8th grade Chemistry Terms

Matter -
anything that has mass and takes up space
any substance with a defined molecular structure.
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.
substance that cannot be broken down into simpler substance. Substance made up of the same atoms.
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.
homogeneous mixture composed of two or more substances. ex. air, steel, kool-aid
the degree to which a material conducts electricity. ex. metals are conductors, nonmetals are non-conductors, metalloids are semi-conductors.
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.
substance changes from a solid to a gas. ex. dry ice.
the smallest particle of an element that still has its properties.
the central part of an atom, containing protons and neutrons.
positively charged particles which, along with neutrons fill the nucleus of an atom
neutral particles which, along with protons, are found in the nucleus of an atom
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.
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.
substance that exists before a chemical reaction begins. Left side of the equation
substance that exists after a chemical reaction occurs. Right side of the equation
a number written before a symbol or formula to balance an equation "the big number" in front. It shows the number of molecules.
number in a chemical formula that indicates the number of atoms of the element it follows. "the little number"
a substance formed from the chemical combination of two or more elements. Ex. H2O
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.
certain elements that have properties of both metals and non-metals. Ex. Silicon
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)
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
prepared or created artificially, man-made, not found in nature.
ability to be hammered or pounded into thin sheets
ability to be drawn into a thin wire
"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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