Unit: 2 Atomic Structure

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Atom	The smallest particle of an element that represents its physical and chemical properties.
Atomic Number	The number of protons in an atom. The atomic number defines the element. The atomic number is indicated by subscript notation. For example, the symbol refers to a carbon atom with an atomic mass number of 14 (carbon-14). Its atomic number is 6.
Charge	A positive or negative value of an ion due to the presence or absence of electrons. A positive charge results when there are fewer electrons than protons. A negative charge results when there are more electrons than protons.
compound	A substance composed of two or more different elements chemically combined in a definite ratio. A compound can be broken down by a chemical change.
Electron	A small, negatively charged particle residing in shells outside the nucleus of an atom.
Electron Cloud Model	A quantum model of the atom that proposes a region of most probable electron location, called a state or electron cloud, rather than a specific orbit for an electron as it moves about the nucleus.
Element	A substance that cannot be decomposed by chemical change. All known elements are listed in the Periodic Table.
Excited State	An atom with one more electrons not in the ground state or lowest energy level.
Ion	An atom that becomes either positively or negatively charged due to the loss or gain of electrons. An anion is a negatively charged ion. A cation is a positively charged ion.
Isotopes	Atoms with the same atomic number but a different number of neutrons. For a given element, the number of protons in the nucleus remains constant, but the number of neutrons may vary. For example, 14C and 12C are isotopes of carbon.
Neutral (charge)	Not having an electrical charge.
Neutron	A subatomic particle with a mass of approximately one atomic mass unit and zero charge.
Nucleons	The particles that compose the nucleus; protons and neutrons.
Nucleus	The small, positively charged, dense core in the center of an atom. contains neutrons and protons
Orbital	A region in an atom in which there is a high probability of finding electrons.
Proton	A subatomic particle with a mass of approximately one atomic mass unit and a unit positive charge
Rutherford Model of the Atom	A model of atomic structure in which the positive charge of an atom, and most of its mass, is concentrated in a small dense core called the nucleus, with the orbiting negatively charged electrons widely separated from the nucleus. Most of the atomic volume is space. Rutherford proposed this model on the basis of his scattering experiments.
Shells	In the Bohr Model of the atom, the discrete areas around the nucleus in which electrons are located; also called the ;principal energy levels.
Subatomic Particles	Particles that make up an atom; neutrons, protons, electrons.
Wave Mechanical Model of the Atom	A model of the atom in which the electrons are thought to reside in regions (clouds) of varying probability. The shape of the cloud depends upon the orbital (quantum number) of the electron.

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