Covalent Bonding

Review Reactivity Stability Chemical bond Lewis dot symbol

Covalent bond Bond in which two or more valence electrons are shared by two atoms Occurs with elements close to each other on the periodic table Between a nonmetal and a nonmetal Ex: H2O, NH3 (ammonia), CH4 (methane) What types of atoms are H and O (metal / nonmetal / semimetal) ? A covalent bond forms between what kinds of atoms?

3 Bond Types Single Covalent Bond Double Covalent Bond Triple Covalent Bond

Single Covalent Bonds Each atom shares one pair of electrons Total of 2 electrons shared H—H Lewis Structure

Double Covalent Bonds O2 Each atom shares two pairs of electrons Total of 4 electrons shared O2 Lewis Structure Label bonding electrons and lone pairs Oxygen molecule

Triple Covalent Bond N2 Each atom shares three pairs of electrons Total of 6 electrons shared Lewis Structure N2 Nitrogen molecule

Bond Length

Bond Lengths Triple bond < Double Bond < Single Bond

Bond Strength Bond Strengths Triple bond > Double Bond > Single Bond **Size: the smaller the atom, the stronger the bond (the further away from the nucleus the bonding electrons are, the more shielding there is making it easier to break the bond) Name the covalent bonds in order of decreasing bond strength.

Electronegativity

Electronegativity Ability of an atom to attract towards itself electrons in a chemical bond

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Most electronegative element! Trend

Covalent Bond nonpolar polar H—H H—Cl equal sharing of electrons Electron density is symmetrical Unequal sharing of electrons Electron density is asymmetrical (greater in one region) H—H H—Cl

Dipole moment e- poor e- rich F H d+ d- H F electron rich region electron poor region F H H F d+ d- BONDS, NOT MOLECULE!!!

Classification of bonds by difference in electronegativity Bond Type Nonpolar Covalent 0 < and < 2 Polar Covalent  2 Ionic Increasing difference in electronegativity Covalent share e- Polar Covalent partial transfer of e- Ionic transfer e-

For each bond, indicate the shift in electron density.

Practice Which of the following bonds is nonpolar covalent, which is polar covalent, and which is ionic? The bond in CsCl The bond in H2S The NN bond in H2NNH2

Substance Molecule Compound Two or more atoms chemically bonded together Two or more elements chemically bonded together

Molecules Diatomic HCl CO

Memorize Diatomic Elements elements that exist as two H2, O2, N2, Cl2, Br2, I2, F2 HONClBrIF “Magnificent 7” Unpack the title (di / atomic / molecule  2 / atoms / sharing electrons) **pronounced molecular hydrogen, molecular oxygen… Diatomic molecules with identical atoms are homonuclear diatomic molecules.

Molecules Polyatomic O3 C6H12O6 CO2 NH3

Compound Molecular C6H12O6 C2H5OH CO Binary Molecular Compound HCl CO2 NH3 CO2 Binary Molecular Compound

Intermolecular forces Attractive forces between molecules 3 types: London dispersion Dipole-dipole Hydrogen bond

London dispersion Attractive forces between atoms or nonpolar molecules that arise as a result of temporary dipoles induced by the atom or molecules movement Usually increase with molar mass weakest

Dipole-dipole Attractive forces between polar molecules due to their shift in electron density within their molecule Orientation of Polar Molecules in a Solid

Hydrogen Bond Special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and and electronegative O, N, F atom strongest A & B are N, O, or F A H … B or

Total Attraction Hydrogen bond Dipole-dipole Dispersion premium Hydrogen bond Dipole-dipole Dispersion *Like different TV channel packages basic

Molecular Compound Properties Tend to be soft solids, liquids, or gases at room temperature Low melting and boiling points Poor conductors of heat and electricity Non-electrolytes

A Lewis structure is a model that shows bonding electrons as lines and nonbonding electrons (lone pairs) as dots. 7e- 7e- 8e- 8e- F F + F single covalent bond lone pairs lone pairs F Lewis structure of F2 lone pairs lone pairs F single covalent bond

Lewis structure of water single covalent bonds 2e- 8e- 2e- H + O + H O H or Double bond – two atoms share two pairs of electrons 8e- 8e- 8e- O C or O C double bonds Triple bond – two atoms share three pairs of electrons 8e- N 8e- or N triple bond