Spring 2016

 There are two types of covalent bonds ◦ Nonpolar Covalent Bonds (share equally) ◦ Polar Covalent Bonds (share unequally)

 There are two types of covalent bonds ◦ Nonpolar Covalent Bonds (share equally) ◦ Polar Covalent Bonds (share unequally)

A Polar Covalent Bond is unequal sharing of electrons between two atoms (HCl) In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge

A Nonpolar Covalent Bond is equal sharing of electrons between two atoms (Cl 2, N 2, O 2 )

You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements Type of BondElectronegativity Difference Nonpolar Covalent 0  0.4 Polar Covalent 0.5  1.9 Ionic 2.0  4.0

What type of bond is HCl? (H = 2.1, Cl = 3.1) Your Turn To Practice N(3.0) and H(2.1) N(3.0) and H(2.1) H(2.1) and H(2.1) H(2.1) and H(2.1) Ca(1.0) and Cl(3.0) Ca(1.0) and Cl(3.0) Al(1.5) and Cl(3.0) Al(1.5) and Cl(3.0) Mg(1.2) and O(3.5) Mg(1.2) and O(3.5) H(2.1) and F(4.0) H(2.1) and F(4.0) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond.

No bond is purely ionic or covalent … they have a little bit of both characters When there is unequal sharing of electrons a dipole exists Dipole is a molecule that has two poles or regions with opposite charges Dipole is a molecule that has two poles or regions with opposite charges A dipole is represented by a dipole arrow pointing towards the more negative end A dipole is represented by a dipole arrow pointing towards the more negative end

P- Br P = 2.1 Br = 2.8 P –Br  +  - Practice H(2.1) – S(2.5) F(4.0) - C(2.5) C(2.5) - Si(1.8) N(3.0) – O(3.5)

Intermolecular attractions are weaker than ionic, covalent, and metallic bonds Besides ionic, metallic, and covalent bonds, there are also attractions between molecules There are 2 main types of attractions between molecules: Van der Waals and Hydrogen

 Van der Waals forces consists of the two weak attractions between molecules 1. dipole interactions – polar molecules attracted to one another 2. dispersion forces – caused by the motion of electrons (weakest of all forces)

Hydrogen Bonds are forces where a hydrogen atom is weakly attracted to an unshared electron pair of another atom

This other atom may be in the same molecule or in a nearby molecule, but always has to include hydrogen This other atom may be in the same molecule or in a nearby molecule, but always has to include hydrogen Hydrogen Bonds have about 5% of the strength of an average covalent bond Hydrogen Bonds have about 5% of the strength of an average covalent bond Hydrogen Bond is the strongest of all intermolecular forces Hydrogen Bond is the strongest of all intermolecular forces

A Network Solid contains atoms that are all covalently bonded to each other A Network Solid contains atoms that are all covalently bonded to each other A few solids that consist of molecules do not melt until the temperature reaches 1000ºC or higher called network solids (Example: diamond, silicon carbide) A few solids that consist of molecules do not melt until the temperature reaches 1000ºC or higher called network solids (Example: diamond, silicon carbide) Melting a network solid would require breaking bonds throughout the solid (which is difficult to do)