Compound Names and Formulas Unit 7 Section 3 Notes Compound Names and Formulas

REVIEW: Where an atom is located in the periodic table can be used as a tool for figuring out what ions are formed by different elements: Atoms of Group 1: ions form a +1 charge Atoms of Group 2: ions form a +2 charge Atoms of Group 13: ions form a +3 charge Atoms of Group 15: ions form a -3 charge Atoms of Group 16: ions form a -2 charge Atoms of Group 17: ions form a -1 charge Atoms of Group 18: do not form ions because they have a full outer energy level

Naming Ionic Compounds Ionic compounds are formed by the strong attraction between oppositely charged ions, cations (positive ions) and anions (negative ions) Contain a metal and a nonmetal The metal is ALWAYS listed first, followed by the nonmetal. The name of the metal stays the same For nonmetals, drop the ending and add –ide. Examples: nitride, sulfide, fluoride, oxide, bromide, iodide

An ionic compound must have a total charge of zero. Example: Calcium chloride: Calcium has a +2 charge and chloride has a -1 charge. For calcium chloride to have a total charge of zero, there must be 2 chloride ions for every calcium ion. So, the formula is CaCl2.

Anything NOT in groups 1, 2, or 13 must show their charge in Roman Numerals in parentheses when they form ions. Example: FeO and Fe2O3 would both be named iron oxide by the rules so far. They are not the same compound, so their compound names are different. The charge of the iron cation in Fe2O3 is different from the charge of the iron cation in FeO. FeO, Iron (II) oxide is a black powdery substance. Fe2O3, Iron (III) oxide is a component of rust.

The roman numeral shows the cation’s charge. Fe2O3 is made of Fe3+ ions, so it is named iron (III) oxide. How do you know the charge on iron is +3? Each oxygen ion has a -2 charge, and there are 3 of them. -2 times 3 is -6, so the charge on iron has to be +6. There are 2 iron ions, so 6/2 = 3. FeO is made of Fe2+ ions, so it is named Iron (II) Oxide. How do you know the charge on iron is +2? Each oxygen ion has a -2 charge, and there is only 1 of them. The charge on Fe has to be +2 because there is only one of them.

Once you have determined a chemical formula, always check the formula to see if it makes a neutral compound. Compounds are ALWAYS neutral.

Steps used to write formulas for Ionic Compounds: Writing Ionic Compounds: Example:Write the chemical formula for aluminum fluoride. Steps used to write formulas for Ionic Compounds: Write the symbols and charges for the ions with the cation (metal) first. Al+3 F-1 Write the Lewis structure for each element and show the transfer of electrons or use the puzzle pieces. Al F F F

Write the chemical formula Write the chemical formula. Show with subscripts the number of each ion needed to make a neutral compound. AlF3 Practice: Write the formulas for the following ionic compounds: Lithium oxide Beryllium chloride Titanium (III) nitride Rubidium Oxide

Naming/Writing Covalent Compounds Two nonmetals SHARE electrons so BOTH have 8 valence electrons. Exception: Hydrogen: only needs 2 valence electrons to be “full” Use numerical prefixes when naming covalent compounds The prefixes tell how many atoms of each element there are. Example: N2O4 is dinitrogen tetroxide You cannot reduce the formulas!

Naming/Writing Covalent Compounds Rules: If there is only one atom of the first element, it doesn’t get a prefix. Example: CO is named Carbon Monoxide The element that is farther to the right in the periodic table is second and ends in –ide. Example: BF3 is named Boron Trifluoride Sometimes, the a in prefixes is dropped if it is next to a vowel. Example: N2O4 is named Dinitrogen Tetroxide instead of Dinitrogen Tetraoxide.

Prefixes used for covalent compounds Number Prefix 1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

(Metal cation + Nonmetal anion) Does the compound have a metal? No YES Covalent (Two Nonmetals) Ionic (Metal cation + Nonmetal anion) Place metal first followed by nonmetal ending in -ide Place the nonmetal furthest to the left on the periodic table first, then the other nonmetal ending in –ide. Contain a Transition Metal? Yes No Use prefixes to tell the number of atoms in the compound. Use Roman Numerals to tell the valence of the metal. DO NOT Use Roman Numerals. Examples: dinitrogen trioxide nitrogen trichloride Examples: Sodium chloride Magnesium nitride Examples: Iron (III) oxide Copper (II) chloride