One way in which elements differ from each other is the structure of the electron cloud in each element’s atoms. in an electron cloud, an electron that is farther away from the nucleus has

The electron cloud is split up in 3 areas. 

1) Inner Electron Cloud
2) Outer Electron Cloud
3) Valence Electrons

Your inner cloud is the electrons CLOSEST to the nucleus.
Your outer cloud is the electrons in the MIDDLE of the Inner and Valence.
Your valence electrons are the OUTER LAYER of electrons. These electrons are important to bonding, and also are what decide where on the periodic table of elements. For example: 

197
Au
79

This element is GOLD. It has 1 valence, therefor it is where it is in the period. Ionization could change this number however.

The masses of the objects and their densities