Atomic Models, Characteristic of a Wave

crest

highest point of the wave

through

lowest point of the wave

wavelength

distance from one crest/through to the next (m)

wave height

height from through to crest

wave steepness

ration of wave height to wavelength (height : wavelength)

amplitude

distance from the center of wave to the bottom of the through

wave period

time for one full wavelength to pass a given point

John Dalton’s Atomic Theory

• matter is composed of extremely small particles called atoms. an atom is the smallest unit of an element that can participate in a chemical change.

• an element consists only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element.

• atoms of one element differ in properties from atoms of all other elements.

• a compound consists of atoms of two or more elements combined in a small, whole-number ratio. in a given compound, the numbers of atoms of each of its elements are always present in the same ratio.

• atoms are neither creator nor destroyed during a chemical change (instead, rearranged to yield substances that are different from those present before the change)

• in chemical reactions, atoms are combined, separated, or rearranged

JJ Thomson’s Plum Pudding Model

• atom consists of a sphere of positive matter within which electrostatic forces determined the positioning of the negatively charged corpuscles.

• explains the overall neutral charge of atom

• negatively charged swims in positively charged sea

Rutherford’s Nuclear Atom Model (Alpha Scattering Experiment; Rutherford Planetary Model)

• positively-charged particles and most of the mass of an atom was concentrated in an extremely small volume. nucleus (positively charged core) is the region of the atom.

• negatively-charged electrons surround the nucleus of an atom. electrons surrounding the nucleus revolve around it with very high speed in circular paths called orbits.

• electrons being negatively charged and nucleus being a densely concentrated mass of positively charged particles are held together by a strong electrostatic force of attraction.

• mass of an atom is concentrated in the nucleus

Bohr’s Solar System Model of the Atom

• electrons assume only certain orbits around the nucleus. these orbits are stable and called stationary orbits.

• each orbit has energy associated with it.

  • e.g., orbit closest to the nucleus has an energy E1, the next closest E2, and so on

• light is emitted when an electron jumps from a higher orbit to lower orbit and absorbed when it jumps from a lower to higher orbit

  • emitted (higher to lower)

  • absorbed (lower to higher)

• energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies.

Erwin Schrödinger’s Quantum or Wave-Mechanical Model

• electrons are not in a circular orbits around the nucleus.

• electrons are in a 3-D region around the nucleus called atomic orbitals.

• atomic orbital describes the probable location of the electron.