The difference between mechanical and chemical weathering is
a. the length of time each takes to break
b. that only chemical weathering involves water
c. the way they affect the makeup of a rock
d. all of the above

hey your not cool]      

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.