Unit 7 science exam study guide

matter
anything that has mass and takes up space

elements
the simplest pure substances, and they cannot be broken down into any other substances

compound
pure substance made of two or more elements that are combined chemically in a specific ratio

mixture
two or more substances—elements, compounds, or both—that are in the same place but are not chemically combined

atom
the smallest particle of an element

scientific theory
a well-tested idea that explains and connects a wide range of observations

models
physical, mental, visual, and other representations of an idea to help people understand what they cannot observe directly

electrons
Negatively charged particles that move around outside the nucleus of an atom

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central-block">nucleus
The central core of the atom, containing protons and usually neutrons

protons
Small, positively charged particles that are found in the nucleus of an atom

energy level
A region around the nucleus in which electrons of the same energy are likely to be found

neutrons
Small, uncharged particles that are found in the nucleus of an atom

valence electrons
The electrons that are in the highest energy level of an atom and that are involved in chemical reactions

electron dot diagram
A representation of the valence electrons in an atom, using dots

chemical bond
the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them

symbol
A one- or two-letter set of characters that is used to identify an element

atomic number
the number of protons in the nucleus of an atom

period
A row of elements across the periodic table

group
Elements in the same column

family
another name for a group

noble gases
The elements in Group 18

halogens
The elements in Group 17

alkali metal
An element belonging to Group 1 of the periodic table

ion
an atom or group of atoms that has an electric charge

polyatomic ions
Ions that are made of more than one atom

ionic bond
the attraction between two oppositely charged ions

ionic compound
A compound that consists of positive and negative ions

chemical formula
a combination of symbols that shows the ratio of elements in a compound

subscript
tells you the ratio of elements in the compound

crystal
An orderly, three-dimensional pattern of ions or atoms in a solid

covalent bond
The chemical bond formed when two atoms share electrons

molecule
a neutral group of atoms joined by covalent bonds

double bond
A chemical bond formed when atoms share two pairs of electrons

triple bond
A chemical bond formed when atoms share three pairs of electrons

molecular compound
a compound that is composed of molecules

polar bond
A covalent bond in which electrons are shared unequally

nonpolar bond
A covalent bond in which electrons are shared equally

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