1. Bohr predicted that the energy of an electron in a hydrogen atom is
E = - k
____ n2
E is the energy of the e-
k is the Bohr Constant, x J
n is the Bohr Orbit
For energy values:
Positive means repulsive energy (because it’s a high value)
Negative means attractive energy (because it’s a low value)
Therefore, an e-s energy in an atom will always be negative
EX3-1 (of 11)

2. Calculate the energy of an e- in the 3rd Bohr Orbit of a hydrogen atom
E = - k
____ n2
= x J
__________________ 32
= x J
EX3-2 (of 11)

3. Calculate the energy change when an e- drops from n = 2 to n = 1 in a hydrogen atom.
E2 = - k
____ n2
= x J
___________________ 22
= x J
E1 = - k
____ n2
= x J
___________________ 12
= x J
EX3-3 (of 11)

4. Calculate the energy change when an e- drops from n = 2 to n = 1 in a hydrogen atom.
The energy change (ΔE) is equal to the final energy state minus the initial energy state:
ΔE = E1 - E2
= ( x J) – ( x J)
= x J
For CHANGES in energy:
Positive means energy was absorbed
Negative means energy was released
Therefore, this hydrogen atom released energy
EX3-4 (of 11)

5. Calculate the energy change when an e- drops from n = 2 to n = 1 in a hydrogen atom.
The energy released is given off as a photon, and the photon’s energy is the absolute value of ΔE:
Ephoton = | ΔE │
= | x J │
= x J
EX3-5 (of 11)

6. If an electron is removed from an atom, the atom has been IONIZED
Calculate the ionization energy of a ground state hydrogen atom
E1 = - k
____ n2
= x J
___________________ 12
= x J
Eout =
0 J
EX3-6 (of 11)

7. If an electron is removed from an atom, the atom has been IONIZED
Calculate the ionization energy of a ground state hydrogen atom
ΔE = Eout - E1
= (0 J) – ( x J)
= x J
The positive energy change means that the hydrogen atom absorbed this energy to release the electron
EX3-7 (of 11)

8. Measuring the Wavelengths in Hydrogen’s Emission Spectrum
EX3-8 (of 11)

9. e = λ
sin ϴ = e/d
d sin ϴ = e = λ
EX3-9 (of 11)

10. tan ϴ = x/l
ϴ = tan-1 (x/l)
remember: λ = d sin ϴ
λ = d sin [tan-1 (x/l)]
EX3-10 (of 11)