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UNIT 2
CHEMISTRY
Chapter 5
I. Properties and Changes
Note: Good scientists are questioning,
sceptical, persistent & honest
1. The Particle Theory of Matter
a) All matter is made up of extremely tiny
particles called atoms
b) Each pure substance has its own kind of
particle, different from the particles of other
pure substances
c) Particles attract each other.
d) Particles are always moving
e) Particles at a higher temperature move
faster (on average) than particles at a
lower temperature
2. Scientific Model
– any understanding that allows a
scientist to picture the processes of
nature that cannot be simply or directly
seen.
Example – Particle Theory of Matter
– points a & b: what matter looks like
– Points c-e: how matter behaves
See bottom of page 156
II. A Matter of Behavior Mixtures
In nature particles may be mixed in different ways.
A mixture is a substance that contains more
that one type of particle.
1. Mechanical Mixtures (Heterogenous)
– Mixtures in which particles are not
evenly scattered. All parts can be seen.
E.g. raisin bran, trail mix, gravel, etc.
2. Solutions (Homogenous)
– Mixtures in which types of particles are
evenly scattered. One type of particle
(solute) is dissolved in the other
(solvent) material. Not all parts can be
seen.
– E.g.. Salt water
3. Pure Substances
– Contain only one type of particle
– Includes elements and compounds
E.g. water, oxygen, etc.
III. Changes In Matter
1. Physical Changes
a) A change in the substance but no new
substance is formed
b) They are often reversible
• E.g.. Phase Changes – solid, liquid & gas
• Change in shape – cutting or bending
2. Chemical Changes
a) A change in a substance(s) in which at
least one new substance (with new
properties) is formed.
b) Often difficult or impossible to reverse
E.g. – Burning paper, electrolysis of water
to form H2 and O2
3. Physical Properties
– Can be observed or measured without a
chemical change happening
E.g. phase, color, temperature, density (d =
m/v)
4. Chemical Properties
– Can be observed only during a
chemical change.
E.g. combustability
5. Qualitative Property
a) Describes the quality of a property
b) Cannot be measured
E.g. smells really bad, a yellow solid
6. Quantitative Property
a) Describes a property using a number
E.g. volume, mass, density, freezing point,
melting point
See Table 5.2 on page 164
7. Evidence of Chemical Change
a)
b)
c)
d)
e)
f)
Heat is produced or absorbed.
The starting material is used up.
A change in color.
A material with new properties forms.
Gas bubbles form.
Grains of a solid (precipitate) form
when 2 liquids are mixed.
Changes of State
Gas
GAS
VAPORIZATION/
EVAPORATION
CONDENSATION
SUBLIMATION
SUBLIMATION
LIQUID
MELTING/
FUSION
FREEZING/
SOLIDIFICATION
SOLID
SOLID
The changes on this side use energy
The changes on this side give off energy
Activities/Assignment
– Teacher Demonstration
– Steamboat
– Investigation 5-A, page 160-161
– Read pages 152-169 and do CYU on
page 169 1-4
– AIMS #1
IV. Historical Ideas About the
Nature of Matter
1. Ancient Greek Philosophers (500
B.C.E.)
a) Wondered why matter behaves as it
does
b) Manipulated ideas in their minds but did
no experiments
c) Empidocles proposed that matter was composed of
four elements: earth, water, air & fire
d) Democritus suggested that matter was made of tiny
particles that could not be broken down further. He
called these particles “atomos,” which means
indivisible.
1. This model was later rejected by
Aristotle and Socrates and predominant
thinking went back to the four element
theory. This lasted for the next 2000
years.
2. Alchemists (500-1600
A.C.E.)
a) First people to perform handson experiments. They were
part pharmacist, part mystic
and secretive.
b) Three main beliefs
–
–
–
Some elements could be
changed into others
(especially into gold
There was a substance that
would grant eternal life
They could produce a
universal solvent that could
dissolve all substances
3. Modern Chemists (1600-Present)
a) Sir Francis Bacon (1561-1626)
–
–
contributed the scientific method.
argued that science should be based on the
basis of experimental knowledge rather than
speculation.
b) Robert Boyle (1627-1691)
–
–
–
1661 published “The Skeptical Chymist”
wrote about elements as being “unmingled
bodies.”
Recognized that elements could be
combined to form compounds.
But didn't know which materials were which.
c) Joseph Priestly (late 1700’s)
–
–
First person to isolate oxygen scientifically
He didn’t know it was an element
d) Antoine de Lavoisier (1743-1794)
– defined elements as “pure substances
that cannot be chemically broken
down into simpler substances. (We still
use this definition today.)
– Discovered and identified 23 elements
based on careful measurement.
– Identified air as a mixture of oxygen
and some other gas.
V. Models of Atomic
Structure
1. Dalton’s “Billiard Ball” Model (early
1800’s) page 183
Dalton’s Atomic Theory (cont’d)
a) All elements are composed of atoms. Atoms
are solid, indivisible & indestructible
particles.
b) Atoms cannot be created nor destroyed in a
chemical change.
c) All atoms of the same element are identical
in mass and size, but they are different in
mass and size from the atoms of other
elements.
d) Compounds are created when atoms of
different elements link together in definite
proportions.
2. Thomson’s “Raisin Bun” Model of
the Atom (1904)
a) Discovered electrons (very light negative
particles) through experiments that involved
passing an electrical current through a gas.
This disproved Dalton’s theory that the atom
was indivisible.
b) Discovered protons (heavier positive
particles)later using more advanced
apparatus.
c) Thomson proposed the following:
•
•
•
Electrons have a small mass and a negative
charge
An atom is a sphere of positive electricity
Negative electrons are embedded in the positive
sphere, so that the resulting atom is neutral or
uncharged.
3. Rutherford’s “Nuclear” Model
a) Shot alpha particles (a
type of radiation)
through gold foil to test
Thomson’s model and
discovered a dense,
positively charged core
in the atom called the
nucleus.
b) He proposed
•
•
•
•
The nucleus is a very tiny, dense, and
positively charged core of an atom.
All of the atom’s positively charged
particles, called protons, are contained in
the nucleus.
The nucleus is surrounded by mostly
empty space.
Rapidly moving, negatively charged
electrons are scattered outside the nucleus
around the atom’s edge in what is referred
to as an electron cloud.
4. Bohr’s “Planetary” Model (1913)
a) Improved on Rutherford’s model by
placing electrons in specific orbits
about the nucleus.
b) He proposed:
•
•
Electrons move around the nucleus in
nearly circular paths called orbits, much
like how planets circle the Sun.
Each electron in an orbit has a definite
amount of energy. Electrons can move
within these energy levels without loss of
energy.
• The nucleus is surrounded by mostly empty
space.
• Rapidly moving, negatively charged
electrons are scattered outside the nucleus
around the atom’s edge in what is referred
to as an electron cloud.
5. Einstein’s Quantum (“Wave”) Model
of the Atom – Quantum Mechanics
a) Bohr’s model worked well in
explaining the behaviour of simple
atoms such as hydrogen, that contained
few electrons, but it did not explain the
more complex atoms.
b) The Quantum Model proposed the
following:
•
Electrons do not move about the atom’s
nucleus in a definite path like planets
around the sun
• It is impossible to determine the exact
location of an electron.
• The probable location of an electron is
based on its energy.
• Energy levels are divided into four
sublevels, and each sublevel is made up of
several pairs of electrons called orbitals.
• Electrons move randomly in electron
clouds called orbitals.
Assignment
– AIMS Booklet #3
– Timeline of Atomic Models Diagrams
VI. Bohr-Rutherford
Diagrams
1. Proton (p) – A positively charged
subatomic particle.
2. Neutron (n) – a neutrally charged
subatomic particle.
– Protons and neutrons make up the
nucleus of an atom and each one has a
mass of approximately one atomic unit.
3. Electron (e) – a negatively charged
subatomic particle that “orbits” the
nucleus in rings/shells. It has a mass
so small that it generally doesn’t
count.
4. Atomic mass – the total amount of
mass of an atom and is equal to the #
of protons + # of neutrons.
5. Electron Shells
a) The electrons move around the nucleus
in orbits called shells.
b) The more energy the electron has, the
further it is from the nucleus.
c) The shells can hold:
–
–
–
K shell = 2 e’s
L shell = 8 e’s
M shell = 8 e’s (18 if forced)
6. Drawing Bohr-Rutherford Diagrams
a) Find the element on the periodic table
b) The atomic # = # of p’s = # of e’s
c) Find the atomic mass on the periodic
table (round off to the nearest whole #)
d) # of n’s = atomic mass – # of p’s
e) Draw the nucleus as a circle with the #
of p’s and n’s inside
f) Draw the same number of e’s as p’s
placing them in the shells (in pairs)
g) Practice
Assignment
–
–
–
–
BLM 7-18
Bohr-Rutherford Model Practice
Practice Quiz
Bohr-Rutherford diagrams for the
first 20 elements.
– Quiz
VII. The Periodic Table
1. History
a) In the 1850s there were about 50
known elements.
b) They were named by the people who
had found them.
c) The lists were made in alphabetical
order.
d) Unfortunately that meant reorganizing
the entire table when new elements
were found.
2. Dmitri Mendeleev
a) Organized elements in groups
(families) with similar characteristics.
b) He arranged them in columns with the
lightest first and the heaviest last.
c) Mendeleev’s system allowed the
periodic table to grow since he could
leave room for the elements that
seemed to be missing.
d) It also allowed people to “look for” the
missing elements.
3. Families
a) Alkali Metals
– very reactive family (1 e- beyond
stability)
– shiny, ductile, malleable
– solids at room temperature
– conduct electricity and heat
b) Alkaline Earth Metals
– fairly reactive family (2 e- beyond
stability)
– shiny, ductile, malleable
– solids at room temperature
– conduct electricity and heat
c) Halogens
– very reactive family (1 e- short of
stability)
– non-metal
– don’t conduct heat or electricity well
– all gases (except bromine) at room
temperature.
d) Noble gases
– completely non-reactive (don’t
socialize with other families)
– all are gases at room temperature
– stable octet (outer shell)
– don’t conduct heat or electricity
– used in light bulbs
e) Coinage Metals
a) got their name because early currency was
made from these elements
b) they are all shiny and very malleable
(hammered) and ductile (stretched into
wire)
c) all are valuable
d) they occur in their natural forms (earliest
metals discovered)
e) they are not very reactive
f) fairly high melting points
f) Transition Metals
•
Iron & Lead
•
•
Lead has a low BP
Iron has a high BP
4. Patterns in the Periodic Table
a) Metals on the left, non-metals on the
right
b) atomic number increases left to right
c) atomic mass increases down a group
d) elements in a period (row) have same
number of electron shells
e) elements in a group have same number
of valence (outer shell) electrons (e-)
f) outer families are more reactive (except
noble gases)
Assignment
• AIMS #2 & #4
• Crosswords 1 & 2
• Elementary My Dear Watson
VIII. Atoms vs. Ions
1. Atoms
a) # of protons = # of electrons
b) neutral charge
c) are ‘happiest’ when they have full
valence shells or empty valence shells.
They are very dissatisfied if they “don’t
quite have a full shell”
2. Ions
a) atoms which have gained or lost
electrons to get a full or empty valence
shell.
b) have charges on them. (electrons are
negative!)
c) MetaLs Lose electrons to get empty
valence shells. They become positive
ions.
Eg) Alkali Metals like Na lose 1 e- and
become Na1+
Eg) Alkaline Earth Metals like Mg lose 2
e- and become Mg 2+
d) Non-metals gain electrons to get full
valence shells. They become negative
ions.
Eg) If Cl gains 1 electron it becomes Cl1-
3. Chemical Bonding
a) Atoms always bond with each other
through the valence electrons.
b) There are 3 ways in which atoms bond
together. We will only study 1 way.
c) Ionic bonds
–
–
–
Occur between metals and non-metals
Metals happily transfer their electrons to
non-metals which happily accept the
electrons.
Electrons transfer making two oppositely
charged IONS which stick together
d) Ionic compounds are formed
e) Ionic compounds:
–
–
–
have high melting points. (strong ionic
bonds)
usually dissolve easily in water
are electrolytes – materials that conduct
electricity when molten or when dissolved
(aqueous)
Assignment
– AIMS #5
– AIMS #6
4. Writing Chemical Formulas
– Positive ions balance negative ions to
form neutral compounds
E.g. Na + Cl
NaCl
Find the type/charge of
ion formed – From the
family/group
Describe how many ions
are needed to balance the
charges
Write the compound
(metal first)
Na (1+) + Cl (1-)
1Na + 1Cl
NaCl
E.g. Mg + Cl
Find the type/charge of
ion formed – From the
family/group
Describe how many ions
are needed to balance the
charges
Write the compound
(metal first)
MgCl2
Mg (2+) + Cl (1-)
1Mg + 2Cl
MgCl2
Assignment
– AIMS # 7
– AIMS #8
– BLM 8-1, 8-2 (2 pages), 8-3 & 8-4
1. Naming Ionic Compounds
2. Ionic Compounds – electrons are
transferred from metals to nonmetals. The ions stick together.