notes:
Atomic theory is one scientific theory that has been adjusted over the years as new evidence has come to light. It is still changing today.

15. Figure: 05-05
Title:
Carbon from the Periodic Table
Caption:
The atomic number designates the number of protons. The atomic mass is the average isotope mass.
Notes:
The atomic mass for each element can be calculated from the masses of the individual isotopes and their percent abundance.

16. Example – Chemical Symbols
How many protons does a sulfur atom have?

17. Example – Chemical Symbols
How many electrons does a sulfur atom have?

18. Example – Chemical Symbols
How many electrons does a sulfide ion, S2-, have?

19. Example – Chemical Symbols
How many protons does an aluminum ion, Al3+, have?

20. Example – Chemical Symbols
How many electrons does an aluminum ion, Al3+, have?

21. Example – Chemical Symbols
An atom has 5 protons, 5 electrons, and 6 neutrons. What is the atomic number?

22. Example – Chemical Symbols
An atom has 5 protons, 5 electrons, and 6 neutrons. What is the name of the element?

23. Example – Chemical Symbols
An atom has 5 protons, 5 electrons, and 6 neutrons. What is the mass number?

24. Example – Chemical Symbols
An atom has 5 protons, 5 electrons, and 6 neutrons. What is the charge?

25. Example – Chemical Symbols
An atom has 20 protons, 18 electrons, and 20 neutrons. What is the atomic number?

26. Example – Chemical Symbols
An atom has 20 protons, 18 electrons, and 20 neutrons. What is the name of the element?

27. Example – Chemical Symbols
An atom has 20 protons, 18 electrons, and 20 neutrons. What is the mass number?

28. Example – Chemical Symbols
An atom has 20 protons, 18 electrons, and 20 neutrons. What is the charge?

29. Example – Chemical Symbols
What is the atomic notation for an atom that has 17 protons, 20 neutrons, and 17 electrons?

30. Example – Chemical Symbols
What is the atomic notation for an atom that has 15 protons, 16 neutrons, and 18 electrons?

31. Isotopes
Atoms which differ only in the number of neutrons present in the nucleus.

32. Example – Atomic Mass Calculate the atomic mass of magnesium given
Mass (amu)
%abundance
Mg-24
23.985
78.70
Mg-25
24.986
10.13
Mg-26
25.983
11.17

33. Example – Atomic Mass Calculate the atomic mass of chlorine given
Mass (amu)
%abundance
Chlorine-35
34.969
75.78
Chlorine-37
36.966
24.22

34. Example – Atomic Mass
Lithium has two isotopes: lithium-6 at 7.420% and lithium-7 at 92.58%. If the atomic mass of lithium is amu and the mass of lithium-6 is amu, what the mass of lithium-7?

35. Example – Atomic Mass
Bromine has two isotopes. Bromine-79 the most abundant isotope at 50.69% has a mass of amu. What is the mass of bromine-81?