Transcript Chapter 6: Chemical Bonding

Chapter 6:
Chemical Bonding
Section 1: Introduction
to Chemical Bonding
Section 1: Introduction to Chemical Bonding
BELL RINGER: 11/29
Imagine getting onto a crowded elevator.
What happens as more and more people
get onto the elevator? How does it make
you feel? How do you think the people
around you feel?
(Also – think about the feeling you get when you’re on
a crowded train)
Section 1: Introduction to Chemical Bonding
Imagine getting onto a crowded elevator. As
people squeeze into the confined space, they
come in contact with each other. Many people will
experience a sense of being too close together.
When atoms get close enough, their outer
electrons repel each other. At the same time,
however, each atom’s outer electrons are strongly
attracted to the nuclei of the surrounding atoms.
Section 1: Introduction to Chemical Bonding
 Objectives:
 Describe how scientific inferences are drawn from
scientific observations and provide examples from the
content being studied
 Distinguish between bonding forces holding compounds
together and other attractive forces, including hydrogen
bonding and van der Waals forces
Section 1: Introduction to Chemical Bonding
 Atoms seldom exist as independent particles in nature.

Oxygen you breathe and water you drink are combinations
of atoms that are held together by chemical bonds.
 Chemical Bond – a mutual electrical attraction between
the nuclei and valence electrons of different atoms that
binds the atoms together.
 Chemicals are bonded together because as individuals
particles they are at relatively high potential energy

Nature wants potential energy minimalized
Visual Concept
Types of Chemical Bonding
 When atoms bond, their valence electrons
(electrons in the s & p orbitals of the HIGHEST
energy level) are redistributed in ways that make
the atom MORE stable.
1. Ionic bonding – chemical bonding that results
from the electrical attraction between cations
(positive ions) and anions (negative ions)
 In a purely Ionic Bond – atoms completely give up
electrons to other atoms
Visual Concept
Types of Chemical Bonding
2. Covalent bonding – results from the sharing of
electron pairs between atoms
Visual Concept
 In a purely covalent bond – the shared electrons are
“owned” equally by the two bonded atoms
Types of Chemical Bonding – Ionic or Covalent?
 Bonding is rarely purely covalent or purely ionic
 Usually the bonds fall somewhere in between
depending on how strongly the atoms of each
element attract electrons
Visual Concept
Remember: electronegativity – measure of an atom’s
ability to attract electrons
 The degree to which the bonding is covalent (sharing)
or ionic (giving up electrons) is determined by:
 Calculating the difference in the elements’
electronegativities
Visual Concept
Types of Chemical Bonding – Ionic or Covalent?
 Examples:
 What is the
difference in
electronegativity of
Fluorine (F) and
Cesium (Cs)?
 4.0 – 0.7 = 3.3
Types of Chemical Bonding – Ionic or Covalent?
Sample Problem A
Determine bonding between sulfur, S (2.5), and the
following elements: hydrogen, H (2.1); cesium, Cs
(.7); and chlorine, Cl (3.0). In each pair, which atom
will be more negative?
Types of Chemical Bonding – Ionic or Covalent?
Sample Problem A Solution
The electronegativity of sulfur is 2.5. The
electronegativities of hydrogen, cesium, and
chlorine are 2.1, 0.7, and 3.0, respectively. In
each pair, the atom with the larger
electronegativity will be the more-negative atom.
Bonding between
sulfur and:
hydrogen
cesium
chlorine
Electroneg.
difference:
2.5 – 2.1 = 0.4
2.5 – 0.7 = 1.8
3.0 – 2.5 = 0.5
Bond type:
polar-covalent
ionic
polar-covalent
More
negative:
sulfur
sulfur
chlorine