6.2 LEWIS STRUCTURE ADDITIONAL NOTES DRAWING LEWIS STRUCTURES MOLECULES
BIG IDEA: Bonds can happen where atoms have unpaired
electrons.
BIG IDEA: Atoms share pairs of electrons. The pairs of
shared electrons become a bond.
H has 1 unpaired electron, O has 2 unpaired electrons
N has 3 unpaired electrons and C has 3 unpaired electrons
The H atoms share the electron they have to create a pair.
BIG IDEA: A dash represents a pair of shared electrons.
BIG IDEA: Some atoms form more than one bond.
Here Oxygen shares two pairs of electrons to form two
bonds called a double bond.
BIG IDEA: Many shapes can form, chains, circles etc.
EXAMPLE 1 – the bonds formed in a water molecule.
EXAMPLE 2 – the bonds formed in a molecule of ammonium.
EXAMPLE 3 – the bonds formed in a molecule of methane. Notice that all electrons are shared between the central
Carbon and the surrounding hydgorgens. Carbon can create 4 bonds and Hydrogen can form a single bond.
LEWIS STRUCTURE & DIAGRAM FOR EXAMPLE FOR BUTAN WHICH IS A CHAIN OF 4 CARBONS. .
WHAT IS THE CHEMICAL FORMULA FOR BUTANE?
Lewis Dot Structures in 5 Steps
Follow these step tutorial to draw Lewis Dot Structures for molecules and polyatomic ions. We’re going to be working
with 5 different molecules or ions: CO2, H2O, BCl3, PF3, and NH4+.
1) Arrange the atoms appropriately and as symmetrically as possible .
The least abundant atom goes in the middle. The middle central atom will typically be the most metallic (least
electronegative). Usually, the arrangement that is most symmetrical is correct. Examples: C & Si (4 valence
electrons) will be a central atom(s)
2) Count up the total number of valence electrons that should be in the structure at the end .
3) Draw single bonds between the central atom and each surrounding atom .
Note that each single bond (dash) represents two electrons which are shared.
4) Place the remaining electrons, in pairs, around the atoms in the structure.
I usually start with the outer atoms. Note that H can only participate in a single bond (See water below) These
electrons do not participate in a bond so they are drawn as dots.
5) Move pairs around so that each element has an octet
(exceptions: H only needs 2 electrons). The final total number of electrons in the structure should equal the
number counted in Step 2.
BIG IDEA: SHARED ELECTRONS FORM A BOND.
BIG IDEA: SHARED ELECTRONS ARE REPRESENTED AS A DASH.
http://plone.scottsdalecc.edu/borick/docs/lewis2.pdf/view
http://plone.scottsdalecc.edu/borick/docs