ESCS Unit 3: Atomic Structure Study Guide
Section 1: History of Chemistry
1) Democritus:
a. What did he think that matter was made of?
b. What word did he coin for this?
c. Why was his atomic theory revised?
2) John Dalton:
a. On what experiments did Dalton base his ideas about atoms?
b. Describe the major concepts of his atomic theory
i. .
ii. .
iii. .
iv.
c. Describe his model of the atom.
d. Why was his theory accepted so well?
3) J. J. Thomson
a. His experiments first provided evidence of what?
b. What device did he use to make his discovery, and what evidence did he find?
c. What did people call his atomic model?
d. What do we call the particle that he discovered, and how did he know what electrical charge it had?
4) Ernest Rutherford:
a. Describe Rutherford’s gold foil experiment:
b. What evidence did the experiment produce about atoms?
c. Describe his atomic model:
5) Niels Bohr
a. How was Bohr’s atomic model similar to Rutherford’s model?
b. How do electrons move in around the atom in Bohr’s model?
c. What new concept about energy did Bohr’s model include?
d. What evidence did Bohr have to support his ideas about electrons and energy?
6) Erwin Schrödinger & Werner Heisenberg
a. How does the electron cloud model describe the location of electrons?
7) James Chadwick
a. What subatomic particle did he discover?
b. Where would you expect to find this particle?
Section 2: Atomic Structure
8) Subatomic particle descriptions:
a. Name the three subatomic particles:
b. Give the location where each can be found:
c. Give their electric charges:
d. Give their relative masses:
e. Describe the composition and characteristics of the nucleus:
9) Atomic number and mass number:
a. What determines the atomic number of an atom?
b. What determines the atomic mass of an atom?
c. How can you determine how many neutrons will be in a given atom?
d. For an atom to be neutral, what subatomic particles have to have been present in the same number?
e. What number is unique for any given element?
10) Isotopes
a. Define “isotope”:
b. What is same about all isotopes of a given element?
c. What is different between isotopes of a given element?
d. What determines the listed atomic mass for an element with many isotopes?
11) Electron energy levels:
a. The number of energy levels filled in an atom is determined by what?
b. What causes an electron to jump to a different energy level?
c. Define ground state:
d. Define excited state:
e. What causes the glow of a neon light?
f. In a flame test, which color corresponds with the highest excited energy level and which with the
lowest?
12) Complete the following table:
Element
Symbol
Atomic
Number
Se
Atomic
Mass
Mass
Number
78.96
79
Protons
Neutrons
Electrons
6
30.974
26
Xe
40
Br
79.904
80
20
25
22.990
47
13) Draw a Bohr Diagram for Carbon, Sodium, and Sulfur at their ground state and one at an excited state.
ESCS Unit 3: Atomic Structure Study Guide
Key
Section 1: History of Chemistry
1) Democritus:
a. What did he think that matter was made of? - Tiny particles that could not be divided.
b. What word did he coin for this? – “atom”
c. Why was his atomic theory revised? did not have a scientific basis/no evidence; new info
2) John Dalton:
a. On what experiments did Dalton base his ideas about atoms? Working with gases to combine
elements into compounds
b. Describe the major concepts of his atomic theory
i. Every element made of atoms that could not be subdivided
ii. Atoms of same element all alike; atoms of different elements have different masses
iii. Compounds contain more than one element
iv. Elements join into compounds in fixed ratios
c. Describe his model of the atom. - a tiny, solid, indestructible sphere with a unique mass for each
element
d. Why was his theory accepted so well? - There was evidence to support it.
3) J. J. Thomson
a. His experiments first provided evidence of what? – subatomic particles
b. What device did he use to make his discovery? – cathode ray tube (passed electricity through
sealed gas tube)
c. What did people call his atomic model? Plum pudding (today we would have said chocolate chip
ice cream) – negative charges in a positive dense bulk
d. What do we call the particle that he discovered, and how did he know what electrical charge it had?
– electron; attracted to positive plate, so it’s negative
4) Ernest Rutherford:
a. What [was] Rutherford’s gold foil experiment? Shooting alpha particles into gold foil, tracking
which way particles went after hitting foil
b. What evidence did the experiment produce about atoms? – some particles bounced back, so must be
very small, positively charged mass in center of atom surrounded by negative electrons
c. Describe his atomic model: - nucleus surrounded by electrons moving around large volume of
space
5) Niels Bohr
a. How was Bohr’s atomic model similar to Rutherford’s model? – both had small nucleus
surrounded by electrons
b. How do electrons move in around the atom in Bohr’s model? - electrons move in set paths around
the nucleus of an atom, like planets around the sun
c. What new concept about energy did Bohr’s model include? - electron’s path around the nucleus
defines its energy level
d. What evidence did Bohr have to support his ideas about electrons and energy? Energy of electrons
moving between levels can be measured (beams of light)
6) Erwin Schrödinger & Werner Heisenberg
a. How does the electron cloud model describe the location of electrons? - the most likely locations of
electrons in atoms, based on probability
7) James Chadwick
a. What subatomic particle did he discover? neutron
b. Where would you expect to find this particle? nucleus
Section 2: Atomic Structure
8) Subatomic particle descriptions:
a. Name the three subatomic particles: proton, neutron, electron
b. Give the location where each can be found: nucleus – proton & neutron; electrons in electron
cloud
c. Give their electric charges: proton is +; electron is - ; neutron is neutral
d. Give their relative masses: proton ~ neutron are about equal in mass; electron ~1/2000th as much
e. Describe the composition and characteristics of the nucleus: protons with (+) and neutrons
(neutral) for net + charge; almost all of atom’s mass in nucleus
9) Atomic number and mass number:
a. What determines the atomic number of an atom? - # of protons
b. What determines the atomic mass of an atom? - # of protons + # of neutrons
c. How can you determine how many neutrons will be in a given atom? Atomic mass # – atomic
number (i.e. # of protons) = # of neutrons
d. For an atom to be neutral, what subatomic particles have to have been present in the same number? –
protons (+) and electrons (-)
e. What number is unique for any given element? Protons (atomic #)
10) Isotopes
a. Define “isotope”: - atoms of an element with differing numbers of neutrons (and hence, differing
atomic mass)
b. What is same about all isotopes of a given element? # of protons (& # of electrons in neutral atom)
c. What is different between isotopes of a given element? # of neutrons
d. What determines the listed atomic mass for an element with many isotopes? - weighted average,
isotopes have a greater effect than uncommon ones
11) Electron energy levels:
a. The number of energy levels filled in an atom is determined by what? – how many electrons the
atom has (always fill lowest first)
b. What causes an electron to jump to a different energy level? Atom gains or loses energy
c. Define ground state: - all the electrons in an atom have lowest possible energy
d. Define excited state; - at least one electron at a higher energy level than ground state
e. What causes the glow of a neon light? – electrons dropping from excited state to ground state by
emitting energy as light
f. In a flame test, which color corresponds with the highest excited energy level and which with the
lowest? Red is lowest; violet is highest
12) Complete the following table: [black is given; red italics is correct answer]
Element
Atomic
Atomic
Mass
Protons
Neutrons Electrons
Symbol
Number
Mass
Number
34
34
45
34
Se
78.96
79
C
12.011
12
6
6
6
6
P
15
31
15
16
15
30.974
Fe
55.847
56
26
30
26
26
54
131.30
131
54
77
54
Xe
Zr
40
91.22
91
51
40
40
35
35
45
35
Br
79.904
80
Ca
20
40.08
40
20
20
20
Mn
54.938
55
25
30
25
25
Na
11
11
12
11
22.990
23
Ag
47
107.87
108
61
47
47
13) Draw a Bohr Diagram for Carbon, Sodium, and Sulfur at their ground state and one at an excited state.
C
C