How Atoms Interact:
Chemical Bonding
Day 3
Curriculum
• Big Idea: Chemical bonding occurs as a result of
attractive forces between particles.
• Concept #1: The type of bonding that occurs between
atoms is related to the valence electrons of those atoms.
• Concept #2: Chemical bonding can be covalent, polar
covalent, or ionic.
• Concept #3: Lewis dot diagrams are useful for studying
the structure and bonding nature of atoms.
PA Standard: 3.2.C.A2 “Explain how atoms combine to
form compounds through both ionic and covalent
bonding.”
Today’s Agenda
• Opener: What is a polyatomic ion?
• Finish Paper Ion Lab
• Notes on Ionic and Covalent Bonding
(lewis dot diagram handout)
• Closure: What is the difference between
an ionic bond and a covalent bond?
Take Home Assignment: Quiz tomorrow on
bonding. Review handouts and notes.
Valence Electrons
• are electrons in the highest occupied
energy level of an element’s atoms.
• determine the chemical properties of an
element
• can be found for the representative
elements by looking at the group number
(I, II, III, IV, V, VI, VII, VIII)
Number of Valence Electrons
• Carbon (group IV)
has 4 valence
electrons
• Lithium (group I) has
1 valence electron
• Neon (group VIII) has
8 valence electrons
• So, how many valence electrons do each
of the following elements have?
a. He
b. Li
c. F
Electron Dot Structures
show valence electrons as dots
• Draw the lewis dot diagram for the
following elements:
a. Magnesium
b. Argon
c. Chlorine
The Octet Rule
• In forming compounds, atoms tend to achieve
the electron configuration of a noble gas (8
valence electrons).
• Metallic elements tend to lose their valence
electrons, leaving a complete octet in the nextlowest energy level.
• Nonmetallic elements tend to gain electrons or
to share electrons with another nonmetallic
element to achieve an octet.
• So…. How many valence electrons is
each element trying to obtain?
Formation of Cations and Anions
• An ion is an atom with a charge.
• A cation is a positively charged ion that
has been formed by losing electrons
(losing negative charge)
• An anion is a negatively charged ion that
has been formed by gaining electrons
(gaining negative charge)
Formation of Cations
Ionic Bonds and Ionic Compounds
Ionic Compounds
• compounds composed of cations and anions
• electrically neutral
Ionic Bonds
• The electrostatic forces that hold ions together
Formula Units
• chemical formula: shows the kinds and numbers
of atoms in the smallest representative unit of a
substance.
Example: sodium chloride is NaCl
• formula unit: lowest whole-number ration of ions
in an ionic compound.
Examples:
NaCl – 1:1
MgCl2 – 1:2
AlBr3 – 1:3
What is the formula unit for
magnesium chloride?
Properties of Ionic Compounds
• Most ionic
compounds are
crystalline solids at
room temperature.
• Ionic compounds
generally have high
melting points.
• Ionic compounds can
conduct an electric
current when melted
or dissolved in water.
• Covalent Bond –
sharing of electrons to
hold atoms together
• So, how is a covalent bond different than a
ionic bond?