Chapter 4Chapter 4

Arrangement of ElectronsArrangement of Electrons

In AtomsIn Atoms

Properties of Light

• Light as a wave– Diffraction– Interference

• Light as a particle– Photoelectric effect

• Dual Nature of Light – light can behave as both a wave and a particle.– Electromagnetic Radiation – energy that

travels through space as a wave

You can treat it three ways

Electromagnetic Spectrum

Wave Diagram

Wave Mechanics

• Wavelength – – distance between corresponding point on adjacent waves (m)

• Frequency – – (f) – number of waves that pass a certain point in a given time (waves/s) or (/s, s-1) or (Hz)

• Speed of a wave = v = – For light c=(c=3x108 m/s)

Proof Light is a Wave

• Diffraction – bending of a wave around a barrier.

• Interference – combining of waves that cross paths (superposition).

Proof Light is a Particle• Photoelectric effect –

emission of electrons from a metal when the metal is struck by certain frequencies of light.

• E E • E = hE = h

– h = 6.626x10h = 6.626x10-34-34 Js Js– Plank’s ConstantPlank’s Constant

E = h E = h

c = c =

c / c /

E = h c / E = h c /

Niels BohrNiels Bohr – explained the spectral lines observed in excited gases

Hydrogen Emission Spectrum

Balmer, Paschen, and Lyman Series

The DeBroglie HypothesisThe DeBroglie Hypothesis

If light can behave as both a wavewave and a particle,

can electrons also have this dual nature?

p

h

pmvmv

h

mv

hv

mvhv

mvhc

mvh

cv

mch

mcEhE

momentum

ocitiesslower velfor

and

2

2

2

2

2

2

The Quantum ModelThe Quantum Model

Heisenberg’s Uncertainty Heisenberg’s Uncertainty PrinciplePrinciple – it is impossible to know both the exact position and the momentum (velocity) of a small particle at the same time.

Schrodinger’s Wave Schrodinger’s Wave EquationEquation – describes the probability of finding an electron at some distance from the nucleus in terms of the wave function

Implications of Heisenberg and Implications of Heisenberg and SchrodingerSchrodinger

• These ideas say it is impossible to know where an electron is at any point in time. Therefore we can only say where an electron is most probably located at any time. We call that region an orbital.

Orbital – 3d region around a nucleus where an electron is likely to exist

Quantum Numbers – 4 numbers used to Quantum Numbers – 4 numbers used to describe the location of an electrondescribe the location of an electron

• Principle Quantum Number – (n) – tells the main energy level of the electron.

• Angular Momentum Quantum Number – (l) – describes the shape of the orbital.

• Magnetic Quantum Number – (m) – tells the orientation of the orbital around the nucleus.

• Spin Quantum Number – (s) – indicates the direction of the spin of the electron on its own axis.

Pauli’s Exclusion Principle – No two electrons have the same set of 4 quantum numbers

• Possible values for the quantum numbers– n = 1,2,3,…7 max # of e- in energy level =2n2n22

– l = n-1 l = 0,1,2,…6 or s,p,d,f,g…

– m = (-l,…0…+l)– s = +/- 1/2

Principle Quantum Number

Tells the main energy level (how far from the nucleus) of an electron

#e-/energy level = 2n2

Angular Momentum Quantum Number – Azimuthal Quantum Number

• Tells the type (shape) of the orbital

Magnetic Quantum NumberMagnetic Quantum Number – tells orientation around the nucleus

Spin Quantum Number

s = -1/2 s = +1/2

Electron Configurations – shorthand way of representing the arrangement of electrons in an atom

• Pauli’s Exclusion PrinciplePauli’s Exclusion Principle – no two electrons have the same set of four quantum numbers (everybody’s different)

• Aufbau Principle – electrons occupy the lowest possible energy level (electrons are lazy)

• Hund’s Rule – orbitals of equal energy are occupied by one electron before any one orbital is occupied by two electrons, and all electrons in singly occupied orbitals have the same spin (everybody gets one before anybody gets two)

Order of Orbital Filling

Order of Orbital Filling

Helium ??

Electron Configurations for 1st Period

2+

Notations for 2nd and 3rd Periods

Orbital Notation

Orbitals Notations for 3p’s

Periodic Table with Electron Configurations

Noble Gas Notations

Here are some examples: O 1s22s22p4 Si 1s22s22p63s23p2 Ca 1s22s22p63s23p64s2 Cr 1s22s22p63s23p63d54s1 Br 1s22s22p63s23p63d104s24p5 La 1s22s22p63s23p63d104s24p64d104f1

5s25p66s2

O [He]2O [He]2ss2222pp44 Si [Ne]3Si [Ne]3ss2233pp22 Ca [Ar]4Ca [Ar]4ss22 Cr [Ar]3Cr [Ar]3dd5544ss11 Br [Ar]3Br [Ar]3dd101044ss2244pp55 La [Xe]4La [Xe]4ff 1 166ss22..

O [He]2O [He]2ss2222pp44 Si [Ne]3Si [Ne]3ss2233pp22 Ca [Ar]4Ca [Ar]4ss22 Cr [Ar]3Cr [Ar]3dd5544ss11 Br [Ar]3Br [Ar]3dd101044ss2244pp55 La [Xe]4La [Xe]4ff 1 166ss22..

Homework

• Pages 124-126

• Numbers 6,10,11,14,18,19,22,30,31,32,33,35,37,38,46,48,50