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first thought atom was a solid, indestructible, indivisible mass

solid; indestructible; indivisible

Democritus thought the atom was a ... , ... , ... mass.

J.J. Thomson

said that the atomic model did not take into account electrons and protons

electrons; protons

J.J. Thomson said that the atomic model did not take into account ... and ...

Ernest Rutherford

proposed that electrons surrounded a dense, positively charged nucleus and the rest of the atom was empty space

Niels Bohr

said that electrons were arranged in orbits around the nucleus

Niels Bohr

said that electrons in a particular path have a fixed energy

fixed energy

Niels Bohr said that electrons in a particular path have a ... ...

energy level

region around the nucleus where the electron is likely to be moving


Energy levels are more closely spaced the ... the distance from the nucleus.


the higher the energy level, the ... energy the electron has.


amount of energy required to move an electron from one energy level to the next higher one

quantum leap

an abrupt change of energy levels

quantum mechanical model

the present day atomic model

most probable location

The quantum mechanical model does not show paths, instead it shows the ... ... ... of an electron.


The denser the place in the cloud of the electron cloud model, the ... the probability of finding an electron.


came up with the mathematical equation showing energy and location of electron

energy; location

Schrodinger came up with a mathematical equation showing the ... and ... of electron

principal quantum number

principal energy level or shell


number of ... is the same as the principal quantum number

atomic orbitals

regions within a sublevel where electrons can be found


maximum of ... electrons per orbital

ground state

lowest possible energy state


high energy systems are ...

electron configurations

ways in which electrons are arranged around the nucleus of atoms

Aufbau Principle

electrons enter orbitals of lowest energy first


energy levels can ...

Pauli Exclusion Principle

for two electrons to occupy the same orbital, they must have opposite spins

orbital pair

two oppositely spinning electrons occupying the same orbital

Hund's Rule

before a second electron can be placed in any orbital, all orbitals of that sublevel must contain at least one electron


For neutral atoms, the sum of the superscripts is the number of ... in the atom.

valence shell

outermost principal energy level of an atom that includes at least one electron

valence electrons

electrons in the valence shell

excited state

condition of an atom whose electrons are at higher energy levels than the ones they normally occupy

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