Bohr Model (Shell Model)• Evidence suggested electrons occupied specific

energy levels (shells) while “orbiting” around nucleus

• Essentially based on Coulomb’s Law

𝑭𝒐𝒓𝒄𝒆=𝒌 𝒒𝟏𝒒𝟐

𝒓𝟐

k = coulomb’s constantq = object with a charger = radius (distance between the 2 charged particles)

Was used to help explain why electrons didn’t come “crashing” into the nucleus (since opposites attract)• Attractive force

between nucleus and electron is balanced by electron’s centrifugal force

The Bohr model makes great predictions BUT there’s a couple things about electrons we discovered:• Uncertainty • Electron spin

Uncertainty:- Heisenberg Uncertainty Principle

We can never know BOTH the:• Location of an electron• Momentum of an electron

Because of this, we realized that electrons live in these “clouds” of probability• Don’t follow specific orbits

Orbital• Where electrons

spend their time

Electrons have a Spin• Clockwise or counter-clockwise

magnetic spin

As a result of this electron spin:• Only two (max) electrons can

exist in an orbital

This forced us to modify our “shell” (Bohr) model in order to better align with the evidence of reality• Quantum mechanical model of the atom• Computers allowed us to complete complex equations and software to predict how

atoms are going to interact

Orbitalss orbital

p orbitals

d orbitals

f orbitals

ALL of these orbitals simply represent “clouds” of probability where electrons sit

Quantum Numbers

Size (n)• Size of the orbital• As n gets larger then the area in which the electron occupies gets

larger as well

Shape (l)• Shape of the orbital• Can be either an s, p, d, f

Orientation (ml)• Tells us the number of orientations the orbitals can have• s 1 orientation• p 3 orientations• d 5 orientations• f 7 orientations

Spin (ms)• Clockwise (+1/2)• Counter-clockwise (-1/2)• Dictates that only 2 electrons can exist in an orbital

These numbers allow us to predict WHERE electrons are most likely to be found which allows us to predict:• What an atom

looks like• How atoms

are going to interact

Electron Configuration

• Distribution of electrons• Where the electrons are found in atoms

OR in ions

Ionization energy• Amount of energy it takes

to remove an electron• Can be quantified using

Coulomb’s Law

Multielectron atoms or ions• Shells, subshells, and orbitals similar ionization energy

Nucleus Core electrons Valence electrons

shield

Atomic number

hydrogen

Each box represents and orbitalEach arrow represents an electron

Atomic number

helium

Each box represents and orbitalEach arrow represents an electron

Atomic number

lithium

Each box represents and orbitalEach arrow represents an electron

Atomic number

beryllium

Each box represents and orbitalEach arrow represents an electron

Atomic number

boron

Each box represents and orbitalEach arrow represents an electron

Atomic number

carbon

Each box represents and orbitalEach arrow represents an electron

Atomic number

nitrogen

Each box represents and orbitalEach arrow represents an electron

Atomic number

oxygen

Each box represents and orbitalEach arrow represents an electron

Atomic number

fluorine

Each box represents and orbitalEach arrow represents an electron

Atomic number

neon

Each box represents and orbitalEach arrow represents an electron

Atomic number

sodium

Each box represents and orbitalEach arrow represents an electron

Atomic number

magnesium

Each box represents and orbitalEach arrow represents an electron

Periodicity1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

hydrogen 1s1

Periodicity1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

boron 1s22s22p1

Periodicity1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

neon 1s22s22p6

Periodicity1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

sodium 1s22s22p63s1

Periodicity1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

chromium 1s22s22p63s23p64s23d4

[Ar]4s23d4Same thing