CHAPTER 9 COVALENTCOMPOUNDS

PROPERTIES OF COVALENT COMPOUNDS COMPARISON IONIC COVALENT IONIC COVALENT transfer of e-’s sharing of e-’s transfer of e-’s sharing of e-’s metals/nonmetals nonmetals metals/nonmetals nonmetals crystal lattices molecules crystal lattices molecules mostly solids solids, liquids, gases mostly solids solids, liquids, gases conductors when non-conductors conductors when non-conductors molten/dissolved molten/dissolved high m.p./b.p. low m.p./b.p. high m.p./b.p. low m.p./b.p.

STRUCTURES COVALENT BONDING Based on electronegativity Electrons are shared. Electrons are shared. NONPOLAR COVALENT BOND electrons are shared equally---no difference in electronegativity (0 % difference) The 7 diatomic elements: Br 2 I 2 N 2 Cl 2 H O F Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

NOF Cl Br I H C. Molecular Nomenclature The Seven Diatomic Elements Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2

Covalent bonding continued: POLAR COVALENT BONDS difference in electronegativity and electrons are not shared equally difference in electronegativity and electrons are not shared equallyBASICALLY if there are 2 different nonmetals involved in the bond, it is a polar covalent bond if there are 2 different nonmetals involved in the bond, it is a polar covalent bond

PRACTICE Identify the type of bonding 1. BCl 3 2. CaO 3. Cl 2 4. NH 4. NH 3 5. NaCl 6. SO 6. SO 2 7. CH 7. CH 4 1. polar covalent 2. ionic 3. nonpolar covalent 4. polar covalent 5. ionic 6. polar covalent 7. polar covalent

* PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-NUMBER C. Molecular Nomenclature

Guidelines for Naming Covalent Compounds Prefix System: Binary Covalent means---2 nonmetals Prefix System: Binary Covalent means---2 nonmetals 1. Less electronegative atom comes first. 2. Add prefixes to indicate # of atoms for each element. Never use mono- prefix on first element. 3. Change the ending of the second element to -ide.

NAME THESE CO CO N 2 O N 2 O P 2 O 5 P 2 O 5 IF 7 IF 7 SCl 6 SCl 6 S 4 N 2 S 4 N 2 carbon monoxide carbon monoxide dinitrogen monoxide dinitrogen monoxide diphosphorous pentoxide diphosphorous pentoxide iodine heptafluoride iodine heptafluoride sulfur hexachloride sulfur hexachloride tetrasulfur dinitride tetrasulfur dinitride

WRITING FORMULAS FOR COVALENT COMPOUNDS The name tells you the formula. The name tells you the formula. Just use the prefixes. Just use the prefixes.

WRITE THESE chlorine monofluoride chlorine monofluoride nitrogen trichloride nitrogen trichloride boron trifluoride boron trifluoride carbon disulfide carbon disulfide nitrogen monoxide nitrogen monoxide dichlorine heptoxide dichlorine heptoxide ClF ClF NCl 3 NCl 3 BF 3 BF 3 CS 2 CS 2 NO NO Cl 2 O 7 Cl 2 O 7

Homework page , 96, 97a-c, 98a&c Name the following: Name the following: NF 3 NF 3 NO NO SO 3 SO 3 SiF 3 SiF 3 SeO 2 SeO 2 SeO 3 SeO 3 N 2 F 7 N 2 F 7 S 4 N 4 S 4 N 4 Write the formula: Write the formula: Sulfur difluoride Silicon tetrachloride Carbon tetrafluoride Silicon dioxide Chlorine trifluoride

DRAWING STRUCTURAL DIAGRAMS 1. Find total # of valence e Arrange atoms - singular atom is usually in the middle. 3. Form bonds between atoms (2 e - ) Distribute remaining e - to give each atom an octet (recall exceptions) If there aren’t enough e - to go around, form double or triple bonds.

DRAWING STRUCTURAL DIAGRAMS 1. Find total # of valence e Arrange atoms - singular atom is usually in the middle. 3. Form bonds between atoms (2 e - ) Distribute remaining e - to give each atom an octet (recall exceptions) If there aren’t enough e - to go around, form double or triple bonds.

MOLECULAR SHAPES Molecules have shapes based on how valence electrons are shared or unshared Molecules have shapes based on how valence electrons are shared or unshared VSEPR theory Valence Shell Electron Pair Repulsion theory VSEPR theory Valence Shell Electron Pair Repulsion theory

TO DETERMINE MOLECULAR SHAPE Use VSEPR (valence shell electron pair repulsion) rules: 1) Draw the Lewis dot structure for the molecule 2) Identify the central atom 3) Count total # of electron pairs around the central atom 4) Count # of bonding pairs of electrons around the central atom 5) Count # of lone pairs of electrons around the central atom 6) Look at summary chart, identify shape

MOLECULAR POLARITY TO DETERMINE THE POLARITY OF A MOLECULE, not a bond, you must know the type of bond and the shape. TO DETERMINE THE POLARITY OF A MOLECULE, not a bond, you must know the type of bond and the shape. POLAR MOLECULES must meet 2 criteria: POLAR MOLECULES must meet 2 criteria: Must have a polar covalent bond AND Must have a polar covalent bond AND Must have an asymmetrical shape: trigonal pyramidal, angular, or 2 element linear Must have an asymmetrical shape: trigonal pyramidal, angular, or 2 element linear If both criteria are not met, it is not a polar molecule, it is either a nonpolar molecule or an ionic compound. If both criteria are not met, it is not a polar molecule, it is either a nonpolar molecule or an ionic compound.

RESONANCE STRUCTURES More than one valid structure can be drawn More than one valid structure can be drawn Differ only in position of electron pairs Differ only in position of electron pairs Occurs quite often in polyatomic ions Occurs quite often in polyatomic ions s/MERLOT/drawlewis/dls.html s/MERLOT/drawlewis/dls.html s/MERLOT/drawlewis/dls.html s/MERLOT/drawlewis/dls.html See page 256 See page 256