How many valence electrons are there in each of the following elements AND COMPOUNDS (add up the valence electrons for each atom). Show your addition for the compounds:
18) Ca
19) P
20) Se
21) NH3
22) NF3
23) Al2(CO3)3

Explanation:

Ca = +2

P = -3

Se = 0

NH3=

N = -3 , H = +1 , H3 = 3 x +1 = +3

-3 + (+3) = 0

NH3 = 0

NF3

N = -3, F = -1 , F3 = 3 x (-1) = -3

-3 + -3 = -6

Al2(CO3)3

CO3

C= +4, O = -2, O3 = 3 x (-2) = -6

CO3 = +4 + (-6) = +4 - 6 = -2

(CO3)3 = 3 x (-2) = -6

Al = +3, Al2 = 2 x (+3) = +6

Al2(CO3)3 = +6 + (-6)= 0

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.