| A | B |
|---|
| atom | the smallest particle of an element that has all of the element's chemical properties |
| brownian motion | the haphazard movement of tiny particles suspended in a gas or liquid resulting from their bombardment by the fast-moving atoms or molecules of the gas or liquid |
| atomic nucleus | the core of an atom, consisting of 2 basic subatomic particles- protons and neutrons |
| element | a pure substance consisting of only one kind of atom |
| atomic number | the number that designates the identity of an element, which is the number of protons in the nucleus of an atom; in an neutral atom the atomic number is also the number of electrons in the atom |
| the periodic table of elements | a chart that lists the elements in horizontal rows by their atomic number and in vertical columns by their similar electron arrangements and chemical properties |
| quantum mechanics | the theory of the small-scale world that includes predicated wave properties of matter |
| isotopes | different forms of an atom that contains the same number of protons but different numbers of neutrons |
| atomic mass unit (amu) | the standard unit of atomic mass, which is equal to 1/12 the mass of the common atom of carbon, arbitrarily given the value of exactly 12. One amu has a mass of 1.661 x 10 -24 grams |
| compound | a material in which atoms of different elements are chemically bonded to one another |
| mixture | a substance whose components are mixed together without combining chemically |
| molecule | a group of atoms held together by a sharing of electrons. atoms combine to form molecules |
| antimatter | a "complementary" form of matter composed of antiparticles having the same mass as particles of ordinary matter but being opposite in charge |
| dark matter | unseen and unidentified matter that is evident by its gravitational pull of stars in the galaxies. along with dark energy, dark matter constitutes perhaps 90% of the stuff in the universe |
