Lesson 2: Naming Compounds and Writing Formulae.

Key Points: 1. Identify a compound as ionic or molecular. 2. Write formulae and proper names for chemical compounds. Ions and Ionic Compounds Ionic compounds occur when a metal (left side of table) and an non- metal (right side of table) react to form a new molecule. In these molecules electrons are typically lost by the metal and gained by the non-metal, thus both elements have outer electron shells that are full, i.e. they are like the nearest noble gas. Naming and Balancing Compounds: Binary Compounds: The name of a binary ionic compound is the name of the metal (cation) and the name of the non-metal (anion). The name of the metal is stated in full, and the name of the non-metal has an –ide suffix, for example magnesium oxide, sodium fluoride, aluminum sulfide. Naming and Balancing Compounds: Remember name both ions. Names are never capitalized! When using the formulas, balance the charges of each ion. A true compound should have a net charge of zero. Charges are positive on metals and negative on nonmetals and are equal to the group number. Example: aluminum + chlorine aluminum chloride

Al (s) + Cl2 (g) AlCl3 Multi-Valent Metals: Most transition metals have several possible charges (give up different numbers of electrons). This must be shown when naming compounds. To do this we use a roman numeral to denote which form of the metal was used. Example: copper(II)• sulfate Example: Fe2+ + O2- FeO

iron + oxygen iron(II) oxide Try the following examples:

1. NaCl 2. KF 3. HI 4. CaBr2 5. AlAt3 6. Cs2S 7. Na2O 8. BaSe 9. RaTe 10. LiF 11. Rb2S 12. SrI2 13.CaO 14.MgSe

Try these multivalent examples:

1. Fe2O3 2. CoS 3. MnCl4 4. CuS 5. SnTe2 6. HgAt2 7. PoI4 8. Sb2S3 9. Ni3N2 10.RuO2 Molecular Compounds Molecular compounds arise when two non-metals react to form a new substance. Because nonmetals usually have negative charges, no one element gets to keep the electrons, so the electrons are shared between the two elements in a covalent bond. Molecular Compounds Naming Molecular Compounds: Molecular compounds arise when two or more non-metals react to form a new substance. In these compounds electrons are shared rather than gained or lost and these compounds are quite stable. The difference between naming ionic compounds and molecular compounds is that in molecular compounds we use prefixes to denote the number of atoms of each element are involved.

Example CS2 = carbon disulfide or N2O = dinitrogen monoxide. As in ionic compounds the ide suffix is only added to the last word.

Example: P4O10 = tetraphosphorus decaoxide Try the following examples:

1. NI3 2. CI4 3. N2O3 4. TeAt2 5. P2S3 6. OS 7. Si3P4 8. SCl2 9. SiH4 10. B4C3 11. As2Se3 12. SBr2 13. N2S3 14. P4S8 15.TeCl2

Below are a mix of ionic and molecular compounds, denote which are which by using an I or an M and then name them:

1. LiCl 2. CrF3 3. PBr3 4. ZnI2 5. SiO2 6. CS4 7. TcI7 8. NaOH 9. Ca(SO4) 10.K(MnO4) 11. NO 12. Be(CN)2 13. Ba(CN)2 14. NaHCO3 15. PO4 Converting Chemical Names Into Formulas Step 1: We must decide whether the compound is ionic or molecular. How do we tell the Difference? Ionic:

Step 2: Ionic: Write the formula for the metal and indicate the ionic charge (1+, 2+etc.)) Step 3: Ionic: Write the formula for the non-metal and indicate its charge. (1-, 2- etc.) Step 4: Ionic: Balance the charges by using the appropriate number 2+ 1- of metal or non-metal ions. 1Ca + 2Cl = CaCl2 calcium chloride Converting Chemical Names Into Formulas

Molecular:

Step 2: Molecular: Write the formula for each element involved in the compound. Step 3: Molecular: By reading the prefixes (di, tri, tetra, penta, etc.) indicate the number of ions of each element present in the

compound. CS2 = carbon disulfide P4O10 = tetraphosphorus decaoxide