What

in the world is an element?

Ch. 3 Section 1

An Element is…A substance that cannot be separated or broken down into simpler substances by a physical or chemical change

• The smallest particle of an element that has the properties of that element is called an atom.

• An atom is the basic building block of matter.

»The solid cobalt is already broken down as far as it can be. It is an element, which means no physical or chemical change will change what it is.

Cobalt

Atoms• All elements are

made of atoms.• Atoms of the same

element are alike.– Ex: All carbon atoms

look the same

• Atoms of different elements are different.– Ex: Carbon atoms and

helium atoms look different.

A meteorite might travel more than 400 million kilometers to reach Earth. But the particles of iron in a meteorite , a steel spoon, and steel braces are alike.

They are all the same pure substance.

History of Elements• In 1813, a system of

representing elements with symbols was introduced.–Each symbol consists

of one or two letters.–Two letters are

needed for a chemical symbol when the first letter of that element’s name has already been used.

Common Elements

Aluminum AlBromine BrCalcium CaCarbon CGold AuHelium HeHydrogen HNitrogen N

What is a pure substance?

A pure substance is a substance in which there is only one type of

particle that makes it up.

All of the elements on the periodic table are pure

substances!

What are properties of elements?

•Each element has its own unique set of characteristic properties such as: •boiling point,•melting point,•reactivity with an acid •density

•An element may share a property with another element, however other properties can be used to tell the elements apart.

Examples: Helium and Krypton are both unreactive gases. However, their densities differ. So, you could use the property of density to tell the two apart.

Krypton is more dense than air, so if put in a balloon, it would sink.

Identifying Elements by Properties...

Cobalt Iron Nickel

Open your books to pg. 57 and read

Figure 2This figure shows how each element has its own unique properties. You use these properties to tell the elements apart and to classify them.

How are the elements classified?

They are grouped by the properties they share!•Metals

•Nonmetals

•Metalloids

Metal-an element that is shiny and that conducts heat and electricity well.

-They are malleable (can be hammered into thin sheets)

-They are ductile (they can be drawn into thin wires)

Nonmetal-an element that conducts heat and electricity poorly

- solid non-metals are dull in appearance, brittle, and unmalleable

-Few familiar objects are made with them

Metalloid-an element that has properties of both metals and nonmetals.

-Called semi-conductors-Some are shiny-Some are dull-Somewhat malleable and ductile

-They conduct heat and electric current well

The states

Of matter are…

Solids

Liquids

Gases

Compounds

Chapter 3 Section 2

Compounds• Compounds

are pure substances.

• Compounds are made from more than one element that are chemically combined.

Familiar Compounds

Compound Elements Combined

Table Salt sodium and chlorine

Water hydrogen and oxygen

Vinegar hydrogen, carbon, and oxygen

Carbon Dioxide carbon and oxygen

Baking Soda sodium, hydrogen, carbon, and oxygen

Compounds• Just as each element has its own

physical properties, so does each compound.

• They also can be recognized by their chemical properties

• Compounds join together in a specific mass ratio each time they form. – Ex: Water forms at a 1:8 ratio of hydrogen

and oxygen. For every 1g of hydrogen there is, there must be 8g of oxygen. Without this, water would not be formed.

Compounds Continued…

• the properties of a compound are very different from the properties of the elements that form itexample:

• sodium is a metal that burns easily

• chlorine is a poisonous gas• they combine to form sodium chloride or table salt

Why do compounds form?

• compounds are formed as the result of a chemical change

• the elements combine to form a new substance with new properties

• a chemical change is also required to break a compound down

Breaking Down Compounds

• Compounds can be broken down into the elements that formed them, or simpler substances through chemical changes. – Heat – Electrolysis

Example:Water can be broken down into the elements– hydrogen and oxygen that formed it in the first place.