1. Ionic
Bonds
&
Formulas
NaCl

2. Na+ NaCl Cl– Ionic Compounds: Ionic Bonds:
(e-s completely separate)
-composed of + cations and – anions but…
they are electrically neutral overall (net charge = 0)
Na+
NaCl
Cl–
Ionic Bonds:
electrostatic (Coulombic) attraction between + & – ions in ionic compounds.

3. NaCl CaS PbO2 Ca2S2 Pb2O4 1+ 1– 2+ 2– 4+ 2– + – + – – + – + + – + –
Binary Compounds:
contain only two different atoms
Chemical Formula:
shows type & number of atoms in substance.
Formula Unit:
the lowest whole-number ratio of atoms in an ionic compound. + – + – – + – + + – + –
1+ 1–
2+ 2–
4+ 2–
NaCl
CaS
PbO2
Ca2S2
Pb2O4

4. Writing Formulas of Ionic Compounds:
1. Write symbol of cation(+), then anion (–). (That is metal first and then non-metal).
2. Write charge of each ion as a superscript.
3. Write subscripts to balance the charges
(crisscross charges)
4. Erase charges (neutral compound).
potassium oxide
magnesium nitride K+ + 2– 2+
Mg2+
N3– K O Mg 3– N
Mg2+
N3– K+
O2–
Mg2+
K2O
Mg3N2
+2 –2
+6 –6

5. Writing Formulas of Ionic Compounds:
NAME
FORMULA
Ca2+ O2–
CaO
calcium oxide _________
aluminum oxide _________
magnesium phosphide _________
lithium sulfide _________
(lowest ratio)
Al3+ O2–
Al2O3
Mg2+ P3–
Mg3P2
Li+ S2–
Li2S

6. 1. Which chemical formula is correct? KO MgS2 CaO Na2Br
Quick Quiz!
1. Which chemical formula is correct? KO
MgS2
CaO
Na2Br

7. 2. Which chemical formula is incorrect? KF2 CaS MgO NaBr
Quick Quiz.
2. Which chemical formula is incorrect?
KF2
CaS
MgO
NaBr

8. charges vary but always +1+ 2+ 3+ 3– 2– 1–
transition
metals
charges vary but always +

9. – Cl
Lewis dot diagrams
[Na]+
AlCl3