1. Chapter 4 review

2. Whose work is credited with being the beginning of the modern atomic theory?
Distinguish between the ancient ideas and modern ideas of an atom.
John Dalton
Ancient: atoms were indivisible, solid piece of matter
Modern: subatomic particles, can be divided

3. State the main points of Dalton’s atomic theory.
All matter is composed of atoms
Atoms of an element are identical
Atoms cannot be subdivided, created or destroyed
Atoms combine in simple whole-number ratios to form chemical compounds
In chemical reactions, atoms are combined, separated, or rearranged

4. Define matter and give 2 examples
Term for substance
Ex. Pen, paper, book, elements, etc
What is found in the nucleus of an atom?
Neutrons, protons
What is the charge of the nucleus
Positive (because of the protons)

5. Who developed the “plum pudding” model of the atom?
J.J. Thompson
Describe the positive charge distributed in the plum pudding model.
Evenly distributed throughout atom
“positively charged pudding”

6. Explain why atoms are electrically neutral.
Arrange the subatomic particles in order of increasing mass: neutron, electron, proton
Electron is smallest, neutron is largest
Explain why atoms are electrically neutral.
The number of protons = number of electrons
Which particles account for most of an atom’s mass?
Protons and neutrons – they are the largest subatomic particles

7. Which subatomic particle was discovered by researchers working with cathode-ray tubes?
Electrons
What happened to the cathode-ray stream when a negatively charged plate was beside the tube?
The stream moved away from the negatively charged plate

8. What kind of particles were used in the gold foil experiment?
What caused the deflection of the alpha particles in Rutherford's gold foil experiment?
The nucleus, which is very dense
What kind of particles were used in the gold foil experiment?
Alpha particles

9. How is an atom’s atomic number related to its number of protons
How is an atom’s atomic number related to its number of protons? To electrons?
How do isotopes differ? How are they similar?
How is the mass number related to the number of protons and neutrons an atom has?
Atomic number = # protons, # electrons
Different # of neutrons, same # protons
Mass number = # protons + neutrons

10. Define atomic mass unit.
What are the benefits of developing the atomic mass unit as a standard unit of mass?
Does the existence of isotopes contradict part of Dalton’s original atomic theory? Explain.
Standard unit for subatomic particle
Easier to work with compared to grams
Yes – Dalton’s theory stated that atoms were identical in mass

11. Magnesium has 3 isotopes. Calculate its average atomic mass.
Exact weight
% abundance
Mg – 24
23.99 amu
79%
23.99 x 0.79 = amu
Mg – 25
24.99 amu
10%
24.99 x 0.10 = amu
Mg – 26
25.99 amu
11%
25.99 x 0.11 = amu
= amu

12. Silver has 2 isotopes. Ag-107 has a percent abundance of 52% and Ag-109 has a percent abundance of 48%. What is the average atomic mass?
Exact weight
% abundance
Ag – 107
107 amu
52%
107 x 0.52 = amu
Ag – 109
109 amu
48%
109 x 0.48 = amu
= amu