8th Grade Science
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What is matter?
Matter is anything that has mass and takes up space.
Who is Aristotle?
A Greek teacher 2000 years ago who believed matter was made from four elements: earth, air, fire, and water.
Who was Democritus?
Greek scientist who disagred with Aristotle's ideas. Invented idea of atoms.
Means cannot be divided.
Who was J. J. Thompson?
In the late 1800s, discovered electrons. Proved atoms were real.
Who was Ernest Rutherford?
Discovered nucleus of atom.
Who was Neils Bohr?
In 1913 described the atom as a planetary model.
Who is James Chadwick?
In 1932 discovered neutrons.
Explain the electron cloud model.
The nucleus is surrounded by speeding electrons in a three-dimensional, layered cloud.
What is the fourth state of matter?
Plasma - consists of matter that has lost electrons.
What are the three ordinary states of matter?
Solid, liquid, and gas.
Explain the kinetic-molecular theory.
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.
List physical properties of matter.
They include color, shape, odor, taste, and form such as a solid, liquid, or gas. Also density, texture, and hardness, melting and biling points.
Describe the chemical properties of matter.
The way different types of matter combine or interact with each other to form new substances.
What are physical changes?
Changes in which the properties of matter change but the identity of the matter does not.
What are chemical changes?
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.
What are compounds?
They are created when two or more different kinds of atoms combine.
Roughly how many different elements are there?
More than 100.
What are the basic building blocks of matter?
What is an element made up of?
All the same kind of atoms, each with the same number of protons in its nucleus.
How are elements represented on the periodic table?
By symbols used by scientists around the world.
Can an element be broken down into simpler substances and still be that element?
WHat are molecules?
Any combination of two or more atoms that are chemically combined. They may be of the same or different elements.
What makes up the atom?
Protons, neutrons, and electrons.
What is a proton?
A very small particle that has a positive charge.
What is an electron?
A particle smaller than a proton that has a negative charge.
What is a neutron?
About the same size and mass as the proton, the neutron has no charge.
What is quantum?
A definite amount of energy.
What are quarks?
More than 100 different kinds of particles found in the atom that make up the protons and neutrons.
What is the atomic number of an atom?
The specific number of protons an element has. The number of protons equals the number of electrons.
What is atomic mass?
Atomic mass equals the number of protons and neutrons in an atom.
What is an isotope?
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.
Who invented the periodic table of elements?
Describe the arrangement of the periodic table.
Elements are arranged in periods - the horizontal rows, and groups, the vertical columns.
How many periods and groups are there in the table of elements?
There are 17 periods and 18 groups.
Describe elements in the same period.
Elements that are in the same period have electrons in the same energy levels.
Describe elements that are in the same groups.
Elements that are in the same group often have similar physical and chemical properties.
What do the colors on the periodic table indicate.
Which elements are metals, nonmetals, and noble gases.
What does the red line on the periodic table indicate?
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.
Describe the characteristics of metals.
- -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
Describe the characteristics of nonmetals.
- -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
Describe the characteristics of metalloids.
- -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
Describe the characteristics of noble gases.
- -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.
What is a dilute solution?
When a small amount of solute is dissolved in a solvent.
What is a concentrated solution?
When a large amount of solute is dissolved in the solvent.
What is a saturated solution?
When a solvent has dissolved all the solute it can at its present temperature. More solute will not dissolve.
What is a metal alloy?
A solid solution made by melting and mixing two or more metals.
What is a suspension?
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.
What is a compound?
When two or more different kinds of atoms combine chemically.
What are chemical formulas?
The way compounds are written using the symbols of the elements that combine to make the compound.
How are compounds classified?
Organic or inorganic.
What is the difference between an organic compound an inorganic compound??
Organic compounds always contain carbon. Inorganic compounds do not.
What is the force that binds atoms together?
A chemical bond.
What is a chemical bond?
Bonds occur when atoms gain, lose, or share elecrons in their outer energy level.
What are the three types of chemical bonds?
Covalent, ionic, and metallic.
Describe covalent bonds.
- -occur when atoms share electrons.
- -generally melt at low temps.
- -do not conduct electricity when in solution
- -examples: carbon dioxide, water, ozone, sugar
Describe ionic bonds.
- -electrons are exchanged between atoms
- -generally melt at high temps
- -conduct electricity when in solution
What are ions?
Atoms that gain or lose electrons: they have different properties than the original atom.
What is a cation?
Positive ions which form when atoms lose electrons.
What are anions?
Negative ions which form when atoms gain electrons.
What are metallic bonds?
- -result from the attraction between positive ions and surrounding electrons (electron sea).
- -similar to ionic bonds.
- examples: gold, copper, silver, mercury
What is valence?
The number of electrons an atom can give or receive to form a bond.
What is a chemical reaction?
A chemical reaction occurs when bonds between atoms are made or broken. Energy changes always accompany chemical reacions.
What is a reactant?
The initial substance in a chemical reaction.
What is the product?
The new substance produced in a chemical reaction.
What is an exothermic reaction?
When a chemical reaction gives off energy.
What is an endothermic reaction?
A chemical reaction that needs energy.
What is a chemical equation?
The symbols used to describe what happens in a reaction.
What are the five different kinds of chemical reactions?
Composition, decomposition, replacement, ionic, and combustion.
Describe composition reactions.
- -occur when two or more atoms combine
Examples: exploding fireworks, a burning match, etc.
Describe decomposition reactions.
- -occur when a compound breaks down into simpler substances.
- - AB->A+B
- Examples: production of lime from linestone, digestion of food
Describe combustion ractions.
- -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
Describe replacement reactions.
- -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
Describe ionic reactions.
- -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
What are factors that affect chemical reactions?
Surface area of the reactant exposed, amount of reactants, temperature, catalysts.
What are enzymes?
Catalysts in your body that spead up or bring about chemical reactions.
What are catalysts?
Substances that speed up the rate of chemical reactions but are not permanently altered in the reaction.
What is an acid?
- 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
What are bases?
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
What are indicators?
Special substances that test for the presence of acids and bases.
What is the pH scale?
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.
What is the neutral solution on the pH scale?
Water. It has a value of 7.
What is Neutralization?
It occurs when acids and bases are mixed together.
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