atoms

atom time line:

daltons cannonball —> thompsons plum pudding —> rutherfords nuclear model —> bohr’s planetary model —> wave mechanical

atomic number:

• identifies element

• equals number of protons

• nuclear charge

• number of electrons in atom

mass number:

• round atomic mass to a whole number

• atoms mass found in nucleus

• equals sum of protons and neutrons

• mass number - atomic number = neutrons

• ex. 12 - 6p = 6n

electron configuration

• shows number and arrangement of electrons in main energy levels

• all atoms are electrically neutral bc number of protons = number of electrons

nucleus

center of atom contains protons and neutrons

principle energy levels

contains electrons within orbitals

john daltons model (cannonball)

dense, hard, invisible sphere with no particles

thompson - cathode ray tube

• plum pudding model - sphere, positive, electrons are embedded randomly throughout

rutherfords gold foil

observations:

• most alpha particles passed straight through foil

• small amount of alpha particles deflected to the side at an angle

  conclusion:

• atom is small, dense, positive nucleus and is composed of mostly empty space

bohrs model

planetary model - electrons orbit nucleus like planets orbit the sun

• placed the electrons in energy levels (shells) outside of nucleus

• electrons travel on a set pathway or orbit around nucleus

wave mechanical model

electrons surround nucleus in their principle energy levels but are divided and in orbits