Top-Rated Free Essay

Science Grade 8

Topics: Chemistry, Chemical element, Temperature / Pages: 9 (2060 words) / Published: Jun 9th, 2013

* 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.


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.


Homogeneous Heterogeneous

The concentration of a solution is the amount of solute in a given amount of solvent.
Mixing 2g of sugar in a 250ml glass of water would sweeten the solution.
The solvent dissolves the solute.
The sugar is considered the solute in the solution.
The water is considered the solvent in the solution.
The solution is the mixture of water and sugar.
Adding solute (or removing solvent) to a solution would increase the concentration.
Adding solvent (or removing solute) to a solution would dilute the concentration.

Properties and changes
We use characteristic properties to identify substances or the group to which the pure substance belongs. Characteristic properties never change and are unique to the substance in question. Some might be physical properties, which do not change the nature of the substance while others might be chemical characteristic properties, which might change the nature of the substance. Examples: Density, Boiling Point, Melting Point, Freezing point, Electric conductivity, Reaction to litmus paper (pH levels), Solubility... Non-characteristic properties to do not help us identify specific substances and can vary from one substance to another. Examples: Mass, Shape, Volume, Color, Amount...
Water always boils at 100ºC. That cannot be changed. Therefore Boiling Point of water is a Characteristic Property. To test the Boiling Point of water, we must heat it up. This identification process does not change the water. Therefore Boiling Point is a Characteristic Physical property.

Characteristic Properties Non-Characteristic Properties * Density (Physical property) - Mass * Boiling Point (Physical property) - Shape * Melting Point (Physical property) - Volume * Freezing Point (Physical property) - Color * Electric conductivity (Physical property) - Amount * Reaction to litmus paper (Chemical property)

Matter can be changed in one of two ways:
Physical changes: Changes that alter the appearance of a substance but not its chemical properties.
Deformation: Changes in the appearance of a substance.
Dissolution: Combining a solute into a solvent.
Phase change: Changes from one phase to another. There are 6 types of phase changes.

Chemical changes: Changes that can alter a substance chemically therefore rendering it a different substance.
Oxidation: A chemical reaction that involves Oxygen.
Decomposition: A transformation from complex molecules to simpler molecules.
Synthesis: A transformation from simple molecules to more complex molecules.
Precipitation: The formation of a precipitate in a solution.


Physical Changes Chemical Changes
1) Deformation 1. Oxidation
2) Dissolution 2. Decomposition
3) Phase changes: 3. Synthesis a) Solidification: From Liquid phase to Solid phase 4. Precipitate b) Fusion: From Solid phase to Liquid phase c) Condensation: From Gas phase to Liquid phase d) Evaporation: From Liquid phase to Gas phase e) Deposition: From Gas phase to Solid phase f) Sublimation: From Solid phase to Gas phase

Example: Freezing water will change its phase from liquid to solid. The particles will slide over each other until the temperature gets cold enough so that they slow down. As ice forms, each particle will keep its spot and strongly bond with neighboring particles as in solids. Ice is considered a solid. Ice and water have different densities; however, the particles in the ice have not changed chemically. Therefore solidification is a physical change.
There are four clues to help us identify whether a change occurred to a substance is chemical. Those are:
a) Release of gas. (Ex: bubbles forming)
b) Release of heat or light (Ex: explosion)
c) Creation of a precipitate (Ex: Residue being formed, digestion, exhaust)
d) A color change (Ex: Rust)

Science Review Notes
September 2012 – January 2013

Matter Sept 6 2012 There are three phases of matter: 1) Solid (uniformly bonded together) 2) Liquid (loosely bonded together) 3) Gas (not bonded together)

Periodic Table of Elements

A table that organizes pure elements (atoms that have the same amount of protons) according to their atomic mass (weight).
A pure element is matter that is made of one type of atoms found in the Periodic Table of Elements ex: hydrogen (H), gold (Au).
A molecule is matter that is made up of 2 or more types of atoms found in the Periodic Table of Elements ex: NaCl (salt), O3 (ozone), H2O (water). Atoms
Atoms consist of 3 particles: 1) Neutrons (particle that is neutral) 2) Protons (particle that is positively charged) 3) Electrons (particle that is negatively charged)

Mass Sept 7 2012
Mass: the total weight of an object on earth.
Units of measurements: mg–milligram=1/1000th of a gram G – gram = 1000mg Kg – kilogram = 1000g T – Ton = 1000kg

Volume: the amount of space taken by an object.
Units of measurements: mL, L – liquids Mm3, cm3, m3, km3

Density: (M/V)
Ex: 1L of water weighs 1kg. What is its density?
O= m/v=1kg/1L =1kg/per L =1000g/L

1) M=17g, v=10mL D =? 17kg/10mL =1.7g/mL 2) M=2g, v=12mL D =? 2g/12mL =0.167g/mL 3) M=7g, v=21mL D =? 7g/21Ml =0.3g/mL

Object 1) 2g/mL M=11g V=? 11g/26 per mL=5.5mL
Object 2) 0.8g/mL M=16g V=? 16g/0.8g per mL=20mL
Object 3) 3.5g/mL M=7g V=? 7g/3.5g per mL=2mL


Components of atoms:

- Electrons (-)
* Neutrons (neutral) * Protons (+)

H (1): 1 electron, 1 proton, 1 neutron
Ca (20): 20 electrons, 20 protons, 20 neutrons
All atoms are the same size, but have a different amount of electrons, protons ad electrons depending on the rank it has in the Periodic Table of Elements.

Non characteristic properties:
-freezing point
-electric conductivity

Characteristic properties:

- density
- boiling point
- melting point
- solubility
- electric conductivity Chemical:

-pH levels

Characteristic Property: Properties that help define substances all characteristic properties are unique to their substance. These properties cannot be changed.

Non-Characteristic Property: Properties that do not define substances. These properties can be changed.

Mass: The weight of a substance. Describes how heavy atoms are (depending on the number of protons). Ex: 10mL of water = 10g 10L of water = 10kg 5000kg of water = 5000kg

Volume: volume measures the amount of space an object occupies. Rulers, tape measures, graduated cylinder and overflow cans are used to measure volume.

Temperature: Temperature describes how fast particles will be agitated. The higher the temperature, the faster the agitation of particles and vice versa. A thermometer is an instrument used to measure temperature.

pH scale: A scale used to measure the acidity or alkalinity of a substance. Litmus paper is the instrument used to measure the acidity or alkalinity.

Sept 14th 2012

Agitation of particles increases with temperature and will cause the substance to expand.

Solid – Ice – particles aren’t agitated
Liquids – Water – particles are agitated depending on temperature
Gases – Vapor – particles are extremely agitated.

Sept 18th 2012
Convert the following: 1) 0.827kg = 827g 2) 0.1834kg = 183.4g 3) 0.054kg = 54g 4) 0.09kg = 900g 5) 0.000021t = 210g 6) 110.000mg = 110g

1) 827g ÷ 1.5L = 0.551g/mL 2) 183.4g ÷ 1.5L = 0.122g/mL 3) 54g ÷ 1.5 = 0.036g/mL 4) 900g ÷ 1.5 = 0.6g/mL 5) 210g ÷ 1.5 = 0.14g/mL 6) 110g ÷ 1.5 = 0.073g/mL

Sept 20th 2012
Water: 1g/mL
Mercury: 80g/mL
Alcohol: 0.79g/mL Conversions mg ÷100 g ÷100 kg ÷100 t ÷100 t x100 kg x100 gx100 mg x100 Oct 10th 2012
Physical and Chemical Changes
Physical Changes (doesn’t change the characteristic changes)
-Phase changes: 1) solidification (freezing) (liquid to solid) 2) fusion (melting) (solid to liquid) 3) evaporation (liquid to gas) 4) condensation (gas to liquid) 5) sublimation (solid to liquid) 6) deposition (gas to solid)

Chemical Changes (changes the characteristic properties)
-hints that indicate a chemical change has occurred:
1) Release of gas (decomposition)
2) Heat or light is produced (light = decomposition) (heat = synthesis)
3) A colour change occurs (rust) (oxidation)
4) A residue is formed (digestion, exhaust) (precipitation)
In order to make a change, you need to use power (mechanical energy)

Oct 12th 2012
Physical Changes: Molecules stay intact, characteristic properties do not change (lighting upon electric light bulb) 1) Deformation: (ripping a paper in half) (shape is different) 2) Dissolution: (sugar mixed with water) (there is no precipitate) 3) Phase Change: –solidification –fusion –sublimation –deposition –evaporation –condensation

Oct 16th 2012

Chemical Changes: Molecules can be altered and characteristic properties might also change (iron rusts with oxygen) 1) Oxidation: a chemical change involving oxygen (ex: rust) 2) Decomposition: transformation of complex molecule into simple molecules or atoms (breaks down) 3) Synthesis: transformation of simple molecules or atoms into more complex molecules (N and H combined = NH3 which is poisonous) (combination) (dying you hair) 4) Precipitation: foundation of a precipate (mix two things together and they don’t dissolve but form a solid at the bottom / a precipate) (sugar mixed with gasoline solidifies and make a syrup-like substance)

Characteristic Properties: properties that help define substances. All characteristic properties are unique, to their substance. These properties cannot be changed.
-freezing point
-boiling point
-melting point
-conduction of heat
-pH level
-electric conductivity

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