Presentation on theme: "Bond and Molecular Polarity Courtesy of Mr. Christopherson."— Presentation transcript:
Bond and Molecular Polarity Courtesy of Mr. Christopherson
Polar Bonds l When the atoms in a bond are the same, the electrons are shared equally. l This is a nonpolar covalent bond. l When two different atoms are connected, the atoms may not be shared equally. l This is a polar covalent bond. l How do we measure how strong the atoms pull on electrons?
Electronegativity l A measure of how strongly the atoms attract electrons in a bond. l The bigger the electronegativity difference the more polar the bond. 0.0 - 0.5 Covalent nonpolar 0.5 - 1.0 Covalent moderately polar 1.0 -1.7 Covalent polar >1.7 Ionic
How to show a bond is polar l Isn’t a whole charge just a partial charge means a partially positive means a partially negative l The Cl pulls harder on the electrons l The electrons spend more time near the Cl H Cl
Polar Molecules l Molecules with a positive and a negative end l Requires two things to be true ¬ The molecule must contain polar bonds This can be determined from differences in electronegativity. Symmetry can not cancel out the effects of the polar bonds. Must determine geometry first.
Is it polar?.. H Cl Polar HH O FF B F Nonpolar H H H N Polar Nonpolar FF Cl F F F Xe FF NonpolarPolar Cl C H C H H XeF 4 CCl 4 CH 3 Cl HClH2OH2O BF 3 NH 3
Intermolecular Forces What holds molecules to each other?
Intermolecular Forces l They are what make solid and liquid molecular compounds possible. l The weakest are called van derWaal’s forces - there are two kinds l Dispersion forces l Dipole Interactions –depend on the number of electrons –more electrons stronger forces –bigger molecules
l Depend on the number of electrons l More electrons stronger forces l Bigger molecules more electrons fluorine (F 2 ) is a gas bromine (Br 2 ) is a liquid iodine (I 2 ) is a solid Dipole interactions
l Occur when polar molecules are attracted to each other. l Slightly stronger than dispersion forces. l Opposites attract but not completely hooked like in ionic solids.
Dipole interactions l Occur when polar molecules are attracted to each other. l Slightly stronger than dispersion forces. l Opposites attract but not completely hooked like in ionic solids. HFHF HFHF
Hydrogen bonding l Are the attractive force caused by hydrogen bonded to F, O, or N. l F, O, and N are very electronegative so it is a very strong dipole. l The hydrogen partially share with the lone pair in the molecule next to it. l The strongest of the intermolecular forces.
Hydrogen Bonding H H O ++ -- ++ H H O ++ -- ++
Hydrogen bonding H H O H H O H H O H H O H H O H H O H H O