8th Grade Science

Matter is anything that has mass and takes up space.

A Greek teacher 2000 years ago who believed matter was made from four elements: earth, air, fire, and water.

Greek scientist who disagred with Aristotle's ideas. Invented idea of atoms.

Means cannot be divided.

In the late 1800s, discovered electrons. Proved atoms were real.

Discovered nucleus of atom.

In 1913 described the atom as a planetary model.

In 1932 discovered neutrons.

The nucleus is surrounded by speeding electrons in a three-dimensional, layered cloud.

Plasma - consists of matter that has lost electrons.

Solid, liquid, and gas.

This theory states that all atoms have energy: hence, all atoms move.

Atoms of solids have less kinetic energy than atoms of liquids and gases, making them move more slowly. This slower movement allows the atoms to hold tightly to surrounding atoms. The strong attraction between the atoms of solids makes them rigid.

Matter that changes from a solid to a gas or a gas to a solid without becoming liquid.

They include color, shape, odor, taste, and form such as a solid, liquid, or gas. Also density, texture, and hardness, melting and biling points.

The way different types of matter combine or interact with each other to form new substances.

Changes in which the properties of matter change but the identity of the matter does not.

Thos in which one type of matter is changed into another type of matter having different properties.

A solid substance that separates from a solution.

They are created when two or more different kinds of atoms combine.

More than 100.

Atoms.

All the same kind of atoms, each with the same number of protons in its nucleus.

By symbols used by scientists around the world.

No.

Any combination of two or more atoms that are chemically combined. They may be of the same or different elements.

Protons, neutrons, and electrons.

A very small particle that has a positive charge.

A particle smaller than a proton that has a negative charge.

About the same size and mass as the proton, the neutron has no charge.

A definite amount of energy.

More than 100 different kinds of particles found in the atom that make up the protons and neutrons.

The specific number of protons an element has. The number of protons equals the number of electrons.

Atomic mass equals the number of protons and neutrons in an atom.

Atoms of the same element that have different numbers of neutrons.

Atoms always have the same number of protons. The neutrons of the same element can vary.

The atomic mass is then the average of all its isotopes.

Dmitri Mendeleev

Elements are arranged in periods - the horizontal rows, and groups, the vertical columns.

There are 17 periods and 18 groups.

Elements that are in the same period have electrons in the same energy levels.

Elements that are in the same group often have similar physical and chemical properties.

Which elements are metals, nonmetals, and noble gases.

The red line separates the metals on the left from the nonmetals on the right.

These elements sometimes act like metals and sometime act like nonmetals.

• -good conductors of heat and electricity
• -ductile and malleable
• -have a shiny appearance or luster
• -high density
• -usually form compounds by losing electrons
• -examples: gold, copper, silver, iron

• -poor conductors of heat and electricity
• -brittle solids
• -most exist naturally as gases or solids
• -low density
• -usually form compounds by gaining electrons
• -examples: carbon, sulfur, oxygen, nitrogen

• -have some characteristics of metals
• -fairly good conductors of electricity
• -used to make semiconductors for computers and other electronic devices
• -examples: silicon, germanium, boron, arsenic

• -outer energy level completely filled
• -very stable elements, do not react readily with other elements
• -examples: helium, neon, argon, radon

A mixture is formed when any two elements or compounds are blended together but are not chemically combined.

A mixture in which one substance (solute) is dissolved in another (solvent).

The part of a solution that dissolves another material.

The solute is the material that is dissolved.

When a small amount of solute is dissolved in a solvent.

When a large amount of solute is dissolved in the solvent.

When a solvent has dissolved all the solute it can at its present temperature. More solute will not dissolve.

A solid solution made by melting and mixing two or more metals.

A solution formed when a solvent cannot actually dissolve the solute because the molecules of the solute are larger than the molecules of the solvent.

When two or more different kinds of atoms combine chemically.

The way compounds are written using the symbols of the elements that combine to make the compound.

Organic or inorganic.

Organic compounds always contain carbon. Inorganic compounds do not.

A chemical bond.

Bonds occur when atoms gain, lose, or share elecrons in their outer energy level.

Covalent, ionic, and metallic.

• -occur when atoms share electrons.
• -generally melt at low temps.
• -do not conduct electricity when in solution
• -examples: carbon dioxide, water, ozone, sugar

• -electrons are exchanged between atoms
• -generally melt at high temps
• -conduct electricity when in solution

Atoms that gain or lose electrons: they have different properties than the original atom.

Positive ions which form when atoms lose electrons.

Negative ions which form when atoms gain electrons.

• -result from the attraction between positive ions and surrounding electrons (electron sea).
• -similar to ionic bonds.
• examples: gold, copper, silver, mercury

The number of electrons an atom can give or receive to form a bond.

A chemical reaction occurs when bonds between atoms are made or broken. Energy changes always accompany chemical reacions.

The initial substance in a chemical reaction.

The new substance produced in a chemical reaction.

When a chemical reaction gives off energy.

A chemical reaction that needs energy.

The symbols used to describe what happens in a reaction.

Composition, decomposition, replacement, ionic, and combustion.

• -occur when two or more atoms combine
• -A+B->AB

Examples: exploding fireworks, a burning match, etc.

• -occur when a compound breaks down into simpler substances.
• - AB->A+B
• Examples: production of lime from linestone, digestion of food

• -occur when substances are combined with oxygen, releasing large amounts of light and heat energy.
• -usually involve the burning of hydrocarbons, compounds made up of carbon and hydrogen.

Examples: burning of natural gas, oil, coal; burning of wood

• -occur when one element is replaced by a similar element.
• A+BC-> AC+B, or AB+CD->AC+BD

Examples: copper plating, silver plating, chrome plating

• -Similar to replacement reactions except ions are involved.
• -Form precipitates, solids that settle out of the solution.
• A+B- + AD+CB

Examples: pigments used in paints

Surface area of the reactant exposed, amount of reactants, temperature, catalysts.

Catalysts in your body that spead up or bring about chemical reactions.

Substances that speed up the rate of chemical reactions but are not permanently altered in the reaction.

• A substance that produces hydronium ions when the react with water.
• -formulas begin with H
• -sour taste
• -turn litmus paper red
• -release hydrogen gas when they react with metals
• -pH value less than 7

A substance that releases hydroxide ions which give bases their special chemical characteristics.

• -formulas end with OH
• -bitter taste
• -turn litmus paper blue
• -slippery feel
• -pH value greater than 7

Special substances that test for the presence of acids and bases.

The strength or weakness of an acid or base is measured on the pH scale. This measures how many hydronium ions are in the solution.

Water. It has a value of 7.

It occurs when acids and bases are mixed together.