francium

Cations are smaller than their parent atoms, and so the Ca2+ ion is smaller than the Ca atom. Because Ca is below Mg in group 2A of the periodic table, Ca2+ is larger than Mg2+. Consequently, Ca > Ca2+ > Mg2+.

Ca is larger than the Ca2+ because Ca2+ has a greater positive charge and electrons repel the nucleus.

The smallest possible size for anything in the universe is the Planck Length, which is 1.6 x10-35 m across.

Hydrogen

Oganesson

upper right corner

Atoms are really small. So small, in fact, that it’s impossible to see one with the naked eye, even with the most powerful of microscopes. Now, a photograph shows a single atom floating in an electric field, and it’s large enough to see without any kind of microscope.

The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

Atoms cannot be created nor destroyed, and they are indestructible; they cannot be broken into smaller parts. This was based on the Law of Conservation of Mass. It was later learned that atoms can break into smaller parts. All atoms of an element are identical, in both mass and properties.

Atoms were created after the Big Bang 13.7 billion years ago. As the hot, dense new universe cooled, conditions became suitable for quarks and electrons to form. Quarks came together to form protons and neutrons, and these particles combined into nuclei.