View Full Version : Chemistry Help: Wavelength and Energy Levels

squirrell751

02-01-2011, 10:45 AM

hey guys. my chem teachers never really helped us with this as she only briefly went over this crap in my previous classes but now im asked to do these all the time and i cant figure them out for the life of me can you guys help? i try to do them but get nothing close to what the answer actually is. i realize they may be a lot of work and give big thanks and appreciation in advance to those who help and give in an effort

1. What is the wavelength in nanometers of an electromagnetic radiation which has frequency of 6.40 x 10^14/s. The speed of electromagnetic radiation is 3.00 x 10^8 (constant im guessing). Answer: 469 nm

2. Calculate the energy of a bluish green line in a hydrogen spectrum with a wavelength of 486 nm. Answer: 4.09 x 10^-19J

3. What is the wavelength in nanometers of light emitted when the electron in a hydrogen atom undergoes a transition from energy level n = 6 to n = 3? Answer: 1095nm

Tip Top

02-01-2011, 10:52 AM

wavelength = c/f

christ just google it this is everywhere

Stickiy

02-01-2011, 01:36 PM

1) As TipTop says, wavelength = c (speed of light / em radiation) / f (frequency)

2) E = h f = h (c / wavelength)

h = Planck's Constant = 6.63 x 10-34 m^2 kgs^-1

3) You need to know the energy of level n = 6 and n = 3, I don't know those without searching.

E(photon) = E(n=6) - E(n=3)

Then E(photon) = h f = h (c / wavelength)

That's what you need.

Pay attention in class :)

Heisman2

02-01-2011, 01:46 PM

hey guys. my chem teachers never really helped us with this as she only briefly went over this crap in my previous classes but now im asked to do these all the time and i cant figure them out for the life of me can you guys help? i try to do them but get nothing close to what the answer actually is. i realize they may be a lot of work and give big thanks and appreciation in advance to those who help and give in an effort

1. What is the wavelength in nanometers of an electromagnetic radiation which has frequency of 6.40 x 10^14/s. The speed of electromagnetic radiation is 3.00 x 10^8 (constant im guessing). Answer: 469 nm

As mentioned above, wavelength = c/f. The important thing here is units. If you start with wavelength in nm, frequency in 1/s, then you need c in units of nm/s. The speed that you listed is definitely a constant, although you need to know the units for it (m/s for the number you listed). Just be careful with units and this question is easy.

2. Calculate the energy of a bluish green line in a hydrogen spectrum with a wavelength of 486 nm. Answer: 4.09 x 10^-19J

Here you need to relate wavelength to energy. To do this you'll need Planck's constant. The relevant equation and the value of the constant, including units, is here: http://en.wikipedia.org/wiki/Planck_constant. Again, be careful with units and this is easy.

3. What is the wavelength in nanometers of light emitted when the electron in a hydrogen atom undergoes a transition from energy level n = 6 to n = 3? Answer: 1095nm

For this you need the Rydberg equation for the Hydrogen atom. You can see this here: http://mooni.fccj.org/~ethall/rydberg/rydberg.htm

If you still have trouble with these post back and I'll try to actually work them out.