Chemical Bonding Ionic, Metallic and Covalent Bonding

Chemical BondingChemical BondingIonic, Metallic and Ionic, Metallic and Covalent BondingCovalent Bonding

Chemical BondingChemical Bonding

Atoms in compounds are held Atoms in compounds are held together by chemical bonds.together by chemical bonds.

Chemical bonds result from the Chemical bonds result from the sharing or transfer of electrons sharing or transfer of electrons between pairs of atoms.between pairs of atoms.

Valence electronsValence electrons All elements in the same group All elements in the same group

behave similarly because they have behave similarly because they have the same number of valence the same number of valence electrons.electrons.

Valence electronsValence electrons are the are the electrons in the highest occupied electrons in the highest occupied energy level of an element’s energy level of an element’s atoms.atoms.

Remember….Remember….

The The number of valence electronsnumber of valence electrons in a in a representative element is the representative element is the same as same as the group number.the group number.

ExamplesExamples: : Na has 1 valence electron, Na has 1 valence electron, Mg has 2, Mg has 2, Al has 3, Al has 3, Si has 4, Si has 4, P has 5, etc.P has 5, etc.

III. Covalent BondingIII. Covalent Bonding

In covalent bonding, the bonded In covalent bonding, the bonded atoms atoms shareshare electrons. electrons.

Molecules form as atoms share Molecules form as atoms share electrons in covalent bonds.electrons in covalent bonds.

Describing electron pairs in Describing electron pairs in electron dot diagramselectron dot diagrams

In Lewis dot structures, “dot-dot” In Lewis dot structures, “dot-dot” pairs are called pairs are called unshared pairsunshared pairs or or lone pairslone pairs..

““Dashes” are called Dashes” are called shared pairsshared pairs or or bonding pairsbonding pairs..

Lewis dot structuresLewis dot structures

Only the valence electrons are shown in Only the valence electrons are shown in electron dot structures.electron dot structures.

Practice Problems: Practice Problems:

3) 3) a) Draw the electron dot notation for a potassium a) Draw the electron dot notation for a potassium atom.atom.

b) Draw the electron dot notation for a potassium b) Draw the electron dot notation for a potassium ion.ion.

(4) (4) a) Draw the electron dot notation for a sulfur atom.a) Draw the electron dot notation for a sulfur atom.

b) Draw the electron dot notation for a sulfur ion.b) Draw the electron dot notation for a sulfur ion.

K

[K+1]

S

[ S -2]

The Octet RuleThe Octet Rule

In forming compounds, In forming compounds, atoms react atoms react to gain the electron to gain the electron configuration of a noble gas.configuration of a noble gas.

An octet is 8. Remember, most noble An octet is 8. Remember, most noble gases have 8 valence electrons gases have 8 valence electrons (except helium).(except helium).

Electron configurations for Electron configurations for cationscations

cationcation (positive ion) forms when an (positive ion) forms when an atom atom losesloses electrons. electrons.

NaNa++ and achieves the same electron and achieves the same electron structure as neon.structure as neon.

““Isoelectronic”Isoelectronic”

NaNa++ ion is ion is isoelectronicisoelectronic with a neon with a neon atom.atom.

Na (1sNa (1s22 2s 2s22 2p 2p66 3s 3s11) ) NaNa++ (1s (1s22 2s 2s22 2p 2p66) + 1) + 1ee--

Ne (1sNe (1s22 2s 2s22 2p 2p66))

Electron configurations for Electron configurations for anionsanions

An An anionanion (negative ion) forms when (negative ion) forms when an atom an atom gainsgains electrons. electrons.

ClCl-- has the same electron structure has the same electron structure as argon.as argon.

The ClThe Cl-- ion is ion is isoelectronicisoelectronic with the with the argon atom.argon atom.

I. Ionic BondingI. Ionic Bonding

Ionic bonds form from the transfer of Ionic bonds form from the transfer of electrons between atoms.electrons between atoms.

Metals give electrons to nonmetals. Metals give electrons to nonmetals. The metal forms a cation (+) and the The metal forms a cation (+) and the nonmetal forms an anion (-).nonmetal forms an anion (-).

Ionic BondingIonic Bonding

Ionic bonds are the forces of Ionic bonds are the forces of attraction between positive and attraction between positive and negative ions in ionic compounds.negative ions in ionic compounds.

Remember: opposite charges attract.Remember: opposite charges attract.

The total negative charges equal the The total negative charges equal the total positive charges, so ionic total positive charges, so ionic compounds are neutral.compounds are neutral.

How to Represent an Ionic BondHow to Represent an Ionic Bond

Electron Dot Notations:Electron Dot Notations:

Na + Cl Na + Cl [ ] [ ] [ ] [ ]

Practice Problems: Practice Problems: (1) Draw the electron dot notation for the (1) Draw the electron dot notation for the formation of an ionic compound between formation of an ionic compound between aluminum and brominealuminum and bromine..

(2) Draw the electron configuration notation for (2) Draw the electron configuration notation for the formation of an ionic compound between the formation of an ionic compound between magnesium and magnesium and nitrogennitrogen..

Na +1 Cl -1

Properties of Ionic CompoundsProperties of Ionic Compounds

1.1. Ionic compounds form between Ionic compounds form between metals and nonmetalsmetals and nonmetals..

2.2. They have They have high melting pointshigh melting points..

3.3. They are generally They are generally soluble in soluble in water. water.

Properties of Ionic CompoundsProperties of Ionic Compounds4.4. Ionic compounds are Ionic compounds are

good conductors good conductors of electricityof electricity when when melted or dissolved melted or dissolved in waterin water..

For a compound to For a compound to conduct electricityconduct electricity, it , it must have must have charged charged particlesparticles (ions) (ions) that that are free to move are free to move (in (in liquid state or solution).liquid state or solution).

Properties of Ionic CompoundsProperties of Ionic Compounds

5.5. Ionic Ionic compounds are compounds are crystalline crystalline solids at room solids at room temperaturetemperature..

The ions in this The ions in this beautiful CuSObeautiful CuSO44 crystal are arranged crystal are arranged in a repeating, in a repeating, three-dimensional three-dimensional pattern.pattern.

Ionic crystalsIonic crystals

The The coordination coordination numbernumber of an ion of an ion is the number of is the number of opposite charged opposite charged ions that surround ions that surround the ion.the ion.

In NaCl, each NaIn NaCl, each Na++

ion is surrounded ion is surrounded by by 66 Cl Cl-- ions. ions.

Crystalline PatternsCrystalline Patterns

II. Bonding in MetalsII. Bonding in Metals

Metals are made of closely packed Metals are made of closely packed cations, instead of neutral atomscations, instead of neutral atoms..

Because of a metal’s low ionization Because of a metal’s low ionization energy, the valence electrons energy, the valence electrons become mobile, and drift freely.become mobile, and drift freely.

Bonding in metalsBonding in metals

Metallic bondingMetallic bonding is the is the attraction of the free-floating attraction of the free-floating valence electrons for the valence electrons for the positively charged metal ionspositively charged metal ions. . This force of attraction holds This force of attraction holds metals together.metals together.

The mobile valence electrons of The mobile valence electrons of metals explain why…metals explain why…

Metals areMetals are malleablemalleable (can be (can be pounded into sheets) and pounded into sheets) and ductileductile (can be pulled into wires).(can be pulled into wires).

The metal cations can slip past each The metal cations can slip past each other, being separated by the sea of free other, being separated by the sea of free floating electrons.floating electrons.

What happens when you pound an What happens when you pound an ionic crystal vs. a metal crystal with a ionic crystal vs. a metal crystal with a

hammer?hammer?

The mobile valence electrons of The mobile valence electrons of metals explain why…metals explain why…

2.2. Metals are good conductors of Metals are good conductors of electricity.electricity.

To be a conductor of electricity, charged To be a conductor of electricity, charged particles must be free to move….particles must be free to move….

the electrons can flow freely within the the electrons can flow freely within the metal.metal.

Metal AlloysMetal Alloys

Two metals can be mixed together to form Two metals can be mixed together to form alloys.alloys.

Remember: The Remember: The octet ruleoctet rule applies applies to covalent bonding, too!to covalent bonding, too!

Draw an FDraw an F22 molecule. molecule.

Draw an FDraw an F22 molecule. molecule.

A A single covalent bondsingle covalent bond forms when 2 forms when 2 atoms share a pair of electrons.atoms share a pair of electrons.

Draw an ODraw an O22 molecule. molecule.

Draw an ODraw an O22 molecule. molecule.

A A double covalent bonddouble covalent bond forms when two forms when two atoms share two pairs of electronsatoms share two pairs of electrons

Draw an NDraw an N22 molecule. molecule.

Draw an NDraw an N22 molecule. molecule.

A A triple covalent bondtriple covalent bond forms when two forms when two atoms share three pairs of electrons.atoms share three pairs of electrons.

Sigma and pi bondsSigma and pi bonds Sigma bondsSigma bonds are bonds that lie directly are bonds that lie directly

on the bond axis (from one atom’s center on the bond axis (from one atom’s center to the other atom’s center).to the other atom’s center).

Pi bondsPi bonds do not lie on the bond axis. do not lie on the bond axis.

A A single covalent bondsingle covalent bond is 1 sigma bond. is 1 sigma bond. A A double covalent bonddouble covalent bond is 1 sigma + 1 pi is 1 sigma + 1 pi

bond.bond. A A triple covalent bondtriple covalent bond is 1 sigma + 2 pi is 1 sigma + 2 pi

bonds.bonds.

Central vs. terminal atomsCentral vs. terminal atoms

The central atom in a molecule is the The central atom in a molecule is the atom with the most metallic atom with the most metallic character (least electronegative).character (least electronegative).

Hydrogen cannot be a central atom Hydrogen cannot be a central atom because it has only one electron to because it has only one electron to use to form bonds. It must be a use to form bonds. It must be a terminal atom.terminal atom.

Draw:Draw:

1.1. Methane, CHMethane, CH44

2.2. Ammonia, NHAmmonia, NH33

3.3. Water, HWater, H2200

4.4. Carbon dioxide, COCarbon dioxide, CO22

5.5. Ethane, CEthane, C22HH6 6

6.6. Ethylene, CEthylene, C22HH44

7.7. Acetylene, CAcetylene, C22HH22

Draw carbon monoxide.Draw carbon monoxide.

Draw carbon monoxide.Draw carbon monoxide.

A A coordinate covalent bondcoordinate covalent bond forms when forms when one atom contributes both bonding one atom contributes both bonding electrons in a covalent bond.electrons in a covalent bond.

Draw ozone.Draw ozone.

Draw ozone.Draw ozone.

ResonanceResonance occurs when 2 or more occurs when 2 or more equally valid Lewis dot structures can be equally valid Lewis dot structures can be drawn for a molecule.drawn for a molecule.

Bond PropertiesBond Properties

1.1. Bond orderBond order

Bond order = 1Bond order = 1 when there is a single bond when there is a single bond (1 sigma bond)(1 sigma bond)

Bond order = 2Bond order = 2 when there is a double bond (1 when there is a double bond (1 sigma + 1 pi) sigma + 1 pi)

Bond order = 3Bond order = 3 when there is a triple bond (1 when there is a triple bond (1 sigma + 2 pi) sigma + 2 pi)


2.2. Bond length Bond length

Single bonds are long and weak.Single bonds are long and weak. Double bonds are shorter and Double bonds are shorter and

stronger.stronger. Triple bonds are shortest and Triple bonds are shortest and

strongest.strongest.


3.3. Bond energy Bond energy

Bond energy increases as bond order Bond energy increases as bond order increases.increases.

Atoms are held more tightly when Atoms are held more tightly when there are multiple bonds.there are multiple bonds.


3.3. Bond polarity Bond polarity

When the two atoms involved in a When the two atoms involved in a bond have the bond have the samesame value of value of electronegativity, the electron pair is electronegativity, the electron pair is shared equally, and the bond is shared equally, and the bond is described as a described as a nonpolar bondnonpolar bond. .


3.3. Bond polarity (continued) Bond polarity (continued)

When the two atoms in a bond have When the two atoms in a bond have different different electronegativity values, the pair electronegativity values, the pair is is notnot shared equally, and it is described shared equally, and it is described as a as a polar covalent bondpolar covalent bond..

The electron pair is attracted toward the The electron pair is attracted toward the more electronegative atom, giving it a more electronegative atom, giving it a slightly negative charge.slightly negative charge.

Exceptions to the octet rule:Exceptions to the octet rule:

Draw BFDraw BF33.. ExceptionException: Fewer than 8 valence : Fewer than 8 valence

electronselectrons

Draw NODraw NO22.. ExceptionException: Odd number of electrons: Odd number of electrons

Draw PFDraw PF55 and SF and SF66.. ExceptionException: Expanded valence: Expanded valence

VSEPR TheoryVSEPR Theory

VValence alence SShell hell EElectron lectron PPair air RRepulsion epulsion Theory allows us to predict the Theory allows us to predict the molecular structures of compounds.molecular structures of compounds.

Because pairs repel each other, they Because pairs repel each other, they move as far apart as possible, yet move as far apart as possible, yet they are “tied” to the central atom. they are “tied” to the central atom. The pairs orient themselves to make The pairs orient themselves to make the angles between them as large as the angles between them as large as possible.possible.


Structural Pairs (electron domains)Structural Pairs (electron domains) consist of consist of sigma bonds and lone pair sigma bonds and lone pair electrons.electrons.

Pi bonds lie beside sigma bonds and Pi bonds lie beside sigma bonds and do not take up any space.do not take up any space.


2 structural pairs = linear geometry2 structural pairs = linear geometry 3 structural pairs = trigonal planar 3 structural pairs = trigonal planar

geometrygeometry 4 structural pairs = tetrahedral 4 structural pairs = tetrahedral

geometrygeometry

5 and 6 structural pairs lead to expanded 5 and 6 structural pairs lead to expanded valence (trigonal bipyramidal for 5 and valence (trigonal bipyramidal for 5 and octahedral for 6)octahedral for 6)

Molecular polarityMolecular polarity

A molecule is described as polar if it meets A molecule is described as polar if it meets two criteria:two criteria:

1) it is made of polar bonds, and 1) it is made of polar bonds, and 2) it is unsymmetrical.2) it is unsymmetrical.

A molecule can be made of polar bonds A molecule can be made of polar bonds yet still be a nonpolar molecule because of yet still be a nonpolar molecule because of symmetry (COsymmetry (CO22, CH, CH44, etc.), etc.)

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Chemical Bonding Ionic, Metallic and Covalent Bonding