Describe why certain types of atoms will tend to lose electrons, while others will gain electrons?

Whether an atom typically gains or loses electrons has to do with how many electrons it has in its outermost electron level. These electrons are called valence electrons. A simple rule of thumb is that atoms want to have the outer most level of electrons full. If an atom's outermost "orbit" has only a couple of electrons in it, it is easier to lose those electrons so that the filled orbit under it is now the outermost orbit. If an atom is only a couple of electrons short of having a full outer orbit, then the atom is "wanting" to gain those extra electrons, in order to be full and stable. In general, as you go left and down the periodic table of elements, atoms will lose electrons more easily. As you go right across the table, the atoms will typically want to gain electrons. That is until you get to the far right column. These are the noble gasses, and their outermost electron level is full. Any additional electrons would need to start a new level.