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8th grade Chemistry Terms

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Matter -
anything that has mass and takes up space
Chemical
any substance with a defined molecular structure.
Mass
the amount of matter in an object. Measured with a triple beam balance in grams.
volume -
the amount of space an object takes up. Liquid volume is BEST measured with a graduated cylinder. Also measured in beakers or flasks. Measured in millliters and liters.
Water displacement
method to determine the volume of an irregular shaped solid. Record the initial volume. Drop the object in the water. Record the final volume. The difference in the volume is the volume of the irregular shaped solid.
Element
substance that cannot be broken down into simpler substance. Substance made up of the same atoms.
Mixture
two or more substances combined physically.can be separated by physical means which include evaporation, distillation, straining, magnetism, etc.
Heterogeneous Mixture
components of the mixture are not uniform throughout. Ex. soil, salad dressing, granite
Homogeneous Mixture
components of the mixture are uniform throughout. Ex. kool-aid, salt water, air.
Solution
homogeneous mixture composed of two or more substances. ex. air, steel, kool-aid
Conductivity
the degree to which a material conducts electricity. ex. metals are conductors, nonmetals are non-conductors, metalloids are semi-conductors.
Reactivity
refers to the chemical reactivity of elements. how the elements react with one another to form compounds. The reactivity is dependent upon the number of valence electrons.
Melting point
temperature at which a solid can change to a liquid. physical property and can used to ID unknown substances. melting point of water is O C and 32 F.
Boiling Point
temperature at which liquid boils. changes from a liquid to a gas. can be used to ID substances. for water is 100 C and 212 F.
Sublimation
substance changes from a solid to a gas. ex. dry ice.
Atom
the smallest particle of an element that still has its properties.
nucleus
the central part of an atom, containing protons and neutrons.
protons
positively charged particles which, along with neutrons fill the nucleus of an atom
neutrons
neutral particles which, along with protons, are found in the nucleus of an atom
electrons
negatively charged particle that surrounds the nucleus of an atom. It exist in electron shells in a Bohr atomic model.
Valence electrons
the electrons in the outermost energy level of an atom, the electrons responsible for the BONDING and REACTIVITY of atoms. Remember "happy 8". Atoms need 8 valence electrons to be the most stable.
Ionic bond
chemical bond in which electrons from one atom are given to another atom making the donor atom positively charged and the atom receiving electrons negatively charged. Ex. NaCl. Table salt. Sodium chloride.
Covalent Bond
chemical bond in which atoms share electrons when they combine. Ex. CH4 H2O
Chemical change
change in which the identity of a substance changes due to its chemical properties and forms a new substance or substances.
physical change
change in which the properties of a substance change but the identity of the substance always remains the same.
Chemical reaction
process that produces chemical change. Resulting in a new substance formed. Evidence of a chemical reaction are: color change, precipitate formed, bubbles produced (gas), energy absorbed or given off during a reaction.
Precipitate
solid formed as a result of a chemical reaction. Two liquids combine and a solid is created.
endothermic reaction
chemical reaction that absorbs or requires heat . The reaction gets colder. Ex. Vinegar and baking soda.
Exothermic reaction
energy is released during the reaction. The reaction gives off heat. It gets warmed. Ex. Calcium chloride and vinegar.
Reactants
substance that exists before a chemical reaction begins. Left side of the equation
Products
substance that exists after a chemical reaction occurs. Right side of the equation
Coefficient
a number written before a symbol or formula to balance an equation "the big number" in front. It shows the number of molecules.
subscript
number in a chemical formula that indicates the number of atoms of the element it follows. "the little number"
Compound
a substance formed from the chemical combination of two or more elements. Ex. H2O
Molecule
the smallest particle of a compound that still retains its characteristics.
Law of Conservation of Mass/Matter
states that the total mass of the reactants will always equal the total mass of the products. Matter cannot be created or destroyed.
Alkali metals
group 1 of the periodic table. Have 1 valence electron making them highly reactive.
Alkaline earth metals
group 2 of the periodic table.
atomic number
number on the periodic table that represents the number of protons in an atom
atomic mass
number on the periodic table that represents the number of protons and neutrons in an atom.
Halogen family
group 17 of the periodic table. Have 7 valence electrons. They are unstable gases.
Metalloids
certain elements that have properties of both metals and non-metals. Ex. Silicon
Metals
most of the elements in groups 1-15 of periodic table. Have characteristics good conductors, shiny surfaces, malleable, ductile, and solid at room temp (except Mercury)
Nonmetals
most elements in groups 14-17. ex. Carbon
Noble Gases
group 18 of the periodic table. Have 8 valence electrons so they do not combine easily with other elements. Most stable elements
synthetic
prepared or created artificially, man-made, not found in nature.
Malleable
ability to be hammered or pounded into thin sheets
Ductile
ability to be drawn into a thin wire
Mendeleev
"Father of the periodic table", noticed the trends on the periodic table exist due to the number of protons in each element.

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