Pure and Polar Covalent Bond

A bond is made up of two electrons. A Covalent Bonds is formed by equal sharing of electrons. That is, if two atoms wish to form a covalent bond, then each atom contributes one electron for

the bond and they thus form a covalent bond in between them. For example, two Hydrogen atoms form a covalent bond to form a hydrogen molecule, H

– see Figure 1 below). The covalent

bond in hydrogen is a single bond. Similarly, the covalent bond in chlorine molecule is a single bond (see Figure 2 below). If atoms can share two electrons each, then they form a double bond as

in Oxygen (see Figure 3 below). If atoms can share three electrons each, then they can from a Triple bond as in Nitrogen Molecule (See Figure 4 below). Covalent bond can vary in strength

depending on whether the bond is single, double, or triple; a triple bond is stronger than a double bond, and a double bond is stronger than a single bond. Remember that always valence electrons

are shared in covalent bonding. We use the electronic dot structure to explain covalent bonding. Covalent is generally formed between nonmetals. And atoms of the same element can form

covalent bond – For example, we have Eight elements that form the self- covalent bond to form the Diatomic Molecules. They are Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine,

Iodine, and Astatine.

Hydrogen atoms Hydrogen Molecule Chlorine atoms Chlorine Molecule Oxygen atoms Oxygen molecule

Figure 1 Figure 2 Figure 3

Figure 4

Methane Carbon tetrachloride

CCl

Single Bond Single Bond Double Bond

Oxygen atoms share two electrons

and form a double bond in the

oxygen molecule, O

O=O

Chlorine atoms share one electrons

and form a single bond in the

chlorine molecule, Cl

Cl—Cl

H—H

Carbon is an important

element that forms

covalent bonds. Let us

look at the atomic

structure of carbon

Carbon has four valence electrons.

Therefore, it has some interesting

bonding features. It can form a single

bond as in Methane or Carbon

tetrachloride.

Pure and Polar Covalent Bond: Dr. R: Name:-------------------------------------------------; Period:-------Date:------

Standard: SPS1b: Compare and contrast ionic and covalent bonds in terms of electron movement.

At At

See the Periodic Table

Below

Covalent Bond is

formed by

elements, which

cannot lose or

gain electron

Daily Formative Assessment: Fill in the Blanks

1. A ------------------ Bond is formed when elements cannot lose or gain electron.

2. A Covalent Bond is formed by ----------- ---------- of the Valence electrons

3. Covalent bond is generally formed between -----------------.

4. Atoms of the ----------element can form covalent bond. For example, all the ------------

-Elements are formed by covalent bond.

The diatomic elements are:

5. Covalent bond can vary in --------------depending on whether the bond is ----------------

------------, or ----------------;

a triple bond is ------------ than a -------- bond, and a ---------- bond is stronger than a --

----------- bond.

6. Remember that always only ---------- electrons are shared in covalent bonding.

7. We use the ------------ dot structure to explain covalent bonding.

Daily Formative Assessment

Draw the Covalent bond of Hydrogen, Nitrogen, and Oxygen molecules

Daily Formative Assessment

1. Draw the Covalent bond of Methane and Carbon tetrachloride

A covalent Bond is of two types: Pure Covalent Bond or Polar Covalent Bond

Covalent Bond

Pure covalent Bond

Polar Covalent Bond

Pure covalent compounds are also called as non-polar

compounds.

2. How many types of covalent bonds are there? What are they?

3. What is the other name for Pure Covalent compound?

Slightly Polar Strongly Polar

If the two atoms connected by a covalent bond are the same or have same of close by electronegativity values, then such a covalent bond is called Pure Covalent

Bond. Electronegatiivty is the pulling power of a bonded over a bonded pair of electrons.

If the two atoms are same or similar in electronegativity, then they are going to pull the

two electrons of the bond with equal force and the bond will remain at the center. That is

the bond will be equidistant from both the atoms. Therefore, both the atoms will remain

neutral like atoms. So a Pure covalent bond connects neutral atoms and no charges are

formed. Hydrogen, Chlorine, Carbon dioxide, Methane, and Carbon tetrachloride are

examples of pure covalent compounds

If the two atoms are different and have different

electronegativity values, then they are going to pull the two

electrons of the bond with unequal force and the bond will not

remain at the center. It will move to one side toward one of the

two atoms. That is the bond is closer to one atom and farther

than the other atom.

Because of the disposition of the electrons of the bond, the

atoms cannot remain neutral, but would become polarized. That

is they will acquire some partial charges; the atom to which bond

has moved closer will acquire partial negative charge and the

atom to which the bond is farther will acquire a partial negative

charge.

Hydrogen chloride is a good example of a Polar Covalent

compound.

See the bottom box on the right and look at the

electronegativities of elements in the Electronegativity Periodic

Table.

Hydrogen atom and chlorine atom combine to form hydrogen chloride. The bond is a

covalent bond since each of them equally share the electrons of the bond. However,

chlorine is more electronegative than hydrogen. Therefore, it pulls the bonded electrons

toward itself. As a result, the bond becomes a Polar Covalent Bond and a Dipole is

formed. So, the Hydrogen Chloride molecule is a Dipole.

Electronegativity (EN) is given in numeric values. See Electronegativity

Periodic Table below: The following rule is used to determine whether a

bond is Pure Covalent Bond or a Polar Covalent Bond:

1. If the electronegativity difference (usually called ΔEN) is less

than 0.5, then the bond is nonpolar covalent.

2. If the ΔEN is between 0.5 and 1.6, the bond is considered polar

covalent

Electronegativity difference between hydrogen and

chlorine

Hydrogen has an electronegativity of 2.1, and

chlorine has an electronegativity of 3.0. The

electron pair that is bonding HCl together shifts

toward the chlorine atom because it has a larger

electronegativity value.

Water is a polar covalent compound. See Explanation on Page 5

Note that the bond is equidistant from the two atoms in Pure Covalent Bond. In

the Polar Covalent Bond, the bond is closer to one atom than the other atom.

Covalent Bond Interim Review

1. Covalent Bond is formed when elements cannot lose or gain electron

2. A Covalent Bond is formed by equal haring of the Valence electrons

3. Covalent bond is generally formed between nonmetals.

4. Atoms of the same element can form covalent bond. For example all the Diatomic

Elements are formed by covalent bond.

The diatomic elements are: Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine,

Iodine, and Astatine,

5. Covalent bond can vary in strength depending on whether the bond is single, double,

or triple;

a triple bond is stronger than a double bond, and a double bond is stronger than a

single bond.

6. Remember that always valence electrons are shared in covalent bonding.

7. We use the electronic dot structure to explain covalent bonding.

8. Electronegativity determines whether the covalent bond formed is a Pure Covalent

Bond or a Polar Covalent Bond.

9. A Pure covalent bond is formed when the electronegativity values between the atoms

is zero or less than 0.5

10. A polar covalent bond is formed when the electronegativity difference between the

atoms is between 0.5 and 1.6.

11. In the Periodic Table, the Electronegativity increases as you move from Left

to Right and it decreases as you move from top to bottom.

Daily Formative Assessment: Fill in the blanks

1. Covalent Bond is formed when elements cannot ------- or -------electron

2. A Covalent Bond is formed by --------- ---------- of the Valence electrons

3. Covalent bond is generally formed between --------------------.

4. ---------- of the ------- ------------ can form covalent bond. For example all the ----------

--- --------------- are formed by covalent bond.

The diatomic elements are: -----------------------------------------------------------------------

--------------------------------------------------------------------------------------

5. Covalent bond can vary in ---------- depending on whether the bond is single, -------

---------, or --------------; a ---------- bond is stronger than a -------- bond, and a ---------

- bond is stronger than a ----------- bond.

6. Remember that always valence electrons are --------- in covalent bonding.

7. We use the --------------- -------- ------------ to explain covalent bonding.

8. -------------------- determines whether the covalent bond formed is a -------- Covalent

Bond or a ------------- Covalent Bond.

9. A ------- covalent bond is formed when the electronegativity values between the

atoms is --------- or less than -------.

10. A -------- covalent bond is formed when the electronegativity difference between

the atoms is between ------- and ---------.

11. In the Periodic Table, the Electronegativity ------------------- as you move from Left to

Right and it -------------------------- as you move from top to bottom.

Properties of Covalent Compounds

Pure Covalent Compounds

Polar Covalent Compounds

Insoluble or very slightly soluble in

water

Soluble in water

Low Melting Point

Slightly Higher Melting Point

Low Boiling Point

Slightly Higher Boiling Point

Low vapor pressure

Somewhat higher vapor pressure

Strong odor

Mild odor

Mostly Liquids or gas or vapors;

some or very low melting waxy

substances.

Mostly Liquids and some are semisolids

like cheese. Rarely, some are gases like

carbon dioxide.

Do not conduct electricity

Do not conduct electricity by

themselves, and can conduct electricity

when dissolved in water.

Examples:

Butter, camphor, Iodine, Wax,

Hydrogen, Oxygen, Nitrogen

Examples

Cheese, Carbon dioxide, Water, Alcohol,

pure vinegar

Cheese has a lot of intermolecular forces because it is a protein; butter has no

strong intermolecular forces because it is a fat.

Daily Formative Assessment

Take Covalent Bonding Quiz at Softschools Chemistry Quiz: Chemical

Bonding: II Covalent Bonding

On a Separate sheet of paper draw Polar covalent bond in Hydrogen

Chloride and water.

Intermolecular Forces Determine Melting and Boiling Points

Pure covalent molecules are internally very strongly bonded to each other

atom because of equal sharing of electrons. It is because of this strong

internal bonding, covalent molecules tend to behave in isolated way and have

weak connections to other molecules. Therefore, they need very little energy

to move and show low melting and boiling points.

Polar covalent molecules are dipoles and therefore they tend to have strong

intermolecular forces – the positive pole of one molecule can attract the

negative pole of another molecule and they tend to stay together. We have to

supply some energy to separate the molecules and make them move.

Therefore, polar covalent molecules have higher melting and boiling points

tahtn the pure covalent compounds.

O=C=O

X Electron from Carbon Two Double Bonds

• Electron from Oxygen

Behaves like a Pure

Covalent Molecule

Carbon dioxide is a Polar Covalent Molecule but it

behaves like a Pure Covalent Molecule

The situation of Carbon dioxide is unique. Carbon equally shares two

electrons with each oxygen atom. Therefore, there it forms one double

bond with one oxygen and another double bond with the second oxygen.

Carbon dioxide is actually a polar covalent bond because of the

electronegativity difference between carbon and oxygen. However, the

two oxygen atoms are on either side of carbon and they pull the bonded

pairs of electrons equally in opposite directions. Therefore, there is no net

effect of the pull. This means that although carbon dioxide is a polar

covalent molecule, it behaves normally like the pure covalent molecule.

Water is a Polar Covalent Molecule

Electronegativity Values: H = 2.1; O = 3.5. The difference is 3.5-2.5 = 1.4. Since the

difference in electronegativity is in the range 0.5 to 1.6, the bond is a Polar Covalent

Bond. Unlike carbon dioxide the pull is toward the center, that is, toward oxygen.

Therefore, the pulling power of oxygen is double and water is really strongly polar

and it results in water molecule being a dipole.

In other words, the covalent bond in water is considerably polarized and there is

somewhat appreciable amount of partial charges in water. It is because of this

nature, water is able to readily dissolve all ionic compounds and also other polar

covalent compounds like carbon dioxide. As we are aware the drinking soda is a

solution of carbon dioxide in water – it is actually carbonic acid – a weak compound

between water and carbon dioxide:

Electronegativity Values: C = 2.5; O = 3.5. The

difference is 3.5-2.5 = 1.0. Since the difference

in electronegativity is in the range 0.5 to 1.6, the

bond is a Polar Covalent Bond.

Two different charges

on the molecule makes

water a Dipole. A dipole

is a polar covalent

molecules with partial

positive and partial

negative charges.

Water

molecule

is a

dipole

Carbon

dioxide

molecule is a

dipole

Pure or Non-polar compounds dissolve in Non-Polar Compounds – The like likes the like

1. We saw that Pure or Non-polar or covalent molecules will not dissolve in water. The reason is water is a polar solvent and it will not let in a

mon-polar substance. Even if water dissolves any non-polar molecule, it will do so only to a very small extent. For example, the solubility of

oxygen is: 6.04 milliliters (mL) of oxygen per liter of water. Nitrogen gas does dissolve in water.

2. Pure or Non-Polar compound dissolve in non-polar solvents.

3. Non-polar solvents are solvents that are not water or not water-like. Example: Benzene, Toluene, Hexane, Pentane or Kerosene. So wax will

dissolve in toluene and not in water. The nail-polish will not dissolve in water but will dissolve in the nail polish remover, namely, acetone.

4. Daily Formative Assessment:

Discuss why carbon dioxide behaves like a pure

covalent molecule although it is a polar molecule?

Provide neat diagrams to support your discussion.

With Neat diagrams, explain the Polar

Covalent Bond Formation in Water Molecule.

Explain what you understand by the term,

“dipoles”

Discuss why carbon dioxide is able to dissolve in

water to form drinking soda, which is chemically

carbonic acid.

Taking real-world examples, prove that oxygen is

dissolved in water.

Analogy: Homeopathy System of Medicine: similia similibus

curantur: Like cures the like