Question

Write a detailed procedure for converting a chemical formula into a Lewis structure and how to determine the shape, and polarity from this Lewis structure.Write a detailed procedure in your own words for converting a chemical formula into a Lewis structure and how to determine the shape, and polarity from this Lewis structure.

Answer 1

A Lewis Symbol for an element is composed of a chemical symbol surrounded by dots that are used to represent valence electrons. An example of a Lewis symbol is shown below with the element Carbon, which has the electron configuration of 1s²2s²2p²:

This Lewis symbol shows that carbon has four valence electrons in its outer orbital and these four electrons play a major role in bonding of carbon molecules.

Lewis symbols differ slightly for ions. When forming a Lewis symbol for an ion, the chemical symbol is surrounded by dots that are used to represent valence electrons, and the whole structure is placed in square brackets with superscript representing the charge of the ion. An example of a Lewis symbol for the cation and anion of Carbon is shown below:

Cation of Carbon

Anion of Carbon

To construct Lewis Structures one can generally abide by the following steps:

1. Find how many valence electrons (N) are in the molecule that needs to be shown on the Lewis Structure by using the periodic table. Find the charge, add an electron for every negative charge and remove an electron for every positive charge.
2. Draw out the single bonds and initial framework, called the skeleton, of the molecule.
3. Complete the octets around the non-central atoms i.e. the terminal atoms by using the lone-pairs of electrons.
4. Compare the number of electrons currently depicted to the number needed (N) in the central atom and add electrons to it if less the number is less than N.
5. If there are extra lone-pair electrons and the octet rule is not filled for the central atom, use the extra electrons to form double or triple bonds around the central atom.
6. Check the formal charge of each atom.

When constructing the structures keep in mind the following:

• The dots surrounding the chemical symbol are the valence electrons, and each dash represents one covalent bond (consisting of two valence electrons)
• Hydrogen is always terminal in the structure
• The atom with the lowest ionization energy is typically the central atom in the structure
• The octet rule means there are 8 valence electrons around the atoms, but for hydrogen the maximum is 2 electrons

Lewis Structures can differ based on whether the electrons are shared through ionic or covalent bonds.

An example of covalent bonding can be seen below with the reaction of Hydrogen and Fluorine:

+=

Hydrogen has one valence electron and Fluorine has seven valence electrons; together the elements form the noble gas configuration. The Hydrogen atom shares its electron with Fluorine atom so that the Hydrogen atom has 2 electrons and the Fluorine atom has 8 electrons. Therefore both atoms have their outermost shells completely filled.

In this case shape will be lineare and more polar due to electronegativity difference.