Atomic Models and Electron Configuration

The history of the atomic model

•Democritus• Created in 400 BC• Atoms are indivisible and

indestructible• Not scientifically proven

•Dalton• Each element was

composed of identical atoms.

• Atoms of different elements can physically or chemically combine in simple whole number compounds.

• Atoms of one element can never be changed into another.

• Chemical reactions occur when atoms are separated, joined, or rearranged

•Thomson• Discovered the

electron• Created the first

model with subatomic particles

• Created the plum pudding model

•Rutherford• Performed the gold

foil experiment• Discovered the

nucleus and the proton

• Electrons move around the nucleus

•Bohr Model• The electrons are

found in specific circular paths called orbits around the nucleus

• Each orbit is at a fixed energy level

• Electrons can gain or lose a quantum of energy to move up or down the orbits

• This model is the easiest to use when visualizing the atom but is not correct.

The Quantum Mechanical Model

•Was developed by Erwin Schrodinger

•The energy of electrons is restricted to certain values

•The electrons do not have specific paths around the nucleus

•Instead an electron’s location is described as a probability

Atomic Orbitals•Solving Schrodinger’s equations led to atomic

orbitals•An atomic orbital is a region of space around

the nucleus that has a high probability of having an electron in it.

•The energy levels of an electron are labeled by the principal quantum number n

•n represents the energy level and distance from the nucleus

•Each orbital can hold 2 electrons

Electrons in the Orbitals•The maximum number of electrons than

can occupy a principal energy level is given by the formula 2n2

Energy Level n Maximum number of electrons

1 2

2 8

3 18

4 32

Sublevels

•There are 4 sublevels to each energy level that have specific shapes and can hold a certain number of electrons

Size of Orbitals

•The shape of an orbital is the same, but change size according to energy level

1s 2s

Electron Configurations•To write out an electron configuration for

an element, write out the orbitals in order from lowest to highest and fill it with electrons.

•To write out the orbitals, follow the periodic table

•Orbitals must be filled in order of lowest to highest energy level