Chemistry Chapter 4 (pearson)
Democritus
a Greek philosopher who was among the first to suggest the existence of atoms; believed they were indivisible and indestructible
cathode ray
a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure
John Dalton
an English chemist and schoolteacher who transformed Democritus's ideas on atoms into a scientific theory by using experimental methods
atomic mass
an element is a weighted average mass of the atoms in a naturally occurring sample of the element
isotopes
atoms that have the same number of protons but different numbers of neutrons
atomic mass unit (amu)
defined as one twelfth of the mass of a carbon-12 atom
J.J. Thomson
discovered the electron
James Chadwick
discovered the neutron
E. Goldstein
discovered the proton
protons
positively charged subatomic particles located in the nucleus
electrons
negatively charged subatomic particles located around the nucleus
neutrons
subatomic particles with no charge but with a mass nearly equal to that of a proton located in the nucleus
atomic number
the number of protons in the nucleus of an atom of that element
atom
the smallest particle of an element that retains its identity in a chemical reaction
nucleus
the tiny central core of an atom and is composed of protons and neutrons
mass number
the total number of protons and neutrons in an atom
Dalton's atomic theory
1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element. 3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds, → proved to be incorrect 4. Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.