Covalent Bonds: Notes 5-3 Key Ideas: 1. What holds covalently boned atoms together? 2. What are the properties of molecular compounds? 3. How does unequal sharing of electrons affect molecules? - + + -

COVALENT BOND A force that bonds two atoms together by a sharing of electrons Each pair of shared electrons creates a bond Usually occurs between atoms of non-metals H O H Example – Water (H2O) - - - - + - + + - - - - -

How Covalent Bonds Form

How Covalent Bonds Form The oxygen atom in water and the nitrogen atom in ammonia each have eight valence electrons as a result of forming covalent bonds with hydrogen atoms.

How Covalent Bonds Form Double and triple bonds can form when atoms share more than one pair of valence electrons.

Types of Covalent Bonds Different covalent bond types share a different number of valence electrons Water (H2O) Carbon Dioxide (CO2) Nitrogen (N2) Single Bonds Share 2 Electrons Double Bonds Share 4 Electrons Triple Bonds Share 6 Electrons

Unequal Sharing : Polar Covalent Bond The unequal sharing of valence electrons between two atoms that gives rise to negative and positive regions of electric charge Results from an atom’s electronegativity – the ability to attract electrons to itself A molecule in which the polar covalent bonds does not cancel out will be polar. + + + + Electron Cloud Bonded hydrogen atoms showing equal sharing of electrons Hydrogen and fluorine bond with an unequal sharing of electrons Why do you think the two Hydrogen atoms share equally, but the Hydrogen and fluorine do not?

Unequal Sharing of Valence Electrons Versus Equal Sharing In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar. Fluorine forms a nonpolar bond with another fluorine atom. A covalent bond is called nonpolar if the atoms equally share one or more pairs of electrons

Unequal (Polar) Versus Equal (Nonpolar) Sharing of Electrons A water molecule is a polar molecule because of its bent shape. A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape.

Results of Bonding Molecule A neutral group of two or more non-metal atoms held together by covalent bonds Type: Diatomic - molecules consisting of two atoms of the same element bonded together Examples: H2, F2, O2, N2 Compound A pure substance composed of two or more different elements (atoms) that are chemically combined Examples: CO, NO2, NaCl

Molecule, Compound, or Both? Nitrogen Cl2 Chlorine NO2 Nitrogen Dioxide CO2 Carbon Dioxide O2 Oxygen CH4 Methane H2 Hydrogen NO Nitric Oxide H2O Water