Lewis Dot Structures

Lewis Dot StructuresLewis Dot Structures

Predicting compound structures Predicting compound structures and properties using a simple and properties using a simple

theory.theory.

Atoms have a Lewis Dot Symbol Atoms have a Lewis Dot Symbol with a dot for each valence with a dot for each valence electronelectron

HHOO

CaCa

Binary Ionic CompoundsBinary Ionic Compounds

Binary - only two elements in the Binary - only two elements in the compound.compound.

Ionic - compound with metal and Ionic - compound with metal and nonmetal elements (99% of the nonmetal elements (99% of the

time) time)

Lewis Dots- the valence electronsLewis Dots- the valence electrons

The total of the The total of the number of valence number of valence electrons electrons determines how determines how many DOTS!many DOTS!

Each element has Each element has the valence the valence electrons = group #.electrons = group #.

KKgroup 1group 1

..

Lewis Dots- the valence electronsLewis Dots- the valence electrons

Find the group Find the group number from the number from the periodic table ( it is periodic table ( it is the number at the the number at the top of the column).top of the column).

These are the These are the electrons that will electrons that will participate in participate in bondingbonding..

:S::S:group 6group 6

. .

..

IONIC BONDS - Transfer of IONIC BONDS - Transfer of Electrons from metal to nonmetalElectrons from metal to nonmetal

Metal transfers Metal transfers allall of of the electrons in its the electrons in its valence shell, so valence shell, so that it leaves the that it leaves the filled shell beneath.filled shell beneath.

Nonmetal accepts Nonmetal accepts enough electrons so enough electrons so that it has that it has 88 in its in its valence shell.valence shell.

electronelectron

Lithium Fluoride: Binary IonicLithium Fluoride: Binary Ionic

3p3p

Li atomLi atom F atomF atom

9p9p2e2e2e2e

1e1e7e7e

Lithium Fluoride: Binary IonicLithium Fluoride: Binary Ionic

3p3p

LiLi+1+1 ion ion FF-1-1 ion ion

9p9p2e2e2e2e

8e8eCharge = #p - #eCharge = #p - #e

Or you could use the dots!Or you could use the dots!

LiLi FF

LithiumLithiumatomatom

FluorineFluorineatomatom

LiLi+1+1 [ F ][ F ]-1-1

Calcium Sulfide: an Ionic Calcium Sulfide: an Ionic Compound.Compound.

Ca is a metal with 2 Ca is a metal with 2 valence electrons. It valence electrons. It loses them to make loses them to make CaCa+2+2 ion. ion.

S is a nonmetal with S is a nonmetal with 6 valence electrons. 6 valence electrons. It gains 2 electrons It gains 2 electrons to make to make 88. Sulfide . Sulfide ion is Sion is S-2-2..

Ca SCa S

CaCa+2+2[ S ][ S ]-2-2

calcium sulfidecalcium sulfide

calciumcalcium sulfursulfur

Potassium Nitride: an Ionic Potassium Nitride: an Ionic Compound.Compound.

K is a metal with 1 K is a metal with 1 valence electron that it valence electron that it transfers to form Ktransfers to form K+1+1..

N is a nonmetal with 5 N is a nonmetal with 5 valence electrons. It valence electrons. It must gain 3 electrons to must gain 3 electrons to make 8 and Nmake 8 and N-3-3. .

That means 3 K must That means 3 K must transfer their electrons transfer their electrons to each N.to each N.

KK+1+1 KK+1+1[ N ][ N ]-3-3

KK+1+1potassium nitridepotassium nitride

Aluminum Oxide: an Ionic Aluminum Oxide: an Ionic Compound.Compound.

Al is a metal with 3 valence Al is a metal with 3 valence electron that it transfers to electron that it transfers to form Alform Al+3+3..

O is a nonmetal with 6 O is a nonmetal with 6 valence electrons. It must valence electrons. It must gain 2 electrons to make 8 gain 2 electrons to make 8 and Oand O-2-2. .

That means 2 Al must That means 2 Al must transfer their electrons to transfer their electrons to three O.three O.

Notice the sum of ALL Notice the sum of ALL charges equals zero. (3+3+ charges equals zero. (3+3+ -2+ -2+ -2 = 0)-2+ -2+ -2 = 0)

[ O ][ O ]-2-2

AlAl+3+3 [ O ][ O ]-2-2

AlAl+3 +3

[ O ][ O ]-2-2

TO WRITE A BINARY IONIC TO WRITE A BINARY IONIC LEWIS DOT STRUCTURE:LEWIS DOT STRUCTURE:

Write the metal ion Write the metal ion with its positive with its positive charge.charge.

Write the nonmetal Write the nonmetal ion surrounded by 8 ion surrounded by 8 dots in square dots in square brackets with its brackets with its negative charge.negative charge.

NaNa+1+1 [ Cl ] [ Cl ] -1-1

metalmetal

nonmetalnonmetal

Did you notice a pattern?Did you notice a pattern?

All group 1 metals start with 1 valence All group 1 metals start with 1 valence electron, so they all make an ion with electron, so they all make an ion with the charge of the charge of +1 +1 examples: Li examples: Li+1+1, Na, Na+1+1

All group 2 metals start with 2 valence All group 2 metals start with 2 valence electrons, so they all make an ion with electrons, so they all make an ion with the charge of the charge of +2+2 examples: Ca examples: Ca+2+2, Mg, Mg+2+2

All group 3 metals start with 3 valence All group 3 metals start with 3 valence electrons, charge electrons, charge +3+3 example: Al example: Al+3+3

For the nonmetals the pattern is..For the nonmetals the pattern is..

Group 7 elements need 1 electron to Group 7 elements need 1 electron to make 8 so they have a make 8 so they have a -1-1 charge ion. charge ion. Examples: F Examples: F -1-1, Cl , Cl -1-1, Br , Br -1-1, I , I -1-1

Group 6 elements need 2 electrons to Group 6 elements need 2 electrons to make 8 so they have a make 8 so they have a -2-2 charge ion. charge ion. Examples: OExamples: O-2-2, S, S-2-2, Se, Se-2-2

Group 5 elements need 3 electrons so Group 5 elements need 3 electrons so they have a they have a -3-3 charge ion. Example: N charge ion. Example: N-3-3

Naming Binary Ionic CompoundsNaming Binary Ionic Compounds

Name the metal firstName the metal first Name the nonmetal Name the nonmetal

second using an -second using an -ide ending, i.e. oxideide ending, i.e. oxide

NEVER use prefixes NEVER use prefixes to tell how many of to tell how many of each element is each element is present! present! That is only That is only done for covalent.done for covalent.

Formula to NameFormula to Name

NaCl is sodium chlorideNaCl is sodium chloride BeBrBeBr22 is beryllium bromide is beryllium bromide note that no note that no

prefix is used!prefix is used! AlAl22SS33 is aluminum sulfide is aluminum sulfide

KK22O is potassium oxideO is potassium oxide

MgIMgI22 is magnesium iodide is magnesium iodide

Name to Formula (Harder)Name to Formula (Harder)

lithium sulfide lithium sulfide look up the charge on look up the charge on each ion firsteach ion first Li Li+1+1 and S and S-2-2 the charges must total to zerothe charges must total to zero so that so that means there must be 2(+1) + 1(-2) = 0 means there must be 2(+1) + 1(-2) = 0 lithium sulfide is Lilithium sulfide is Li22S.S.

calcium fluoride......... Cacalcium fluoride......... Ca+2 +2 and F and F -1 -1 so so CaFCaF22 is the formula is the formula

Try these Names to FormulaTry these Names to Formula

Sodium phosphideSodium phosphide Magnesium iodideMagnesium iodide Aluminum bromideAluminum bromide Barium sulfideBarium sulfide

Try these Names to FormulaTry these Names to Formula

Sodium phosphide Sodium phosphide NaNa33PP

Magnesium iodide Magnesium iodide MgIMgI22

Aluminum bromide Aluminum bromide AlBrAlBr33

Barium sulfide Barium sulfide BaSBaS

Start thinking about the next Start thinking about the next lecturelecture

Metals that form ions of more than Metals that form ions of more than one charge…..aka variable charge one charge…..aka variable charge

metalsmetals

Variable Charge MetalsVariable Charge Metals

These are metals other than those in These are metals other than those in group 1 and 2 plus Algroup 1 and 2 plus Al+3+3, Zn, Zn+2+2, Ag, Ag+1+1, Cd, Cd+2+2..

Example: Fe is commonly found as FeExample: Fe is commonly found as Fe+2+2 and Feand Fe+3+3. FeO is called iron (II) oxide . FeO is called iron (II) oxide where the roman numeral 2 is the where the roman numeral 2 is the charge on the iron. Fecharge on the iron. Fe22OO33 is iron (III) is iron (III)

oxide, the charge on iron is +3.oxide, the charge on iron is +3.

In-class assignmentIn-class assignment

1) Draw the Lewis Dot 1) Draw the Lewis Dot structures for: KI and Nastructures for: KI and Na33P P

2) Name KI and Na2) Name KI and Na33PP 3) Write the formula and Lewis 3) Write the formula and Lewis

Dot structures for: sodium Dot structures for: sodium sulfide and calcium bromidesulfide and calcium bromide