[itsmovinmovin]

Got some questions that I have attempted, but am not 100% sure on. Thanks in advance!

1. Calculate the total energy of a beam of photons with wavelength 438 nm composed of 7.86E-9 mol photons.
Attempt to answer:
438 nm = 4.38E-7m.
E = hc/lamda = (6.626E-34)(3.00E8) / 4.38E-7 = 4.5352E-19 J / photon.
Converting? (4.5352E-19 J / photon) x (7.86E-9 mol photons) x (6.02E23 / 1 mol) = 2.15E-3 J.

2. A hydrogen atom is in the n=2 state. A stream of 1.13E4 monochromatic photons arrives with a total energy of 1.74E-14J. Is the energy of the photons enough to ionize the hydrogen atom?
Attempt to answer:
E = -Rh(z^2 / n^2)
E = -2.178E-18 (1^2 / 2^2)
E = -5.445E-19 J.
Since 1.74E-14 J > -5.445E-19 J, it is enough energy to ionize the hydrogen atom.

3. Rank the following elements from smallest to largest ionic radius: Rb+, Se2-, Sr2+
Attempt to answer:
Rb+, Sr2+, Se2-

4. Consider the following reaction for a given metal M : 2M (s) + O2 (g) --> M2O2 (s)
Which element, M = Li or Rb, is more reactive? Explain why.
Attempt to answer:
Rb is more reactive because it has lower ionization energy.

5. Which orbital is closes to the nucleus, a 2s orbital or a 2p orbital? How does this affect the relative energies of the orbitals?
Attempt to answer:
A 2s orbital is closer to the nucleus.
The further you get from the nucleus, the higher the relative energies.

[TheJoker]

ya 4 is right, since electrons are farther from nucleus in Rb atom, it is easier for them to react (like you said with the Ionization E)

[macman104]

The setup from 1 and 5 are good, I didn't double check your math.  For 3, think about how the increasing positive charge affects the ions.  The electrons are not placed in a higher shell or anything that is going to dramatically increase the base size of the atom.

[itsmovinmovin]

For 3, Rb+, Sr2+, and Se2- have the electron configuration of Kr. So I guess with this, from smallest to largest, ionic radius would be Sr2+ (loses 2), Rb+ (loses 1), Se2- (gains 2). Correct?

Any ideas on 2?

[macman104]

Correct.  Sorry, can't help on 2 (suppose that's probably not the best thing seeing as I'm almost graduating, lol).

[itsmovinmovin]

Haha, no don't worry, thanks a lot! Just wanted to confirm number 1, "mol photons" is the units of moles x photons, correct?

Anyone with ideas on 2 would be greatly appreciated.

[Yggdrasil]

2. A hydrogen atom is in the n=2 state. A stream of 1.13E4 monochromatic photons arrives with a total energy of 1.74E-14J. Is the energy of the photons enough to ionize the hydrogen atom?
Attempt to answer:
E = -Rh(z^2 / n^2)
E = -2.178E-18 (1^2 / 2^2)
E = -5.445E-19 J.
Since 1.74E-14 J > -5.445E-19 J, it is enough energy to ionize the hydrogen atom.

The setup here is incorrect.  In thinking about how to answer this question, it may be useful to think about how Einstein's experiments with the photoelectric effect led to the development of quantum mechanics.  Also, recall that the absorption of a single photon can ionize an atom, but not all photons have this capability.  What properties of the photon would determine its ability to ionize an atom?