Which statement describes the relationship between bond strength and the melting and boiling points of a substance?
A. Substances held together by hydrogen bonding have lower melting
and boiling points than those held together by Van der Waals
forces.
B. Substances held together by ionic bonding have higher melting
and boiling points than those held together by hydrogen bonding.
C. Substances held together by Van der Waals forces have higher
melting and boiling points than those held together by ionic
bonding
O D. Substances held together by ionic bonding have lower melting and
boiling points than those held together by hydrogen bonding.
SUB

Some material consisting of a collection of microscopic objects is kept at a high temperature. a photon detector capable of detecting photon energies from infrared through ultraviolet observes photons emitted with energies of 0.3 ev, 0.5 ev, 0.8 ev, 2.0ev, 2.5ev, and 2.8ev. these are the only photon energies observed. (a) draw and label a possible energy-level diagram for one of the microscopic objects, which has four bound states. on the diagram, indicate the transitions corresponding to the emitted photons. explain briefly. (b) would a spring–mass model be a good model for these microscopic objects? why or why not? (c) the material is now cooled down to a very low temperature, and the photon detector stops detecting photon emissions. next, a beam of light with a continuous range of energies from infrared through ultraviolet shines on the material, and the photon detector observes the beam of light after it passes through the material. what photon energies in this beam of light are observed to be significantly reduced in intensity (“dark absorption lines”)? explain briefly.

The coefficient of friction is a number that represents the resistance to sliding between two in contact with one another.

Point charges q1 = 51 µc and q2 = −27 µc are placed 1.0 m apart, with q2 on the right. what is the force (in n) on a third charge q3 = 19 µc placed midway between q1 and q2? (assume the positive direction is to the right. indicate the direction with the sign of your answer.)