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Notes: Atomic Structure (Chapters 4)
Essential questions:
1. What components make up an atom?
2. How are atoms of one element different from atoms of
another element?
3. How does the quantum mechanical model of the atom
describe the arrangement of electrons in atoms?
4. What happens when electrons in atoms absorb or release
energy?
Equations:
# Neutrons = Mass # - Atomic #
4.1 DEFINING THE ATOM
A. Early Models of the Atom
Key Question: How did the concept of the atom change from the time of
Democritus to the time of John Dalton?
Answer:_______________________________________________________________________
Atomic Theory Main Ideas (1803)
1. __________________________________________________________________________
2. __________________________________________________________________________
3. __________________________________________________________________________
4. ___________________________________________________________________________
See Figure 4.1. How does a mixture of different atoms of elements differ
from a compound? _________________________________________________________
B. Sizing up the Atom
Key Question: What instruments are used to observe individual atom?
______________________________________________________________________________
Using a ruler, draw a line 1 centimeter long:
_____________________________ atoms of copper = 1 cm
_____________________________________________________________________________________
4.2 STRUCTURE OF THE NUCLEAR ATOM
____________________________________________________________________________________
A. Subatomic Particles
Atom _________________________________________________________________________
Key Question: What are the three kinds of subatomic particles?
________________________________________________________________________________
______________________________________________________________________________
Derived from Greek work __________________ meaning ____________________
Electrons _________________________________________________________________
Democritus (Greek philosopher ___________BC- __________BC)
a) Discovered by English physicist __________________________ in
reasoned _____________________________________________________
_____________ using a ______________________________________.
John Dalton (English chemist & schoolteacher, _____________)
using _______________________________________________________________
_____________________________________________________________________
How was John Dalton able to study atoms even though he was unable
to see them directly? What evidence did he use to form his theory?
___________________________________________________________________
___________________________________________________________________
List two reasons why the ideas of Democritus were not useful in a
scientific sense._______________________________________________
_____________________________________________________________
The diagram above shows electrons moving from left to right in a
cathode-ray tube. Draw an arrow showing how the path of the
electrons will be due to the negative and positive plates.
b) Robert A Millikan (American physicist) in 1909 experimented with
Complete the following table:
oil drops. What two properties of an electron did he find?
1. __________________________________________________
Properties of Subatomic Particles
Particle Symbol
2. ___________________________________________________
B. Atomic Nucleus
Key Question: How can you describe the structure of the nuclear atom?
____________________________________________________________________
___________________________________________________________________________
Nucleus _________________________________________________________________
A. Protons _______________________________________________________
Relative
charge
Relative mass
(proton = 1)
Actual mass
(g)
Electron
e-
9.11 x 10-28
Proton
p+
1.67 x 10-24
Neutron
n0
1.67 x 10-24
4.3 DISTINGUISHING AMONG ATOMS
A. Atomic number and Mass number
Evidence found by ________________________ in a cathode-ray
Key Question: What makes one lement different from another?
tube found positive “canal rays”.
Answer: ______________________________________________________________
B. Neutrons ______________________________________________________
Discovered byEnglish physicist ______________________ in
1932; they are composed of ___________________.
Models of an atom:
1. J.J. Thomson called his model the ____________________________model
where _____________________ were evenly distributed through an atom
with ______________________charged material (not protons).
Atomic number ____________________________________________________
The atomic number defines the element! The symbol for the
atomic number is Z.
Mass number ________________________________________________________
The mass number defines the isotope of that element. The
symbol for mass number is A.
Nuclear Symbol:
2. Ernest Rutherford (JJ Thomson's student) devised the ____________
example:
A
X
foil experiment.
Circle the letter of each sentence that is true about the nuclear theory
of atoms suggested by Rutherford’s experimental results.
a. An atom is mostly empty space.
b. All the positive charge of an atom is concentrated
in a small central region called the nucleus.
c. The nucleus is composed of protons.
d. The nucleus is large compared with the atom as a whole.
e. Nearly all the mass of an atom is in its nucleus. affected by the
placement of the negatively and positively charged plates.
12
C
Z
6
This is example is C-12. Carbon-12 has 6 protons and
6 neutrons, totaling 12 amu.
Complete the following table:
Isotope
Atomic
Number
Mass
Number
Protons
Neutrons
5
5
S-34
V -51
Electrons
B. Isotopes
Key Question: How do isotopes of an element differ?
b. Isotopes of an element do not have a specific natural percent
abundance.
Answer: ______________________________________________________________
c. The average atomic mass of an element is usually closest to that
of the isotope with the highest natural abundance.
Practice problems:
d. Because hydrogen has three isotopes with atomic masses of
about 1 amu, 2 amu, and 3 amu, respectively, the average atomic
mass of natural hydrogen is 2 amu.
1. Three isotopes of oxygen exist: O-16, O-17, and O-18. Write the
nuclear symbol for each, including the atomic number and mass
number.
O-16
O-17
O-18
2. Three isotopes exist for chromium: Cr-50, Cr-52, and Cr-53.
How many neutrons are in each isotope, given the atomic number
of chromium is 24?
3. How do atoms of Neon-20 and Neon-22 differ?
C. Atomic Mass
Key Question: How do you calculate the atomic mass of an
element? Answer: ____________________________________________________
_________________________________________________________________________
Atomic mass unit (amu)
What isotope of carbon has been chosen as the reference isotope
for atomic mass units? ____________________
What is the defined atomic mass in amu of this isotope? ____________
Atomic mass _________________________________________________________
_________________________________________________________________________
Circle the letter of each statement that is true about the average atomic
mass of an element and the relative abundance of its isotopes.
a. In nature, most elements occur as a mixture of two or more
isotopes.
Example problem: Calculating Atomic Mass
Element X has two naturally occuring isotopes. The isotope
with a mass of 10.012 amu (10X) has a relative abundance of
19.91%. The isotope with a mass of 11.009 amu (11X) has a
relative abundance of 80.09%. Calculate the atomic mass of
element X.
Knowns
isotope 10X mass = 10.012 amu relative abundance = 19.91%
= 0.1991
iostope 11X mass = 11.009 amu relative abundance = 80.09%
= 0.8009
Unknown
atomic mass of X = ?
Solve
for 10X 10.012 amu x 0.1991 = 1.993 amu
for 11X 11.009 amu x 0.8009 = 8.817 amu
for element X, atomic mass = 1.993 amu + 8.817 amu
= 10.810 amu (Answer)
Practice problem:
Calculate the atomic mass of bromine. The two isotopes of
bromine have atomic masses and relative abundance of 78.92
amu (50.69%) and 80.92 amu (49.31%). Compare your answer to
the atomic mass of bromine on a periodic table.
Knowns
Unknown
Essential Questions:
1. How does the quantum mechanical model describe the
arrangement of electrons in atoms?
2. What happens when electrons in atoms absorb or
release energy?