chemical bonding and nomenclature

Chemical Bonding and Nomenclature

Chapter 5

What is a Molecule ?

Molecule

A collection of atoms bonded together

Elemental molecules

Atoms from same element

Diatomic: H2, N2, O2, F2, I2, Br2

What is a Molecule

Molecules of Compounds

Atoms of different elements

Simple vs. Complicated

Small vs. extremely large

Properties of Molecules

Molecules have different properties than their elemental component.

Element Properties

O Odorless, colorless very reactive toxic gas

H Odorless colorless gas reactive

Properties of Molecules

Molecule Properties

O2Colorless odorless gas moderately reactive not flammable

H2Colorless odorless gas moderately reactive flammable

H2OColorless odorless liquid, low reactivity

H2O2Colorless odorless liquid high reactivity

Why do molecules form?

To be like the noble gases

The noble gases are perfect hence they do not react with anything

They have 8 valence electrons in their outer most shell

Valence Electrons?

The outermost electrons. Determines the chemical properties of an element

The only electrons that bond

The roman numerals at the top of each group A element

Most elements prefer to have 8 electrons this is called the octet rule. Why?

The Octet Rule

Atoms tend to gain, lose, or share electrons until they have eight valence electrons.

Electron Dot diagrams

A way of keeping track of valence electrons.

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

electron Don’t pair up until you have

too.

X

The Electron 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 electron dot diagram for

Na Mg C O F Al He

Electron Configurations for Cations

Metals lose electrons to attain noble gas configuration.

They make positive ions.

Electron Dots For Cations

Metals will have few valence electrons

Ca

Electron Dots For Cations Metals will have few valence electrons These will come off

Ca

Electron Dots For Cations

Metals will have few valence electrons These will come off Forming positive ions

Ca+2

Electron Configurations for Anions

Nonmetals gain electrons to attain noble gas configuration.

They make negative ions.

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 8 valence electrons . Also called the octet rule.

Ar

Covalent Bonding

How does H2 form?

The nuclei repel

++

How does H2 form?

++

The nuclei repel

But they are attracted to electrons

They share the electrons

Covalent bonds

Nonmetals hold onto their valence electrons.

They can’t give away electrons to bond. Still want noble gas configuration. Get it by sharing valence electrons with

each other. By sharing both atoms get to count the

electrons toward noble gas configuration.

Covalent bonding

Fluorine has seven valence electrons

F

Covalent bonding

Fluorine has seven valence electrons A second atom also has seven

F F

Covalent bonding

Fluorine has seven valence electrons A second atom also has seven By sharing electrons

F F

Single Covalent Bond

A sharing of two valence electrons.

Only nonmetals and Hydrogen.

How to show how they formed

It’s like a jigsaw puzzle.

I have to tell you what the final formula is.

You put the pieces together to end up with the right formula.

For example- show how water is formed with covalent bonds.

Water

H

O

Each hydrogen has 1 valence electron

Each hydrogen wants 1 more

The oxygen has 6 valence electrons

The oxygen wants 2 more

They share to make each other happy

Water Put the pieces together The first hydrogen is happy The oxygen still wants one more

H O

Water

The second hydrogen attaches Every atom has full energy levels

H OH

Multiple Bonds

Sometimes atoms share more than one pair of valence electrons.

A double bond is when atoms share two pair (4) of electrons.

A triple bond is when atoms share three pair (6) of electrons.

Carbon dioxide CO2 - Carbon is central atom

( I have to tell you) Carbon has 4 valence

electrons Wants 4 more Oxygen has 6 valence

electrons Wants 2 moreO

C

Carbon dioxide

Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short

OC

Carbon dioxide Attaching the second oxygen leaves

both oxygen 1 short and the carbon 2 short

OCO

Carbon dioxide

The only solution is to share more

OCO

Carbon dioxideCarbon dioxide The only solution is to share more

OCO

Carbon dioxideCarbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxideCarbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

8 valence electrons

Hydrogen 2 valence e-

Groups 1,2,3 get 2,4,6 valence e-

Expanded octet more than 8 valence e- (e.g.

S, P, Xe)

Radicals odd # of valence e-

Exceptions:

A. Octet Rule

F B FFH O HN O

Very unstable!!

F F

F S F

F F

B. Drawing Lewis Diagrams Find total # of valence e-.

Arrange atoms - singular atom is usually in the middle.

Form bonds between atoms (2 e-).

Distribute remaining e- to give each atom an octet (recall exceptions).

If there aren’t enough e- to go around, form double or triple bonds.

B. Drawing Lewis Diagrams

CF4

1 C × 4e- = 4e-

4 F × 7e- = 28e-

32e- FF C F

F

- 8e-

24e-

B. Drawing Lewis DiagramsBeCl2

1 Be × 2e- = 2e-

2 Cl × 7e- = 14e-

16e-

Cl Be Cl - 4e-

12e-

B. Drawing Lewis DiagramsCO2

1 C × 4e- = 4e-

2 O × 6e- = 12e-

16e-

O C O - 4e-

12e-

C. Polyatomic Ions

To find total # of valence e-: Add 1e- for each negative charge. Subtract 1e- for each positive charge.

Place brackets around the ion and label the charge.

C. Polyatomic Ions

ClO4-

1 Cl × 7e- = 7e-

4 O × 6e- = 24e-

31e- OO Cl O

O

+ 1e-

32e-

- 8e-

24e-

NH4+

1 N × 5e- = 5e-

4 H × 1e- = 4e-

9e- HH N H

H

- 1e-

8e-

- 8e-

0e-

C. Polyatomic Ions

D. Resonance Structures

Molecules that can’t be correctly represented by a single Lewis diagram.

Actual structure is an average of all the possibilities.

Show possible structures separated by a double-headed arrow.

D. Resonance Structures

OO S O

OO S O

OO S O

SO3

Practice

Complete the worksheet

Nomenclature-Naming Chemical Compounds

Atoms and ions

Atoms are electrically neutral.

Same number of protons and electrons.

Ions are atoms, or groups of atoms, with a charge.

Atoms and Ions

Different numbers of protons and electrons.

Only electrons can move.

Gain or lose electrons.

Anion

A negative ion. Has gained electrons. Non metals can gain electrons. Charge is written as a super script on the

right.

F-1 Has gained one electron

O-2 Has gained two electrons

Cations

Positive ions. Formed by losing electrons. More protons than electrons. Metals form cations.

K+1 Has lost one electron

Ca+2 Has lost two electrons

Two Types of Compounds

Molecular compounds

Made of molecules.

Made by joining nonmetal atoms together into molecules.

Two Types of Compounds

Ionic Compounds

Made of cations and anions. Metals and nonmetals. The electrons lost by the cation are gained by

the anion. The cation and anions surround each other. Smallest piece is a FORMULA UNIT.

Formula Unit

The smallest whole number ratio of atoms in an ionic compound.

Ions surround each other so you can’t say which is hooked to which.

Two Types of Compounds

Smallest piece

Melting Point

State

Types of elements

Formula Unit Molecule

Metal and Nonmetal

Nonmetals

solidSolid, liquid or gas

High >300ºC Low <300ºC

Ionic Molecular

Chemical Formulas

Shows the kind and number of atoms in the smallest piece of a substance.

Molecular formula- number and kinds of atoms in a molecule.

CO2

Charges on ions

For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.

Elements in the same group have similar properties.

Including the charge when they are ions.

+2

+1

+3 -3 -2 -1

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.

Transition metals can have more than one type of charge. Indicate the charge with roman numerals in

parenthesis.

Name these

Na+1

Ca+2

Al+3

Fe+3

Fe+2

Pb+2

Li+1

Write Formulas for these

Potassium ion Magnesium ion Copper (II) ion Chromium (VI) ion Barium ion Mercury (II) ion

Naming Anions

Anions are always the same.

Change the element ending to – ide

F-1 Fluoride

Name these

Cl-1

N-3

Br-1

O-2

Write these

Sulfide ion

iodide ion

phosphide ion

Strontium ion

Polyatomic ions

Groups of atoms that stay together and have a charge. Acetate C2H3O2

-1

Nitrate NO3-1

Nitrite NO2-1

Hydroxide OH-1

Permanganate MnO4-1

Cyanide CN-1

Polyatomic ions

Sulfate SO4-2

Sulfite SO3-2

Carbonate CO3-2

Chromate CrO4-2

Dichromate Cr2O7-2

Phosphate PO4-3

Phosphite PO3-3

Ammonium NH4+1

Ions and Ionic Compounds

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

Naming Binary Ionic Compounds

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 CuO Need the charge of Cu O is -2 copper must be +2 Copper (II) chloride

Name CoCl3

Cl is -1 and there are three of them = -3 Co must be +3 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.

copper (I) sulfide Fe2O3 Each O is -2 Fe must be = + 3 iron (III) oxide

Naming Binary Ionic Compounds

Write the names of the following:

KCl

Na3N

CrN

Na2Se

Ternary Ionic Compounds

Will have polyatomic ions At least three elements name the ions

NaNO3

CaSO4

CuSO3

(NH4)2O

Ternary Ionic Compounds

LiCN

Fe(OH)3

(NH4)2CO3

NiPO4

Writing Formulas

The charges have to add up to zero. Get charges on pieces. Cations from name of table. Anions from table or polyatomic. Balance the charges. Put polyatomics in parenthesis.

Writing Formulas

Write the formula for calcium chloride.

Calcium is Ca+2

Chloride is Cl-1

Ca+2 Cl-1

CaCl2

Write the formulas for these Lithium sulfide tin (II) oxide tin (IV) oxide Magnesium fluoride Copper (II) sulfate Iron (III) phosphide Gallium (III) nitrate Iron (III) sulfide

Write the formulas for these

Ammonium chloride

ammonium sulfide

barium nitrate

Things to look for

If cations have (), the number is their charge.

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

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

Molecular Compounds

Molecular compounds

made of just nonmetals

smallest piece is a molecule

can’t be held together because of opposite charges

can’t use charges to figure out how many of each atom

Easier

Ionic compounds use charges to determine how many of each

Have to figure out charges

Have to figure out numbers

Molecular compounds name tells you the number of atoms

Uses prefixes to tell you the number

Prefixes

1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa-

Prefixes

9 nona-

10 deca-

One exception is we don’t write mono- if there is only one of the first element.

Name These

N2O

NO2

Cl2O7

CBr4

CO2

BaCl2

Write formulas for these

diphosphorus pentoxide tetraiodide nonoxide sulfur hexaflouride nitrogen trioxide Carbon tetrahydride phosphorus trifluoride aluminum chloride

Naming Acids

a little tricky so pay attention

Acids

Compounds that give off hydrogen ions when dissolved in water

Must have H in them (somewhere)

will always be some H next to an anion

The anion determines the name.

Naming acids

If the anion attached to hydrogen ends in -ide, put the prefix hydro- and change -ide to -ic acid

HCl - hydrogen ion and chloride ion

hydrochloric acid

H2S hydrogen ion and sulfide ion

hydrosulfuric acid

Naming Acids

If the anion has oxygen in it it ends in -ate or -ite change the suffix -ate to -ic acid

HNO3 Hydrogen and nitrate ions

Nitric acid change the suffix -ite to -ous acid

HNO2 Hydrogen and nitrite ions

Nitrous acid

Name these

HF

H3P

H2SO4

H2SO3

HCN

H2CrO4

Writing Formulas

Hydrogen will always be first

name will tell you the anion

make the charges cancel out.

Starts with hydro- no oxygen, -ide

no hydro, -ate comes from -ic, -ite comes from -ous

Write formulas for these

hydroiodic acid acetic acid carbonic acid phosphorous acid hydrobromic acid