4. ninety-two percent of the atoms of an element have a mass of 28 u, 5% have a mass of 29 u, and the remaining atoms have a mass of 30 u. calculate the average atomic mass and identify
the element.

.92(28)+0.05(29)+0.03(30)=25.76+1.45+0.9=28.11

silicon

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.