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Chapter 4: Basic Atomic Structure
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Part One: What is the structure of an atom?
Democritus (460-370 B.C.).
1. What are two characteristics of Democritus’ idea of an “atom?”
All elements are made of small, indivisible particles called atoms.
Atoms have different properties based on the properties of their element
2. How would Democritus answer the question, “what is an atom?”
An atom is the smallest piece of matter
3. Using the provided clay, model an atom as Democritus described.
The atoms are different shapes, sizes and colors.
John Dalton (1766-1844): Dalton developed the atomic theory.
1. How would Dalton answer the question, “what is an atom?”
An atom is the smallest, indivisible piece of matter, that makes up elements.
2. Did Dalton think all atoms are the same? Explain.
Dalton thought that atoms of the same element are identical but that atoms of different
elements are different.
Using the provided clay, model this part of Dalton’s Theory.
The pink atoms are the same element and are identical but they are different from
the green and blue, which are different elements.
3. According to Dalton, how do compounds form?
According to Dalton, any given compound is always made of the same elements in the same
numbers (proportions).
Using the provided clay, model this part of Dalton’s Theory.
These are two examples of the same compound: The compound always contains
one pink atom and 2 blue atoms
4. According to Dalton, what happens to atoms in a chemical reaction?
According to Dalton, Atoms can neither be created nor destroyed in a chemical reaction.
Using the provided Clay, model this part of Dalton’s Theory.
We start with 4 blue atoms (hydrogen) and end with 4 blue atoms. We start with 2
pink atoms (oxygen) and end with 2 pink atoms
J.J. Thomson (1856-1940): JJ Thomson developed his atom model.
1. What is the name of JJ Thomson’s model? Why did it have that name? Thomson’s model was
the plum pudding model since it was a soup/pudding of positive charges with plums/electrons stuck in
it.
2. How would Thomson have answered the question, “what is an atom?” Thomson would say an
atom has a positive charge with little negative charges stuck throughout.
3. Using the provided clay, model Thomson’s atom. The pink is positively charged with the blue,
negatively charged, electrons stuck in it.
4. How is Thomson’s model of an atom different from what Democritus and Dalton thought an
atom was like? Thomson is now saying that an atom has parts to it, whereas Democritus and
Dalton thought it was indivisible.
Ernest Rutherford (1871-1937); Rutherford shot positively-charged radiation particles at matter
(atoms) and developed his atom model.
1. What is the name of Rutherford’s model? Rutherford’s model is the nuclear atom.
2. How would Rutherford have answered the question, “what is an atom?” Rutherford would say
that the atom is the smallest piece of matter, with a positively charged, heavy nucleus and
electrons orbiting around the nucleus in mostly empty space.
3. Using the provided clay, model Rutherford’s atom.
The blue nucleus has a large mass, the electrons orbit around the nucleus, and the atom is
mostly empty space.
4. How is Rutherford’s model of the atom different from Thomson’s model? Thomson did not
know of the nucleus but Rutherford discovered the positively charged, heavy nucleus.
Part Two: What information do the atomic number and mass number give us about an atom?
Examine the chart for patterns. Use the information from the chart, your periodic table and
your notes to answer the questions below.
Element
H
He
Li
K
Atomic #
1
2
3
19
Mass #
1
4
7
39
# of Protons
1
2
3
19
# of Neutrons
0
2
4
20
# of Electrons
in a neutral
atom
1
2
3
19
1. What is the atomic number? Where do you find the atomic number on your periodic table?
The atomic number is the identifier for different elements’ atoms. It is found above the symbol for the
element.
2. What is the relationship between the atomic number and the number of protons? The atomic
number is the same as the number of protons.
3. What is the relationship between the number of protons and the number of electrons? Why does
this relationship exist? The number of protons and the number of electrons is the same in a neutral
atom. In order for an atom to be neutral, the positive charges (protons) must equal the number of
negative charges (electrons).
4. How do you determine the mass number of an atom?
The mass number is equal to the number of protons plus the number of neutrons.
5. How do you use the mass number to determine the number of neutrons in the element? To
determine the number of neutrons, one subtracts the atomic number (number of protons) from the
atomic mass.
6. Which subatomic particles account for the mass of an atom? Does the mass number reflect that?
The protons and neutrons account for the mass of an atom and the mass number is the number of
protons plus the number of neutrons.
7. Using the provided clay, model one of the elements above.
This is lithium with a mass of 7 amu and an atomic number of 3. It has 3 protons (blue), 4 neutrons
(green), and 3 electrons (pink).
Part Three: Complete the chart below.
Element
Atomic #
B
5
11
5
6
# of Electrons
in neutral
atom
5
F
9
19
9
10
9
Br
35
80
35
45
35
Mn
25
55
25
30
25
Part 3: What are isotopes?
Mass #
# of Protons
# of Neutrons
There are three different kinds of oxygen atoms. Their atomic numbers and mass numbers are
provided for you. Complete the rest of the chart. Then, answer the questions below.
Element
Oxygen-16
Atomic #
8
Mass #
16
# of Protons
8
# of Neutrons
8
# of Electrons
8
Oxygen-17
8
17
8
9
8
Oxygen-18
8
18
8
10
8
1. What do these oxygen atoms have in common? All the oxygen atoms have 8 protons and 8
electrons.
2. How do these oxygen atoms differ? The oxygen atoms have different numbers of neutrons.
3. These oxygen atoms are called isotopes. Based on the information provided, what is an
isotope? Isotopes are atoms of the same element that have different numbers of
neutrons, and therefore, different masses.
4. All the isotopes of oxygen behave the same chemically. Which subatomic particles must be
responsible for how an atom behaves chemically? Electrons are responsible for the behavior
of atoms.
5. What part of Dalton’s theory does the discovery of isotopes prove wrong? Dalton said that
atoms of the same element are identical, but since isotopes are atoms of the same element
and have different numbers of neutrons, Dalton’s theory is proven wrong.
6. Using the provided clay, model each isotope of Oxygen. Teacher initials:
Teacher
Approval:
Oxygen-16
Oxygen-17
Oxygen-18