COVALENT BONDING

Covalent Bonds

A covalent bond is formed when two or more nuclei share electrons in order to achieve a stable electron configuration (noble gas).

Covalent bonds often occur between two non-metals of the same element. (Diatomics) H,O,F,Br,I,N,Cl

Atoms of different elements can also combine to form a covalent bond. Example: water, carbon dioxide

Types of Covalent Bonds

There are different types of covalent bonds. They are: Non-polar Covalent Polar Covalent Multiple Covalent

Double bonds Triple bonds

Nonpolar Covalent Bonds

A nonpolar covalent bond exists when there is an equal sharing of electrons between two nuclei.

Nonpolar covalent bonds are formed between atoms having equal or close electronegativity values. The diatomics always make nonpolar covalent

bonds because they are non-metals and their electronegativity values cancel.

If the electronegativity different is between 0 and 0.4 the compound is considered nonpolar covalent.

Polar Covalent

Atoms involved in a polar covalent bond have an unequal sharing of electrons.

This can be determined based on their differences in electronegativity.

The element with the higher electronegativity value attracts the shared electrons more strongly.

This causes a portion of the molecule to acquire a partially negative charge.

The other end of the polar molecule acquires a partially positive charge.

Common Polar Compounds

H-Cl and H-I are two common polar compounds.

Hydrogen obtains a partially positive charge and the halogens obtain a more negative charge.

This happens because the halogens (group 17) have a higher electronegativity value than hydrogen.

Water

Water is a polar covalent compound. In a water molecule, the oxygen atom

takes on the negative charge and the hydrogens take on the positive charge.

Multiple Covalent Bonds

Atoms in covalent bond may share more than one pair of electrons.

This additional sharing of electrons results in the formation of a multiple covalent bond.

Double bond- the sharing of two pairs of valence electrons.

Triple bond- the sharing of three pairs of valence electrons.

HONC 1234

Every Hydrogen atom has one line connecting it to other atoms or itself. (single bond)

Every Oxygen atom has two lines connecting it to other atoms or itself. (double bond)

Every Nitrogen atom has three lines connecting it to other atoms or itself. (triple bond)

Every Carbon atom has four lines connecting it to other atoms. (not itself because Carbon is not diatomic) – (single bonds)

Examples Using Electron Dot

H H (single)

O O (double)

N N (triple)

Cl Cl (single)

Molecular Substances

A molecule is the smallest discrete particle of an element or compound formed by a covalent bond.

Each atom in a molecule obtains an electron configuration of a noble gas.

Molecular substance can either be solid, liquid, or a gas. The state of matter depends on the strength of the

forces of attraction. Molecules tend to be soft, poor conductors of

heat and electricity, and they have low melting and boiling points.

Molecules

A large majority of all chemical compounds on Earth are covalent (either polar or non-polar).

A vast majority of covalent compounds are organic, meaning they contain carbon and hydrogen.

Plastics, foods, living things, oil, etc. are all organic compounds.

There are thousand of these compounds and we use them everyday.

Polar Molecules

If a molecule contains polar bonds does not mean that the compound itself is polar.

For example, the Hydrogen – Carbon bond is polar but the compound CH4 is a non-polar compound.

To understand this, one must look at the molecules shape.

Asymmetrical molecules are polar Symmetrical molecules are non-polar

because the pull of the various polar bonds offset each other .

Polyatomic Ions

Polyatomic ions are two or more different atoms bonded together that act as one unit.

Polyatomic ions must also contain an ionic bond to be considered stable.

The bonds that hold the polyatomic ion together are covalent.

A polyatomic ion plus a metal will contain both ionic and covalent bonds.

Distinguishing Bonds

Ionic, metallic, and covalent bonds all have different properties.

This table explains the main difference between all three

Bond Melting/Boiling Hardness Conductivity

S L Aq.

Metallic High Hard Yes Yes Yes

Covalent Low Soft No No No

Ionic High Hard No Yes Yes

Intermolecular Forces-Van der Waals Forces

Molecules have attractive forces acting on them in the solid, liquid and gaseous state.

These forces are: Ionic forces Dipole forces Hydrogen bonding Induced dipole