Covalent Structures EQ: How are the chemical formulas and chemical names written for covalent molecules? How do you draw VSEPR diagrams for covalent compounds? What are the names and bonding/lone pairs for each molecular shape?

Ionic Bonding Ionic bonds occur between a metal and a nonmetal, or between a positively charged particle(cation) and a negatively charged particle (anion). Ionic bonds involve a transfer of electrons. Can you identify which of the following are joined by ionic bonds? NaCl - K3N - MgBr2 CO2 - N2 - Al2O3

Covalent Bonding Covalent bonds occur between two nonmetals. A molecule is formed when two or more atoms bond covalently. Covalent bonds involve sharing of electrons.

Diatomic Molecules Certain elements occur in nature as diatomic molecules and not as single atoms (more stable as the molecule) Examples: H2, N2, O2, F2, Cl2, Br2, I2 Diatomic Molecules are bonded together by covalent bonds.

Naming Molecular Compounds The first element written in the formula is always written first, using the element name. The second element is named using the root of the element and the suffix “-ide”. Prefixes are used to indicate the number of atoms of each type that are present in the compound. Exception: Do not use the prefix mono- for the first element Drop the final letter of the prefix when the element name begins with a vowel Common Names: Ozone O3, Methane CH4, Hydrogen peroxides H2O2, Water H2O, Ammonia NH3

Table 1: Common Prefixes Used in Covalent Compounds Number of atoms Prefix 1 Mono- 6 Hexa- 2 Di- 7 Hepta- 3 Tri- 8 Octa- 4 Tetra- 9 Nona- 5 Penta- 10 Deca-

Covalent Names Common Names: Ozone O3 Methane CH4 Hydrogen peroxides H2O2 Water H2O Ammonia NH3

Naming Carbon dioxide CO2: ________________________________ SO2: ________________________________ S2O3: _______________________________ N2O: _______________________________ PCl5: ________________________________ Sulfur dioxide Disulfur trioxide Dinitrogen monoxide Phosphorous pentachloride

Formula Writing Selenium hexafluoride: ___________ Disilicon hexabromide: __________ Diboron monosilicide: __________ Iodine pentafluoride: ________ Hexaboron monosilicide: ________ SeF6 Si2Br6 B2Si IF5 B6Si

Drawing VSEPR Examples CO2 BF3 3. CH4 4. NH3 5. H2O Determine the total number of valence electrons for the compound. Note: Neg/Pos charge will change # electrons Ex: NO3- Choose a central atom (least electronegative) and surround with remaining atoms as outer atoms. H, F, Br, Cl, and I are outer atoms Connect central atom to outer atoms w/a single bond (2 electrons/shared pair) & subtract electrons used Place remaining electrons on outer elements to fill valence shell, any remaining electrons will be placed on the central atom. Make double/triple bonds if necessary All atoms (except H) prefer to have 8 valence e-. Exceptions to this rule are: B – electron deficient, typically only has 6 e– P – can have 10 e– (in compounds such as PCl5) S – can have up to 12 e– (in compounds such as SF6)

Bonds Single: Double: Triple : Consists of 1 sigma bond Weakest bond Longest bond Double: Consists of 1 sigma and 1 pi bond Triple : Consists of 1 sigma and 2 pi bonds Strongest bond Shortest length

Polarity Polar: “opposite ends” Nonpolar: “same ends” Ionic compounds: Positive & Negative ends Polar Covalent: Partially Positive & Negative ends Unequal sharing of electrons = Dipole Ex: H2O Nonpolar: “same ends” Nonpolar Covalent: equal sharing of electrons Dipole moments cancel out Ex: CO2

Resonance structures: Bracket the structure [ ] Indicates resonant bonds with dotted line Polyatomic Ions: Indicate charge top right exterior of bracket

Practice Problems: Draw and Identify CO32- SiS2 OF2

Practice Problems: Draw and Identify PCl3 NH4+ CH3Cl SCl2

Homework Check 8. Nitrogen trifluoride_______ 9. calcium phosphate_______ 10. Phosphoric acid________ 11. aluminum phosphide____ 12. iron(III) sulfide_____ 13. diphosphorus trioxide___ 1. HNO2___________________ 2. KClO2 ___________________ 3. FeCl2___________________ 4. PCl3____________________ 5. H2S_____________________ 6. K3PO3___________________ 7. SO3______________________