Download Chemistry Study Guide Chapter 4

Chemistry Study Guide Chapter 4 - Key
1. Define the following terms: (a) atom, (b) atomic number, (c) mass number,
(d) isotopes (give 2 definitions), (e) atomic mass unit (amu), (f) nucleus, (g) spectroscopy, (h)
ground state, (i) excited state, (j) atomic mass, (k) quantum leap, (l) photon.
(a) Atom: the smallest particle of an element that still has the element’s
properties.
(b) Atomic number: the number of protons in the nucleus of an atom.
(c) Mass number: the number of protons plus the number of neutrons in an
atom.
(d) Isotopes: Atoms with the same atomic number but different mass numbers
or atoms with the same number of protons but a different number of
neutrons.
(e) Atomic mass unit (amu): small unit of mass used to measure atoms,
subatomic particles, etc.
(f) Nucleus: small, dense, positively charged core of an atom containing protons
and neutrons.
(g) Spectroscopy: the study of spectra produced by the excitation of atoms,
especially experimental observation of optical spectra used to determine a
substances identity.
(h) Ground state: the state of lowest energy for an atom.
(i) Excited state: any state of higher energy for an atom.
(j) Atomic mass: the weighted average of all the isotopes of an element.
(k) Quantum Leap: change of an electron from one energy state to another
within an atom.
(l) Photon: small packets of electromagnetic energy
2. Compare and contrast electrons, protons, and neutrons in terms of mass, charge and location.
PARTICLE
SYMBOL
CHARGE
MASS (amu)
LOCATION
electron
proton
neutron
e-
-1
+1
0
0
1
1
orbit nucleus
inside nucleus
inside nucleus
p+
n0
3. What are the units used to express (a) wavelength, (b) frequency.
(a) any units of length (b) cycles/second or hertz.
4. Compare/contrast x-rays and infrared radiation in terms of their speed, wavelength, frequency
and energy.
Both move at the speed of light however x-rays have shorter wavelengths
which give them higher frequencies and energies than infrared radation.
5. Compare and contrast absorption (dark-line) and emission (bright-line spectra) in terms of
their (a) appearance and (b) the changes that occur within atoms which cause each of them to be
produced.
(a) absorption spectra appear as the rainbow colors of the continuous
spectrum with dark lines in it whereas the emission spectra appear as
a black background with brightly colored lines.
(b) absorption spectra are produced when the electrons absorb energy
and move to higher orbits whereas emission spectra are produced
when the electrons release energy and move back to their lower orbits.
6a.) Explain what happened during Rutherford’s gold foil experiment.
(a) Rutherford shot a beam of alpha particles at a sheet of gold foil. Most of the
particles passed through the gold foil although a very small amount bounced
back or were deflected.
(b) What did it show us about the structure of the atom?
(b) This showed that the atom has a nucleus which is very small, dense, and
positively charged and that the electrons surround the nucleus. It also
showed that most of the atom is empty space.
7. Be able to do problems involving mass number, atomic number, and numbers of protons,
neutrons, and electrons.
. Complete this table:
Atomic Number
Mass Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
12
12
11
12
14
23
28
14
14
22
13
70
28
22
48
14
22
15
13
30
75
13
30
45
30
8. How did each of the following contribute to the study of the atom? (a) Democritus, (b) John
Dalton, (c) Lord Ernest Rutherford, (d) Sir Francis Bacon, (e) Antoine Lavoisier,
(f) J. J. Thomson, (g) James Chadwick.
(a) Democritus proposed the first atomic theory.
(b) Dalton had the first scientifically supported atomic theory.
(c) Rutherford discovered the nucleus of the atom.
(d) Bacon was the father of inductive reasoning
(e) Lavoisier was the father of modern chemistry who developed the law of
conservation of mass.
(f) Thomson discovered the electron and isotopes.
(g) Chadwick discovered the neutron.
9. What is the identifying characteristic that makes atoms of one element different from atoms of
another element?
The atomic number (the number of protons) in an atom determines the type
of element it is.
10. Why is the Bohr model of the atom said to be quantized?
As the electrons move about the nucleus there are only certain levels
(quantities) of energy that they can have.
11. Explain what is occurring inside the atom that produces the colors of light that we see in the
flame tests and spectral tubes of different elements.
The atoms absorb energy and the electrons jump to higher orbits. The
electrons then release this energy as they return to their original orbits. The
amount of energy released determines the colors of light that we see.
12. Name three common uses of isotopes.
Isotopes can be used for isotope analysis, radiometric dating, and nuclear
medicine.
13. Calculate the frequency and energy of a microwave with a wavelength of 2.85 cm.
2.85 cm = 2.85 x 10-2 m
c=•
 = c ÷  = 3.00 x 108 m/s ÷ 2.85 x 10-2 m
 = 1.05263 x 1010/s or Hz
 = 1.05 x 1010/s or Hz
E = h •  = (6.63 x 10-34 J ∙ s) (1.05 x 1010/s)
E = 6.9615 x 10-24 J
E = 6.96 x 10-24 J
14. J.J. Thomson conducted a series of three experiments involving cathode rays. What
was the major conclusion of each of the three experiments?
 Experinent 1: Cathode rays seem to be made up of negatively charged
particles.

Experiment 2: Cathode rays are made up of negatively charged particles.

Experiment 3: Cathode rays are made up of negatively charged particles that
come from within atoms (electrons).
15. Silver exists as 51.84% 107Ag and 48.16% 109Ag. The mass of 107Ag is 106.90509 u and the
mass of 109Ag is 108.90476 u. What is the average atomic mass of silver?
[(0.5184)(106.90509 amu)] + [(0.4816)(108.90476 amu)] = [55.42] + [52.45]
= 107.87 so, the atomic weight of Ag = 107.87 amu