Atoms

Matter

What is the Matter?

All matter is composed of elements.

An element is a substance that cannot be broken into simpler substances by ordinary chemical means.

Each element is made up of tiny particles called atoms.

An atom is the smallest part of an element that has properties of that element.

Imagine particles moving at high speed about a central nucleus. The moving particles are called electrons.

The nucleus of the atom contains protons and neutrons.

Each proton has an electric charge that is positive.

Each electron has an electric charge that is negative.

Protons and electrons have equal and opposite charges. Therefore, that atom is electrically neutral.

Atoms are tiny!!!

An atom of iron is about 25 tenmillionths of a meter in diameter.

The Atomic Number is the number of protons in an atom.

It is located above the symbol on a periodic table.

How many neutrons are there in a nucleus?

The “mass number” of the element gives the average number of protons and neutrons in an atom.

Number of neutrons = mass # - atomic #

The mass number is found below the symbol.

Isotopes are atoms of the same chemical element with different mass numbers.

recall the examples we did on the board in class.

A compound is a substance that contains two or more elements chemically combined.

The smallest part of a compound, that still has properties of that compound is a molecule.

A molecule consists of at least two atoms.

A compound can have properties entirely unlike the elements of which it is made.

Water is composed of H and O (2 gases).

Salt is composed of Na and Cl (poisonous by themselves)

In a mixture, the individual elements or compounds keep their own properties and can be present in any proportions.

They can be separated easily by physical means.

For example - Salt Water! (Evaporate the water)

However, the elements in a compound CAN ONLY be separated by chemical means.

For example - Water - Strong electric current