Covalent Lewis Structures Notes

Covalent Compounds

  • Covalent compounds are formed through electron sharing, differing from ionic compounds.

  • They have low melting points and are often gases or liquids at room temperature, with some exceptions.

Properties of Covalent Compounds

  • Not conductive in liquid form.

  • Exceptions to typical behavior can exist (e.g., solid forms).

Exceptions to the Octet Rule

  • Hydrogen typically has fewer than 2 electrons.

  • Boron can have fewer than 8 electrons in its valence shell.

Drawing Covalent Lewis Structures

  1. Calculate total valence electrons.

  2. Place the least electronegative element in the center (H cannot be central).

  3. Connect atoms with a line (each line = 2 shared electrons).

  4. Fill the octets for surrounding atoms and place any remaining electrons on the central atom.

Lone Pairs in Lewis Structures

  • Lone pairs are unshared pairs of electrons that can affect molecular shape.

Here are some practice questions to help you test your knowledge of covalent compounds:

1. Fundamentals and Properties

  • Explain the difference between the formation of covalent bonds and ionic bonds. Covalent bonds form bonds through sharing electrons, ionic bonds are formed form an element giving them to another.

  • Why do covalent compounds often have low melting points compared to ionic compounds? covalent compounds are nonmetal and nonmetal bonds meaning they have lower melting points compared to ionic which are metal and nonmetals meaning they have higher melting points because the metal has naturally a higher melting point

  • Under what conditions might a covalent compound be found in a solid state at room temperature, given they are typically liquids or gases? covalent compounds can be solid at room temp, if they have stronger intermolecular forces, like hydrogen bonds,

  • Why are covalent compounds generally non-conductive in their liquid form?

2. The Octet Rule and Exceptions

  • Which specific element typically has fewer than 2 electrons in its valence shell? hydrogen

  • How many electrons does Boron typically have in its valence shell when forming a covalent compound?

  • Why is the Octet Rule considered a general guideline rather than a universal law for all elements?

3. Drawing Lewis Structures

  • What is the first step in drawing a Lewis structure for any covalent molecule?

  • Why can Hydrogen never serve as the central atom in a Lewis structure?

  • When selecting a central atom, should you choose the most electronegative or the least electronegative element?

  • If you have a single line connecting two atoms in a diagram, exactly how many electrons does that line represent?

4. Advanced Structure Details

  • After filling the octets for all surrounding atoms, where should you place any remaining valence electrons?

  • Define 'lone pairs' and explain how they influence the final geometric shape of a molecule.