UNIT 3 Molecules

Chemistry happens among the electrons. Bonds occur between atoms as a result of interactions among the electrons. When the interaction is to share electrons, the bond is said to be covalent and the entity formed is a molecule. Formed from nonmetals. H H – O – H Structural formula O This is a molecule of water. H 2 O chemical (molecular) formula H

Properties of Molecular Compounds held together by covalent bonds form discrete molecules soft low melting point generally nonconductive includes all organic compounds held together by ionic bonds do NOT form discrete molecules hard, rigid, brittle high melting points conductive when melted or when dissolved in water Properties of Ionic Compounds

Diatomic Molecules When two atoms of the same element form a covalent bond, the result is a diatomic molecule. Seven nonmetal elements exist as diatomic molecules: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 HH+ H – H (H 2 ) Hydrogen exists naturally as a diatomic molecule.

118 1 H2H N2N2 O2O2 F2F Cl 2 4 Br 2 5 I2I2 6 7 Elements that exist as diatomic molecules

Molecular Formulas A molecular formula shows the number and type of elements in a molecule, e.g., the molecular formula for glucose is C 6 H 12 O 6. An empirical formula gives only the relative number and type of elements, e.g., the empirical formula for glucose is CH 2 O. When only one atom of an element is present, no subscript is written. The molecular formula for water is H 2 O. The empirical formula for water is H 2 O.

Nomenclature (Naming) Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Naming Binary Molecular Compounds 1. Name the element farther to the left on the periodic table. (Exception: O is written last unless it’s bonded to F.) 2. If both elements are in the same group, name the lower one first. 3. Give the anion name of the second element (-ide ending). 4. Greek prefixes give the number of each atom in the formula. mono-1 di-2 tri-3 tetra-4 penta-5 hexa-6 hepta-7 octa-8 nona-9 deca-10 COcarbon monoxide CO 2 carbon dioxide P 4 O 10 tetraphosphorus decaoxide N2ON2Odinitrogen monoxide

Nomenclature (Naming) Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Acids Are compounds that produce hydrogen ions (H + ) in water. They are molecular compounds that ionize in water. “aq” is short for aqueous which means water. HCl(g)  H + (aq) + Cl - (aq) or, more correctly, the hydronium ion ( H 3 O + ) HCl(g) + H 2 O  H 3 O + (aq) + Cl - (aq) In general, acids are compounds of with a formula of HX, H 2 X, H 3 X, etc. where X can be an anion from Group 6A or 7A or X can be an oxyanion.

Naming Acids with an Anion Name Which Ends in –ide NOT IN SOLUTION, the name of the acid is just the name of the binary molecular compound: HCl(g) is hydrogen chloride IN SOLUTION, replace hydrogen with hydro- change –ide to –ic add the word “acid” HCl(aq) is hydrochloric acid

Nomenclature (Naming) Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Naming Ternary (Acids with an Anion That Ends in –ate or -ite) Modify the oxyanion name: -ate anion becomes –ic nitrate becomes nitric -ite anion becomes –ous nitrite becomes nitrous then add the word “acid” sulfuric acid sulfurous acid sulfate: SO 4 2- H 2 SO 4 sulfite: SO 3 2- H 2 SO 3 perchlorate: ClO 4 - HClO 4 chlorate: ClO 3 - HClO 3 chlorite: ClO 2 - HClO 2 hypochlorite: ClO - HClO perchloric acid chloric acid chlorous acid hypochlorous acid

Names of Common Chemicals common name or use chemical nameformula water H2OH2O ammonia, window cleaner ammoniaNH 3 (aq) natural gasMethane (70%)CH 4 vinegaracetic acid (5% solution) CH 3 COOH or HC 2 H 3 O 2

Names of Common Chemicals common name or use chemical nameformula hydrogen peroxide H2O2H2O2 drinking alcoholethanol, ethyl alcoholC 2 H 5 OH rubbing alcoholisopropyl alcohol, 2- propanol CH 3 CH(OH)CH 3 nail polish removeracetoneCH 3 COCH 3