Honors Chemistry - Unit 4: Modern Atomic Theory

Honors Chemistry

cathode ray experiment

J.J. Thompson

High-voltage electricity through a cathode ray tube to show the cathode rays were negatively charged particles due to them deflecting from the negative electric and magnetic fields

discover electrons and that atoms were not the smallest particles

electron charge to mass ratio = 1.76 × 10^8 c/g

oil drop experiment

robert millikan

used a partitioned container, radiation, and the rate of falling oil drops with electrons on their surface to identify the charge of an electron (-1.602 × 10^-19 C)

gold foil experiment

ernest rutherford

used alpha radiation, fired at a thin sheet of gold foil, to prove that the majority of an atom is made of empty space and that the majority of the mass of an atom exists in a dense center (large mass, small volume) that has a positive charge

plum pudding model

J.J. Thomson

original model of the atom that described it as an equal distribution of positive and negative charges; it was disproved by the gold foil experiment

electrons

very light, negatively charged particles that travel around the nucleus of an atom; only sub-atomic particle that can be lost or gained in a regular chemical reaction

protons

heavy (relative to an electron), positively charged sub-atomic particles found in the nucleus of an atom

neutrons

heavy (relative to a proton), neutral sub-atomic particles found in the nucleus of an atom; serve as the glue that holds the protons together

isotopes

atoms of the same element that have different masses due to differing numbers of neutrons in the nucleus

mass number

represents the sum of the neutrons and protons present in the nucleus of an atom

atomic number

represents the number of protons in the nucleus of an atom and is expressed on the lower left-hand side of elemental symbol

atomic mass unit

incredibly small unit of mass created by scientists to conveniently deal with matter on atomic and sub-atomic levels; 1 gram (g) is equal to 6.022 x 1023 atomic mass units (amu)

electron cloud

the area around the nucleus where the electrons reside; comprised of electron “shells”

atomic weight

more appropriately referred to as “average atomic weight”, because it is a weighted average of all of the naturally occurring isotopes of an element

angstrom

unit of measure typically used when dealing with atoms; 1 angstrom (Å) is equivalent to 10-10 meters (m)

conversions

1 mole = 6.022 × 10²³ atoms = BLANK g

charge of proton

1.602 ×10^-19 C (+1)

charge of electron

-1.602 ×10^-19 C (-1)

charge of neutron

0

charge of nucleus

positive

what holds the electrons in the atom and prevents them from escaping

the electrostatic forces (from the protons)

what part of the atom has the biggest volume

electron cloud

what part of the atom is the heaviest

nulceus

what is the diameter of an atom

1-5 Angstrom (1/10 of a nm)

how much bigger is an atom than the nucleus

10000 times bigger

how much heavier is a proton than an electron

1836 times bigger

the number of each shell is called the

principal quantum number

valence shell

the outermost shell with electrons in it

core shells

all shells within valence shell

a neutron is how many times heavier than an electron

1839 times heavier

diameter of nucleus

1/10000 of an angstrum