Ionic Bonds & Formulas NaCl -composed of + cations and anions but they are electrically neutral (net charge = 0) Ionic Bonds : electrostatic attraction between + & ions in ionic compounds. Ionic Compounds: Na + Cl NaCl CaSPbO 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. Na 2 Cl 2 Ca 2 S 2 Pb 2 O 2+ 2 4+ 2 Writing Formulas of Ionic Compounds: 1. Write symbol of cation (+), then anion (). 2. Write charge of each ion as a superscript. 3. Write subscripts to balance the charges (crisscross charges) 4. Erase charges (neutral compound). K2OK2OMg 3 N 2 K potassium oxidemagnesium nitride O + 2 Mg N 2+ 3 K+K+ K+K+ O 2 Mg 2+ N 3 Mg 2+ N 3 +2 2+6 6 calcium oxide _________ aluminum oxide _________ magnesium phosphide _________ lithium sulfide _________ Li + S 2 Writing Formulas of Ionic Compounds: NAMEFORMULA CaO (lowest ratio) Al 2 O 3 Mg 3 P 2 Li 2 S Ca 2+ O 2 Al 3+ O 2 Mg 2+ P 3 1. Which chemical formula is correct? A.KO B.MgS 2 C.CaO D.Na 2 Br Quick Quiz! 2. Which chemical formula is incorrect? A.KF 2 B.CaS C.MgO D.NaBr Quick Quiz. 2 1 charges vary but always + transition metals AlCl 3 Cl [Na] + Lewis dot diagrams