Chemistry 8.2. The Nature of Covalent Bonding The colors in this map indicate the concentrations of ozone in various parts of Earth’s atmosphere. Oxygen

Chemistry 8.2Chemistry 8.2

The Nature of Covalent BondingThe Nature of Covalent Bonding

The colors in this map The colors in this map indicate the concentrations indicate the concentrations of ozone in various parts of of ozone in various parts of Earth’s atmosphere. Earth’s atmosphere. Oxygen atoms can join in Oxygen atoms can join in pairs to form the oxygen pairs to form the oxygen you breathe and can also you breathe and can also join in groups of three join in groups of three oxygen atoms to form oxygen atoms to form ozone.ozone.

8.2

8.2The Octet Rule in Covalent The Octet Rule in Covalent BondingBonding

The Octet Rule in Covalent BondingThe Octet Rule in Covalent Bonding

What is the result of electron What is the result of electron sharing in covalent bonds?sharing in covalent bonds?

8.2The Octet Rule in Covalent The Octet Rule in Covalent BondingBonding

In covalent bonds, electron sharing In covalent bonds, electron sharing usually occurs so that atoms attain the usually occurs so that atoms attain the electron configurations of noble gases.electron configurations of noble gases.

8.2

Single Covalent BondsSingle Covalent Bonds


How do electron dot structures How do electron dot structures represent shared electrons?represent shared electrons?


Two atoms held together by sharing a pair Two atoms held together by sharing a pair of electrons are joined by a single covalent of electrons are joined by a single covalent bondbond..

8.2

8.2


An electron dot structure such as An electron dot structure such as H:H represents the shared pair of H:H represents the shared pair of electrons of the covalent bond by electrons of the covalent bond by two dots.two dots.A structural formula represents the A structural formula represents the

covalent bonds by dashes and covalent bonds by dashes and shows the arrangement of shows the arrangement of covalently bonded atoms.covalently bonded atoms.


The halogens form single covalent bonds in their The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.diatomic molecules. Fluorine is one example.

8.2

8.2


A pair of valence electrons that is A pair of valence electrons that is not shared between atoms is not shared between atoms is called an called an unshared pairunshared pair, also , also known as a lone pair or a known as a lone pair or a nonbonding pair.nonbonding pair.


The hydrogen and oxygen atoms attain The hydrogen and oxygen atoms attain noble-gas configurations by sharing noble-gas configurations by sharing electrons.electrons.

8.2


The ammonia molecule has one unshared The ammonia molecule has one unshared pair of electrons.pair of electrons.

8.2


Methane has no unshared pairs of electrons.Methane has no unshared pairs of electrons.

8.2

Section AssessmentSection Assessment

8.1



8.1

Section AssessmentSection Assessmentfor Conceptual Problem 8.1

8.2Double and Triple Covalent Double and Triple Covalent BondsBonds

Double and Triple Covalent BondsDouble and Triple Covalent Bonds

How do atoms form double or triple How do atoms form double or triple covalent bonds?covalent bonds?

8.2

Double and Triple Covalent BondsDouble and Triple Covalent Bonds

Atoms form double or triple covalent Atoms form double or triple covalent bonds if they can attain a noble gas bonds if they can attain a noble gas structure by sharing two pairs or three structure by sharing two pairs or three pairs of electrons.pairs of electrons.


A bond that involves two shared pairs A bond that involves two shared pairs of electrons is a of electrons is a double covalent double covalent bondbond..

A bond formed by sharing three pairs A bond formed by sharing three pairs of electrons is a of electrons is a triple covalent triple covalent bondbond..

Double and Triple Covalent Double and Triple Covalent BondsBonds

Each oxygen atom has one unshared pair Each oxygen atom has one unshared pair of electrons.of electrons.

8.2


8.2


Carbon dioxide gas is soluble in water and Carbon dioxide gas is soluble in water and is used to carbonate many beverages. A is used to carbonate many beverages. A carbon dioxide molecule has two carbon-carbon dioxide molecule has two carbon-oxygen double bondsoxygen double bonds..


Carbon dioxide is an example of a triatomic Carbon dioxide is an example of a triatomic molecule.molecule.

8.2

8.2

Coordinate Covalent BondsCoordinate Covalent Bonds


How are coordinate covalent bonds How are coordinate covalent bonds different from other covalent bonds?different from other covalent bonds?

Coordinate Covalent BondsCoordinate Covalent BondsIn carbon monoxide, oxygen has a In carbon monoxide, oxygen has a

stable configuration but the carbon stable configuration but the carbon does not.does not.

8.2

8.2


As shown below, the dilemma is solved if the As shown below, the dilemma is solved if the oxygen donates one of its unshared pairs of oxygen donates one of its unshared pairs of electrons for bonding.electrons for bonding.

8.2


A A coordinate covalent bondcoordinate covalent bond is a is a covalent bond in which one atom covalent bond in which one atom contributes both bonding electrons.contributes both bonding electrons.

In a structural formula, you can In a structural formula, you can show coordinate covalent bonds as show coordinate covalent bonds as arrows that point from the atom arrows that point from the atom donating the pair of electrons to the donating the pair of electrons to the atom receiving them.atom receiving them.

8.2


In a coordinate covalent bond, the In a coordinate covalent bond, the shared electron pair comes from shared electron pair comes from one of the bonding atoms.one of the bonding atoms.

Coordinate Covalent BondsCoordinate Covalent BondsA A polyatomic ionpolyatomic ion, such as NH, such as NH44

++, is a tightly , is a tightly

bound group of atoms that has a positive or bound group of atoms that has a positive or negative charge and behaves as a unit. negative charge and behaves as a unit.

Most plants need nitrogen that is already Most plants need nitrogen that is already combined in a compound to grow.combined in a compound to grow.

8.2

Coordinate Covalent BondsCoordinate Covalent Bonds8.2


8.2

Section AssessmentSection Assessment8.2

Section AssessmentSection Assessment8.2

Bond Dissociation EnergiesBond Dissociation Energies


How is the strength of a covalent bond How is the strength of a covalent bond related to its bond dissociation energy?related to its bond dissociation energy?

8.2


The energy required to break the The energy required to break the bond between two covalently bond between two covalently bonded atoms is known as the bonded atoms is known as the bond dissociation energybond dissociation energy..A large bond dissociation energy A large bond dissociation energy

corresponds to a strong covalent corresponds to a strong covalent bond.bond.

8.2

ResonanceResonance

ResonanceResonance

How are oxygen atoms bonded in How are oxygen atoms bonded in ozone?ozone?

8.2

ResonanceResonance

Ozone in the Ozone in the upper upper atmosphere atmosphere blocks harmful blocks harmful ultraviolet ultraviolet radiation from the radiation from the sun. At lower sun. At lower elevations, it elevations, it contributes to contributes to smog.smog.

8.2

ResonanceResonance

The actual bonding of oxygen The actual bonding of oxygen atoms in ozone is a hybrid, or atoms in ozone is a hybrid, or mixture, of the extremes mixture, of the extremes represented by the resonance represented by the resonance forms.forms.

8.2

ResonanceResonance

A A resonance structureresonance structure is a structure that is a structure that occurs when it is possible to draw two or occurs when it is possible to draw two or more valid electron dot structures that have more valid electron dot structures that have the same number of electron pairs for a the same number of electron pairs for a molecule or ion.molecule or ion.

8.2

Exceptions to the Octet RuleExceptions to the Octet Rule


What are some exceptions to the rule?What are some exceptions to the rule?

8.2


The octet rule cannot be satisfied in The octet rule cannot be satisfied in molecules whose total number of molecules whose total number of valence electrons is an odd number. valence electrons is an odd number. There are also molecules in which an There are also molecules in which an atom has fewer, or more, than a atom has fewer, or more, than a complete octet of valence electrons.complete octet of valence electrons.

8.2


Two electron dot structures can be drawn Two electron dot structures can be drawn for the NOfor the NO22 molecule. molecule.

8.2


NONO22 is produced naturally by lightning strikes. is produced naturally by lightning strikes.

8.2


The electron dot structure for PClThe electron dot structure for PCl55 can can

be written so that phosphorus has ten be written so that phosphorus has ten valence electrons.valence electrons.

8.2

8.2.8.2.

8.2 Section Quiz.8.2 Section Quiz.

1. 1. In covalent bonding, atoms attain the In covalent bonding, atoms attain the configuration of noble gases byconfiguration of noble gases by losing electrons.losing electrons. gaining electrons.gaining electrons. transferring electrons.transferring electrons. sharing electrons.sharing electrons.

8.2 Section Quiz.8.2 Section Quiz.

8.2 Section Quiz8.2 Section Quiz

2. 2. Electron dot diagrams are superior to Electron dot diagrams are superior to molecular formulas in that they molecular formulas in that they show which electrons are shared.show which electrons are shared. indicate the number of each kind of atom in the indicate the number of each kind of atom in the

molecule.molecule. show the arrangement of atoms in the molecule.show the arrangement of atoms in the molecule.

are easier to write or draw.are easier to write or draw.

END OF SHOWEND OF SHOW

Documents

Chemistry 8.2. The Nature of Covalent Bonding The colors in this map indicate the concentrations of ozone in various parts of Earth’s atmosphere. Oxygen