GENCHEM

law of definite proportions

a compound always has the same relative amounts of the elements that compose it

Joseph Proust

who proposed law of definite proportions

1981

when was the scanning tunneling microscope invented

STM

allows us to create images of matter at the atomic level

neutrons

uncharged subatomic particles

J.J. Thomson

who discovered electrons in 1897

Robert Millikan

known for the oil drop experiment

oil drop experiment

allowed determination of the electron’s charge

plum pudding model

model of the proton

ernest rutherford

designed an experiment in 1907 to test J.J thomson’s plum pudding model of the atom

gold foil experiment

showed that the positively charged protons are located in a tiny core in the very center of the atom

nucleus

center of the atom, includes most of the mass of the atom neutr

James chadwick

who proposed neutrons

atomic number

number of protons in an atom of an element

isotopes

is an atom that contains a specific number of neutrons

cations

positively charged. they have fewer electrons than in the neutral atom

anion

negatively charged. more electrons than in the neutral onemas

mass spectrometry

individual masses of the isoptopes of an element can be determined by

relative atomic mass

average mass of the individual isotopes

63 elements

how many elements are there?

mechanical separation

takes advantage of physical properties such as color and shape

magnetic separation

takes advantage of the physical property of magnetismi

ionic and covalent bond

types of chemical bond

ionic bond

occurs between a metal and a nonmetal

covalent bonds

bond created by the sharing of electrons between atoms

polar covalent

unequal sharing of atoms

electronegativity

ability of an atom to attract bonding electrons

electronegativity scale

tell us which elements have a greater pull on electrons in a covalent bonds

octet rule

tendency of an atom to achieve an electron configuration having 8 valence electrons