Ion, any atom or group of atoms that bears one or more positive or negative electrical charges. Positively charged ions are called cations; negatively charged ions, anions.
All of the elements in the periodic table are monoatomic except the 7 elements that are diatomic atoms. These 7 elements are hydrogen, nitrogen, oxygen, chlorine, bromine, iodine and fluorine. Monoatomic substances are those elements that are stable by themselves.
Polar covalent bonds (because hydrogen and oxygen form polar bonds and are both nonmetals so it's covalent) and hydrogen bonds (because the water molecules are attracted to each other with partial charges, causing specific properties like surface tension).
So in my very bad drawing that I attached in case you're more a visual learner, the d- and d+ show the partial charges of hydrogen and oxygen (making it polar, as the electrons in the bond are more shifted towards oxygen, which is why oxygen has a negative sign) and the yellow dotted line show the hydrogen bonds.
It is energetically favorable for all atoms to have a complete outer
electron shell. Loosely, the atoms on the left hand side of the periodic
table only have a few extra electrons in their outer shell so it is
energetically favorable for them to lose them. The atoms on the right
hand side of the periodic table almost have enough electrons in their
outer shell and so they have a tendency to gain them.
Once electrons have left an electron shell, an atom will have a positive
charge because it has more protons (positive charges) than electrons
(negative charges). Similarly, an electron which has gained electrons to
complete its outer shell will have a negative charge because it now has
more electrons (negative charge) than protons (positive charge).
Increase in temperature makes the atoms speed up, and decrease in temperature makes the atoms move slower.