Chemical BondingChemical Bonding

No one wants to be aloneNo one wants to be alone

Why atoms bondWhy atoms bond

Most atoms are not found alone in quantity Most atoms are not found alone in quantity in the universe, they are bonded to other in the universe, they are bonded to other atomsatoms

All atoms except the ones in Group 18 (the All atoms except the ones in Group 18 (the Noble Gases) have an Noble Gases) have an unstableunstable electron electron configurationconfiguration

Atoms will gain, lose, or share valence Atoms will gain, lose, or share valence electrons until they become stableelectrons until they become stable

Rule of OctetRule of Octet

The major groups of the Periodic Table The major groups of the Periodic Table ((Groups 1, 2, 13, 14, 15, 16, 17Groups 1, 2, 13, 14, 15, 16, 17) will gain, ) will gain, lose, or share electrons until they have 8 lose, or share electrons until they have 8 or 0 valence electronsor 0 valence electrons

0 valence electrons means that layer is 0 valence electrons means that layer is stripped and the full inner layer is stripped and the full inner layer is exposed, making them stableexposed, making them stable

Counting outer shell electronsCounting outer shell electrons

An Electron-Dot Diagram allows us to An Electron-Dot Diagram allows us to draw atoms and show their valence draw atoms and show their valence electron configurationelectron configurationWrite the element’s symbolWrite the element’s symbolBegin placing dots around the symbol equal Begin placing dots around the symbol equal

to the number of outer-shell electronsto the number of outer-shell electrons1 to a side, then double up1 to a side, then double up

Oxidation NumbersOxidation Numbers

The charge on the atom after an atom The charge on the atom after an atom gains, loses, or shares electrons to gains, loses, or shares electrons to become stablebecome stable

This positive or negative number tells you This positive or negative number tells you how many electrons the atom gained or how many electrons the atom gained or lostlost

+1 +2 +3 ±4-3 -2 -1 Ø

IonsIons

When an atom gains or loses electrons, it When an atom gains or loses electrons, it now has a now has a chargecharge

A charged particle is called an A charged particle is called an ionionAtoms losing electrons have a positive charge Atoms losing electrons have a positive charge

and are called and are called anionsanionsAtoms gaining electrons have a negative Atoms gaining electrons have a negative

charge and are called charge and are called cationscations

Types of Chemical BondingTypes of Chemical Bonding

Ionic BondsIonic Bonds are formed: are formed:When one atom (usually a metal) loses 1 or When one atom (usually a metal) loses 1 or

more electrons andmore electrons andAnother atom (usually a nonmetal) gains 1 or Another atom (usually a nonmetal) gains 1 or

more electronsmore electronsThe attraction between positive and negative The attraction between positive and negative

ions (opposites attract) causes the atoms to ions (opposites attract) causes the atoms to stick together with an incredible amount of stick together with an incredible amount of electromagnetic forceelectromagnetic force

More on Ionic BondsMore on Ionic Bonds

Ionic BondsIonic BondsAre created from elements on opposite sides Are created from elements on opposite sides

of the Periodic Tableof the Periodic TableHave unusually high melting and boiling Have unusually high melting and boiling

pointspointsAre usually solids at room temperatureAre usually solids at room temperatureDissolve into aqueous solutions easily Dissolve into aqueous solutions easily

(soluble or miscible)(soluble or miscible)

Types of Chemical BondingTypes of Chemical Bonding

Covalent BondsCovalent Bonds are formed: are formed:When two or more atoms share outer-shell When two or more atoms share outer-shell

electrons to complete their octetelectrons to complete their octetOnce the sharing begins, the atoms can not Once the sharing begins, the atoms can not

go their different ways except to take the go their different ways except to take the electrons that they were sharing and bond to electrons that they were sharing and bond to another atomanother atom

More on Covalent BondsMore on Covalent Bonds

Covalent BondsCovalent BondsAre created from elements somewhat close to Are created from elements somewhat close to

each other on the Periodic Tableeach other on the Periodic TableCan be liquids or solids at room temperatureCan be liquids or solids at room temperatureMany do not dissolve into aqueous solutions Many do not dissolve into aqueous solutions

easily (immiscible)easily (immiscible)

Covalent Bonds and PolarityCovalent Bonds and Polarity

Polar Covalent BondsPolar Covalent BondsFormed when the atoms in a sharing Formed when the atoms in a sharing

relationship don’t share evenlyrelationship don’t share evenlyA slight negative charge appears on the end A slight negative charge appears on the end

of the molecule with the “Stingy” atomof the molecule with the “Stingy” atomA slight positive charge appears on the end of A slight positive charge appears on the end of

the molecule with the “Generous” atomthe molecule with the “Generous” atom

Solubility and PolaritySolubility and Polarity

““Like dissolves like”Like dissolves like” Polar molecules can dissolve other polar moleculesPolar molecules can dissolve other polar molecules Polar molecules can dissolve ionic moleculesPolar molecules can dissolve ionic molecules Nonpolar molecules can dissolve other nonpolar Nonpolar molecules can dissolve other nonpolar

moleculesmolecules

Polar substances can not dissolve nonpolar Polar substances can not dissolve nonpolar substancessubstances

Nonpolar substances can not dissolve polar Nonpolar substances can not dissolve polar substancessubstances

Types of SolutionsTypes of Solutions

Concentrated – high ratio of solute to Concentrated – high ratio of solute to solventsolvent

Dilute – low ratio of solute to solventDilute – low ratio of solute to solvent

Alloy – solutions of metalsAlloy – solutions of metalsAmalgam – solution in Mercury (liquid Amalgam – solution in Mercury (liquid

metal)metal)Aqueous Solutions – water as the solventAqueous Solutions – water as the solvent

Solution ProcessSolution Process

““Surround and Surround and Separate”Separate”

Particles of the Particles of the solvent pull solvent pull particles of solute particles of solute into solutioninto solution

Speeding Up SolutionsSpeeding Up SolutionsAgitationAgitation

Stirring makes particles collide more oftenStirring makes particles collide more oftenSurface AreaSurface Area

Grinding up a solute makes it easier to Grinding up a solute makes it easier to “surround and separate” them into solution“surround and separate” them into solution

TemperatureTemperatureHeating a solution speeds up the particles, Heating a solution speeds up the particles,

increasing the number of collisionsincreasing the number of collisionsNOTENOTE: When dissolving a gas in a liquid, a : When dissolving a gas in a liquid, a

colder liquid slows down the gas particles and colder liquid slows down the gas particles and dissolves more total gasdissolves more total gas

Types of Chemical BondingTypes of Chemical Bonding

Metallic BondsMetallic Bonds are formed: are formed:When one or more metals combine (alloy)When one or more metals combine (alloy)The positive nuclei arrange into a lattice, while The positive nuclei arrange into a lattice, while

the electrons flow freely from atom to atomthe electrons flow freely from atom to atomSometimes called a “Sea of Electrons”Sometimes called a “Sea of Electrons”

More on Metallic BondsMore on Metallic Bonds

Metallic BondsMetallic BondsExplains why metals are lustrous and good Explains why metals are lustrous and good

conductors of electricity (the flow of electrons)conductors of electricity (the flow of electrons)Are solids at room temperatureAre solids at room temperatureMay lose electrons to substances outside of May lose electrons to substances outside of

the bond, causing corrosion or oxidation of the bond, causing corrosion or oxidation of the metals (rusting)the metals (rusting)Usually with Oxygen, forms a nonmetallic Usually with Oxygen, forms a nonmetallic

compound and substantially weakens the metalscompound and substantially weakens the metals

Counting AtomsCounting Atoms A A Chemical FormulaChemical Formula

shows how many of shows how many of which atoms are in a which atoms are in a moleculemolecule

A A SubscriptSubscript is a is a number placed below number placed below and behind a symbol and behind a symbol to show how many of to show how many of which atoms are which atoms are presentpresent

HH22OO

Counting AtomsCounting Atoms

A Coefficient is A Coefficient is placed in front of a placed in front of a molecule to show molecule to show more than one more than one moleculemolecule 3H3H22OO

Counting AtomsCounting Atoms A A Diatomic MoleculeDiatomic Molecule

shows two atoms of the shows two atoms of the same nonmetal (usually same nonmetal (usually in gas form) that have in gas form) that have bonded togetherbonded together

Reactive nonmetals will Reactive nonmetals will bond with one another if bond with one another if no other substance is no other substance is available for bondingavailable for bonding

HH22 NN22

OO22 FF22

II22 ClCl22BrBr22

Polyatomic IonsPolyatomic Ions

A group of atoms that A group of atoms that behave as one atombehave as one atom

Keep together as a unitKeep together as a unit Listed on p. 337Listed on p. 337 If more than one If more than one

polyatomic ion is present polyatomic ion is present in a molecule, in a molecule, parentheses set it apartparentheses set it apart Still use a subscript to Still use a subscript to

show how manyshow how many

Ca(OH)Ca(OH)22

NHNH44ClCl

Counting AtomsCounting Atoms

Write the molecule to be countedWrite the molecule to be countedList the participating atoms (or polyatomic List the participating atoms (or polyatomic

ions) under the formulaions) under the formulaWrite all subscripts, including parenthesesWrite all subscripts, including parenthesesMultiply by the coefficientMultiply by the coefficientSome problems call for a total of atoms, Some problems call for a total of atoms,

some call for individual atomssome call for individual atoms

REVIEWREVIEWWhy atoms bondWhy atoms bondRule of OctetRule of Octet

Exceptions!Exceptions!Electron-Dot DiagramsElectron-Dot DiagramsOxidation NumbersOxidation Numbers IonsIons Ionic BondsIonic BondsCovalent BondsCovalent Bonds

Metallic BondsMetallic BondsElectronegativityElectronegativityReactivityReactivityPolarityPolaritySolubilitySolubilityCounting AtomsCounting Atoms