Unit 2: Matter and Atomic Theory
Ch. 2 Matter and Change, Ch. 4 Atomic Structure, Ch. 5 Electrons in Atoms
Objectives:
1.
Classify matter according to its composition and distinguish among elements, compounds, homogeneous
mixtures, and heterogeneous mixtures.
2.
Distinguish among the three main states of matter.
3.
Classify changes and properties as physical or chemical.
4.
Describe how to recognize a chemical change.
5.
Explain how Democritus described atoms and explain Dalton’s Atomic Theory.
6.
Describe subatomic and subnuclear particles and the overall structure of an atom.
7.
Understand and use atomic numbers and mass numbers to distinguish elements.
8.
Explain the role of isotopes in determining the atomic mass of an element and calculate average atomic mass.
9.
Describe the Bohr atomic model and the role of electron energy levels, which lead to the current quantum
mechanical model.
Vocabulary:
Substance
Physical property
Solid
Liquid
Gas
Vapor
Mixture
Heterogeneous mixture
Homogeneous mixture
Solution
Phase
Element
Compound
Chemical change
Chemical property
Chemical reaction
Reactant
Product
Precipitate
Atom
Atomic Theory
Electrons
Protons
Neutrons
Quarks
Nucleus
Atomic number
Mass number
Isotopes
Atomic mass unit
(AMU)
Energy levels
Quantum mechanical
model
Electron cloud
2.1 Properties of Matter
Read p. 40-42 and make notes by answering the following questions.
State some examples of physical properties.
State the characteristics of a solid, liquid, and gas. How are they similar and how are they different to each other?
Give some examples of a physical change.
2.2 Mixtures
Read p. 44-45 and make notes by answering the following questions.
Give some examples of heterogeneous and homogeneous mixtures.
2.3 Elements and Compounds
Read p. 48-52 and make notes by answering the following questions.
Give some examples of elements and compounds.
How do chemical changes differ from physical changes?
How do the properties of a compound compare to the properties of the elements that make up that compound? State
some properties of sodium chloride and of the elements that make it up, sodium and chlorine.
Explain how elements get their symbols.
Complete this chart.
Matter
Anything with mass and volume.
Pure Substance
Mixture
Matter with constant composition
Matter with variable composition
Element Compound Heterogeneous Homogeneous
Substance made Two or more elements
Mixture
Mixtures
up of only one
that are chemically
type of atom
combined
Examples - gold,
Examples - water,
silver, carbon,
carbon dioxide, sodium
oxygen and
bicarbonate, carbon
hydrogen
monoxide
Mixtures that are made up of
more than one phase
Also called solutions. Mixtures
that are made up of only one
phase
Examples - sand, soil, chicken
soup, pizza, chocolate chip
cookies.
Examples - salt water, pure air,
metal alloys, seltzer water.
State whether the following samples of matter are elements, compounds, homogeneous mixtures, or heterogeneous
mixtures:
Matter
Element, Compound, Homogeneous Mixture or Heterogeneous Mixture
Pepsi
Tin
Brass
Iron Oxide (AKA rust)
Granola
Air
2.4 Chemical Reactions
Read p. 53-54 and make notes by answering the following questions.
What are some words that usually signify a chemical change?
How does a chemical change affect the composition of matter?
What is the purpose of knowing a chemical property of a substance? When are chemical properties observed?
How is a chemical change different from a physical change?
Describe the four possible clues that indicate whether or not a chemical change has taken place. Describe an example
for each clue.
State whether the following is a physical or a chemical change.
Physical or Chemical Change
Change
Water boils and produces vapor
Sugar dissolves in water
Food is digested
Marshmallows are toasted
Grapes turn into wine
A window is broken
4.1 Defining the Atom
Read p. 101-102 and make notes by answering the following questions.
Describe Democritus’s atomic philosophy.
How did Dalton further Democritus’s ideas on atoms?
State Dalton’s Atomic Theory, first by copying it as it appears in the text, but then summarize each point using your
own words.
4.2 Structure of the Nuclear Atom
Read p. 104-108 and complete the following chart.
Particle
Charge
Proton
(composed of quarks)
Relative Mass (u)
Electron
Neutron
(composed of quarks)
4.3 Distinguishing Among Atoms
Read p. 110-117 and make notes by answering the following questions.
What makes one element different from another?
Location
How do you determine the number of neutrons in an element?
Explain how not all atoms of the same element are identical.
How are isotopes of an element different from each other? How are they the same?
Explain how carbon-12 was used to determine AMU.
How is mass number different from atomic mass?
How do you calculate atomic mass?
Explain why the atomic masses of elements are generally not whole numbers.
Complete the following table.
Symbol
Name
12
6C
# Protons
# Electrons
# Neutrons
Calcium
47
18
3
35
7
17Cl
Iron
13
92
2
3
The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and
atomic masses are 69.2% for mass = 62.93 amu and 30.8% for mass = 64.93 amu. Calculate the average atomic mass
of copper. Draw a circle graph to show the relative abundances for copper.
5.1 Models of the Atom p. 127-130
Rutherford’s orbital atomic model could not explain the chemical properties of elements. For example, why do metal
elements, or compounds that contain metals, give off characteristic colours when heated in a flame? Explaining what
leads to the chemical properties of elements requires a model that better describes the behavior of electrons within
atoms.
Niels Bohr proposed that an electron is found only in specific circular paths, or orbits, at fixed distances, around the
nucleus. Each possible electron orbit in this model has a fixed amount of energy. We call these orbits energy levels.
The orbits closest to the nucleus have the lowest energies. Also, the space between each energy level is not equal.
The further you get from the nucleus, the closer the energy levels are to each other. Therefore, in moving from the
first energy level to the second energy level, the electron gains the most amount of energy. As an electron continues
to climb, it still gains energy but the amount it gains is less at each level.
Electrons can move from energy level to energy level by gaining or losing energy. If they move away from the
nucleus, they gain energy; as they move towards the nucleus, they release energy. The amount of energy needed to
move electrons from one energy level to another is called a quantum.
Analogy to the Concept of Energy Levels
An analogy to the concept of energy level is a person walking up a flight of stairs, where the steps continually get smaller
as they go up.
As the person proceeds up the steps, he changes his position and hence his potential energy. Each step of the staircase
corresponds to a different energy level. When the person puts his foot on a step, he is at the energy level of that step. He
cannot put his foot in between the steps, therefore, he cannot be at an "in-between" energy.
The person here is like the electrons. Likewise, the energy of the electrons can only have specific energy values
associated with the energy levels.
Today we use the quantum mechanical model to describe the positions of electrons in an atom. This model states
how much energy each electron has, depending on the location of that electron, and gives the probability of finding an
electron in the various locations around the nucleus. Unlike the Bohr model, the quantum mechanical model does not
involve an exact path the electron takes around the nucleus. The electrons are found within an electron cloud. The
denser the cloud (closer to the nucleus), the higher the probability of finding an electron there.