Chapter 1Elements, Compounds, and Mixtures
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 matter made of?
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 substancesEach 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 elementZinc is an element which makes up penniesCopper is another element and is used to
coat penniesOxygen 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 atomsAn atom is the basic particle from which all
elements are madeDifferent elements have different properties
because their atoms are differentThe atom has a positively charged center, or
nucleus surrounded by a “cloud” of negative charge
The Atomelectron
neutron
proton
What happens when atoms combine?Atoms of most elements have the ability to
combine with other atomsWhen atoms combine they form a chemical
bond – a force of attraction between 2 atomsAtoms 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 elementsA 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 CO2The 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
substancesMost of the materials we see everyday are
not pure – they are mixturesA 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 partsA heterogeneous mixture has larger parts that
are different from each otherExamples 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 separatedA 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 MixturesExamples of methods used to separate
mixtures include magnetic attraction, filtration, distillation, and evaporation
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