Light is an electromagnetic wave

• EM wave- a form of energy that exhibits wavelike behavior as it travels through space

• All the forms of EM radiation form the electromagnetic spectrum

Properties of EM waves

• Speed- all forms of EM radiation travel at 3 x 108 m/s in a vacuum

• Wavelength-the distance between 2 consecutive waves

• Frequency- the # of waves that pass a stationary pt. in one second

• Amplitude- the height of a wave measured from the origin to its crest

Photoelectric Effect

• Refers to the emission of electrons from a metal when light of a specific frequency (or energy) shines on the metal

Particle Description of Light

• Quantum- the minimum quantity of energy that can be lost or gained by an atom

• This relationship is expressed as:

E = hv

Where E = energy

h= Planck’s

constant

v= frequency of light

The Dual Nature of Light

• Light exhibits many wavelike properties but can also be thought of as a stream of particles called photons.

• Photon- a particle of EM radiation having zero mass and carrying a quantum of energy

Bohr’s Model• The electron can circle the nucleus only in

allowed paths or orbits

• In an orbit, an electron has a fixed energy

• The lowest energy state is closest to the nucleus

• An electron can move to a higher orbital if it gains the amount of energy equal to the difference in energy between the initial orbit and the higher energy orbit

Line Emission Spectra• The lowest energy state

of an electron is the ground state.

• A state in which that atom has a higher energy potential is called an excited state.

• As the excited electron falls back to its ground state, it releases EM radiation of an energy that corresponds to the amount of energy gained to reach the excited state.

energy of emitted photon = (atom energy before) - (atom energy

after)

• When the EM radiation released is passed through a prism or diffraction grating- it is separated into a series of specific frequencies of visible light.

• This is referred to as a line emission spectra

DeBroglie’s Idea

• Suggested that electrons could also have a wave nature much like light.

This was based on the fact that:

Electrons can be diffracted (bending)

Electrons exhibit interference (overlapping that results in a reduction of energy)

• It is impossible to determine simultaneously both the position and velocity of an electron.

Schrodinger’s Wave Equation

• Laid the foundation for modern quantum theory.

• Quantum Theory describes mathematically the wave properties of electrons.

• The solutions to this equation give only the probability of finding an electron at a given location.

• Electrons do not travel in neat orbits

• They exist in three-dimensional regions called orbits that indicate the probable location of an electron.

The location of electrons within the atom can be described using quantum numbers:

Principle Orbital (Angular Momentum)MagneticSpin

Principle Quantum Number

• Gives the principle energy level

n= 1, 2, 3, etc.

• Maximum # of Electrons for Orbitals:

1st- 2

2nd – 8

3rd – 18

4th - 32

Orbital Quantum Number

• Tells the shape or type of orbital

• s orbital is doughnut shaped

• p orbital is dumbbell shaped

Suborbital # of electrons # of orbitals

s 2 1

p 6 3

d 10 5

f 14 7

Magnetic Quantum Number

• Designates specific regions of space w/in each energy sublevel

(s, p, d, f)

• Ex.

p sublevel has 3 orbitals

(px, py, pz)

Spin Quantum Number

• Designates direction of electron spin

• Electrons w/in an orbital spin in opposite directions

Governing Rules and Principles

• Pauli Exclusion Principle- only 2 electrons in each orbital

• Aufbau Principle- electrons must occupy lower energy orbitals first

• Hunds Rule- a second electron can not be added to an orbital until each orbital in a sublevel contains an electron

Summary:

Principle Energy Level

Orbitals Max. Electrons

1 s 2

2 s p 8

3 s p d 18

4 s p d f 32