Data

Copy and paste the text below. It is read-only. Select All

Atom The smallest particle of an element that retains its identity in a chemical reaction scanning tunneling microscope an instrument used to generate images of individual atoms John Dalton english chemist and schoolteacher who formulated a theory to describe the structure and chemical reactivity of matter in terms of atoms Democritus Greek philosopher who was among the first to suggest the existence of atoms Electrons negatively charged particles found outside the nucleus Cathode ray a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure Protons positively charged particles located in the nucleus Neutrons subatomic particles with no charge nucleus the center of the atom which contains the protons and neutrons atomic number the number of protons in the nucleus of an atom periodic table an arrangement of elements according to similarities in their properties mass number the sum of the numbers of protons and neutrons in the nucleus of an atom group a vertical column of elements in the periodic table isotopes atoms with the same number of protons but different numbers of neutrons atomic mass unit (amu) 1/12th of the mass of a carbon 12 atom atomic mass weighted average mass of the atoms in a naturally occurring sample of an element period a horizontal row of the periodic table quantum the amount of energy needed to move an electron from one energy level to another atomic orbitals a region in space around the nucleus of an atoms where an electron is likely to be moving energy level the regions around the nucleus within which the electrons have the highest probability of being found quantum mechanical model the modern description of the behavior of electrons in atoms