Chemistry - Atomic Models, Orbital Diagrams, and Electron Configuration

Democritus

• first person to talk about atoms

• created the Atomas Model

• believed matter was “uncuttable”

John Dalton

• 1803 - proposed the Atomic Theory

• created the Atomic Model

Atomic Theory

• atoms are small particles that cannot be created, divided, or destroyed—-”indivisible”

• atoms of the same element are identical

• atoms of different elements have different characteristics

• atoms join with other atoms to make new substances (compounds)

J.J Thomson

• proved that an atom can be divided into smaller parts

• experimented with cathode-ray tubes 

• discovered corpuscles (electrons)

• proposed that atoms are electrically neutral 

• 1897 - proposed the Plum Pudding Model

Plum Pudding Model

• atoms mostly consist of positively charged material (“positive sea”)

• negatively charged particles (electrons) are in fixed positions within the positive sphere 

Cathode-Ray Experiment 

• led to the discovery of electrons

• high voltage caused a beam of particles to shoot from the cathode

• particles were attracted to the positive electric plate

• particles deflected away from the negative side of the magnet

Ernest Rutherford

“Father of Nuclear Physics”

created the Nuclear Model of the atom

1909 - performed the Gold Foil experiment and suggested;

• atoms consist of a small core (nucleus) that contains most of the mass of the atom

• nucleus is made up of positively charged particles called protons

• protons are surrounded by negatively charged electrons

• atoms are mostly empty space

Nuclear Model

• atom has a positively charged core

• negatively charged electrons move around the nucleus 

Gold Foil Experiment

disproved the Plum Pudding Model

radioactive source emitted a beam of positively charged alpha particles

the beam was directed at a thin sheet of gold foil

• most alpha particles passed straight through; this proved that the atom is mostly empty space

• small number of alpha particles repelled against the positive charge of the nucleus 

Niels Bohr

1913 - developed the Planetary Model/Bohr Model

conducted light experiments

believed electrons can ‘jump’ from a path in one level to a path in another level depending on their energy

• gaining energy = electrons move farther away from the nucleus

• losing energy = electrons move closer to the nucleus

Bohr/Planetary Model

incorporated newer discoveries about how the energy of an atom changes when the atom absorbs or emits light

suggests that electrons travel around the nucleus of an atom in orbits or definite paths

• orbits have specific sizes and energy levels

Light Experiments

• when an electron absorbs light energy, it jumps to higher levels/orbits that are far from the nucleus

• when an electron emits light energy, it falls to a lower level/orbit

Erwin Schrodinger

created the Quantum Mechanical Model

1926 - further explained the nature of electrons by proposing that their location cannot be exactly stated

• electrons move around the nucleus in regions called electron clouds/orbitals

• electrons positioned closer to the nucleus are more likely to be found

Orbitals

• orbit-like

• can only hold two electrons

• helps scientists predict the areas where electrons are located

Quantum Mechanical Model

• the most accurate depiction of an atom 

4 Sublevels 

• s sublevel

• p sublevel

• d sublevel

• f sublevel

S Sublevel

• contains 1 orbital

• holds a maximum of 2 electrons

P Sublevel

• contains 3 orbitals

• holds a maximum of 6 electrons

D Sublevel

• contains 5 orbitals

• holds a maximum of 10 electrons

F Sublevel

• contains 7 orbitals

• holds a maximum of 14 electrons

Orbital Diagrams

• displays how electrons are placed in atoms

• each arrow represents an electron

Aufbau’s Principle

• electrons occupy orbitals of lowest energy first

Pauli’s Exclusion Principle

• an orbital can hold only 2 electrons 

• electrons must have opposite spin

Hund’s Rule

• electrons fill all orbitals in a sub-level before doubling up 

Electron Configuration

• exponent represents the number of electrons

• letter represents the sublevel