Ch. 6 & 7 - Covalent Bonding

Ch. 6 & 7 - Covalent Bonding • Molecular or Covalent Compounds(p. 164 – 175, 211 – 213) • Sharing Valence Electrons • Nonmetals Only

Molecules Oxygen molecule, O2 Water molecule H2O Sucrose molecule, C12H22O11

Molecular Nomenclature • Prefix System (binary compounds) 1. Less e-neg atom comes first. 2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element. 3. Change the ending of the second element to -ide.

PREFIX mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca- NUMBER 1 2 3 4 5 6 7 8 9 10 Molecular Nomenclature

Name These • N2O • NO2 • Cl2O7 • CBr4 • CO2 • BaCl2

Write formulas for these • diphosphorus pentoxide • tetraiodine nonoxide • sulfur hexaflouride • nitrogen trioxide • Carbon tetrahydride • phosphorus trifluoride • aluminum chloride • h.w. p. 235 # 10,11

The Terminology • The smallest entity of a covalent compound is called a ___________. • A bond is formed when one pair of electrons is shared. • Some elements,( nitrogen, carbon, and oxygen) can share more than one pair of electrons and form bonds.

The Terminology • A bond is produced when two pairs of electrons are shared. • A bond is produced when three pairs of electrons are shared. • Covalent bonding can also occur between two atoms of the same nonmetal. This forms a molecule.

Diatomic Elements • There are seven diatomic elements: H2 N2 O2 F2 Cl2 Br2 I2 H N O F Cl Br I

Ne Lewis Structures • Octet Rule • Most atoms form bonds in order to obtain 8 valence e- • Full energy level stability ~ Noble Gases

Lewis Structures • Electron dot notations that represent compounds. • Pairs of dots represent shared electrons between bonded atoms • And unshared pairs or lone pairs that belong exclusively to one atom

Drawing Lewis Structures • Determine the type and number of atoms in the molecule. • Write the electron dot notation for each atom. • Determine the total number of valence electrons in the atoms

Drawing Lewis Structures • Arrange the atoms to form a skeleton structure for the molecule. If carbon is present, it is central - otherwise the least electronegative element is central. (hydrogen is never central) Then connect the atoms by electron pair bonds.

Drawing Lewis Structures • Add lone pairs so that hydrogen has a duet and each other nonmetal has an octet • Count the electrons to be sure that the number of valence electrons used is equal to the number available.

Drawing Lewis Structuressingle bonds • CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- F F C F F Each wants an octet: 1 C × 8e- = 8e- 4 F × 8e- = 32e- 40e- -32e- must share 8e-

Practice Single Bonds • CH3I • H2 • F2 • H2O • HCl • NH3 • H2S • CH4 H.W. p. 197 # 39

Drawing Lewis Structuresmultiple bonds • Multiple bonds between nitrogen, carbon, and oxygen are possible

Drawing Lewis Diagramsmultiple bonds • CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- OCO Each wants an octet: 1 C × 8e- = 8e- 2 O × 8e- = 16e- 24e- -16e- must share 8e-

Practice Multiple Bonds • C2H2 • CH2O • HCN • CH4 • CCl4 h.w. p. 197 #41

Polyatomic Ions ( are held together by covalent bonds) • To find total # of valence e-: • Add 1e- for each negative charge. • Subtract 1e- for each positive charge. • Place brackets around the ion and label the charge.

Polyatomic Ions • ClO4- 1 Cl × 7e- = 7e- 4 O × 6e- = 24e- 31e O O Cl O O + 1e- 32e- Each wants an octet: 1 Cl × 8e- = 8e- 4 O × 8e- = 32e- 40e- -32e- must share 8e-

Polyatomic Ions • NH4+ 1 N × 5e- = 5e- 4 H × 1e- = 4e- 9e- H H N H H - 1e- 8e- 4 H × 2e- = 8e- 1 N × 8e- = 8e- 16e- - 8e- must share 8e-

Practice Polyatomic Ions • Phosphate • Sulfate • Nitrate • Chlorate • Chlorite • Hypochlorite h.w. p. 197 #42

Resonance Structures • Molecules that can’t be correctly represented by a single Lewis diagram. • Actual structure is an average of all the possibilities. • Show possible structures separated by a double-headed arrow.

Acids • Acids • Compounds that form H+ in water. • Formulas usually begin with ‘H’. • Examples: • HCl – hydrochloric acid • HNO3 – nitric acid • H2SO4 – sulfuric acid

Naming Binary acids • Includes hydrogen and another nonmetal • use the prefix hydro- and change -ide to -ic acid • HCl - hydrogen ion and chloride ion • hydrochloric acid • H2S hydrogen ion and sulfide ion • hydrosulfuric acid

Naming Oxyacids • Includes hydrogen and a polyatomic ion containing oxygen • Do not include hydro- in the name. • If the polyatomic ion ends in -ate, change it to -ic acid • HNO3 - Hydrogen and nitrate ions • Nitric acid • If the polyatomic ion ends in -ite, change it to -ous acid • HNO2 Hydrogen and nitrite ions • Nitrous acid

Acid Nomenclature binary acids oxyacids

Name these acids • HF • H3P • H2SO4 • H2SO3 • HCN • H2CrO4

Writing Formulas Binary Acids • hydro- nonmetal root-ic acid • Will include hydrogen and a nonmetal • Criss-cross to make the charges cancel out. (the charge on the other element becomes the subscript for hydrogen) • Ex. Hydrochloric acid • Hydrogen and chloride HCl

Writing Formulas Oxyacids • If acid end in –ic, then polyatomic ion ends in –ate. • If acid end in –ous, then polyatomic ion ends in –ite. • Criss-cross to make the charges cancel out. (the charge on the polyatomic ion becomes the subscript for hydrogen) • Ex. Iodic acid • hydrogen and iodate HIO3

Write formulas for these • hydrobromic acid • hydrofluoric acid • phosphoric acid • bromic acid • Hypochlorous acid • hydroiodic acid • acetic acid • carbonic acid • phosphorous acid • Oxalic acid h.w. p. 235 #14,15

Bell Ringer p. 235 # 12

Ch. 6 & 7 - Covalent Bonding