Question

chem 100 - introduction to chemistry - fall 2025
q4. (1 point) true / false (circle one): x - rays travel at a greater speed than visible colors of light because of higher photon energy.
q5. (5 points) the pretty colors observed in firework displays are due to excited electrons in atoms.
a) show the change in the energy level diagram below to explain how a certain color is produced by an excited atom in the burning firework (circle represents the electron):

b) which line on the diagram represents the ground state?

c) what kinds of spectrum is observed from such an atom?

d) if the jump is smaller, then the color would be more red / violet.

Explanation:

Q4

Step1: Recall the speed of electromagnetic waves

All electromagnetic waves (including X - rays and visible light) travel at the speed of light \(c = 3\times10^{8}\space m/s\) in a vacuum. The energy of a photon is given by \(E = h
u\) (where \(h\) is Planck's constant and \(
u\) is the frequency), but energy does not affect the speed.

Q5

a)

When an electron in an atom is excited (by the energy from the firework explosion), it jumps to a higher energy level. When it falls back to a lower energy level, it emits a photon of light. The energy of the photon \(E=h
u\) corresponds to the energy difference between the two levels \(\Delta E=E_{upper}-E_{lower}\). So, draw an electron (circle) moving from a lower energy level to a higher energy level (excitation) and then back to a lower level (emission).

b)

The ground state is the lowest energy state of an atom. On the energy - level diagram, it is the lowest horizontal line.

c)

When electrons in atoms emit light (as in a firework), we observe an emission spectrum. In an emission spectrum, only specific wavelengths (colors) of light are emitted, corresponding to the energy differences between the electron energy levels.

d)

The energy of a photon is related to its wavelength by \(E = h\frac{c}{\lambda}\). A smaller jump (smaller \(\Delta E\)) means a longer wavelength. Red light has a longer wavelength (\(\lambda_{red}\approx620 - 750\space nm\)) than violet light (\(\lambda_{violet}\approx380 - 450\space nm\)). So, if the jump is smaller, the color would be more red.

Answer:

Q4

False

Q5

a) Draw an electron moving up (excitation) and then down (emission) on the energy - level diagram.
b) The lowest horizontal line.
c) Emission spectrum.
d) red