What is matter made of?
 About 450 B.C. a Greek philosopher named
Empedocles proposed that all matter was made of 4
“elements” – air, earth, fire, and water
 He thought all matter was a combination of two or
more of these 4 elements
 People believed this for more than 2,000 years
What is an element?
 In the late 1600’s, experiments by early chemists began
to show that matter is made up of more than 4
elements
 Scientists know that all matter is made up of slightly
more than 110 different substances called elements
What is an element?
 An element is a pure substance that cannot be broken
down into any other substances by either chemical or
physical means
 Elements are the simplest substances
 Each element can be identified by its specific physical
and chemical properties
What are examples of elements?
 Aluminum which is used to make f0il and outdoor
furniture, is an element
 Zinc is an element which makes up pennies
 Copper is another element and is used to coat pennies
 Oxygen and nitrogen which makes up nearly 99% of
Earth’s atmosphere are also elements
What is an atom?
 Since the early 1800’s scientists have known that all
matter is made up of atoms
 An atom is the basic particle from which all elements
are made
 Different elements have different properties because
their atoms are different
 The atom has a positively charged center, or nucleus
surrounded by a “cloud” of negative charge
The Atom
e le c tr o n
n e u tr o n
p r o to n
What happens when atoms combine?
 Atoms of most elements have the ability to combine
with other atoms
 When atoms combine they form a chemical bond – a
force of attraction between 2 atoms
 Atoms can combine to form larger particles called
molecules- groups of 2 or more atoms held together
by chemical bonds
What is a compound?
 In nature, most elements are found combined with
other elements
 A compound is a pure substance made up of 2 or
more elements chemically combined in a set ratio
 For example, water is a compound because it consists
of the elements hydrogen and oxygen
H2O
How is a compound represented?
 A compound may be represented by a chemical
formula, which shows the elements in the compound
and the ratio of atoms
 For example, the chemical formula for carbon dioxide
(the gas you exhale) is CO2
 The number 2 below the symbol for oxygen tells you that
the ratio of carbon atoms to oxygen atoms is 1 to 2
 If there is no number after the element’s symbol, the
number 1 is understood
How is a compound represented?
 If a different ratio of carbon atoms and oxygen atoms
are seen in a formula you have a different compound
 For example, carbon monoxide – a gas produced in car
engines has the formula CO
 The ratio of carbon atoms to oxygen atoms is 1 to 1
What happens to the properties of elements
when they are chemically combined?
 When elements are chemically combined they form
compounds having properties that are different from
those of the uncombined elements
 For example, table sugar, C12H22O11, is a compound
made of the elements carbon, hydrogen, and oxygen
 The sugar crystals do not resemble the gases oxygen
and hydrogen or the black carbon you see in charcoal
What is a mixture?
 Elements and compounds are pure substances
 Most of the materials we see everyday are not pure –
they are mixtures
 A mixture is made up of 2 or more substances –
elements, compounds, or both – that are together in
the same place but are not chemically combined
How do mixtures differ from compounds?
 Mixtures differ from compounds in 2 ways:
 Each substance in a mixture keeps its individual
properties
 The parts of a mixture are not combined in a set ratio
 An example would be soil:
 If you look at soil through a magnifying glass you would
find particles of sand, clay, or even pieces of decaying
plants
What is a heterogeneous mixture?
 A mixture can be heterogeneous or homogenous
 In a heterogeneous mixture you can see the different parts
 A heterogeneous mixture has larger parts that are different
from each other
 Examples of heterogeneous mixtures are soil, a salad, tacos,
vegetable soup, a toy box full of toys, or a toolbox full of
nuts and bolts
What is a homogeneous mixture?
 Homogeneous means “the same throughout”
 In a homogeneous mixture, the substances are so evenly
mixed that you can’t see the different parts
 You might not always know that homogeneous
mixtures are mixtures because you can’t tell by looking
 Homogeneous mixtures can be solids, liquids, or gases
 Examples are solutions such as air, sugar dissolved in
water, brass, juice, milk
How can a mixture be separated?
 Compounds and mixtures differ also in their ability to be
separated
 A compound can be difficult to separate into its elements
because it is held together by chemical bonds
 A mixture is easy to separate into its components because
each component keeps its own property
Examples of How To Separate Mixtures
 Examples of methods used to separate mixtures
include magnetic attraction, filtration, distillation,
and evaporation