Aim: How can we explain energy transitions in an atom?

Do Now:

What were the limitations of the Rutherford model of the atom and how did the Bohr model explain these limitations?

Emission Spectra

• When electron falls from higher to lower level, photon is emitted.

• Shows as bright series of lines.

Visible spectrum

Balmer Series

• Named after Johann Jacob Balmer

1825-1898

Gas Tube Demo

Energy of final level

Energy of initial level

Energy of photon emitted or absorbed

Calculate the energy of the photon emitted when a hydrogen atom

changes from energy state n = 3 to n= 2, in eV and Joules

Ephoton = Ei – Ef

Ephoton = -1.51 eV – (-3.40 eV)

Ephoton = 1.89 eV

1.89 eV * 1.60 x 10-19 J = 3.0x10-19 J 1 eV

For a mercury electron transition from level c to a,

calculate Ephoton, λ, f, and the type of EM wave emitted.

Ephoton = Ei – Ef

Ephoton = -5.52 eV – (-10.38 eV)

Ephoton = 4.86 eV4.86 eV * 1.60 x 10-19 J = 7.77 x 10-19 J 1 eV

c= fλ

3.00 x 108 m/s = f (2.56 x 10-7 m)

f = 1.17 x 1015 Hz

This is ultraviolet light

Ephoton = hc λ

7.77 x 10-19 J = (6.63x10-34 J•s)(3 x 108 m/s) λλ = 2.56 x 10-7 m

An electron in a hydrogen atom drops from n = 4, n = 2. Find

Ephoton (eV and Joules), f, and the color of light.

Ephoton = Ei – Ef

Ephoton = -0.85 eV – (-3.40 eV)

Ephoton = 2.55 eV2.55 eV * 1.60 x 10-19 J = 4.08 x 10-19 J 1 eV

Ephoton = hf

4.08 x 10-19 J = (6.63 x 10-34 J•s)f

f = 6.15 x 1014 Hz

This is blue light

Calculate the energy of the photon needed when a hydrogen atom changes from n =1 to n =∞

Ephoton = Ei – Ef

Ephoton = -13.60 eV – 0.00 eV

Ephoton = -13.60 eV

Ionization Potential• Minimum energy needed to

remove an electron from the ground state to infinity

• For hydrogen -13.6 eV

• For mercury -10.38 eV

• A positive photon energy indicated photon is emitted

• A negative photon energy indicates photon is absorbed

Absorption Spectra• When electron jumps to a

higher energy level a photon is absorbed.

• Shows up as a series of dark lines.

Wave Model• After De Broglie proposed matter waves,

he was able to show the Bohr model could be explained by considering the orbits of a series of waves

Cloud Model (Shrödinger’s Model)

• Quantum mechanics indicates the probability of the electron being in a certain area

• Most probable regions are in area called ‘electron cloud’

• Energy levels of Bohr model are divided into sublevels and orbitals -- together with Cloud model define the current model

Erwin Shrödinger

1887-1961