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