Science Grade 8

Topics: Chemistry, Chemical element, Temperature Pages: 11 (2060 words) Published: June 9, 2013
Mid-YEAR EXAMINATION REVIEW PACKAGE

* Everything around us is considered matter. Everything with a mass and a volume is considered matter. * All matter is made of small invisible particles called atoms. * There are 92 different types of atoms in the universe. * Substances that are made up of one type of atom are called pure elements; therefore there are 92 pure elements in the universe. * Substances made up of more than one type of atom are called mixtures. * Mixtures are made up of groups of atoms called molecules. * Molecules that are made of one type of atom are called simple molecules. Examples: O3 , N2 , S8 * Molecules that are made of more than one type of atom are called compound molecules. Examples: CH4 , C6H12O6 * All matter in the universe can either be a pure element or a mixture. * Energy is not considered matter.

Examples of elements:Examples of mixtures:

* Hydrogen- Wood
* Oxygen- Plastic
* Carbon- Water
* Titanium- Air
* Gold- Rope

* All 92 elements are organized in a table called The Periodic Table of Elements. * The Periodic Table of Elements groups elements according to their weight and characteristic properties. * All matter can be in one of three forms called phases: Solids, Liquids and Gases.

Examples of Solids:Examples of Liquids: Examples of Gases:

* Titanium (Pure element)- Water (Mixture)- Oxygen (Pure element) * Glass (Mixture)- Mercury (Pure element)- Helium (Pure element) * Wood(Mixture)- Blood (Mixture) - Air (Mixture) * Carbon (Pure element)- Melted wax (Mixture)- Methane (Mixture) * Cotton (Mixture)- Bromine (Pure element)- Carbon Dioxide (Mixture)

Particles in each of the three phases are arranged in specific ways.

SOLIDS LIQUIDS GASES

1) Solids:
Particles in a solid are bonded by strong forces of attraction. Each particle (atoms or molecule) keep their locations. All particles vibrate extremely fast at all times. Therefore Solids have a definite shape and volume.

2) Liquids:
Particles in a liquid are bonded by weak forces of attraction. Particles (atoms or molecule) DO NOT keep their location. All particles slide over each other. Liquids take the shape of the containers that they are in. Therefore liquids have an indefinite shape but a definite volume.

3) Gases:
Particles in a gas are not bonded by any forces of attraction. Particles (atoms or molecule) DO NOT keep their location. All particles bounce against each other. Particles in a glass will take the shape of the container they are in and will occupy all the space of that container. Gases must be trapped in a closed container. Therefore gases have an indefinite shape and an indefinite volume.

Types of substances:

Substances that look like they are made of one substance (one color) with the naked eye are considered Homogeneous. Substances that look like they are made of two or more substances (more than one color) with the naked eye are considered Heterogeneous.

Examples of Homogeneous substances:Examples of Heterogeneous substances:

* Mayonnaise- Fizzing Cola
* Orange juice with no pulp- Two toned toothpaste * Blood- Vegetable soup
* A stainless steel fork - A Hamburger * Helium - A handful of earth

If observed with a microscope (not the naked eye) the composition of certain substances might be different. If we can distinguish more than one substance in a homogeneous mixture under the microscope, it is called a colloid. If it still looks like it is made of only one substance (one color) it is referred to as a solution....
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