Molecular Compounds WRITING NAMES AND FORMULAS Chapter 8

Molecular Compounds WRITING NAMES AND FORMULAS Chapter 8. 2

Ionic versus Covalent IONIC COVALENT Bonded Name Salt Molecule Bonding Type Transfer e- Share e- Types of Elements Metal & Nonmetals Physical State Solid, Liquid, or Gas Melting Point High (above 300ºC) Low (below 300 ºC)

Section 8. 2 Naming Molecules • Translate molecular formulas into binary molecular compound names. oxyanion: a polyatomic ion in which an element (usually a nonmetal) is bonded to one or more oxygen atoms • Name acidic solutions. oxyacid Specific rules are used when naming binary molecular compounds, binary acids, and oxyacids.

Molecular Compounds made of just nonmetals smallest piece is a molecule can’t be held together because of opposite charges. don’t use charges to figure out how many of each atom

Ionic compounds use charges to determine how many of each. Have to figure out charges. Have to figure out numbers. Molecular compounds name tells you the number of atoms. Uses prefixes to tell you the number

Naming Molecules Two nonmetals share electrons so both have 8 valence electrons. Neither takes on a charge - no valence. Do not crisscross to determine formula. Must use prefixes in the name. Name tells you the formula. N 2 O 4 is dinitrogen tetroxide. You cannot reduce the formulas!!!

Molecular (Covalent) Nomenclature for two nonmetals Prefix System (binary compounds) Rule 1: The element with the lower group number is written first in the name; the element with the higher group number is written second in the name. Exception: when the compound contains oxygen and a halogen, the name of the halogen is the first word in the name.

Rule 2: If both elements are in the same group, the element with the higher period number is written first in the name. Rule 3: The second element in the name is named as if it were an anion, i. e. , by adding the suffix -ide to the name of the element.

Rule 4: Add prefixes to indicate # of atoms. Omit mono- prefix on the FIRST element. Must use mono with the SECOND element No double vowels when writing names (oa oo)

Acid Nomenclature Acids Compounds that form H+ in water. Formulas usually begin with ‘H’. In order to be an acid instead of a gas, binary acids must be aqueous (dissolved in water) Ternary acids are ALL aqueous Examples: HCl (aq) – hydrochloric acid HNO 3 – nitric acid H 2 SO 4 – sulfuric acid

Summing up: Covalent bonding occurs when two nonmetals share electrons to fill their valence energy level. Never use valence to determine the formula there isn’t any valence Since the two atoms share electrons, they do not take on a charge Always use prefixes in the names NEVER REDUCE Atoms combine to form individual molecules.

Ionic Formula (review) The 5 Steps for writing an ionic compound formula: (I) Write the symbols of the two elements. (II) Write the valence of each as superscripts. (III) Drop the positive and negative signs. (IV) Crisscross the superscripts so they become subscripts. (V) Reduce when possible.

Summing up: Ionic bonding occurs between a metal and a nonmetal. Metals lose all their valence e- and become cations. Nonmetals gain e- to fill their valence level and become anions. Always crisscross valences and reduce to determine the formulas of ionic compounds Do not use prefixes in the names. Ions form a crystalline lattice.

Acid Nomenclature No Oxygen w/Oxygen An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

Acid Nomenclature Flowchart

Acid Nomenclature • HBr (aq) • No oxygen, -ide hydrobromic acid carbonic acid sulfurous acid • H 2 CO 3 • Has oxygen, -ate • H 2 SO 3 • Has oxygen, -ite

Acid Nomenclature • hydrofluoric acid • 2 elements H+ F- HF (aq) • sulfuric acid • 3 elements, -ic H+ SO 42 - H 2 SO 4 • nitrous acid • 3 elements, -ous H+ NO 2 - HNO 2

Name Them! HI (aq) HCl H 2 SO 3 HNO 3 HIO 4

Write the Formula! Hydrobromic acid Nitrous acid Carbonic acid Phosphoric acid Hydrotelluric acid

Nomenclature Summary Flowchart