Transcript Science Unit C Ch. 2 - Zion Central Middle School

atom
 An atom is the smallest particle of an
element that has the chemical properties
of the element
 All atoms of a particular element are the
same
Chemical symbols
 Scientists use chemical symbols to
represent the elements
 They are one or two letter that stand for
the name of an element
Example:
H is for hydrogen
Ca is for Calcium
O is for oxygen
Periodic table
 Russian chemist, Mendeleev published
the table as a way to organize the
elements
 Ordered by their weights of their atoms
and their properties
 The elements in column are similar in
property
Using the periodic table of
elements
 In order by atom weight
 Columns are their group (metals,
nonmetals, semimetals, and noble
gases)
 Each column has similar properties
Atomic
number
Helium
Element
name
2
He
4. 003
Atom
mass
When is a metal not an
element?
When it is an Alloy! An alloy is a solution
of two or more metals with its own
properties.
Example:
Steel (iron, carbon, chromium, nickel)
Bronze ( copper, tin and sometimes zinc)
Why Alloy?
Alloys are useful because their properties
are different from those of the metals
from which they are made.
Some common uses:
Hardware, plumbing, dentistry, tableware,
artwork, building materials
Is an Alloy a mixture or
solution?
An alloy is both, a mixture and a solution!
• Mixture because the elements mixed
together can be different amount (kind of
like the fruit salad)
• Solution because the metal elements are
evenly mixed throughout
Classifying Matter
How can matter be
classified?
Vocabulary
Physical properties
Chemical properties
Substance
Mixture
Element
Compound
Atom
Chemical symbol
Look around the
classroom at different
objects?
What materials do you
think make up these
objects?
Matter
All of the materials you mentioned are
made of matter. They are all different
kinds of matter.
Matter can be identified by its properties, or
characteristics.
Physical properties
 Are characteristics that can be measured
or detected by the senses.
Examples:
Color
Size
Odor
density
Chemical properties
 Describe how matter changes when it
reacts with other matter
Example: the fact that paper burns is a
chemical property of paper
All matter can be
divided into two major
groupsSubstances and Mixtures
Elements and Compounds
Other important words to
know
 Substance- is a material that always has
the same makeup and properties,
wherever it may be found
 Mixture- is a combination of two or more
substances.
Elements
 An element is a substance that cannot be
broken down by simple means into any other
substance
 There are 118 elements (90 found in nature, 22
not found in nature)
Examples:
Aluminum
Copper
compounds
 Is made up of two or more elements that
are chemically combined
Examples:
Water
Sugar
Compounds- how are they
formed?
 When elements combine to form
compounds they are linked with chemical
bonds
Water molecule
Atom of
Oxygen and
two atoms of
Hydrogen
boned
together
Salt molecule
Sodium and chloride
bonded together
Na is a soft metal that
reacts explosively with
water
Chlorine is a
poisonous gas
When atoms combine to form
molecules they loose their property
and together with what they bind
with create new properties for at
molecule
This explains why we can eat table
salt!
Chemical formula
 Chemical formula is a group of symbols
that show the elements in a compound.
 The numbers tell us how many of that
element.
Example: water, H2 O
Two hydrogen and one oxygen
Living vs nonliving things
 We know that all things are made of
matter
 We also know that all things have atoms
and elements, either mixed together or
pure
* **ALL Living things have Carbon ! ****
This is also called organic material!
Organic compounds“living things”
Example:
Cholesterol which is found in cells of living
things.
C 27 H 45 OH
How many atoms are in this molecule of
Cholesterol?
Lesson review:
 Elements and compounds are both
substances, they cannot be broken down
into other substances.
 Elements contain only one kind of atom.
 Compounds are made up of two or more
elements that are chemically combined.
Review cont…
 Two hydrogen atoms and one oxygen
atom have combined to form a single
molecule of a compound of water.
 Use a periodic table to locate certain
elements ( try: Iodine, chlorine, oxygen)
Lesson Part 2
Mixtures vs. compounds
Mixtures and compounds
 Both are made up of more than one
element
But, they are different…
Mixtures
 Elements keep their original properties
Example:
Iron shavings and sand mixture – iron is
magnetic so we could use a magnetic to
separate the sand
Mixtures cont…
 Different composition- which means
different amounts of each element every
time. They may be different depending
on location and time.
Example:
Fruit salad- all recipes(formulas) are different. Some fruit salad had 2
apples, 3 oranges, 1 banana, 12 strawberries. Another one may
have 1 apple, 2 oranges, 5 bananas and 2 strawberries. But they
are both called fruit salad.
Some common mixtures
 Window glass
 Most building material- bricks, cement,
asphalt
 Air
 Human body contains many mixturesblood, sweat, tears, saliva
Separating mixtures
 Using the physical properties like size, appearance,
texture, color, odor, melting point, boiling point, density,
solubility, and magnetic attraction
Example:
Marbles and sand
compounds
 Always have the same composition
 They are chemically bonded, so the
original elements loose their properties
and new properties are created
Example:
Water because it has two hydrogen and
one oxygen and that will never be
different.( same composition)
Review Lesson part 2
Q: Explain why a mixture cannot be
represented by a chemical formula?
A: A mixture does not have a constant
makeup. It cannot be represented by a
chemical formula because the
proportions of the components can vary.
Review cont…
Q: What is the difference between a
mixture and a substance?
A: A substance has a constant makeup
and a set of constant properties; a
mixture does not.
Review cont..
Q: Suppose you has a mixture of iron
pellets, pebbles, and small wood pieces
of all about the same size.
A: Magnet to attract the iron, add water to
the other two and the wood will float and
the pebbles will sink.
Investigation 3
What is a solution?
Vocabulary:
SOLUTION
SOLVENT
SOLUTE
SURFACE TENSION
COHESION
Remember mixtures?
 The main non-living parts of our planet
are mixtures
 Air, Rocks, Water
Facts about mixing:
even mixing vs. uneven mixing
UnevenIf we mixed sand, salt and water together
we would have an uneven mixture
 This means that no matter how hard we tried we could
not take two samples of the mixture and it would have
an even amount of salt, sand and water in each.
 One sample might have more sand and the other more
salt … it is impossible to get them even
What happens if a mixture
is spread evenly?
They are called solutions.
SolutionA solution has two main parts ( solvent,
and solute)
Solvent is the material that is present in the
greater amount
Solute is the material present that is the
smaller amount
Most common solutions
Sugar dissolved in water.
Rate of solutionWhich would dissolve faster, a cube of
sugar or loose sugar grains?
 Stuff only can dissolve if the liquid touches the
surface of the sugar.
 So the loose sugar would dissolve faster
because all of the grains would have the
surface touched.
 The sugar cube would have to dissolve a little
at a time as the liquid dissolved the surface bit
by bit.
What else can effect the
rate of solution?
 Increased temperature (heat it up)
-
Causes the particles to move faster and have more energy
 Increasing the movement of the particles
(stir it up)
-causes the particles to mix together quicker because it bounces the
particles around
Suspension Sometimes a mixture can mix for just a
limited amount of time
A suspension is a liquid mixture in which
some particles are temporarily
suspended in the mixture
Suspension example:
Salad dressing
Suspensions Project
At home use household products to create
a suspension bottle with as many layers
as you can. Write down how much of
each material you used.
Remember –
• density is a factor
• Insolubility is another factor
?
Lesson part 3 review
Q : Explain why salad dressing is not a solution?
A: particles of oil are unevenly distributed in the
mixture. The oil and vinegar will separate with time
Q: What do compounds and mixtures have in
common?
A: Compounds and mixtures are both made with two
or more substances
Lesson part 3 review
continue…
Q: why is an alloy both a mixture and a
solution?
A: It is a mixture because the components can
be present in different amounts. It is a
solution because the metal components are
evenly mixed.
Lesson part 1 summary:
An element is made up of only one kind of
matter; a compound is made up of two or
more kinds of matter that are chemically
combined and can be represented by a
chemical formula.
Lesson part 2 summary:
Mixtures are made up of two or more kinds
of matter that are physically combined;
most mixtures can be separated into their
components, using physical means.
Lesson part 3 summary:
Solutions are mixtures in which the parts
are evenly distributed at the particle level;
an alloy is a solution of two or more
metals.