Classifying Matter According to its
Composition
Mixtures
Elements & Compounds
• Mixtures - Another way to describe matter
• Other ways:
– Physical state
– Chemical and physical properties
– Density
Composition of Matter
Matter
Which can exist as
Pure substance
Element
Compound
Mixture
Homogeneous Heterogeneous
Pure Substance = sample of matter
with only one component
• Elements = pure substances that cannot be
broken down into simper substances with
different properties
• Compounds = a pure substance made up of
two or more elements that are chemically
combined in a fixed proportion by mass
Mixtures
= a combination of two or more substances in
which each retains its own identity
- May be a homogenous mixture
OR
- May be a heterogeneous mixture
Mixtures
• Homogeneous mixtures – A mixture of two or more components that is
uniform throughout.
– Every portion of the sample is identical
- Components cannot be separated out or will not
settle out
- Can exist as a solid, liquid or gas
– For example
• brass (a mixture of zinc & copper.)
• Salt water (Sodium chloride dissolved in water)
• air (a uniform mixture of N2, O2, CO2 and trace gases)
Mixtures
• Heterogeneous mixtures
– have 2 or more components
- components have distinct regions with definite
boundaries
- can be separated by some physical property
- can exist as liquids or solids
For example:
• Soil – bits of sand, black soil, organic matter
• Blood - appears homogeneous but it is actually a
heterogeneous mixture of red and white blood cells that
are visible under a microscope.
In-between Classification
• Colloid or colloidal dispersion - mixture
that is not quite heterogeneous and not quite
homogeneous
• Example – milk is a colloid. The particles
are too small to be seen unaided but are
small enough that they will not settle out
• Others = fog, smoke, whipped cream,
mayonnaise, marshmallows
Another type of Mixture
• Suspension – where
particles are large enough
that they will eventually
settle out
• mixture in which the
particles of one substance
are scattered in another
without dissolving
• Example – making a clay
pot. The clay particles in
the mixture eventually
settle out.
Differentiating between mixtures
Suspension - the particles which are temporarily suspended in the
liquid are large enough to collectively make the material appear
cloudy.
- They will settle out after a while. You can now see that after several
minutes, the particles in the suspension have settled to the bottom.
Differentiating between mixtures
Colloidal dispersion - very small particles spread throughout the
liquid which are large enough to reflect light, but not large enough
to be seen individually.
-may look either clear or cloudy in ordinary room light.
-particles in remain dispersed in the liquid and will not settle out.
Differentiating between mixtures
A solution, on the other hand, will appear
clear even when a light is shown through it.
Classifying Matter as Elements or
Compounds
• Pure substances: is matter that has distinct
properties and a composition that doesn’t vary
from sample to sample. It only has one
component. It’s either an:
– Element: a substance that cannot be broken down
any further into simpler substances with different
properties.
– Compound: a substance that is composed of two or
more elements that are chemically combined in a
fixed proportion by mass.
Classifying Matter
• Elements:
– Simplest from of matter
– Presently 114 known elements
– 90 of them are naturally occurring, rest are manmade
– Every element has its own unique set of physical
and chemical properties
– Each element has its own name and symbol
• Name is always in English
• Symbol will be one capitol letter or a capitol letter
followed by a single un-capitalized letter.
Elements on the Periodic Table
• What is the periodic table?
-a chart that shows all of the known
elements
-give information about each element
Why Know About the Periodic
Table??
• The periodic table is the most important chemistry
reference there is.
• It arranges all the known elements in an informative
array.
• Its main use is to predict the chemical properties of
an element based on where it is located on the table.
• People familiar with how the table is put together can
quickly determine a significant amount of
information about an element.
Some Common Elements & Their Symbols
Carbon
C Aluminum
Al Copper
Cu (cuprum)
Fluorine
F Barium
Ba Iron
Fe (ferrum)
Hydrogen
H Calcium
Ca Lead
Pb (plumbum)
Iodine
I
Cl Mercury
Hg (hydragyrum)
Nitrogen
N Helium
Oxygen
O Magnesium Mg Silver
Ag (argentium)
Sulfur
S Silicon
Sn (stannum)
Chlorine
He Potassium K (kalium)
Si Tin
Think Inside the Box
When you look at the
periodic table, you should
notice that each box
represents a different
element, and each box
contains vital information
about the element,
–
–
–
–
Name
symbol
atomic number
atomic mass
6
C
Carbon
12.011
• The top number is the
atomic number.
• Every element has its
own unique atomic
number.
• The atomic number tells
how many protons are in
one atom of that element.
• Since no two elements
have the same atomic
number, no two elements
have the same number of
protons.
6
C
Carbon
12.011
• The large letter is the
element's symbol
• Just below that is the
element's name.
• Each element has its
own unique symbol
and name.
6
C
Carbon
12.011
• Below the name is the
element's atomic mass.
• The atomic mass is the
sum of the protons and
neutrons in the nucleus
• The atomic mass
essentially gives you an
estimate of how massive
one atom of that element
is
6
C
Carbon
12.011
• The vertical columns of the periodic table (there are
18) are called groups or families.
• The elements in a group have the same number of
electrons in their outer shell.
• As you keep counting the columns and you'll know
how many electrons are in the outer shell.
• All of the elements in a period have the same number of
atomic SHELLS
• Both elements in the top row (the first period) have one shell
for their electrons. All of the elements in the second period
have two electron shells. The number of shells increases as
you go down the table.
• Atoms on the left of the period are usually larger and more
lightweight than the smaller, heavier atoms on the right of the
period.
Electron Shells
• Electrons of atoms with similar energy are grouped
in an energy level called a shell.
• The shells closest to the nucleus contain electrons with
the lowest energies, whereas shells farther away from
the nucleus contain electrons with higher energies
3 Main Categories of Elements
• Metals
• Non-Metals
• Metalloids
3 Main Categories of Elements
Metals
• On the left side of the table
• All are solid except for mercury
• Described as shiny, ductile (most metals can
be drawn out into thin wires), malleable
(most metals can be hammered into thin
sheets )
• All are good conductors of electricity
• All are good conductors of heat
Non-metals
•
•
•
•
On the right side of the periodic table
Some are solid, some are gases.
Bromine is a liquid
Under most conditions are not good
conductors of heat or electricity
Metalloids (semi-metals)
• Elements along the stair-step line
• These elements display the properties of
metals and non-metals, depending upon the
conditions.
Forming Compounds
• Compounds are pure substances made up of
2 or more different elements in a different
proportion.
• Electrons are primarily involved in the
combination of atoms to form compounds.
Composition of Compounds
• Each is put together so that every unit of
that compound is identical to every other
unit
• They are different from every other
compound
Examples of Compounds
• Water - made up of hydrogen and oxygen
• Carbon dioxide – made up of carbon and
oxygen
• Rust – made up of iron and oxygen
• Sugar – Made up of carbon, hydrogen and
oxygen
Naming Compounds
• Chemical formula – describes exactly what
elements and the number of atoms of each element
occurs in the smallest particle of that compound.
• We identify what elements are present by their
symbol
• How many of those elements present are indicated
by the subscript following the symbol.
Chemical Formulas
• Water = H20
means that each unit of water contains 2
atoms of hydrogen and one atom of oxygen
• Sugar (sucrose)= C12H22011
How many atoms of each element are in
sugar?
Review…
Atoms
Molecules
Make up
Matter
Which can exist as
Pure substance
Element
Compound
•Sodium
•Chlorine
•Hydrogen
•Salt
•Water
•Sugar
Mixture
Homogeneous Heterogeneous
•Atmosphere
•Oil & water
•Salt in water •Salt & Pepper
•Black Coffee •Sugar & sand