Chemistry Reference
In-Depth Information
20
10
0
40
18
+
40
2+
32
16
2-
Ne
Ag
Ca
S
Number of protons
10
18
20
16
Number of electrons
Number of neutrons
Next, you'll need to determine the number of electrons in each of the
samples. Remember: If we subtract the charge number from the upper
right-hand side of the elemental notation from the atomic number, found
on the lower left-hand side of the elemental notation, we get the number
of electrons in the atom. Following are the calculations for this step.
Number of electrons shown for Ne
0
= 10 - 0 = 10. This neon atom is
neutral, so it has an equal number of protons and electrons.
Number of electrons shown for Ag
+
= 18 - 1 = 17. This silver atom has
a charge of +1, because it lost one of its electrons (negative charges).
Number of electrons shown for Ca
2+
= 20 - 2 = 18. This calcium atom
has a charge of +2, because it lost two of its electrons.
Number of electrons shown for S
2-
= 16 - (-2) = 18. This sulfur atom
has a charge of -2 because it has gained two extra electrons.
Let's add this information to our table.
20
10
0
40
18
+
40
2+
32
16
2-
Ne
Ag
Ca
S
Number of protons
10
18
20
16
Number of electrons
10
17
18
18
Number of neutrons
Lastly, we need to fill in the information for the number of neutrons
shown in each sample. We simply subtract the atomic number, found in the
lower left-hand corner of the elemental notation, from the mass number,
found in the upper left-hand corner of the elemental notation. For cal-
cium, remember that the atomic number is 20.
The neon atom has (20 - 10) 10 neutrons.
The argon atom has (40 - 18) 22 neutrons.
The calcium atom has (40 - 20) 20 neutrons.
The sulfur atom has (32 - 16) 16 neutrons.
