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.