Bonding
Unit Overview
• Types of bonds
• Why/how bonds form
• Lewis structures (again)
• Writing chemical formulas
• Naming compounds
Chemical Bonds
• link between atoms due to
mutual attraction of nuclei for
e-
Chemical Bonds
Why bond???
• Bonding can result in lower
potential energy (this is usually
associated with a release of
energy)
• Lower energy = greater
stability (greatest stability =
completed energy level/octet)
Chemical Bonds
Octet rule – in forming
compounds, each atom, by
gaining/losing/sharing eachieves an octet of e- in its
highest occupied energy level
Chemical Bonds
Bonds are classified by how the
valence e- are distributed
around nuclei of combined
atoms
Types of Chemical
Bonds
Ionic bond – results from
electrostatic attraction
between positive and negative
ions (usually done when metal
bonds w/ nonmetal)
Types of Chemical
Bonds
Ionic bond
• Created by transfer of e• Active metals readily give up their e-,
usually to a nonmetal atom
• Oppositely charged ions are formed
by this process of transferring e• Cation: + charge
• Anion: - charged ion
Types of Chemical
Bonds
Ionic bond
Forming ionic bonds: e- are transferred
from atom with lower EN value to one
with higher value
• How can you determine if bond is
ionic? See if atoms are active metal
& non-metal or look up EN values to
get difference. (if EN difference is 1.7
 4.0, ionic bond)
Types of Chemical
Bonds
Ionic bond
Types of ions
• Monoatomic – single element with
charge
• Polyatomic – 2 or more elements
with charge
Types of Chemical
Bonds
Ionic bond
Ionic compound – composed of
positive & negative ions
combined so that the positive
& negative charges are equal
in number (Ex. NaCl instead of
Na2Cl or NaCl2)
Properties…
Ionic Compounds
• Held together tightly (attraction of
charges)
–High MP
–High BP
–Hard & brittle crystalline solids
–Dissolve in water (generally)
–Carry a current (very well) in
water
Representing Ionic
Compounds
Empirical formula or Formula unit – indicates
lowest whole number ratio of cations to anions in
any sample of an ionic compound
(ex. NaF = 1 Na+ ion + 1 F- ion)
• This “unit” doesn’t represent something that can
be isolated, it is only the smallest possible ratio
to make a neutral electrical charge
• # of ions in one formula unit depends on the
charges of the ions to be combined (ex. B + F,
Na + Cl, K + O, etc)
Representing Ionic
Compounds
Just a thought…
Can you use the periodic table
to determine the charge of an
ion?
Representing Ionic
Compounds
Determining formula units by
the crisscross & “accounting”
methods
• Ca + Br
•K + P
• Al + O
• Ca + O
3+
1• Al + CN
•Mg2+ + PO43-
Representing Ionic
Compounds
Lewis structures
• Diagrams that show valence eas dots, the inner e- and
nucleus are included in the
letter symbol for the element
being represented
Representing Ionic
Compounds
Lewis Structures
• Group 1
• Group 2
• Group 13
• Group 14
• Group 15
• Group 16
• Group 17
• Group 18
Representing Ionic
Compounds
Lewis Structures
Structures of individual elements
may be joined to form compounds
• pairs of dots (or a dash) between
symbols represent bonds (or
electron pairs), dots adjacent only
to one symbol are unshared e-
Representing Ionic
Compounds
Lewis Structures
Structures of individual elements
may be joined to form compounds
• Lone (unshared) pair of e- – pair
of e- that is not involved in
bonding, but instead belongs
exclusively to one atom
Representing Ionic
Compounds
How to represent ionic bonds
with Lewis diagrams
• KI
• CaO
• BaCl2
• Na3P
• LiBr
• MgH2
• Rb2O
Types of Chemical
Bonds
• Metallic bond – force of
attraction that holds metals
together; consists of the
attraction of free-floating
valence e- for positively
charged metal ions
Types of Chemical
Bonds
• Covalent (molecular) bond –
results from the sharing of ebetween two atoms (usually
done w/ nonmetal atoms)
Covalent Bonds
• The e- are not always equally shared (like
tug of war)
• Bonds between 2 unlike atoms are never
completely covalent - can represent these
bonds by showing partial charges on
respective atoms
• Non-polar covalent – e- are shared
equally ( which only happens between
two identical atoms)
• Polar covalent – e- are not equally
shared (due to differences in EN)
Covalent Bonds
• Atoms that are bonded
covalently form stable
particles called molecules
•Ex. CO2, H2O2, SO2, O2
•7 diatomic molecules to
know - H2, N2, O2, F2,
Cl2, I2, Br2
Covalent Bonds
• Molecular compound –
chemical compound whose
simplest formulas are
molecules
Properties…
Molecular Compounds
• Most are not tightly held
–Most have low MP (due to weak
attractions)
–Most have low BP
–Usually soft, amorphous solids
–Some dissolve in water
–Do not carry current well in water
Representing Molecular
Compounds
• Molecular formula – shows
the types and numbers of
atoms combined in a single
molecule of a compound
•Ex. CO2, H2O2, SO3, O2
Representing Molecular
Compounds
• Structural formula – indicates kind,
number, arrangement, and bonds of the
atoms in a molecule (or polyatomic ion)
1) Single bond – one pair of shared ebetween two atoms
2) Double bond – two pairs of shared
e- between two atoms
3) Triple bond – three pairs of shared
e- between two atoms
Representing Molecular
Compounds
• Structural formula –
arrangement, and bonds of the atoms in a molecule
•Ex.
indicates kind, number,
Representing Molecular
Compounds
Lewis Structures
Ex. F2, NH3, H2O, CH4, O2, CO2,
N2, CH2O, C2H2, PI3
(must draw structures)
Representing Molecular
Compounds
Lewis structures
Octet exceptions:
Less than full octet
•Ex: Boron compounds
such as BF3
Representing Molecular
Compounds
Lewis structures
Octet exceptions:
More than full octet – atoms
beyond 2nd period, most often
S & P (extra e- go to 3d level)
•Ex: SF4
Representing Molecular
Compounds
Lewis Structures
Octet exceptions:
Molecules w/odd # of e- - not full
octet, short-lived & unstable
•Ex: NO, SO32-, NH41+