Bergen Community College Lewis Dot Structures Chemistry Lab Report

Experiment 6: Lewis Dot Structures ( LAP REPORT)

For this experiment, please include your title page, executive summary, pre lab , your main worksheet and conclusion page.

Experiment 6: Lewis Dot
Structures
Objectives:
The objectives of this experiment are:
a) To practice drawing Lewis Structures for various covalently bonded
molecules and polyatomic ions.
b) To use model kits to construct these molecules/ions in order to explore
their structure and shapes.
c) To practice predicting molecular shapes (using VSEPR theory).
Background:
Non-metal atoms bond covalently, resulting in the formation of either neutral
molecules or polyatomic ions.
A covalent bond is formed when non-metal atoms share their valence
electrons, which they do in order to achieve filled valence orbitals like their
nearest noble gas neighbor.
This means that most bonded non-metal atoms will be surrounded by a total
of eight valence electrons via the sharing process – often referred to as the
octet rule.
A notable exception is hydrogen, which only needs two electrons to be like its
nearest noble gas neighbor, helium.
Exceptions to the octet rule will be discussed later.
Figure 6.1 The LDS of the main group
elements.
• A Lewis structure (or electron-dot formula) is a two-dimensional structural
formula showing the arrangement of valence electrons around atoms in
covalently bonded molecules (or polyatomic ions)
•
i.e. molecules where nonmetal atoms are held together because they
share one or more pairs of electrons.
• For example, the Lewis electron dot structure of hydrogen chloride (HCl) is
shown below.
Lewis Structure
• Shows how valence electrons are arranged
among atoms in a molecule.
• Most important requirement
▪ Atoms achieve noble gas electron configuration (octet
rule, duet rule).
Writing Lewis Structures
• Bonding pairs are shared between 2 atoms.
• Unshared pairs (lone pairs) are not shared and not
involved in bonding.
Rules to Write Dot Structures
• Count all the valence electrons
• Determine the central atom (the element there is
only one of)
• Draw single bonds to the central atom
• Put all remaining valence electrons on atoms as
lone pairs
Let’s Try it!
Water H2O
H2
=1×2=2
O
=6×1=6
________________
●●
H-O-H
●●
Total = 8 v.e
All 4 remaining electrons go on O because H is already
happy with 2 v.e. (never give H more than 2 v.e.;
everyone else wants 8 v.e. but H only wants 2.