Chemical Bonding Worksheets Page 3
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22IONIC COMPOUNDS consist of ions (charged particles) held together by ionic bonds.
– ionic bond:
electrostatic attraction holding together positively charged metal cations
and negatively charged nonmetal anions
Thus, an ionic compound is actually a three-
dimensional network of ions, with each cation
surrounded by anions, and vice versa. Consider
the molecular-level image of NaCl at the right.
formula unit: most basic entity of an ionic
compound (eg. NaCl, MgCl
, etc.)
2
– gives the ratio of ions (not actual #) present
– In the 3D representation of NaCl at the right,
+
–
Na
ions are shown in purple and Cl
ions
are shown in green
– Note that the formula, NaCl, indicates a
+
–
1-to-1 ratio of Na
ions and Cl
ions
present, not the actual number of each
ion in the compound.
Every bond between all of the ions must be broken—requiring extremely high temperatures—
to melt the substance
→
At room temperature, ionic compounds exist as solids with very high melting points.
IONIC RADIUS: distance from the nucleus to the outermost electrons in an ion
– an atom loses electrons to form a cation
→ a cation has a smaller radius than its corresponding atom
– an atom gains electrons to form an anion
→ an anion has a larger radius than its corresponding atom
+
11 p
+
+
+
–
11 p
17 p
17 p
loses 1 e
–
gains 1 e
–
11 e
–
–
–
10 e
17 e
18 e
+
Na
ion
Na atom
Cl atom
–
Cl
ion
Ex. 1: Order the following in terms of increasing atomic radius: S, F, P, Cl, He
_______ < _______ < _______ < _______
smallest
largest
+
+
2+
2+
+
Ex. 2: Order the following in terms of increasing ionic radius: H
, Na
, Sr
, Ca
, K
_______ < _______ < _______ < _______ < _______
smallest radius
largest radius
CHEM 121 Tro Chapter 10 F2012
page 3 of 22
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