When bonding to other elements, it is easier for a sodium atom to gain seven electrons than to lose one electron.

it's easier to lose one electron because it's less work for the atom to do and easier to lose one than gain a whole 7, because the atom wants to gain a full outer shell as soon as possible

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).