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.