Chemical Bonds

Bonding: the way atoms are attracted to each other to form molecules, determines nearly all of the chemical properties we see. And, as we shall see, the number “8” is very important to chemical bonding.

008: Chemical Bonds

Molecule – 2 atoms chemically combined, smallest part of compound

Compounds – atoms of 2 or more elements chemically combined, new properties not like the elements it is made of

Law of Definite Proportions

atoms combine in proportions, whole number ratios.

H2O = 2 H for every O

Atoms combine so that their outer energy level is full

Bonds – force of attraction that holds atoms together in a molecule

Octet Rule - all elements want to be happy!!!8e- in outer level, like the noble gases

When atoms combine, electrons are shared or exchanged

Atoms are electrically neutral (p+ = e-)

Ions - Atoms with a charge due to gain or loss of e-

Cation - +charge, lost e-, have more p+ than e-

Anion - –charge, gained e-, fewer p+ than e-

Polyatomic ions – group of atoms acting together and carrying a charge

8 e- in outer level

1 e- in outer level

7 e- in outer level

Ionic Bonds: transfer e-

How can we make Na and Cl happy?

Na gives up e- to Cl

Chemical Formula = NaCl

The positive and negative ions are attracted to each other

The Lewis dot structure for Chlorine

Clchlorine is in group VIIA so it has 7 valence electrons

The Lewis dot structure for calcium

Cacalcium is in group IIA so it has 2 valence electrons

Making calcium chloride

+Ca Cl Cl

Ca( Cl )2

Electropositive elements:

Readily give up electrons

to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.

Potassium & Fluorine

K+ and F-

KF

Potassium fluoride

Aluminum oxide

Al+3O-2

Cross multiply (LCM=6)

Al2O3

+6-6=0 charge

Give up electrons Acquire electrons

He -

Ne -

Ar -

Kr -

Xe -

Rn -

F 4.0

Cl 3.0

Br 2.8

I 2.5

At 2.2

Li 1.0

Na 0.9

K 0.8

Rb 0.8

Cs 0.7

Fr 0.7

H 2.1

Be 1.5

Mg 1.2

Ca 1.0

Sr 1.0

Ba 0.9

Ra 0.9

Ti 1.5

Cr 1.6

Fe 1.8

Ni 1.8

Zn 1.8

As 2.0

CsCl

MgO

CaF2

NaCl

O 3.5

Na+ + Cl- = NaCl

Ca+2 + O-2= CaO Na+ + O-2 = Na2O

Al+3 + S-2 = Al2S

3Ca+2 + N-3 = Ca

3N

2

Ca+2 + Cl- = CaCl2

You try these!

Mg+2 + F- =

NH4

+ + PO4

-3 =

K+ + Cl- =

Al+3 + I- =

Sr+2 + P-3 =

Li+ + Br- =

Sr3P

2

AlI3

MgF2

(NH4)3PO

4

KCl

LiBr

Not NH43

PO4

METALLIC BONDS

e- are shared by all atoms

sea of electrons allow

current to flow through

metal = conductors

In sodium, 1 out of the 11 electrons is released so that

Na has two filled shells. The extra electrons move

around the metal in a “sea” of negative charge. This

negatively charged sea moves around a regular

structure of positive Na ions.

Atoms share electronsPolar Covalent – result of uneven sharing, ends have slight +/- charges

Ex. Water

Single bond: sharing 1 pair of e-

Double bond: sharing 2 pairs of e-

Triple bond: sharing 3 pairs of e-

He -

Ne -

Ar -

Kr -

Xe -

Rn -

F 4.0

Cl 3.0

Br 2.8

I 2.5

At 2.2

Li 1.0

Na 0.9

K 0.8

Rb 0.8

Cs 0.7

Fr 0.7

H 2.1

Be 1.5

Mg 1.2

Ca 1.0

Sr 1.0

Ba 0.9

Ra 0.9

Ti 1.5

Cr 1.6

Fe 1.8

Ni 1.8

Zn 1.8

As 2.0

SiC

C(diamond)

H2O

C 2.5

H2

Cl2

F2

Si 1.8

Ga 1.6

GaAs

Ge 1.8

O 2.0

co

lum

n I

VA

Sn 1.8

Pb 1.8

3.5

Lewis dot structure of a compound NH3

1) How many valence electrons does N have?

N is in group VA so it has 5 valence electrons

2) How many valence electrons does H have?

H is in group IA so each H has 1 valence electron

3) How many total valence electrons are there in this

molecule?

(3 x 1) + 5 = 8

You know it had to be 8 because it has NO CHARGE!

Lewis dot structure of a compound

NH3

N

H

HH

Non-polar: e- are shared equally btwn atoms

Bonding between atoms of the same element or atoms close to each other on table

Polar: uneven distribution of charge

unequal attraction for the shared e-

MOLECULAR ATTRACTIONS

Polar molecules are more

positively charged on one

side and more negative

on the other.

http://programs.northlandcollege.edu/biology/Biology1111/animation

s/hydrogenbonds.html

Tendency of an atom to attract a pair of e- to itself when bonded Ionic bonds: atoms differ greatly

Covalent bonds: atoms similar

Polar covalent: moderate difference

Increases from left to right & decreases from top to bottom

• Ranges from 0.7 to 4.0,

Smaller electronegativity Larger electronegativity

• Large values: tendency to acquire electrons.

Metallic

Ionic

Covalent Polar

Nonpolar

Hydrogen

http://www.chem.iastate.edu/group/Greenbowe/sect

ions/projectfolder/flashfiles/reaction/bonding1.swf

Combining ability of an atom: how many e- it will gain or lose

written as a superscript (top right)

Oxygen: O-2 gains 2 e-

The sum of oxidation numbers in a compound must be zeroH+1 & O-2 = H2O each O needs 2 H atoms

Write symbol of element w/ +oxidation#

Write symbol of element w/ -oxidation #

Add subscripts so that sum of oxidation #s is zero “cross multiply”

Use (parenthesis) around the polyatomic ions

(NH4)2

+1

Write name of cation or + polyatomic ion if it has multiple oxidation numbers, write

the charge as a Roman Numeral Fe2+ would be iron (II) ion and Fe3+ would be iron (III) ion

Write name of – polyatomic ion, if it is an anion, write the root name and

change the ending to “ide”

Naming the ions

Names of main-group monatomic ions are straightforward.

A cation takes the name of the element plus the word "ion."

Na Sr Ba

Na+

sodium ion

Sr2+

strontium ion

Ba2+

barium ion

N O Cl

N3-

nitride ion

O2-

oxide ion

Cl-

chloride ion

For anions, the element name has its

ending replaced with ide.

Example calcium chloride

– calcium is Ca2+ and chlorine is Cl-

– in order to balance charges there needs to be two negative charges to balance the 2+ on the calcium

+2 -1

Common polyatomic ion names

Formula Name

NH4+ Ammonium ion

CO32- Carbonate ion

PO43- Phosphate ion

SO42- Sulfate ion

OH- Hydroxide ion

NO3- Nitrate ion

Anions + Cations = ionic compound name

F- Fluoride ion

CO32- Carbonate ion

PO43- Phosphate ion

SO42- Sulfate ion

OH- Hydroxide ion

NO3- Nitrate ion

Cl- Chloride ion

O2- Oxide ion

S2- Sulfide ion

NH4+ Ammonium ion

Na+ Sodium ion

Ca2+ Calcium ion

Fe3+ Iron(III) ion

Ag+ Silver ion

Al3+ Aluminum ion

Ammonium fluoride

Iron phosphate

Silver oxideNote: Ag has a charge of +1 and oxide has a charge of –2 so

the chemical formula of silver oxide must be Ag2O

What is the correct name for the ionic

compound Na2SO4?

A. disodium sulfate

B. sodium sulfoxide

C. sodium sulfate

D. sodium sulfide

CO2 Carbon Dioxide

H2O Dihydrogen Monoxide

Covalent compounds

Carbon tetrachloride is

A. CCl4

B. CClO4

C. C2Cl4

D. CCl5

TETRA = 4

POLYATOMIC IONS (-1 CHARGE) H2PO4 DiHydrogen phosphate

C2H3O2 Acetate

HSO3 Hydrogen Sulfite

HCO3 Hydrogen Carbonate

NO2 Nitrite

NO3 Nitrate

CN Cyanide

OH Hydroxide

MnO4 Permanganate

ClO Hypochlorite

ClO2 Chlorite

ClO3 Chlorate

ClO4 Perchlorate

POLYATOMIC IONS (-2 CHARGE)

HPO4 Hydrogen Phosphate

C2O4 Oxalate

SO3 Sulfite

SO4 Sulfate

CO3 Carbonate

CrO4 Chromate

Cr2O7 Dichromate

SiO3 Silicate

POLYATOMIC IONS (-3 CHARGE)

PO3 Phosphite

PO4 Phosphate

Rule 1– If two identical elements combine then the name doesn’t change

This happens with the following elements:

1) H2

2) N2

3) O2

4) F2

5) Cl2

6) Br2

These elements always go around in pairs (diatomic molecules). For example, hydrogen looks like this

Rule 2 – When two elements join and one is a halogen, oxygen or sulphur the name ends with ____ide

e.g. Magnesium + oxygen magnesium oxide

1) Sodium + chlorine

2) Magnesium + fluorine

3) Lithium + iodine

4) Chlorine + copper

5) Oxygen + iron

6) KBr

7) LiCl

8) CaO

9) MgS

10)KF

Rule 3 – When three or more elements combine and two of them are hydrogen and oxygen the name ends with

hydroxide

e.g. Sodium + hydrogen + oxygen Sodium hydroxide

1) Potassium + hydrogen + oxygen

2) Lithium + hydrogen + oxygen

3) Calcium + hydrogen + oxygen

4) Mg(OH)2

Rule 4 – When three or more elements combine and one of them is oxygen the ending is _____ate

e.g. Copper + sulphur + oxygen Copper sulphate

1) Calcium + carbon + oxygen

2) Potassium + carbon + oxygen

3) Calcium + sulphur + oxygen

4) Magnesium + chlorine + oxygen

5) Calcium + oxygen + nitrogen

6) AgNO3

7) H2SO4

8) K2CO3

Covalent formulas Ionic formulas

H2O

CO2

NH3

H2

O2

N2

SO2

Water

Carbon dioxide

Ammonia

Hydrogen

Oxygen

Nitrogen

Sulphur dioxide

NaCl

CaCl2

MgO

HCl

H2SO4

HNO3

NaOH

Ca(OH)2

CaCO3

Al2O3

Fe2O3

Sodium chloride

Calcium chloride

Magnesium oxide

Hydrochloric acid

Sulphuric acid

Nitric acid

Sodium hydroxide

Calcium hydroxide

Calcium carbonate

Aluminium oxide

Iron oxide

Even though all atoms want the same number of electrons as the Noble Gases, some want to get or give them more than others. The magnitude of this attraction for electrons is called “Electronegativity”. The more electronegative an atom is, the more it wants the electrons.

Some atoms want to gain electrons so bad, they take them altogether to form negative ions. Some want to lose them so bad that they become positive ions.

H2O Water is a bent molecule. The lone pair of electrons

from the Lewis structure distorts its shape and it becomes a very polar molecule.

NaCl Since Na is a metal it gives up its electron to form Na+

and Cl takes the electron completely to form Cl-.

HCl The Chlorine wants the electrons more than the Hydrogen. Thus we have +δHCl-δ.

Cl2

(Cl—Cl) The Chlorine molecules want the electrons equally so they form a non-polar molecule with NO partial or full charges.

CO2

Carbon Dioxide is a linear molecule. It has no lone pairs of electrons from the Lewis structure. The two oxygen atoms pull equally and make it a non-polar molecule.

..:O:H●●

H

.. ..O::C::O●● ●●

Binary Compounds have two types of atoms

(not diatomic which has only two atoms).

Metals (Groups I, II, and III) and Non-Metals

Metal _________ + Non-Metal _________ideSodiumChlorine

Sodium Chloride NaClMetals (Transition Metals) and Non-Metals

Metal ______ +Roman Numeral (__) + Non-Metal ________ideIron IIIBromine

Iron (III) Bromide FeBr3

Compare with Iron (II) Bromide FeBr2

Metals (Transition Metals) and Non-MetalsOlder System

Metal (Latin) _______ + ous or ic + Non-Metal ________ideFerrousBromine

Ferrous Bromide FeBr2

Compare with Ferric Bromide FeBr3

Non-Metals and Non-Metals

Use Prefixes such as mono, di, tri, tetra, penta, hexa, hepta, etc.

CO2 Carbon dioxide CO Carbon monoxide

PCl3 Phosphorus trichloride CCl4 Carbon tetrachloride

N2O5 Dinitrogen pentoxide CS2 Carbon disulfide

Name the following.

CaF2

K2S

CoI2

SnF2

SnF4

OF2

CuI2

CuI

SO2

SrS

LiBr

Strontium Sulfide

Lithium Bromide

Copper (I) Iodide or Cuprous Iodide

Sulfur dioxide

Copper (II) Iodide or Cupric Iodide

Oxygen diflouride

Tin (IV) Flouride or Stannic Flouride

Tin (II) Flouride or Stannous Flouride

Cobalt (II) Iodide or Cobaltous Iodide

Potassium Sulfide

Calcium Flouride

Ammonium……………...

Nitrate……………………

Permanganate…………. .

Chlorate…………………

Hydroxide……………….

Cyanide………………….

Sulfate…………………...

Carbonate……………….

Chromate………………..

Acetate…………………..

Phosphate……………….

NH4+

NO3-

MnO4-

ClO3-

OH-

CN-

SO4 2 -

CO32-

CrO42-

C2H3O2-

PO43-