Molecular Compounds and their Covalent Bonds the next new chemistry idea!

Molecular Compounds who - nonmetallic elements how - shared electrons between atoms not always equally why - each atom wants a complete octet what type of bond ≡ covalent bond where - majority of biological molecules

Covalent bonds – strong vs strong Attractive forces between atoms in molecules Usually involving nonmetal elements in groups 4A, 5A, 6A, and 7A Involve sharing electrons so every atom gets to be “noble” for a bit

Single Covalent Bonds It’s all about sharing electrons H2 1S1 + 1S1

Covalent bond shorthand Single covalent bonds (1 shared e pair) H : H Lewis dot configuration H - H structural formula molecular shape

Lewis Dot Rules for Molecular Compounds Look up the Z’s of each atom Determine # of valence electrons for each atom Write element symbols and place 1 e pair between the central and the adjacent atom Place remaining e pairs so that there are 4 e pairs around each outer atom Make sure total number of valence electrons are accounted for, if not. . . Place any extra e’s around central atom

Case 1: Molecules with a Single Covalent Bond Br2

Case 2: Molecules with Single Covalent Bonds CH4 IN this case one of the 2s carbon orbitals is promoted to a p orbital

Side bar – Who’s in the Middle? atom with a subscript of “1” or atom with the smallest subscript

Case 3: Molecules with Single Covalent Bonds NH3 IN this case one of the 2s carbon orbitals is promoted to a p orbital

Practice – Single Covalent Bonds PCl3 H2O OF2

then there’s . . . Double and Triple Covalent Bonds Some atoms share more than one pair of electrons Double covalent bonds share 2 pairs of electrons Triple covalent bonds share three pair of electrons

Double Covalent Bonds O2 CO2

Double and Triple Bonds C2H4 C2H2

Coordinate Covalent Bonds One atom donates both bonding electrons CO NH4+1 Most polyatomic ions contain covalent and coordinate covalent bonds

Covalent Compound Practice SO2 SO3 N2O H3O+ SO3-2

Which Bond – When? it’s all about Electronegativity Definition – the “grabbiness” of an atom for an electron; the more grabby, the greater the EN value ex, F = 4.0; Na = 0.9; C = 2.5; H = 2.1; O = 3.5 Use EN difference to determine bond type Ionic bonds – EN difference ≥ 1.5 Covalent Bonds - EN Difference < 1.5

Covalent Bond Polarity Nonpolar Covalent bonds – equal sharing 0.0 < Electronegativity difference < 0.4 Polar Covalent Bond – unequal sharing 0.4 < Electronegativity difference < 1.5 Line becomes arrow from positive to negative

Practice – Which Bond Type? Chemical Bond EN difference I, PC, NPC H-F |2.1 – 3.98|= 1.88 I C-H |2.55 – 2.1|= 0.45 NPC Cl-O K-Cl O-H C-O S-O Br-Br

Molecular Polarity

Molecular Polarity examples CH4 CH3Cl HCl NH3 H2O

Ionic cf Covalent Compounds

Ionic cf Covalent Compounds Property Ionic Compound Molecular Compound Representative Unit Bond Type Element Groups Physical State Melting Point Solubility in water Electrical Conductivity