Arrangement of Electrons in Atoms

Chapter 4

Properties of Light

• Electromagnetic Radiation- which is a form of energy that exhibits wavelength behavior as it travels through space.

• Electromagnetic Spectrum- has γ-rays, x-rays, UV , visible light, IR, Microwaves(Radar), Radio waves (TV radio, short waves, long waves)

• Wavelength-is the distance between points on successive waves

• Frequency- as the number of waves that pass a given point in a specific time (s)

• C= speed of light 3 X 10 8 m/s

• . λ = wavelength

• . v = frequency or sometimes (f)

Photoelectric Effect

• Quantum-is the minimum quantity of energy that can be lost or gained by an atom.• Photoelectric effect-refers to the

emission of electrons from a metal when light shines on the metal

Photoelectric Effect

• Plank’s equation- E =hv

• Plank’s constant = h =6.626 X 10 -34 j s• E = energy• V = is the frequency of the radiation

emitted

Quantum theory

• Photon- is a particle of electromagnetic radiation having zero rest mass and carrying a quantum of energy.

• Ephoton = hv

• Ground state- the lowest energy state of an atom

• Excited state- has to do with the highest energy state and PE

Line Emission Spectrum

• Lyman series- parts a-e in the UV area of Hydrogen

• Balmer series- parts a-e are in visible light area of Hydrogen

• Paschen series- parts a-d are in infrared area of Hydrogen

Bohr model

• The Bohr Model is probably familar as the "planetary model" of the atom.

• Electrons arranged as planets around the nucleus.

Quantum Mechanics

• Schrödinger Wave Equation (1926)– finite # of solutions quantized energy levels

– defines probability of finding an e-

Quantum Mechanics

• Heisenberg Uncertainty Principle– Impossible to know both the velocity and position

of an electron at the same time

Quantum Numbers

• Orbital (“electron cloud”)– Region in space where there is 90% probability of

finding an e-

Orbital

Quantum Numbers

• Four Quantum Numbers:– Specify the “address” of each electron in an atom

Quantum Numbers

Principal Quantum Number ( n )

– Energy level

– Size of the orbital

– n2 = # of orbital's in the energy level

Quantum Numbers

2. Angular Momentum Quantum # ( l )– Energy sublevel

– Shape of the orbital

s

p

d

f

n = # of sublevels per leveln2 = # of orbital's per levelSublevel sets: 1 s, 3 p, 5 d, 7 f

Quantum Numbers

• Orbitals combine to form a spherical shape.

Quantum Numbers

2s

2pz

2py

2px

Quantum Numbers

. Spin Quantum Number ( ms )

– Electron spin +½ or -½

– An orbital can hold 2 electrons that spin in opposite directions.

Quantum Numbers

Quantum Numbers

• Pauli Exclusion Principle– No two electrons in an atom can have the same 4

quantum numbers.

– Each e- has a unique “address”:

Quantum Numbers

• Principal #• Ang Momentum #• Magnetic #• Spin #

• Energy level• Sublevel (s,p,d,f)• Orbital• Electron

Electron configuration

• Electron configuration- arrangement of electrons in an atom

• Aufbau principle- an electron occupies the lowest energy orbital that can receive it.

• Pauli exclusion principle-no two electrons in the same atom can have the same set of four quantum #’s

Electron Configuration

• Hund’s rule- orbital's of equal energy are each occupied by one electron before any orbital is occupied by a second electron and all electrons in singly occupied orbital's must have the same spin.

•

Electron Configuration

• Noble gas configuration- using the last noble gas as a short cut method for electronic configuration.