Chapter 16: Covalent Bonding

Chapter 16:Covalent Bonding

The Nature of Covalent Bonds

4 Types of Covalent Bonds

• 1. Single Covalent bonds• 2. Double Covalent bonds• 3. Triple Covalent bonds• 4. Coordinate Covalent bonds

Chapter 16: Covalent Bonding-- The Nature of Covalent Bonding --

Single Covalent Bonds• Two atoms share one pair of electrons• Each atom ideally achieves an octet in a covalent bond so that they resemble the

electron configuration of a noble gas

• Structural formula is a chemical formula showing the arrangment of atoms in a molecule


Array of sodium ions and chloride ions: Collection of water molecules:

Formula unit of sodium chloride: Molecule of water:

Na+ Cl- H O H

Chemical formula: NaCl Chemical formula: H2O


Single Covalent Bonds• Covalent bonds result from combinations of nonmetals (I.e., group 4A, 5A, 6A,

and 7A elements)

• Unshared pairs– Also known as lone pairs– Pairs of valence electrons that are not shared between atoms of a molecule– Unshared pairs do not change form in a structural formula


Single Covalent Bonds - Halogens


Single Covalent Bonds – Larger Molecules


Single Covalent Bonds – Larger Molecules• Spreading out the electrons

– More stability– Less energy required

• Preferred arrangements


Double Covalent Bonds• Bonds that involve two shared pairs of electrons• Used to attain stable noble-gas configurations


Double Covalent Bonds


Double Covalent Bonds -- Exceptions• Oxygen gas (O2)

– Expectation: formation of a double-bond to achieve octets– Evidence: formation of a single-bond with two electrons in the gas being

unpaired


Triple Covalent Bonds• Bonds that involve three shared pairs of electrons• Used to attain stable noble-gas configurations


Coordinate Covalent Bonds• Covalent bond in which an atom contributes both bonding electrons• Structural formulas of coordinate covalent bonds show the bonds as arrows that

point from the atom donating the pair of electrons to the atom receiving them• Examples

– Carbon monoxide (CO)– Ammonium ion (NH4

+)– Sulfur dioxide (SO2)


Coordinate Covalent Bonds – Carbon Monoxide (CO)

An octet has been achieved for each molecule, but oxygen contributes the electrons needed.


Coordinate Covalent Bonds – Ammonium Ion (NH4+)

An octet has been achieved for each molecule, but nitrogen contributes the electrons needed.


Bond Dissociation Energies• Total energy required to sever the bond between two covalently bonded atoms• High in carbon compounds, resulting in high stability of carbon compounds• Table 16.3, page 448

Example: H – H + 435 kJ H + H

This means that it would require 435 kJ of energy to break the bond between the two atoms in a hydrogen gas molecule (H2).


Resonance

• Structures that occur when it is possible to write two or more valid Lewis dot structures that have the same number of electron pairs for a molecule or ion

• Structures are in constant resonance• NOTE: Single bonds are longer than double bonds; double bonds are longer than

triple bonds


Exceptions to the Octet Rule• Impossibilities occur where using the octet rule does not work.• Examples:

– Nitrogen dioxide (NO2)– Oxygen gas (O2)– Phosphorus pentachloride (PCl5)– Sulfur hexafluoride (SF6)


Exceptions to the Octet Rule – Nitrogen Dioxide (NO2)


Exceptions to the Octet Rule – Phosphorus Pentachloride (PCl5)


Exceptions to the Octet Rule – Sulfur Hexafluoride (SF6)


Exceptions to the Octet Rule• Cases for exceptions

– More than 8 valence electrons– Less than 8 valence electrons

• How to draw– Typically, the central atom will be the first one listed in the formula.– Hydrogens and halogens will typically surround the central atom.

• Diamagnetic– Substance weakly repelled by a magnetic field

• Paramagnetic– Substance strongly attracted to a magnetic field– These substances have molecules containing two or more unpaired electrons.– Not to be confused with ferromagnetism (as with magnets)– Mass if offset in a magnetic field

Chapter 16: Covalent Bonding

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