Atomic Theory continues… Where are the electrons?

What we already know… Democritus developed the concept of the atom. Dalton identified it as a solid, indivisible mass. Thomson described it as “Plum Pudding”. Rutherford said it has a nucleus containing protons and neutrons. But, no one has said anything about where the electron is…

Bohr’s Model …until Niels Bohr (1913) Bohr developed what came to be known as the “Planetary Model”. Described the electrons as moving around the nucleus in concentric circular paths called orbits. Each orbit requires a specific amount of energy for an electron to travel its path. (Energy Level)

Planetary Model

Bohr’s Model There is also a specific amount of energy required to move from one orbit to another. (Quantum) As electrons move into orbits further from the nucleus, Their increased energy and decreased attraction to the protons allow them to leave the atom more easily. It is much more difficult for atoms close to the nucleus to leave the atom than those that are farther away.

Bohr’s Model gets tested… Erwin Schrödinger attempted to follow the path of an electron through an atom to graph the orbits. He started with the simplest atom Hydrogen – 1 electron Plotted points representing the location of the electron at various times. His graph did NOT look like a circle…(which is what they expected)

Schrödinger’s Plot of Hydrogen

A New View With this new information, Schrödinger identified a probability area where the electron traveled. Probability area became known as an ORBITAL. Schrödinger and friends identified several different probability areas and therefore needed a new model.

Quantum Mechanical Model Uses a series of 4 numbers to identify the probability area for each electron in an atom. Each electron has its own set of 4 numbers. 4 numbers are the QUANTUM NUMBERS

Quantum Numbers Principle Quantum Number (n) Sublevel Refers to main ENERGY LEVELS Identifies the distance from the nucleus n = 1, 2, 3, 4, 5, 6, 7 Sublevel Refers to the orbital Identifies the shape of the probability area s, p, d, f

Quantum Numbers Orientation in 3D Spin Refers to the axes Identifies the position of the area in 3D X, Y, Z or combination such as XY Spin Refers to the direction of spin Identifies spin as either clockwise or counterclockwise +1/2, -1/2 or , 

Quantum Numbers Things to know The number of electrons that can fit in any single energy level can be found using the following formula: e- = 2n2 Ex. Energy level 1 (n=1) has 2 electrons Ex. Energy level 2 (n=2) has 8 electrons The number of sublevels in an energy level is equal to the number of the energy level. Ex. Energy level 1 has 1 sublevel Ex. Energy level 2 has 2 sublevels

Quantum Numbers Things to know Sublevels are always used in this order s, p, d, then f Each sublevel has a different shape S is spherical P is “dumb-bell” shaped D is “clover leaf” shaped F is complex

Sublevel shapes

Sublevel shapes

Sublevels combined… Energy Level 1 Energy level 2 Energy level 3

Quantum Numbers Things to know Each sublevel has a different number of orbitals. s has 1 p has 3 d has 5 f has 7 Each orbital can only contain 2 electrons. If 2 electrons are in a single orbital, they must have opposite spin. Each sublevel must be filled with electrons BEFORE moving on to the next sublevel.