Download Chemistry Terms

Chemistry Terms
atomic mass unit (amu) One twelfth the mass of a carbon 12 atom. Since there are 6 protons and 6
neutrons in the nucleus of a carbon 12 atom, 1 amu is about the mass of one proton or one neutron.
atomic mass (of an element) The mass of one atom of the element in amu. It is also the mass of one
mole of atoms of the element in grams.
atomic number The atomic number of an element is the number of protons in the nucleus of each atom.
Avagadro's number Equal to 6.022 × 1023, it is the number of particles in one mole. It is also the number
of amu in one gram.
chemical reaction A process in which atoms and molecules interact, resulting in the alteration of their
molecular structures.
covalent bond An atomic bond in which an electron is a resident of the outer electron shell of both
atoms involved in the bond.
electric charge The property that a particle must have in order to feel the electromagnetic force. It can
be positive or negative.
electromagnetic (EM) force The fundamental force of nature that a particle feels if it has electric charge.
electron By far the lightest of the 3 particles that make up atoms. They orbit the nucleus and have an
electric charge of -1.6 × 10-19 Coulombs.
electron affinity The tendency of an atom to aquire extra electrons. Elements toward the right side of
the periodic table have greater "affinity" for electrons (except for the far right column).
electron shell A spherical region centered on the nucleus of an atom in which an electron resides. From
the inside out, the orbitals hold respectively 2, 8, 8, 18, 18, 32 electrons.
element All atoms with the same number of protons in their nuclei are said to be atoms of the same
element.
endothermic (reaction) A chemical reaction that requires an input of energy to drive it.
exothermic (reaction) A chemical reaction in which energy is released to the environment.
hydrogen bond A hydrogen atom that's already covalently bonded to another atom can be attracted to
a third already bonded atom if that atom has a slightly negative electric charge as a result of its bond.
ionic bond A bond between atoms in which an electron from one atom leaves and resides in the other
shell of the other atom, giving both atoms a net electric charge such that they attract each other and
stick together.
isotope Elements can have more than one isotope. Two isotopes of the same element differ in the
number of neutrons in each nucleus.
metallic bond The kind of bond holding atoms together in metals. The bonding electrons are not
residents of the outer shells of any atoms, but are free to move amongst the atoms.
neutron One of the two types of particles that make up an atomic nucleus. Its electric charge is zero.
non-metal Elements that do not exibit metallic properties. They occupy the upper right portion of the
periodic table of elements.
nucleon The general name for the particles that make up atomic nuclei. Protons and neutrons are
nucleons.
periodic table of elements A gridlike listing of the known elements that is arranged such that elements
within vertical row have similar properties.
proton One of the two types of particles that make up an atomic nucleus. It has an electric charge of
+1.6 × 10-19 Coulombs.
screening (of charge) An electron closer to its nucleus than another electron will repel the other
electron, countering the effects of one nuclear proton and thus "screening it" from the effects.
strong force The attractive force between nucleons that holds atomic nuclei together.
valence shell The outer electron shell of an atom.