1.
In the notation, 1s2, the number 1 represents the ________ __________ where electrons are located.
energy level
outer shell
2.
The four parts, or blocks, on the periodic table are _____, _____, d, and f.
s, p
a, b
3.
The 2 in 1s2 represents the number of __________ located in that energy level.
electrons
protons