Unit #4

CP Chemistry

Bohr Quantum Numbers Quantum Mechanical Model

Bohr worked with the concepts of energy, wavelength and frequency

Each color of light is associated with a different energy

Each atom gives off its own unique color so..

Electrons of different atoms have different energies

Each atom has its own specific electron arrangement

Electrons are in Energy levels in the atom

When an electron goes from an excited state back down to its ground state the atom emits light

n = 3n = 4

n = 2n = 1

Doesn’t work. Only works for hydrogen atoms. Electrons don’t move in circles. The quantization of energy is right, but

not because they are circling like planets.

Back to the drawing board

Valence electrons- the electrons in the outermost energy levels (not d).

Core electrons- the inner electrons Ground state – all electrons are on the

lowest possible energy levels Excited State – some electrons have

more energy than usual, causing some electrons to be in a higher energy level than they should be in

Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space

Organized on the Electromagnetic Spectrum according to wavelength and frequency

Frequency(v) = number of cycles in one secondMeasured in hertz 1 hz = 1 cycle/second

Wavelength () = Length of one waveMeasured in unit of distance (m, nm, etc.)

There are many Different and Higher Energy = Higher Frequency /

Lower Wavelength Radio waves, microwaves, x rays and

gamma rays are all examples. Visible Light is only the part our eyes

can detect.ammaRays

Radiowaves

As we know, the amount of energy is related to the wavelength

Different wavelengths will show different colors

Each element gives off it own unique set of colors

Therefore each element gives off its own unique amount of energy

Electrons are constantly in motion and give off energy when they move from an excited state to ground state

Planck found energy came in packets

A Packet of energy is called a quantum

A quantum is the minimum amount of energy that can be gained or lost by an atom

Einstein said that light can be viewed as a stream of particles called photons

A Photon is a particle of radiation with zero mass and carrying a quantum of energy

Is energy a wave like light, or a particle?

Yes Concept is called the Wave -Particle

duality.

What about the other way, is matter a wave?

Yes, hence the quantum mechanical model

Each element has a specific number of electrons

In an atom electrons are arranged in a specific arrangement

We know this because each element has its own atomic spectra

Different energy = different colors= different electron arrangement

A totally new approach. De Broglie said matter could be like a

wave, like standing waves. The vibrations of a stringed instrument.

How we keep track of electrons Principal quantum number (n) energy

level of the electron. Is a number from 1-7

Angular momentum quantum number (l) gives the shape of the orbital

Has values between 0 and n-1

S orbitalsl = 0

1 orbital per energy level

P orbitalsl = 1

3 orbitals per energy level

D orbitalsl = 2

5 orbitals per energy

level

F Orbitalsl = 3

7 orbitals per energy level

F orbitals

Magnetic quantum number (m I)

Takes a guess at what orbital the electron is in

Gives the axis orientation Tells direction in each shape (x,y,z) Is a value between – l and + l

Electron spin quantum number (m s)

Can have 2 values. either +1/2 or -1/2

We follow 3 rules to get the correct electron configuration for each atom

1. Aufbau Principle2. Pauli exclusion Principle3. Hund’s Rule

Aufbau is German for building up. As electrons are added to the atom they

arrange themselves in orbitals The orbitals are in order of lowest

energy (1s) to the highest energy The order of the triangle Fill up in order of energy levels.

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2

• 2• electrons

2s2

• 4

2p6 3s2

• 12

3p6 4s2

• 20

3d10 4p6

5s2

• 38

4d10 5p6 6s2

• 56

Only 2 electrons per orbital Electrons in the same orbital must have

opposite spins Spin is represented by an arrow

Hund’s Rule- The lowest energy configuration for an atom is the one that has the maximum number of unpaired electrons in the orbital.

C 1s2 2s2 2p2

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

He with 2 electrons