MondayNovember 5, 2012

(Worksheet - Ionic Bonds, the Octet Rule, and Lewis Structures)

Bell RingerMonday, 11-5-12

Oxygen forms covalent bonds with  carbon and sulfur, but forms ionic bonds with sodium and magnesium. What is the BEST inference for this difference in how oxygen behaves?

A Oxygen bonds randomly with elements in unpredictable  ways .

B The difference in atomic radii between the groups accounts for the difference in behavior .

C Oxygen only bonds with elements that have a smaller atomic mass.

D Electronegativity differences between the bonding elements allow electrons to be

either shared or donated.

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Ionic Bonds

A chloride ion, Cl−, has a charge of 1−.

A sodium ion, Na+, has a charge of 1+.Na+

Cl-

In sodium chloride, these ions combine in a one-to-one ratio (Na+Cl−) so that each positive charge is balanced by a negative charge, resulting in a neutral charge for the

unit as a whole.

Na+ Cl-

NaClThe chemical

formula for sodium chloride is usually written simply as

NaCl.

Ionic Bonds

Ionic BondsAn ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are

equal.

NaCl MgCl2

Ionic BondsExample

Na → Na+ + e-

e- + Cl → Cl-

Na+ + Cl- → NaCl

Sodium has 1 valence electron and loses it to

become stable, but in doing so takes on a 1+ charge.Chlorine has 7 valence

electrons and gains 1 to become stable, but in doing

so takes on a 1- charge.

The two oppositely-charged ions attract each other and

form an ionic bond. The compound is neutral.

Dot Notations of Na and Cl

Ionic BondsExample

Ca → Ca2+ + 2e-

2e- + 2F → 2F-

Ca2+ + 2F- → CaF2

Calcium has 2 valence electrons and loses them to become stable, but in doing

so takes on a 2+ charge.Two fluorine atoms have 7 valence electrons each and

each gains 1 to become stable, but in doing so both

take on a 1- charge.The calcium ion attracts

both of the fluoride ions and form an ionic bond. The

compound is neutral.

Dot Notations of Ca and F

In order to be neutral, this compound must exist in a 1:2 ratio.

CaF2

The Octet RuleNoble Gas atoms normally

exist singly in nature.

The reason for this is because they have a

completely filled valence shell (outer lane.)

He has 2 electrons in its valence shell, while all other NG’s have 2 in their s-orbital and 6 in their p-orbitals for a total of 8 electrons.

This configuration is what is needed to be stable.

All other atoms must fill their valence shells through bonding.

The Octet RuleBond formation follows the Octet Rule, which states that chemical compounds

tend to form so that each atom, by gaining, losing or sharing electrons, has an octet of electrons (8) in its highest occupied energy level.

The Octet RuleFor example , fluorine has an electron configuration

notation of

1s2, 2s2, 2p5

In fluorine’s highest occupied energy level it has 2 electrons in the s sublevel and 5 electrons in the p

sublevel.

The total number of electrons in fluorine’s highest occupied energy level is therefore

2 + 5 = 7One fluorine atoms bonds to a second fluorine atom to

form F2 (fluorine gas, a compound).

Each atom shares one of its valence electrons with its partner to get 8 electrons in the valence shell.

The Octet RuleFluorine

The shared electron pair effectively fills each atom’s

outermost energy level_____ _____ _____ _____ _____

1s2 2s2 2px 2py 2pz_____ _____ _____ _____ _____

1s2 2s2 2px 2py 2pz

Electron-Dot NotationIn compounds, a pair of

dots between two symbols represents the shared pair of electrons.An unshared pair (lone

pair) is a pair of electrons that is not

involved in bonding and that belongs exclusively

to one atom.

The pair of dots representing a shared pair of electrons in a

covalent bond is often replaced by a dash.

Lewis StructuresElectron Dot Notation

representations are termed Lewis Structures.

Lewis Structures are formulas in which:

– an element’s atomic symbol represents its nuclei and inner-

shell electrons.–dot pairs or dashes between two atomic symbols represent valence electron pairs in covalent bonds.

–dots adjacent to only one atomic symbol represent unshared

valence electrons.

Lewis StructuresLewis structural formulas indicate the

kind, number, arrangement and bonds but not the unshared pairs of

the atoms in a molecule.

F-FH-Cl

A covalent bond produced by the sharing of one pair of electrons

between two atoms is called a single bond.

Lewis Structures ExampleDraw the Lewis structure of iodomethene, CH3IThe formula shows one carbon atom, one iodine

atom, and three hydrogen atoms.Write the electron-dot notation for each type of

atom in the molecule.Carbon is in Group 14 and has four valence

electrons. Iodine is in Group 17 and has seven valence electrons. Hydrogen above Group 1 has

one valence electron.

WorksheetIonic Bonds, the Octet Rule,

and Lewis Structures