Valence Electrons, Ions, and Lewis Dot Diagrams

Valence Electrons, Ions, and Lewis Dot Diagrams

Unit 4

Keeping Track of Electrons

The electrons responsible for the chemical properties of atoms are those in the outer energy level.Valence electrons

Valence electrons - The s and p electrons in the outer energy level.

Core electrons -those in the energy levels below.

Keeping Track of Electrons

Atoms in the same columnHave the same outer electron configuration.Have the same valence electrons.

Easily found by looking up the group number on the periodic table.

Group 2A - Be, Mg, Ca, etc.- 2 valence electrons

Lewis Dot diagrams

A way of keeping track of valence electrons.

How to write themWrite the symbol.Put one dot for each valence

electronDon’t pair up until they have to

Xe

The Lewis Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side.Until they are forced to pair up.

Write the Lewis dot diagram for

NaMgCOFNeHe

Electron Configurations for Cations

Metals lose electrons to attain noble gas configuration.

They make positive ions.If we look at electron configuration it

makes sense.Na 1s22s22p63s1 - 1 valence electronNa+ 1s22s22p6 -noble gas configuration

Electron Dots For Cations

Metals will have few valence electrons

Ca

Electron Dots For Cations

Metals will have few valence electronsThese will come off

Ca

Electron Dots For Cations

Metals will have few valence electronsThese will come offForming positive ions

Ca+2

Electron Configurations for Anions

Nonmetals gain electrons to attain noble gas configuration.

They make negative ions.If we look at electron configuration it makes

sense.S 1s22s22p63s23p4 - 6 valence electronsS-2 1s22s22p63s23p6 -noble gas

configuration.

Electron Dots For Anions

Nonmetals will have many valence .electrons.

They will gain electrons to fill outer shell.

P P-3

Stable Electron Configurations

All atoms react to achieve noble gas configuration.

Noble gases have 2 s and 6 p electrons.8 valence electrons .Also called the octet rule.

Ar

+2

+1

+3 -3 -2 -1

Unit 4: Chapter 8

Ionic Bonding

+2

+1

+3 -3 -2 -1

Properties of Ionic Compounds

Crystalline structure.A regular repeating arrangement of ions in

the solid.Ions are strongly bonded.Structure is rigid.High melting points- because of strong

forces between ions.

Crystalline structure

Ionic Bonding

Anions and cations are held together by opposite charges.

Ionic compounds are called salts.Simplest ratio is called the formula unit.The bond is formed through the transfer of

electrons.Electrons are transferred to achieve noble

gas configuration.

Do they Conduct?

Conducting electricity is allowing charges to move.

In a solid, the ions are locked in place.Ionic solids are insulators.When melted, the ions can move around.Melted ionic compounds conduct.

First get them to 800ºC.

Dissolved in water they conduct.

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Ionic solids are brittle

+ - + -

+- +-+ - + -

+- +-

Strong Repulsion breaks crystal apart.

Ionic Bonding

Na Cl

Ionic Bonding

Na+ Cl-

Ionic Bonding

All the electrons must be accounted for!

Ca P

Ionic Bonding

Ca P

Ionic Bonding

Ca+2 P

Ionic Bonding

Ca+2 P

Ca

Ionic Bonding

Ca+2 P-3

Ca

Ionic Bonding

Ca+2 P-3

Ca P

Ionic Bonding

Ca+2 P-3

Ca+2 P

Ionic Bonding

Ca+2 P-3

Ca+2 P

Ca

Ionic Bonding

Ca+2 P-3

Ca+2 P

Ca

Ionic Bonding

Ca+2 P-3

Ca+2P

-3

Ca+2

Ionic Bonding

Ca3P2

Formula Unit

Naming ions

We will use the systematic way.Cation- if the charge is always the same

(Group A) just write the name of the metal.Examples

Sodium ion = Na+

Barium ion = Ba2+

Silver ion = Ag+

Zinc ion = Zn2+

Naming Anions

Anions always have the same charge.Change the element ending to – ideExamples

Fluorine as an ion= F-1 fluorideChlorine as an ion= Cl- chlorideOxygen as an ion= O2- oxide

Name these

Cl-1 N-3 I-1 S-2

Chloride ionNitride ionIodide ionSulfide ion

Write these

Oxide ionFluoride ionPhosphide ionStrontium ion

O2-

F-

P3-

Sr2+

Naming Binary Ionic Compounds

Binary Compounds - 2 elements.Ionic - a cation and an anion.To write the names just name the two

ions.Easy with Representative elements

(Group A)NaCl = Na+ Cl- = sodium chloride

MgBr2 = Mg+2 Br- = magnesium bromide

Writing Formulas

The charges have to add up to zero.Get charges on pieces.Charges for Cations come from the

periodic table.If it is a transition metal, the charge is the

roman numeralAnions from the periodic table.Criss- Cross the charges to determine

subscripts

The Criss-Cross Rule

Write the formula for calcium chloride.Calcium is Ca+2 Chloride is Cl-1 Criss Cross the charges to determine the

subscripts

Ca+2 Cl-1( only the numbers, not the signs)

ANSWER: CaCl2

Naming ions with Transition Metals

Transition metals can have more than one type of charge.

Indicate the charge with roman numerals in parenthesis.

ExamplesNi+2 = nickel (II) ionNi+ = nickel (I) ion

Naming Binary Ionic Compounds

Write the formulas for each the following

1. Chromium (III) nitride

2. Scandium (II) phosphide

3. Lead (II) oxide

4. Lead (IV) oxide

•CrN

•Sc3P2

•PbO

•PbO2

Naming Binary Ionic Compounds with Transition Metals

The problem comes with the transition metals.

Need to figure out their charges.The compound must be neutral.

same number of + and – charges.

Use the anion to determine the charge on the positive ion.

Naming Binary Ionic Compounds

Write the name of CuONeed the charge of CuO is -2copper must be +2

ANSWER: Copper (II) oxide

Name CoCl3

Cl is -1there are three of them = -3

Co must be +3 ANSWER: Cobalt (III) chloride

Naming Binary Ionic Compounds

Write the name of Cu2S.Since S is -2, the Cu2 must be +2, so each one

is +1.ANSWER: copper (I) sulfide

Fe2O3 Each O is -2 3 x -2 = -62 Fe must = +6, so each is +3.

ANSWER: iron (III) oxide

Write the formulas for these

Lithium sulfide

tin (II) oxide

tin (IV) oxide

Magnesium fluoride

Iron (III) phosphide

Iron (III) sulfide

1. Li2S

2. SnO

3. SnO2

4. MgF2

5. FeP

6. Fe2P3

Polyatomic ions

Groups of atoms that stay together and have a charge.

You must memorize these by the midterm

Nitrate NO3-1

Hydroxide OH-1

Sulfate SO4-2

Phosphate PO4-3

Ammonium NH4+1

Write the formulas for these

Ammonium chlorideammonium sulfidebarium nitrateCopper (II) sulfategallium nitrate

Ternary Ionic Compounds

NaNO3

CaSO4

CuSO3

(NH4)2O

Ternary Ionic Compounds

LiCN

Fe(OH)3

(NH4)2CO3

NiPO4

Things to look for

If cations have (), the number is their charge.If not it only has 1 charge, look on the periodic

table

If anions end in -ide they are probably off the periodic table (Monoatomic)

If anion ends in -ate or -ite it is polyatomic

Metallic Compounds

Metallic Bonds

How atoms are held together in the solid.Metals hold onto there valence electrons

very weakly.Think of them as positive ions floating in a

sea of electrons.

Sea of Electrons

+ + + ++ + + +

+ + + +

Electrons are free to move through the solid.Electrons are said to be “delocalized”

Metals conduct electricity.

Properties of Metallic Compounds

Metal ions bonded togetherCan be atoms of different metals

Hammered into shape (bend).Ductile - drawn into wires.Melting and boiling points vary (based on

metal)Good conductors of electricity as a solid

Malleable

+ + + ++ + + +

+ + + +

Malleable

+ + + +

+ + + ++ + + +

Electrons allow atoms to slide by.