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Mark S. CracoliceEdward I. Peters

Mark S. Cracolice • The University of Montana

Chapter 12Chemical Bonding

Monatomic Ions

Noble gas electron configurations are generally the most stable.

Metal atoms can achieve a noble gas electron configuration by emptying their valence orbitals. Nonmetal atoms can achieve the electron configuration of the next noble gas by receiving more electrons on their emptied valence orbitals.

Monatomic Ions

Lithium atom, which has electron configuration 1s22s1 can achieve the electron configuration of helium 1s2 by losing one electron on orbital 2s, and thus becomes a cation Li+.

Li - e → Li+

1s22s1 1s2

Monatomic Ions

Oxygen atom, whose electron configuration is 1s22s22p4, can achieve the electron configuration 1s22s22p6 of neon by receiving two more electrons on its 2p orbitals, and becomes ion O2-.

O + 2e → O2- 1s22s22p4 1s22s22p6

Monatomic Ions

Fluorine atom, whose electron configuration is 1s22s22p5 can achieve the electron configuration 1s22s22p6 of neon by accepting one electron on its 2p orbital, and becomes anion F-

F + e → F- 1s22s22p5 1s22s22p6

Monatomic Ions

Sodium atom, whose electron configuration is 1s22s22p63s1, can achieve the electron configuration 1s22s22p6 of neon by giving away one electron on its 3s orbital, and becomes cation Na+.

Na - e → Na+ 1s22s22p63s1 1s22s22p6

Monatomic Ions

Magnesium atom whose electron configuration is 1s22s22p63s2, can achieve the electron configuration of neon by giving away two electrons on its 3s orbital, and becomes cation Mg2+

Mg - 2 e → Mg2+

1s22s22p63s2 1s22s22p6

Monatomic Ions

Chlorine atom whose electron configuration is 1s22s22p63s23p5, can achieve the electron configuration of argon by receiving one electron on its 3p orbital, and becomes ion Cl-.

Cl + e → Cl-

1s22s22p63s23p5 1s22s22p63s23p6

Monatomic Ions

Potassium atom (1s22s22p63s23p64s1) can achieve the electron configuration 1s22s22p63s23p6of argon by losing one electron on its 4s orbital, and becomes ion K+.

K - e → K+

1s22s22p63s23p64s1 1s22s22p63s23p6

Monatomic Ions

Calcium atom (1s22s22p63s23p64s2) can achieve the electron configuration of argon by losing two electrons on its 4s orbital, and becomes ion Ca2+.

Ca - 2 e → Ca2+

1s22s22p63s23p64s2 1s22s22p63s23p6

Monatomic Ions

There are some exceptions to the rules discussed here. For example tin forms both Sn2+ and Sn4+

Sn - 2 e → Sn2+

[Kr]5s24d105p2 [Kr]5s24d10

Sn - 4 e → Sn4+

[Kr]5s24d105p2 [Kr]4d10

Configuration with filled sublevel 4d is stable

Monatomic Ions

Lead forms both Pb2+ and Pb4+

Pb - 2 e → Pb2+

[Xe]6s24f145d106p2 [Xe]6s24f145d10

Pb - 4e → Pb4+

[Xe]6s24f145d106p2 [Xe]4f145d10

Configuration with filled sublevel 5d is stable

Monatomic Ions

Ionic Bonds

Crystal: A solid with a definite geometric structure.

Ionic compounds: compounds made up of ions.

Ionic Bond : The electrostatic forces that hold the ions in fixed position in the crystal are called ionic bonds .

Ionic bonds are very strong.

Ionic Bond in sodium chloride

Ionic Bond in sodium chloride

Ionic Bonds

The bonds in an ionic crystal are very strong, which is why nearly all ionic compounds are solids at room temperature.

Solid ionic compounds are poor conductors of electricity because the ions are locked in place in the crystal.

Only when ionic compounds are melted or dissolved that the ions are free to move and able to carry electric current.

Covalent Bonds: Hydrogen molecule

Hydrogen molecule H2

In the hydrogen molecule, the electrons reside primarily in the space between the two nuclei.

The electron cloud or charge density is concentrated in the region between the nuclei.

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Covalent Bond in Hydrogen Molecule

Covalent Bonds: Hydrogen molecule

The simultaneous attraction of each electron by the two protons generates a force that pulls the protons toward each other and balances the repulsive force between protons and repulsive force between electrons.

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Covalent Bonds

The type of bonding in which electrons are shared by nuclei is called covalent bond.

Using Lewis symbols, the formation of hydrogen molecule can be represented as:

H + H ----> H : H or H-H

The two dots or the straight line drawn between the two atoms represent the covalent bond.

Covalent Bonds

By sharing electrons, each hydrogen atom in the molecule has two electrons.

Each hydrogen atom has a filled valence shell.

The pair of electrons with opposite spin shared by two atoms is called bonding pair.

Covalent Bond and ionic bond

Covalent bond: Each atom has a noble gas electron configuration but shares electron pair(s) to do so.

Ionic bond: Each ion has its own noble gas electron configuration

Covalent BondsH • + • H

or

The two dots or the straight line drawnbetween the two atoms represent the

covalent bond that holds the atoms together.

Covalent Bonds in F2

Fluorine molecule F2. Fluorine atom has the following electron configuration :

1s22s22p5 

When two fluorine atoms form a molecule, they share their unpaired electrons on orbitals 2p, so that each atom has eight electrons (octet rule). 

 

Covalent Bonds

A half-filled 2p orbital from one F atom overlaps ahalf-filled 2p orbital from the other F atom.

Covalent BondsLewis Diagram, Lewis Formula, Lewis Structure

Electron-dot symbols used to show the bondingarrangement among atoms in a molecule.

Lone pairsUnshared electron pairs in a Lewis diagram,

not involved in bonding.

Bonding pairThe pair of electrons shared by two atoms in a Lewis diagram.

Covalent BondsOctet Rule

Covalent bonds tend to form between nonmetal atoms by filling the overlapping valence electron orbitals with the maximum

number allowed, two in the s orbital and two in each of the three p orbitals, for a total of eight (octa-) valence electrons.

Covalent bonds tend to formwhen half-filled orbitals overlap.

Polarity & Covalent BondsNonpolar Covalent Bond

A bond in which bonding electrons are sharedequally by the two nuclei.

The charge density is centered in the regionbetween the bonded atoms.

A bond between identical atoms is always nonpolar.

Polarity & Covalent BondsPolar Covalent Bond

A bond in which the bonding electrons are sharedunequally by the two nuclei.

The charge density is shifted toward one atomand away from the other.

Polarity & Covalent Bonds

A bond with an unsymmetrical distribution of bonding electron charge is a polar covalent bond.

In the hydrogen fluoride molecule HF , the fluorine atom has a stronger attraction for the shared electrons than the hydrogen atom.

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Polarity & Covalent BondsThe result is that the HF molecule has the following charge distribution:

Polarity & Covalent Bonds

Electronegativity

Bond polarity in covalent bonds may be described in terms of the electronegativities of the bonded atoms.

The electronegativity of an element is the ability of its atom in a molecule to attract shared electrons to itself

The higher the electronegativity, the stronger is the attraction of the atom for bonding electrons.

Polarity & Covalent BondsThe electronegativity is highest at the upper right region of the periodic table and lowest at the lower left region

Polarity & Covalent Bonds

The polarity of the bond increases as the difference in electronegativity increases.

For example the following variation in bond polarity is expected

  0 0.4 0.9 1.4 1.9H-H < S-H < Cl-H < O-H < F-H

Polarity & Covalent BondsThe polarity of a bond can be estimated by

calculating the difference between theelectronegativity values for the bonded elements.

A C — F bond (4.0 – 2.4 = 1.6)is more polar than

A C — H bond (2.4 – 2.1 = 0.3)

The bonding electrons are displaced toward theelement with the highest electronegativity value.

Multiple BondsSingle bond: one electron pair shared.

Double bond: two electron pairs shared.Triple bond: three electron pairs shared.

Double and triple bonds are multiple bonds.

H H \ /

H — H C = C : N N : / \ H H

H2 C2H4 N2

Atoms Bonded to More Than One Atom

Formation of a Water Molecule From Its Atoms:

Atoms Bonded to More Than One Atom

Additional Molecules with AtomsBonded to Two or More Other Atoms:

H H H | \ /

H — C —H C = C H — C C — H | / \ H H H

Multiple Equivalent Structures: Resonance

We can write three valid structures for nitrate ion

The nitrate ion is represented by a blend of all structures.The blended structure is called resonance hybride of three

Lewis structures.(a mule is a hybride of a horse and a donkey.)

Resonance is a blending of structures with the same arrangement of atoms but different arrangement of electrons

Exceptions to the Octet RuleOdd-Electron Molecules

The molecule with one unpaired electron is called a radical.One of the atoms must have an incomplete octet.

nitrogen monoxide nitrogen dioxide 5 + 6 = 11 valence electrons 5 + 2(6) = 17 valence

electrons

Exceptions to the Octet RuleMolecules with More Than Four

Electron Pairs Around the Central Atom

Atoms of elements in the third period and higher have empty d orbitals and big size, can have more than four electron pairs surrounding them:

phosphorus pentafluoride sulfur hexafluoride

Exceptions to the Octet RuleMolecules with Fewer Than Four

Electron Pairs Around the Central Atom

Compounds of beryllium and boron are surroundedby two and three pairs of electrons, respectively:

beryllium difluoride boron trifluoride

Paramagnetic property of oxygenLiquid oxygen becomes trapped in the field of a strong magnet

because oxygen molecule has 2 unpaired electrons:

Limitation of Lewis DiagramOxygen

No Lewis diagram can be drawn for oxygen that matches experimental evidence about its paramagnetic property.

Molecular orbital theory can better explain the paramagnetic property of oxygen molecule.

http://www.mpcfaculty.net/mark_bishop/molecular_orbital_theory.htm

Metallic BondsMetallic Bond

Attractive force between positively-chargedmetal ions in a crystal and the negatively-charged

electrons that move among them.

Metallic Bonds

Metallic BondsMetals

Electrons in a metal are said to be delocalizedbecause they are not confined to a localized region

near a single atom or a pair of atoms.

AlloyA solid mixture of two or more elements

that has macroscopic metallic properties.

Metallic Bonds

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