Science 9 – Chemistry 2
Sci 924 – Sci 926
Quick Review
 Law of Conservation of Mass review
– In a chemical change, the total mass of the new
substance is always the same as the total mass of the
original substance.
 Law of Definite Composition
– Compounds are pure substances that contain two or
more elements mixed together in fixed or definite
proportions.
 Therefore, we know that the mass of reactants
must equal the mass of the products in every
chemical reaction.
Dalton’s Atomic Theory
 Dalton found that the particle theory could
not explain why the properties of a
compound are different then the properties
of the element that make it up.
 The particle theory could not explain how
particles of different substances could
combine or decompose to form new ones.
 Then came Dalton’s theory:
– All matter is made up of sm.particles clld atoms.
– Atoms can’t be created or destroyed or split
– All atoms of the same element are the same
size and weight
– Atoms of different elements differ in size and
weight
– Compounds are created when atoms of
different elements link together in definite
proportions
Eg. Water and peroxide both contain H and O2 but in
different proportion. Water is 11%H and 89% O2
whereas peroxide is 6% H and 94% O2
The Scientific Process
Revised
Hypothesis
Theory
Observations
Experiments
Hypothesis
Laws, Theories, Models and
Observations
 Law- describes and summarizes what always
happens.
 Theory – a creative way to describe why
something happens.
 Observation- Scientists observe how matter
behaves and reacts during experiments.
– Many observations and experiments are needed before
a hypothesis can become an accepted theory.
 Model – helps to picture structures or processes
that cannot be directly seen.
Classifying Elements
 As elements were discovered, they were given names.
The scientist who first discovered an element had the right
to name it.
 Over time there were many elements with very long names
 So, a system of element symbols was developed.
 The symbol system is universal which means the same
chemical symbols are used by scientists throughout the
world
 As more and more elements were discovered, Scientists
needed a way to classify the elements and organize their
observations.
 Thus the invention of the periodic table by Dmitri
Mendeleev.
 The periodic table invented my Mendeleev is still used
today with a few modifications.
Ways of Classifying Elements
State at Room
Temp.
Appearance
Conductivity
Malleability
and ductility
Metals
Eg. Mercury,
Silver, Gold,
Copper
Solids
Except for
Mercury
Shiny
Good conductors
of heat and
electricity
Malleable
Ductile
Non-Metals
Eg. Oxygen,
Sulpher
Some gas
Some solid
One liquid
Bromine
Not very shiny
Poor conductors
of heat and
electricity
Brittle
Non ductile
Metalloids
Eg. Silicone
Solids
Can be shiny or
dull
May conduct
electricity
Poor heat
conductors
Brittle
Non ductile
Groups of Elements
 Alkali Metals
– Highly reactive (Boom!)
– Has one unpaired electron
– Gives up the unpaired electron
 Alkaline Metals (Earth metals)
– Can react vigorously but not as reactive as the Alkali metals
 Noble Gases
– Unreactive or inert gases
– All the electrons here have “dates”
 Halogens
–
–
–
–
Highly reactive
Have unpaired electrons
Takes an electron
Corrosive
 There are other groups and families but were are only covering these.
 A couple things:
– Sci 926 will be changing. Check to make sure
my name is in the assignment before you
complete it.
 There will be a quiz at the end of Sci 926 on
the periodic table and symbols!