Geologists can estimate the age of rocks by their uranium-238 content. the uranium is incorporated in the rock as it hardens and then decays with first-order kinetics and a half-life of 4.5 billion years. a rock is found to contain 82.6% of the amount of uranium-238 that it contained when it was formed. (the amount that the rock contained when it was formed can be deduced from the presence of the decay products of u−238.)

If the particles in a sample of matter have an orderly arrangement and move only in place, the sample is a

Draw the skeletal structures of two different molecules that are each made of 5 carbon atoms and 12 hydrogen atoms.

Why is the bond angle in a water molecule less than the bond angle of methane? a. the central oxygen atom in water has two lone pairs of electrons, whereas the central carbon atom in methane has no lone pairs. b. the central hydrogen atom in water has one lone pair of electrons, whereas the central carbon atom in methane has two lone pairs. c. the central oxygen atom in water has four lone pairs of electrons, whereas the central carbon atom in methane has only one lone pair. d. the central oxygen atom exerts more repulsive force on surrounding atoms than the central carbon atom in methane does. reset next