An atom. From the smallest to the largest, every atom (excluding noble gases) shares the same desire: to be able to have a complete octet, that is, a valence shell full of eight electrons! Why? Just as you are unstable in life when something is missing, atoms are unstable because they lack the electrons needed for an octet. However, these atoms are intelligent and find ways to get what they want. What they do is what we now call chemical bonding! The number of valence electrons determines how unstable an atom is, which determines the electronegativity of an atom. Looking at the periodic table (PTofE), you can see that in the upper right corner are the highest electronegativities, with a maximum of fluorine. However, in the bottom left corner you can see that this is where the lowest electronegativities are found, reaching the limit at Francium. The electronegativity of each atom determines the type of bonds it forms when paired with another atom. The different types of bonds that can be created are: metallic bonds, ionic bonds, polar and non-polar covalent bonds...