Lewis Structures, Molecular Geometry,

Polarity, Intermolecular Forces

Kelly Franks, Juliet Hurvich , Lauren Cunningham

LEWIS STRUCTURES

➔ The pair of dots between two symbols represents the shared pair of a covalent bond.

➔ Each fluorine atom is surrounded by three pairs of electrons that are not shared in bonds.

➔ An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom.

➔ Covalent Bonds are represented by dashes

➔ Valence Electrons: the outer level of electrons

➔ Resonance Structure: one of two or more Lewis structures for a single molecule can be drawn to represent a molecule

➔ Bond Energies: Single bond < Double bond < Triple bond

Key Terms & Tips:

1. Draw skeletal structure of compound showing what atoms are bonded to each other. Put least electronegative element in the center.

2. Count total number of valence e-. Add 1 for each negative charge. Subtract 1 for each positive charge.

3. Complete an octet for all atoms except hydrogen4. If structure contains too many electrons, form double and triple

bonds on central atom as needed.

DRAW, COUNT, COMPLETE, FORM

Lewis Structure Steps:

1. NF3

2. H2O

Examples:

Answers:

Nitrogen Trifluoride

Water

MOLECULAR GEOMETRY

VESPR Theory (Valence eletrron shell pair repulsion) -- used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion

Definitions

1. Identify the name and shape of the bond angles of perchlorate.

2. Identify the name and shape of the bond angles of phosphorus fluoride.

Sample Problems:

1. Tetrahedral, 109.5 degrees

2. trigonal bipyramidal, 120 and 90 degrees

Answers:

Polarity

● Polarity-- how equal bonding electrons are shared between elements

● Polar Bond or Polar Covalent Bond-- covalent bond with greater electron density around one of the two atoms

● Electronegativity-- the ability to attract electrons

Definitions:

● If the difference in electronegativities between atoms is:○ 0 to .3 = nonpolar covalent bond ○ .4 to 1.7 = polar covalent bond ○ greater than 1.7 = ionic bond

Determining Type of Bond

● usually soft and squishy● not soluble in water● can’t conduct electricity● low melting/boiling point

Properties of Covalent Bonds

● hard and brittle● tightly packed solids in a crystal lattice● usually soluble in water ● conducts electricity when dissolved● high melting points

Properties of Ionic Bonds

1) Classify NaCl as ionic, nonpolar covalent, or polar covalent.

2) Classify PCl3 as ionic, nonpolar covalent,

or polar covalent.

Questions

1) ionic

2) polar covalent

Answers

Intermolecular Forces

• Intermolecular Force- attractive force between molecules

• These forces hold atoms together

• If you have one type of force, you automatically have all the forces weaker than that one

Key Terms & Tips:

1. London Dispersion Forces

2. Dipole-Induced Forces

3. Dipole-Dipole Forces

4. Hydrogen Bonds

Forces Weakest to Strongest:

• also called Van Der Waals Forces

• attractive forces between 2 nonpolar molecules

• very brief interaction

London Dispersion Forces

• also called dispersion forces

• attractive forces that arise as a result of temporary dipoles induced in atoms or molecules

Dipole-Induced Forces

• attractive forces between polar molecules

• oppositely charged ends of the molecules will attract each other

Dipole-Dipole Forces

• hydrogen of one molecule attracted to the directly connected oxygen, nitrogen, or fluorine of another

• special kind of dipole-dipole bond

Hydrogen Bonds

• attractive forces between an ion and a polar molecule

• need to be 2 different types of molecules

Ion-Dipole Forces

1. Which of these molecules is capable of forming a hydrogen bond?a. MgO b. HF c. HCl d. NaF

2. What is the strongest intermolecular force in the molecule HCl?

3. What type of force is acted on CH4?

Questions:

1. b. HF

2. dipole-dipole

3. London Dispersion

Answers

http://quizlet.com/34556897/prybella-midyear-project-flash-cards/