As for your first two questions, it's a simple matter of difference of electronegativities.
click below and then scroll down to the periodic table at the bottom
http://en.wikipedia.org/wiki/ElectronegativityThe values you see there are electronegativities, or the ability for one atom to attract electrons from another while in a bond.
subtract the electronegativities of the two elements bonding.
If the difference is less than .3, than it is a non-polar covalent bond.
If it is greater than .3 but less than 1.7, it is a polar covalent bond.
If it is greater than 1.7, it is an ionic bond
In a non-polar covalent bond, electrons are shared equally between atoms
In a polar covalent bond, the electrons are going to spend more time in orbit around the atom with the higher electronegativity, thereby making it the negative pole, and making the other atom the positive pole.
In a ionic bond, the atom with the higher electronegativity completely "steals" an electron from the other atom, which causes one atom to have a -1 charge, while the other has a +1 charge. A goode example is salt, or sodium chloride.
Na+Cl-