Arrange the following molecules in order of increasing average molecular speed. All are at the same temperature. methane, carbon dioxide, sulfur dioxide, neon

Given the same temperature, all of the gases are considered to have the same kinetic energy, i.e.

1

2

⋅

m

v

2

... It follows that the LIGHTER gases are moving FASTERand so we simply take the order of decreasing molecular mass to assign molecular speed, from fastest to slowest...

Explanation:

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.