Chemistry

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Element

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The simplest form of matter that has a unique set of properties; an element cannot be broken down into simpler substances by chemical means.

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Mixture

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A physical blend of two or more substances that are not chemically combined.

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Compound

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A substance that contains two or more elements chemically combined in a fixed proportion.

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Substance

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Matter that has a uniform and definite composition; either an element or a compound; also called pure substance.

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Atom

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The smallest particle of an element that retains its identity in a chemical reaction.

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Phase

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Any part of a sample with uniform composition and properties.

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Solution

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A homogenous mixture; consists of solutes dissolved in a solvent.

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Mass

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A measure of the amount of matter that an object contains; the SI base unit of mass is the kilogram.

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Reactant

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A substance present at the start of a reaction.

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Product

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A substance produced in a chemical reaction.

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Solid

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A form of matter that has a definite shape and volume.

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Liquid

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A form of matter that flows, has a fixed volume, and an indefinite shape.

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Gas

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A form of matter that takes the shape and volume of its container; a gas has no definite shape or volume.

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Vapor

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Describes the gaseous state of a substance that is generally a liquid or solid at room temperature.

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Atomic number

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The number of protons in the nucleus of an atom of an element.

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Mass number

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The total number of protons and neutrons in the nucleus of an atom.

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Proton

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A positively charged subatomic particle found in the nucleus of an atom.

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Neutron

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A Subatomic particle with no charge and a mass of 1 AMU; found in the nucleus of an atom.

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Electron

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A negatively charged subatomic particle.

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Isotope

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Atoms of the same element that have the same atomic number but different atomic masses due to a different number of neutrons.

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Ion

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An atom or group of atoms that has a positive or negative charge.

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Nuclear fission

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The splitting of a nucleus into smaller fragments , accompanied by the release of neutrons and a large amount of energy.

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Nuclear fusion

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The process of combining nuclei to produce a nucleus of greater mass.

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Ionic Bond

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The electrostatic attraction that binds opposite charged ions together.

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Covalent Bond

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A bond formed by the sharing of electrons between atoms.

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Polar Bond

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A covalent Bond between atoms in which the electrons are shared unequally.

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Polar molecule

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A molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive.

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Empirical formula

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A formula with the lowest whole-number ratio of elements in a compound; the empirical formula of hydrogen peroxide (H2O2) is HO.

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Molecular formula

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A chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound.

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Quantum

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The amount of energy needed to move an electron from one energy level to another.

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Energy level

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The specific energies an electron in an atom or other system can have.

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Metal

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One of a class of elements that are good conductors of heat and electric current; metals tend to be ductile, malleable, and shiny.

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Nonmetal

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An element that tends to be a poor conductor of heat and electric current; nonmetals generally have properties opposite to those of metals.

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Metalloid

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An element that tends to have properties that are similar to those of metals and nonmetals.

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Electronegativity

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The ability of an atom to attract electrons when the atom is in a compound.

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Period

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A horizontal row of elements in the periodic table.

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Family

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A vertical row of elements on the periodic table.

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Representative element

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An element in an "A" group in the periodic table; as a group these elements display a wide range of physical and chemical properties. In their atoms, the s and p sublevels in the highest occupied energy level are partially filled.

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Noble gas

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8th family of elements. Don't lose or gain electrons.

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Transition metal

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One of the group B elements in which the highest occupied s sublevel and a nearby d sublevel generally contain electrons.

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Inner transition metal

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An element in the lanthanide or actinide series; the highest occupied s sublevel and nearby f sublevel of its atoms generally contain electrons; also called inner transition element.

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Atomic orbital

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A mathematical expression describing the probability of finding an electron at various locations; usually represented by the region of space around the nucleus where there is a high probability of finding an electron.

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Sublevel

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Electron orbitals. They are the S,P,D, and F blocks.