Why atomic groups usually are negatively charged?

Atomic groups, such as NO3(1-), SO4(2-), PO4(3-), and many amino acids in physiological conditions, usually are negatively charged. Why is that?

Some walls are built with stones. Between stones, we will apply fine grained cement to glue the stones together. If the amount of cement is not enough, the wall might crumble easily.

In atomic groups, nucleus are like big stones. They are large and positively charged. They repel each other. They need fine grained and negatively charged electrons to glue them together. If the amount of electrons is not enough, the atoms don’t stick into atomic groups or molecules, which are electrically neutral. So most atomic groups are negatively charged.

There are few positively charged atomic groups, such as NH4(+). Hydrogen atoms are very small.