Formation of Compounds Formation of Compounds and Moleculesand Molecules

Chemical BondsChemical Bonds

The process of gaining, losing or sharing The process of gaining, losing or sharing electrons that hold the atoms togetherelectrons that hold the atoms together

IonsIons Atoms with a + or – chargeAtoms with a + or – charge

Cations: positive charge (protons > electrons)Cations: positive charge (protons > electrons)• Na loses electronNa loses electron Na Na++

Anions negative charge (electrons > protons)Anions negative charge (electrons > protons)• Cl gains electron Cl gains electron Cl Cl--

Ionic BondsIonic Bonds

Created by the chemical attraction Created by the chemical attraction between atoms that have gained or lost between atoms that have gained or lost electrons and thus carry and electric electrons and thus carry and electric chargecharge

+ =

Sodium metal

(Na)

Chlorine gas

(Cl)

+ = Table Salt

(NaCl)

Three steps in an ionic bondThree steps in an ionic bond

Step 1: Formation of ionsStep 1: Formation of ions One atoms loses an electron to anotherOne atoms loses an electron to another

• Formation of cationFormation of cation Na atom loses an electron to a Cl atomNa atom loses an electron to a Cl atom If fewer than four electrons in outer shell, more likely to If fewer than four electrons in outer shell, more likely to

lose an electron (positive charge, Na+)lose an electron (positive charge, Na+)

• Formation of anionFormation of anion If more than four electrons in outer shell, less likely to If more than four electrons in outer shell, less likely to

lose electron and more likely to gain one (negative lose electron and more likely to gain one (negative charge, Cl-)charge, Cl-)

Three steps in an ionic bondThree steps in an ionic bond

Step 2: Attraction of oppositesStep 2: Attraction of opposites Na+ is attracted to Cl- because of opposite Na+ is attracted to Cl- because of opposite

chargescharges Step 3: Formation of ionic bondStep 3: Formation of ionic bond

The association of Na and Cl ions form the The association of Na and Cl ions form the ionic compound NaCl (sodium chloride)ionic compound NaCl (sodium chloride)

Let’s take another look at Let’s take another look at ionic bondsionic bonds

Covalent BondCovalent Bond

Covalent bond: a bond created by sharing Covalent bond: a bond created by sharing of electronsof electrons

Molecule: two or more atoms held Molecule: two or more atoms held together by a covalent bond that behave together by a covalent bond that behave as a single unitas a single unit

Single Covalent BondSingle Covalent Bond

One shared electronOne shared electron Hydrogen molecule:Hydrogen molecule:

Only form that hydrogen is found as in natureOnly form that hydrogen is found as in nature Two hydrogen atoms share their electrons Two hydrogen atoms share their electrons

with each otherwith each other Similar to tossing a baseball back and forth Similar to tossing a baseball back and forth

between two peoplebetween two people• Each person shares equal amount of time with the Each person shares equal amount of time with the

ballball

Double Covalent BondDouble Covalent Bond

Sharing two pairs of electronsSharing two pairs of electrons Space filling model shows picture of Space filling model shows picture of

moleculesmolecules Structural formula uses lines to show bonds:Structural formula uses lines to show bonds:

• Hydrogen: H-HHydrogen: H-H• Oxygen: O=OOxygen: O=O• Carbon dioxide O=C=OCarbon dioxide O=C=O

Let’s take another look at covalent Let’s take another look at covalent bondingbonding

ReviewReview

What is the difference between ionic What is the difference between ionic bonds and covalents bonds?bonds and covalents bonds? Ionic bonding: atoms lose or gain electronsIonic bonding: atoms lose or gain electrons Covalent bonding: atoms share electronsCovalent bonding: atoms share electrons

What is the difference between What is the difference between compounds and molecules?compounds and molecules? Compounds: formed through ionic bondingCompounds: formed through ionic bonding Molecules: formed through covalent bondingMolecules: formed through covalent bonding

From Atoms to MoleculesFrom Atoms to Molecules

Polar Covalent BondsPolar Covalent Bonds

Polar covalent bond: unequal sharing of Polar covalent bond: unequal sharing of electronselectrons

Polar Covalent BondsPolar Covalent Bonds Water:Water:

Oxygen atom forms covalent bond with two Oxygen atom forms covalent bond with two hydrogen atomshydrogen atoms

The oxygen atom has a much stronger The oxygen atom has a much stronger attraction for the shared electrons than the attraction for the shared electrons than the hydrogen atoms do (electrons spend most of hydrogen atoms do (electrons spend most of their time orbiting around the oxygen nucleus)their time orbiting around the oxygen nucleus)

Polar covalent bondsPolar covalent bonds

Because it has two extra electrons part of Because it has two extra electrons part of the time, the oxygen atom develops a the time, the oxygen atom develops a slight negative charge and the hydrogen slight negative charge and the hydrogen atoms become weakly positiveatoms become weakly positive

Hydrogen BondHydrogen Bond

Attraction between a hydrogen atom and Attraction between a hydrogen atom and an atom such as oxygen or nitrogen that is an atom such as oxygen or nitrogen that is either part of another molecule or located either part of another molecule or located at a distant site on the same molecule.at a distant site on the same molecule.

Both the hydrogen atom and the other Both the hydrogen atom and the other atom must be involved in a polar covalent atom must be involved in a polar covalent bondbond

Molecular View of Solution Molecular View of Solution FormationFormation

Why does salt dissolve in water?Why does salt dissolve in water? Dissolving salt in waterDissolving salt in water