General chemistryLesson 3 of 6 in the course Chemical Bonding and Molecular Geometry

Lewis Symbols and Structures: Bonding, Electron Counting, and Octet Exceptions

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

A Lewis symbol consists of an elemental symbol surrounded by one dot for each valence electron. Valence electrons are the electrons in an atom’s outermost shell and are the electrons involved in chemical bonding.

For main-group elements, the group on the periodic table helps predict the number of valence electrons. For example, sodium has one valence electron, oxygen has six, and chlorine has seven. Dots are placed around the element symbol, with one dot on each side before dots are paired.

All flashcards

What is a Lewis symbol?
An elemental symbol surrounded by dots, with each dot representing one valence electron.
What is a Lewis structure?
A drawing that shows how atoms are bonded in a molecule or polyatomic ion and represents the valence-electron pairs.
What does a single dash between atoms mean?
It represents one shared pair of electrons, which is a single covalent bond.
What is a lone pair?
A pair of valence electrons on an atom that is not shared in a bond.
How do Lewis symbols distinguish a cation from an anion?
A cation has lost electron dot(s) and is marked with a positive charge; an anion has gained electron dot(s) and is marked with a negative charge. Ions are often enclosed in brackets.

Quiz questions

  1. Nitric oxide, NO, has 11 total valence electrons. What does this imply for its Lewis structure?Answer: At least one electron remains unpaired.
  2. In the basic Lewis structure of BF₃, how many electrons surround the boron atom?Answer: Six electrons.
  3. In the Lewis structure of XeF₂, how many lone pairs are assigned to xenon after the fluorine atoms have complete octets?Answer: Three lone pairs.
  4. In the usual Lewis model, why do second-period elements such as carbon and oxygen not have expanded octets?Answer: Their valence shells are limited to eight electrons in this model.
  5. What shape is the C₆₀ fullerene molecule known as buckminsterfullerene?Answer: A spherical carbon cage.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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