LOGO
Lecture 2 (book chapter 4):
Introduction to covalent bounding
Organic Chemistry – FALL 2015
Course lecturer :
Jasmin Šutković
21th October 2015
Contents
International University of Sarajevo
4.1 Introduction to Covalent Bonding
4.2 Lewis Structures
4.3 Exceptions to the Octet Rule
4.4 Resonance
4.5 Naming Covalent Compounds
4.6 Molecular Shape
4.7 Electronegativity and Bond Polarity
4.8 Polarity of Molecules
4.9 FOCUS ON HEALTH & MEDICINE:
Covalent Drugs and Medical Products
Introduction
Most compounds that we come in contact with in
our daily lives are covalent compounds, formed
by sharing electrons between atoms.
 Body – formed by water
 Most Drugs
 Industrial Chemical products ; nylon , gasoline,
pesticides,
COVALENT BONDS are created by
SHARING electrons between two atoms
(elements)
Hydrogen is called a diatomic molecule because it
contains just two atoms.
In addition to hydrogen, six other elements exist as
diatomic molecules:
nitrogen (N2), oxygen (O2), fluorine (F2),chlorine (Cl2),
bromine (Br2), and iodine (I2).
Covalent bounding in the
periodic table
 RULEs :
 Covalent bond are formed by two




nonmetals
Ionic bonds are formed by metal and
nonmetal!
Covalent bond are also formed when a
metalloid binds to nonmetal
Examples :
Methane (CH4), Ammonia (NH3) and H2O
 Methane – natural gas- simplest Alkane
 Ammonia – agricultural fertilizer –
colorless, specific smell, building block of
many drugs
 Water
……………………………………………
…………………
FOCUS ON THE HUMAN BODY
COVALENT MOLECULES AND THE
CARDIOVASCULAR SYSTEM
Besides water, our bodies proteins, that compose muscle, the
carbohydrates that are metabolized for energy, stored fat, and
DNA, the carrier of genetic information, are all covalent
molecules.
Some covalent compounds related to the chemistry of the
heart include water, the most prevalent covalent compound
in the body;
oxygen, which is carried by the protein hemoglobin to
the tissues;
glycine, a building block of the proteins that compose
heart muscle; and
nitroglycerin, a drug used to treat some forms of heart
disease.
LEWIS STRUCTURES
 Molecular formula shows the number of atoms in
a compound, but it does not tell us what atoms
are bound to each other.
 A Lewis structure, in contrast, shows the
connectivity between the atoms, as well as
where all the bonding and nonbonding
valence electrons reside.
Book page 98,99 and 100 – see examples
Multiple bonds
Examples of double Bonds
O2
CO2
C2H4
Examples of triple Bonds
N2
C2H2
EXCEPTIONS TO THE OCTET RULE
 Most of the common elements in covalent compounds—
carbon, nitrogen, oxygen, and the halogens—generally
follow the octet rule.
 Hydrogen is a notable exception, because it
accommodates only two electrons in bonding.
 Additional exceptions include elements such as
boron in group 3A, and elements in the third row and
later in the periodic table, particularly phosphorus
and sulfur.
Group 3A elements
Elements in group 3A of the periodic table, such as boron,
do not have enough valence electrons to form an octet in
a neutral molecule.
A Lewis structure for BF3 illustrates that the boron atom
has only six electrons around it. There is nothing we can
do about this! There simply aren’t enough electrons to
form an octet.
3th ROW elements in PT
Phosphorous and Sulfur
Resonance
 Resonance Structures
 Structures that occur when it is possible to
write two or more valid electron dot
structures for a molecule.
Environmental Ozone
 O3 molecule
Ions (Book Chapter 3)
 An ion is an atom or molecule in which the total
number of electrons is not equal to the total
number of protons, giving the atom a net positive
or negative electrical charge.
 In chemical terms, if a neutral atom loses one or
more electrons, it has a net positive charge and
is known as a cation. If an atom gains electrons,
it has a net negative charge and is known as
an anion.
Naming cations
Cations of main group metals are given the name of
the element from which they are formed.
 It is common to add the word “ion” after the name of the
metal cation to distinguish it from the neutral metal itself.
 For example, when the concentration of sodium in a
blood sample is determined, what is really measured is
the concentration of sodium ions (Na+).
If a metal is able to form two different cations (Fe2+
and Fe3+) then we need method to distinguish
the cations.
Naming anions
PHYSICAL PROPERTIES OF IONIC
COMPOUNDS
 Ionic compounds are crystalline solids composed of ions,positive
charged cations and negative charged anions
 When a compound melts to form a liquid, energy is needed to
overcome some of the attractive forces of the ordered solid, to form
the less ordered liquid phase!!
 Ionic compounds have very high melting points. For
example, the melting point of NaCl is 801 °C.
 When an ionic compound dissolves in water, the ions are separated,
and each anion and cation is surrounded by water molecules, as
shown in Figure 3.4.
 The interaction of the water solvent with the ions provides the energy
needed to overcome the strong ion–ion attractions of the crystalline lattice.
POLYATOMIC IONS
 Sometimes ions are composed of more
than one element. The ion bears a charge
because the total number of electrons it
contains is different from the total number
of protons in the nuclei of all of the atoms.
Examples
Nonmetal polyatomic ions
WRITING FORMULAS FOR IONIC
COMPOUNDS WITH POLYATOMIC IONS
Unequal charge example
FOCUS ON HEALTH & MEDICINE
USEFUL IONIC COMPOUNDS
 Ionic compounds are found in drugs!
 Examples include calcium carbonate (CaCO3), the antacid in Tums;
magnesium hydroxide [Mg(OH)2], on of the active components in the
antacids Maalox and milk of magnesia; and iron(II) sulfate (FeSO4), an
iron supplement used to treat anemia.
Naming covalent
compounds
MOLECULAR SHAPE
We can now use Lewis structures to determine the shape around a particular
atom in a molecule.
Consider the H2O molecule. The Lewis structure tells us only which atoms are
connected to each other, but it implies nothing about the geometry.
What does the overall molecule look like? Is H2O a bent or linear molecule?
ELECTRONEGATIVITY AND
BOND POLARITY
H2O
The two charges are present
with a negative charge in the
middle (red shade), and a
positive charge at the ends
(blue shade).
POLAR MOLECULE
Bond polarity
 In chemistry, polarity refers to a separation of electric
charge leading to a molecule or its chemical groups having an
electric dipole or multipole moment.
 Molecular polarity is dependent on the difference
in electronegativity between atoms in a compound and
the asymmetry of the compound's structure.
 Polarity underlies a number of physical properties including surface
tension, solubility, and melting- and boiling-points.
 Atoms with high electronegativities — such
as fluorine, oxygen, and nitrogen — exert a
greater pull on electrons than atoms with
lower electronegativities.
 In a bond, this can lead to unequal sharing
of electrons between atoms, as electrons
will be drawn closer to the atom with the
higher electronegativity.
Hydrogen-fluoride
In a molecule of hydrogen fluoride
(HF), the more electronegative atom
(fluoride) is shown in yellow.
Because of the electrons spend more
time by the fluorine atom in the H-F
bond, the red represents partially
negatively charged regions.
POLAR MOLECULE
 In the ozone, O3, molecule the two O–O
bonds are nonpolar (there is no
electronegativity difference between atoms
of the same element).
Readings
 Book Chapter 3 and 4. Chapter 3 follow
according these slides and chapter 4 read
completely.