Chemical Bonds
What does the word BOND
mean to you?
Chemical Bond
• attractive force between atoms or ions
in a molecule or compound.
• Formed by:
– transferring e- (losing or gaining)
– sharing e-
What do you think a
Chemical Formula is?
Chemical Formulas
• chemical formula –
– elements that make up a compound
– exact number of atoms of each element in a unit of
the compound
• Example : H2O
• H for the element hydrogen
• O for the element oxygen
• subscript number 2 written after the H for
hydrogen
• What do you think the 2 means?
Formulas
• Subscript means
“written below”
• subscript - how
many atoms of
that element are
in a unit of the
compound
Lesson Check
• How many hydrogen atoms are present
in one molecule of ammonium acetate,
NH4C2H3O 2?
How about Carbon atoms?
How about Oxygen atoms?
Nitrogen?
Hydrogen?
Why do you think the Nobel
gases are stable? (they
don’t bond with anything)
The Unique Noble Gases
All Nobel gases are
stable: They have FULL
outer shells!
Stability
• Octet Rule
– most atoms form bonds in order to have
valence e- (This is important)
– full outer energy level
– like the Noble Gases!
Ne
• Stability is the driving force behind
bond formation!
8
Hydrogen
• Hydrogen - one electron in its lone
energy level
• single dot - hydrogen’s outer energy level
is not full.
• stable when it is part of a compound
(when it has a full outer shell)
Helium
• helium’s - two electrons in outer shell
• Contains full outer energy level by itself
• chemically stable
• Helium rarely forms compounds
Other Elements
• look at the elements in Groups 1, 2, and
13 through 17, what do you notice about
their outer shell?
Outer Levels —Getting Their
Fill
• Why do atoms want to fill their outer
shell with electrons?
• To become STABLE!
• How do elements trying to become
stable, gain or lose their outer
electrons?
• by combining with other atoms that also
have partially complete outer electron
shells.
To achieve Stability, atoms
will:
• Transferring e- Ionic Bond
• Sharing e- Covalent Bond
Lesson Check
What is a chemical bond?
the force that holds atoms together in a
compound
What is an ion? (REVIEW)
An atom with an unequal number of electrons and
protons, giving the atom a charge
How do atoms achieve stability?
By gaining, losing, or sharing electrons
Why do atoms gain or lose electrons?
To achieve STABILITY
The Ionic Bond
• Ionic bond - attraction between
opposite charges of ions in an ionic
compound
– Transfer of electrons takes place.
• Ionic Bonds – NO NET CHARGE on
compound
• What kind of elements (metals, nonmetals,
metalloids) do you think bond ionically?
Ionic bonds - formed by bonding between
metals and nonmetals.
Outer Electron shells —
Getting Their Fill
• i.e. sodium and
chlorine.
• When they bond,
sodium loses one
electron and
chlorine gains one
electron.
Chemical bonds change
properties of elements
• compound has properties
that different than individual
elements
• Sodium chloride – Na (metal)
Cl (gas)
Ionicly Bonded Compounds
NaF
NaCl
TiO2
Potassium
Iodine
Potassium Iodide - KI
Used in nutritional supplements
to prevent iodine deficiency
Magnesium
Chlorine (gas)
Magnesium Chloride- MgCl2
Used to prepare tofu and soymilk
You Try It
How does the ionic bond form between:
Potassium and Bromine?
Magnesium and Chlorine?
Sodium and Fluorine?
How would you write the compound?
Ionic Bonding Practice
Sharing Electrons – Covalent
bonding
• Some elements don’t like to lose or gain
electrons.
• Look at Carbon…
• Look at Hydrogen…
• What do you notice about the number of
electrons in their valence shell?
Sharing Electrons
• Stability gained by sharing electrons,
not by losing or gaining electrons.
• Covalent bond –forms
when atoms share
electrons
• Molecule achieves
stability
• What is the
substance called if it
is formed via an ionic
bond????
Look at Carbon, how many electrons does it
need to fill its outer shell?
Look at Hydrogen, how many electrons does
it need to fill its outer shell?
How would these two bond?
Carbon has 4 valence
electrons, it needs 4 to fill its
outer shell
Hydrogen as 1, needs 1 to fill
its outer shell
4 Hydrogen will share their
electrons with Carbon, filling
carbon’s outer shell
Carbon will share its 4
electrons, 1 for each
Hydrogen
The result is a covalent bond
Lesson Check - Bonding
How would you draw the following molecules
(show the electron dot structure):
Chlorine and Chlorine?
Phosphorus and Hydrogen?
Silicon and Hydrogen?
• What kind of elements (metals, nonmetals,
metalloids) do you think bond covalently?
• Look at the periodic table…which elements
need less than 3 or 4 electrons to fill
their valence shell?
Covalent bonds - formed by bonding
between nonmetals and nonmetals.
• A single covalent bond is made up of two
shared electrons.
• Energy Level is stable for each atom
Multiple Bonds – more than one
pair of electrons
• Example – Nitrogen (N2).
• 3 Pairs of electrons – Triple Bond
Let’s Try It!
How would you draw the following molecules
(show the electron dot structure):
Carbon and Oxygen?
Chlorine and Chlorine?
Hydrogen and Carbon?
Phosphorus and Hydrogen?
Iodine and Iodine?
Hydrogen and Oxygen?
C H ?
You Try It!
Covalent Bonding
Practice
Ionic vs. Covalent Lab
Unequal Sharing in Covalent
Bonds
• Electrons are not always shared equally in
covalent bond.
• Due to:
– Size of atom (sound familiar?)
– Charge of nucleus
– Total number of electrons in atom (sound
familiar?)
Hydrogen Chloride -HCl
• Which attracts electrons
more…Hydrogen or Chlorine?
Polar Covalent Molecule
Polar Covalent Molecule
• Charge is neutral, but not
equally distributed
• Slightly positive end,
slightly negative end
Chlorine gas – Cl2
• Do you think Chlorine gas is a polar
molecule?
Nonpolar Covalent Molecule
Nonpolar Covalent Molecule
• Charge is neutral, electrons shared
equally
O2
• No oppositely charged ends
How do you tell if a molecule is
Polar or Nonpolar?
• CO?
• Linear, so one will always attract electrons more than another
• HCl?
• Anytime there is one Hydrogen, it will be polar (hydrogen is
weak!)
• Molecules with Oxygen, Nitrogen?
• Because these atoms attract electrons with a lot of strength,
they are always polar
• Cl2?
• Diatomic, always nonpolar
• C2 H2 ?
• Most carbon containing molecules are nonpolar
Review - Ionic vs. Covalent
Review - The Ionic Bond
• Attraction between 2 oppositely
charged Ions
• transferring e-from a metal to a
nonmetal
Review - Covalent Bond
• Attraction between neutral atoms
• Sharing of e- between two nonmetals
Review - Nonpolar Covalent Bond
– e- are shared equally
– usually identical atoms
Review - Polar Covalent Bond
– e- are shared unequally between 2
different atoms
– partial opposite charges
+


Review - Covalent Bond
• Nonpolar
• Polar
• Ionic
Review - Ionic or Covalent?
• IONIC BONDS –
• Metallic and Non-Metallic (NaCl, NaF)
• COVALENT BONDS
• Non-Metal and Non-Metal (CO2, SiBr4 )
You Try It!
• Covalent bonding – polar, nonpolar