Bond Types

Let’s Look At 3 Types of Bonds Ionic Polar Covalent (Molecular) Nonpolar Covalent (Molecular)

Remember Electronegativity? The tendency for an atom to attract electrons to itself in a bond The higher the value, the better it is at attracting electrons. The difference in the electronegativity values determines what type of bond will be formed.

Electronegativity Electronegativity is a scale from 0.7 (Cs) to 4.0 (F). Electronegativity generally increases across a period and decreases down a group.

Electronegativity Values Why don’t the noble gases have a value? They don’t attract electrons!

Ionic Bonds If the electronegativity difference is greater than 2.0, one atom will pull the electron completely away from other atom. The electrons are NOT shared. An Ionic Bond is formed as + and – attract. Electronegativity of Na is 0.9; Cl is 3.0. 3.0 – 0.9 = 2.1; difference > 2.0, so…Ionic!

Polar Covalent Bonds Covalent bonds share electrons The shared pairs are pulled, similar to a tug-of-war, between the nuclei of the atoms sharing the electrons. If the electronegativity difference is between 0.4 – 2.0, one side of the bond becomes slightly more negative and the other side becomes slightly more positive. This is a Polar Covalent Bond.

Polar Covalent Bonds ∂- ∂+ Cl H ∂+ ∂- Slightly The electronegativity of H is 2.1; Cl is 3.0. 3.0 – 2.1 = 0.9; difference is b/w 0.4 – 2.0, so…Polar Covalent!

Polar Covalent Bonds The electronegativity of O is 3.5; H is 2.1. 3.5 – 2.1 = 1.4 Difference is b/w 0.4 – 2.0, so… Polar Covalent!

Nonpolar Covalent Bonds When the atoms have equal pull, causing the electrons to be equally shared, the bond is Nonpolar Covalent. Neither side of the bond is even slightly positive or negative. The electronegativity difference is b/w 0.0 – 0.4. This is the type of bond that occurs between 2 atoms of the same element. (H2, O2, Cl2, etc.)

Nonpolar Covalent Bonds The electronegativity of H is 2.1. 2.1 – 2.1 = 0 The difference is b/w 0.0 – 0.4, so…Nonpolar!

3 Different Types of Bonds

Nonpolar or Polar Molecules We now know how to determine if the bond b/w atom and atom in a compound is polar or nonpolar. But…what about the whole molecule?

Nonpolar or Polar Molecules Draw the Lewis Structure. If the central atom has any unshared pairs, the molecule is polar.

Nonpolar or Polar Molecules If there are no unshared pairs on the central atom, look at the atoms around the central atom. If they are all the same, the molecule is nonpolar. If any one of them is different, the molecule is polar. In a 2-atom molecule, if the bond between the 2 atoms is polar then the whole molecule is polar.

Nonpolar or Polar Molecules H2O CO2 HCN CH3Cl Polar Nonpolar HCl Polar Polar N2 Nonpolar Polar

Attractions Between Molecules Van der Waals Forces Weaker than either the ionic or covalent bonds that form between atoms in a compound. Responsible for determining whether a compound is a liquid, gas, or solid 3 basic types from weakest to strongest (London) Dispersion forces Dipole interaction Hydrogen bonding

London Dispersion Forces Weakest of all molecular attractions Caused by the motion of electrons producing a temporary polarity. Strength of dispersion forces generally increases as # of electrons in the molecule increases. All molecules have these weak attractions.

London Dispersion Forces

Dipole Interaction Occurs when polar molecules are attracted to one another

Hydrogen Bonds Occurs b/w molecules in which H is covalently bonded to either O, N, or F, which are very electronegative Causes very polar molecules that are strongly attracted to each other Still only has about 5% of the strength of a covalent bond

Hydrogen Bonds + Very Important!! Reason ice is less dense than water Reason for the relatively high b.p. of water Responsible for the double helix of the DNA molecule O H + 2 lone pairs