3. Chemical Bonding
3.9. Dipoles. Polar and non-polar Molecules
Polar covalent bonds may cause dipoles to form
In the hydrogen chloride molecule, the bond between the hydrogen atom and the chlorine atom is polar.
- Cl is more electronegative than H
- Electrons spend more time with Cl than with H
- The molecule becomes a dipole: δ+H–Clδ–
Methane, CH4, is not a dipole
The carbon and the hydrogen atoms bind to each other with electron pair bonds (covalent bonds).
- The electron pairs are as far from each other as possible.
- The electron pairs point into the corners of a tetrahedron (a triangular pyramid).
Ammonia, NH3, is a dipole
The nitrogen and the hydrogen atoms bind to each other with polar electron pair bonds (covalent bonds).
- One electron pair is non-binding ⇒ The ammonia molecule is a trigonal pyramid.
- Nitrogen is more electronegative than hydrogen.
- The ”nitrogen end” is more negatively charged than the ”hydrogen end”.
Water, H2O, is a dipole
The oxygen and the hydrogen atoms bind to each other with polar electron pair bonds (covalent bonds).
- Two electron pairs are non-binding ⇒ The water molecule is bent.
Oxygen is more electronegative than hydrogen.
- The ”oxygen end” is more negatively charged than the ”hydrogen end”.
- The molecule becomes a dipole.
Carbon dioxide, CO2, is not a dipole
Because of the two areas with high electron density, the CO2 molecule becomes linear.
- Oxygen is more electronegative than carbon.
- One of the ”oxygen ends” is NOT more negatively charged than the other one ⇒ carbon dioxide is not a dipole.
How can you tell if a molecule is a dipole or not?
The VSEPR theory in short (explained in greater detail on this page):
- Look at the structure!
- Draw a Lewis formula.
- Count the areas with high electron density.
- Place the high-density areas as far apart from each other as possible – in 3D.
Ethylene glycol – Not necessarily a dipole, but still polar.
In the above configuration, the ethylene glycol molecule is not a dipole, because the positive and negative charges coincide with the center of the molecule.
It is, however, polar.
- The OH groups make the molecule polar.
- NHx groups also make molecules polar.
Glucose and hexane
- 1. States of Matter. The Atom and the Periodic Table
- 1.1. Matter. States of Matter
- 1.2. Elements and Chemical Compounds. Pure Substances and Mixtures
- 1.3. The Birth of Chemistry
- 1.4. Atomic Theory. The Atomic Model
- 1.5. Atomic Number, Mass Number, and Atomic Mass
- 1.6. Electron Configurations
- 1.7. Beyond Bohr's Atomic Model
- 1.8. Redox Reactions
- 1.9. The Structure of the Periodic Table
- 1.10. The Noble Gases
- 1.11. The Alkali Metals and the Halogens
- 1.12. The Alkaline Earth Metals and the Oxygen Group
- 1.13. A Few of the Elements in Group 13, 14, and 15
- 2. Chemical Calculations
- 2.1. Physical Quantity, Magnitude, and Units
- 2.2. Atomic Mass, Molecular Mass, and Unit Mass
- 2.3. Amount of Substance, Molar Mass, and Mass
- 2.4. Stoichiometry. Conservation of mass
- 2.5. Water of Crystallization
- 2.6. Calculating the Formula of a Chemical Compound
- 2.7. From Empirical to Molecular Formulas
- 2.8. Equivalent Amounts of Substance and Masses
- 2.9. Gases and Pressure
- 2.10. Concentrations
- 2.11. Dilutions
- 2.12. Yield
- 2.13. Limiting Reactants
- 3. Chemical Bonding
- 3.1. How Ionic Compounds are Formed
- 3.2. Precipitations
- 3.3. Names and Formulas of Ionic Compounds
- 3.4. Ionic Bonds
- 3.5. Properties of Ionic Compounds
- 3.6. Metal Bonding
- 3.7. Covalent Bonding
- 3.8. Polar Covalent Bonding
- 3.9. Dipoles. Polar and non-polar Molecules
- 3.10. The VSEPR Theory
- 3.11. Hydrogen Bonding. The Peculiar Water
- 3.12. Equals Solves Equal
- 3.13. Solubility of Gases in Water
- 3.14. Solubility of Salts in Water
- 4. Thermochemistry
- 5. Chemical Equilibrium
- 5.1. Reaction Rates
- 5.2. The Law of Mass Action
- 5.3. Calculations on Chemical Equilibrium
- 5.4. Heterogenous Equilibria. Solubility Product
- 5.5. Is the System at Equilibrium? The Reaction Quotient Q
- 5.6. Changing the Concentrations in a System in Equilibrium.
- 5.7. Diluting or Compressing Systems in Equilibrium, or Changing the Temperature
- 6. Acids and bases
- 7. Oxidation and Reduction
- 8. Electrochemistry
- 9. Organic Chemistry
- 9.1. Alkanes
- 9.2. Chain Isomers. Nomenclature
- 9.3. Haloalkanes
- 9.4. Nucleophilic Substitution
- 9.5. Alkenes
- 9.6. Electrophilic Addition. Markovnikov’s Rule
- 9.7. Elimination
- 9.8. Alkynes
- 9.9. Arenes and Aromatic Compounds
- 9.10. Alcohols
- 9.11. Oxidation of Alcohols
- 9.12. Aldehydes and Ketones
- 9.13. Thiols and Disulfides
- 9.14. Ethers
- 9.15. Amines
- 9.16. Nitro Compounds and Organic Nitrates
- 9.17. Carboxylic Acids
- 9.18. More on Carboxylic Acids
- 9.19. Stereoisomerism
- 9.20. Esters
- 9.21. Lipids
- 9.22. Mono-, Oligo-, and Polysaccharides
- 9.23. Amino Acids
- 9.24. Nucleotides
- 10. Biochemistry
- 10.1. Proteins
- 10.2. Enzymes
- 10.3. Catabolic Processes
- 10.4. Carrier Molecules
- 10.5. Glycolysis
- 10.6. Beta-oxidation
- 10.7. The Citric Acid Cycle
- 10.8. The Metabolism of Amino Acids
- 10.9. The Electron Transport Chain
- 10.10. Anabolic Processes
- 10.11. Gluconeogenesis and Fatty Acid Synthesis
- 10.12. DNA: Structure and Function
- 11. Analytical chemistry