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8th Grade STAAR Objective 3

Terms in this set (27)

Atom
smallest particle of an element; contains protons, neutrons, and electrons
Nucleus
the central core of an atom containing protons and neutrons
Protons
located in nucleus; has a positive charge; determine element's identity
Neutrons
located in nucleus; neutral (no) charge
Electrons
located in electron cloud around nucleus; has a negative charge
Valence Electrons
electrons in the outer most energy level of an atom; determine the chemical propeties of an element (ex. reactivity - how elements will react with other elements/compounds)
Elements
pure substances; found on periodic table; represented by chemical symbol
Compounds
made of two or more elements; formed by chemical reaction; represented by a formula
Metal
elements found on the left and center of the periodic table; usually solid, are shiny, conduct electricity, malleable
Nonmetal
elements found on the right of the periodic table; usually gas, are dull, do not conduct electricity, brittle (not malleable)
Metalloid
elements located between metals and nonmetals on the periodic table (along bold stair-step line); have characteristics of both metals and nonmetals
Period
rows in the periodic table; elements in same period have same number of energy levels; elements in same period are not alike in properties
Group
columns in periodic table; also known as "families"; elements in same group have similar physical and chemical properties because they have the same number of valence electrons
Physical Properties of Matter
how matter is described according to physical characteristics; characteristics that can be observed without changing the substance into something else; ex. luster
Chemical Properties of Matter
characteristics that can be observed when a substance interacts with another substance; ability to react; inability to react; usually hidden
Physical Changes in Matter
a change in the form or appearance of a material that does not change it into a new substance; a change in size, shape, or state of matter; no new matter is formed; ex. melting ice, tearing paper, dissolving kool-aid, mixing salt and pepper, muscles of stomach grind food into smaller pieces
Chemical Reaction (Chemical Changes in Matter)
atoms are rearranged to make new substances with new properties different than the original substance; starts with reactants, ends with products; ex. rusting nails, decaying matter, burning wood, digesting food is mixed with acid in digestive systemt to break down protein molecules (carbohydrates broken down into sugars)
Evidence of Chemical Reaction
-production of gas
-formation of precipitate
-change in temperature
-change in color
-change in odor
Chemical Formulas
way of describing elements and number of atoms that make up one molecule of a compound; uses symbols, subscripts and coefficients
Finding Number of Elements in Chemical Formula
count the capital letters
Finding Number of Atoms in Chemical Formula
count the capital letters and numbers
Chemical Equation
way of writing changes in the arrangement of atoms during a chemical reaction; uses symbols, subscripts and coefficients; balanced when equation has the same number of atoms of each element on both sides of the equation
Law of Conservation of Mass
matter can neither be created nor destroyed, it can only change form; the mass of all substances before a chemical reaction must equal the mass of all substances after a chemical reaction
Atomic Number
top number in the element square on the periodic table; identifies the number of protons and electrons in a neutral atom
Mass Number
decimal number found beneath the symbol in the element square on the periodic table; usually rounded off to find the number of neutrons
Finding the Number of Protons or Electrons in an Atom
look at the atomic number on the periodic table
Finding the Number of Neutrons in an Atom
round off the atomic mass to the nearest whole number and subtract the atomic number from it.
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