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UNIT 2
CHEMISTRY
Chapter 5
I. Properties and Changes
Note: Good scientists are questioning,
sceptical, persistent & honest
 The Particle Theory of Matter
All matter is made up of extremely tiny
particles called atoms
 Each pure substance has its own kind of
particle, different from the particles of other
pure substances
 Particles attract each other.



Particles are always moving
Particles at a higher temperature move
faster (on average) than particles at a
lower temperature
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.

Mechanical Mixtures (Heterogenous)
Mixtures in which particles are not evenly
scattered. All parts can be seen.
E.g. raisin bran, trail mix, gravel, etc.
–
Solutions (Homogenous)

–
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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
Pure Substances

Contain only one type of particle
–
Includes elements and compounds
E.g. water, oxygen, etc.
–
III. Changes In Matter

Physical Changes
A change in the substance but no new
substance is formed
 They are often reversible

E.g.. Phase Changes – solid, liquid & gas
 Change in shape – cutting or bending

Chemical Changes

A change in a substance(s) in which at
least one new substance (with new
properties) is formed.

Often difficult or impossible to reverse
E.g. – Burning paper, electrolysis of water to
form H2 and O2

Physical Properties

Can be observed or measured without a
chemical change happening
E.g. phase, color, temperature, density (d =
m/v)
–
Chemical Properties

Can be observed only during a chemical
change.
E.g. combustability
–
Qualitative Property



Describes the quality of a property
Cannot be measured
E.g. smells really bad, a yellow solid
Quantitative Property

1.
Describes a property using a number
E.g. volume, mass, density, freezing point,
melting point
See Table 5.2 on page 164
Evidence of Chemical Change

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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
LIQUID
SOLID
The changes on this side use energy.
The changes on this side give off energy
Activities/Assignment
–
Teacher Demonstration
–
–
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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

Ancient Greek Philosophers (500 B.C.E.)
Wondered why matter behaves as it does
 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.
Cutting the Cheese

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.
Alchemists (500-1600 A.C.E.)

First people to perform handson experiments. They were part
pharmacist, part mystic and
secretive.
Three main beliefs

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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
Modern Chemists (1600-Present)

Sir Francis Bacon (1561-1626)

–
–
contributed the scientific method.
argued that science should be based on the
basis of experimental knowledge rather than
speculation.
Robert Boyle (1627-1691)

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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.
Joseph Priestly (late 1700’s)
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First person to isolate oxygen
scientifically
He didn’t know it was an element
Antoine de Lavoisier (1743-1794)
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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)

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All elements are composed of atoms.
Atoms are solid, indivisible & indestructible
particles.
Atoms cannot be created nor destroyed in a
chemical reaction.
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.
Compounds are created when atoms of
different elements link together in definite
proportions.
2.
Thomson’s “Raisin Bun” Model of the
Atom (1904)
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.
Discovered protons (heavier positive
particles)later using more advanced
apparatus.
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
 Shot Helium 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.
gold foil
helium nuclei
helium nuclei
He found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to
their surprise, some helium nuclei bounced straight
back.
He proposed

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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)
Improved on
Rutherford’s
model by
placing
electrons in
specific orbits
about the
nucleus.
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
4.
Bohr’s “Planetary” Model (1913)
He proposed:

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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
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.
Einstein’s Quantum (“Wave”) Model
of the Atom – Quantum Mechanics
5.
The Quantum Model proposed the
following:

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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
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AIMS Booklet #3
Timeline of Atomic Models Diagrams
VI.

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Bohr-Rutherford Diagrams
Proton (p) – A positively charged
subatomic particle.
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.


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.
Atomic mass – the total amount of
mass of an atom and is equal to the #
of protons + # of neutrons.
Electron Shells

The electrons move around the nucleus
in orbits called shells.
The more energy the electron has, the
further it is from the nucleus.
The shells can hold:

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–
–
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K shell = 2 e’s
L shell = 8 e’s
M shell = 8 e’s (18 if forced)
Drawing Bohr-Rutherford Diagrams
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Find the element on the periodic table
The atomic # = # of p’s = # of e’s
Find the atomic mass on the periodic
table (round off to the nearest whole #)
# of n’s = atomic mass – # of p’s
Draw the nucleus as a circle with the # of
p’s and n’s on the inside
Draw the same number of e’s as p’s
placing them in the shells (in pairs)
Practice
Assignment
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BLM 7-18
Bohr-Rutherford Model Practice
Practice Quiz
Bohr-Rutherford diagrams for the first 20
elements.
Quiz
VII. The Periodic Table
History

In the 1850s there were about 50 known
elements.

They were named by the people who
had found them.

The lists were made in alphabetical
order.

Unfortunately that meant reorganizing
the entire table when new elements
were found.
Dmitri Mendeleev

Organized elements in groups
(families) with similar characteristics.

He arranged them in columns with the
lightest first and the heaviest last.

Mendeleev’s system allowed the
periodic table to grow since he could
leave room for the elements that
seemed to be missing.

It also allowed people to “look for” the
missing elements.
Families
1.
Alkali Metals


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
very reactive family (1 e- beyond
stability)
shiny, ductile, malleable
solids at room temperature
conduct electricity and heat
2.
Alkaline Earth Metals

fairly reactive family (2 e- beyond
stability)
shiny, ductile, malleable
solids at room temperature
conduct electricity and heat



3.
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.
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4.
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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
5.
a)
b)
c)
d)
e)
f)
Coinage Metals
got their name because early currency
was made from these elements
they are all shiny and very malleable
(hammered) and ductile (stretched into
wire)
all are valuable
they occur in their natural forms (earliest
metals discovered)
they are not very reactive
fairly high melting points
6.
Transition Metals
Iron & Lead
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Lead has a low BP
Iron has a high BP
Patterns in the Periodic Table
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Metals on the left, non-metals on the
right
atomic number increases left to right
atomic mass increases down a group
elements in a period (row) have same
number of electron shells
elements in a group have same number
of valence (outer shell) electrons (e-)
outer families are more reactive (except
noble gases)
Assignment
•
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AIMS #2 & #4
Crosswords 1 & 2
Elementary My Dear Watson
VIII. Atoms vs. Ions
Atoms
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# of protons = # of electrons
neutral charge
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”
Ions

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atoms which have gained or lost
electrons to get a full or empty valence
shell.
have charges on them. (electrons are
negative!)
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 eand become Mg 2+

+++++
++++++
Na
atom
-----
------
+++++
++++++
Na+
ion
----------
Non-metals gain electrons to get full
valence shells. They become negative
ions.
Eg) If Cl gains 1 electron it becomes Cl1
+++++
-----
+++++
------
++++++
------
++++++
------
++++++
------
++++++
------
Cl
atom
Clatom
Chemical Bonding

Atoms always bond with each other
through the valence electrons.
There are 3 ways in which atoms bond
together. We will only study 1 way.
Ionic bonds
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–
–
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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
Ionic compounds are formed
Ionic compounds:

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–
–
–
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
–
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AIMS #5
AIMS #6
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
Na (1+) + Cl (1-)
Describe how many ions
are needed to balance the
charges
1Na + 1Cl
Write the compound (metal
first)
NaCl
E.g. Mg + Cl
MgCl2
Find the type/charge of ion
formed – From the
family/group
Mg (2+) + Cl (1-)
Describe how many ions
are needed to balance the
charges
1Mg + 2Cl
Write the compound (metal
first)
MgCl2
Assignment
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AIMS # 7
AIMS #8
BLM 8-1, 8-2 (2 pages), 8-3 & 8-4

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Naming Ionic Compounds
Ionic Compounds – electrons are
transferred from metals to non-metals.
The ions stick together.