Making CompoundsMaking Compounds

Making Compounds Making Compounds

Chemical compounds form so that Chemical compounds form so that each atom has an octet of each atom has an octet of electrons in its valence level. electrons in its valence level.

This can occur by This can occur by gaininggaining, , losinglosing or or sharingsharing electrons. electrons.

Octet RuleOctet RuleOctet Rule – 8 is Great!!Octet Rule – 8 is Great!! ►An atom is stable when it has a full An atom is stable when it has a full

valence layer, an electron configuration valence layer, an electron configuration like the nearest Noble Gas.like the nearest Noble Gas.

►Atoms gain or lose valence electrons to Atoms gain or lose valence electrons to

become stablebecome stable a positive cation has lost electronsa positive cation has lost electrons a negative anion has gained electronsa negative anion has gained electrons

Remember…Formation of Remember…Formation of IonsIons

►The number of electrons that an atom The number of electrons that an atom can gain or lose depends on the can gain or lose depends on the number of valence electrons.number of valence electrons.

SbSb SbSb

In general, metals lose electrons, In general, metals lose electrons, nonmetals gain them to become nonmetals gain them to become stable.stable.

+ 3e-

-3

RbRb RbRb+

+ e-

Ionic CompoundsIonic Compounds► Ionic bonding is the combining of two or more Ionic bonding is the combining of two or more

ions to form an electrically-neutral compound.ions to form an electrically-neutral compound.

► The negatively and The negatively and positively charged positively charged ions are attracted to ions are attracted to each other (like a each other (like a magnet) based on magnet) based on their opposite charge.their opposite charge.

Ionic CompoundsIonic Compounds

► Ionic Compounds form when there is a transfer Ionic Compounds form when there is a transfer of electrons between a of electrons between a metalmetal and and non metalnon metal..

► The ionic compound they form is electrically The ionic compound they form is electrically neutral. The sum of the charges of the positive neutral. The sum of the charges of the positive ions equals the sum of the charges of the ions equals the sum of the charges of the negative ionsnegative ions

► When placed in water, the ionic compound When placed in water, the ionic compound dissociates into its respective ions. This may dissociates into its respective ions. This may result in the solution being able to conduct result in the solution being able to conduct electricity.electricity.

Cl–

Ionic bondingIonic bonding► Ionic bonding involves 3 steps (3 energies)Ionic bonding involves 3 steps (3 energies)► 1) loss of an electron(s) by one element, 2) 1) loss of an electron(s) by one element, 2)

gain of electron(s) by a second element, 3) gain of electron(s) by a second element, 3) attraction between positive and negativeattraction between positive and negative

Na Cl

e–1) 2)

3)

Na+

Sodium ChlorideSodium Chloride►Sodium is a group 1 metal, it has 1 Sodium is a group 1 metal, it has 1

electron it was to lose to have a full electron it was to lose to have a full outer shell.outer shell.

►Chlorine is a group 7 nonmetal, it Chlorine is a group 7 nonmetal, it wants to gain 1 electron to have a full wants to gain 1 electron to have a full outer shell.outer shell.

Na + Na

Cl

+Cl-+

What about MgClWhat about MgCl22??

Mg + Cl

Cl

Mg Cl+2 -

Cl-

And Aluminum Oxide AlAnd Aluminum Oxide Al22OO33??

OAl

O

OAl

O-2

O-2

O-2

Al+3

Al+3

Properties of Ionic Properties of Ionic CompoundsCompounds

Crystal Pattern – every ion is attracted to all other ions with the opposite charge.

This results in a repeating 3-dimensional pattern

Chloride ion

Sodium ion

Properties of Ionic Properties of Ionic CompoundsCompounds

High Melting Point – the attraction in the crystal pattern leads to very strong bonds, resulting in a high melting point.

Conductivity – Solid ionic compounds do not conduct electricity. When dissolved in water, or melted, ionic compounds conduct electricity.

Covalent CompoundsCovalent Compounds

►When electrons are not transferred When electrons are not transferred from one atom to another, they from one atom to another, they shareshare electrons.electrons.

►Covalent compounds share electrons Covalent compounds share electrons to achieve stable noble gas electron to achieve stable noble gas electron configurations.configurations.

1 bond = 2 shared electrons1 bond = 2 shared electrons

Steps for Drawing Lewis Steps for Drawing Lewis StructuresStructures

1.1. Count the total number of valence eCount the total number of valence e --

2.2. Identify the central atom (the first atom Identify the central atom (the first atom written unless it is H)written unless it is H)

3.3. Draw the Lewis diagram for the central Draw the Lewis diagram for the central atom and place all other atoms around itatom and place all other atoms around it

4.4. Complete the octet for all atoms by Complete the octet for all atoms by pairing up unpaired epairing up unpaired e-- between atoms. between atoms. Each pairing represents 1 bond.Each pairing represents 1 bond.

5.5. Check your structure by counting the Check your structure by counting the number of valence enumber of valence e-- around each atom. around each atom.

Step 1 – Methane (CHStep 1 – Methane (CH44))

►Count the number of valence electrons Count the number of valence electrons available to each atom in the compound.available to each atom in the compound.

C = 4 valence electrons

H = 1 valence electron

Step 2 – Methane (CHStep 2 – Methane (CH44))

► Identify the central atom (the first Identify the central atom (the first atom written unless it is H).atom written unless it is H).

CH4 – central atom is C

Step 3 – Methane (CHStep 3 – Methane (CH44))

►Draw the Lewis diagram for the central Draw the Lewis diagram for the central atom and place all other atoms around itatom and place all other atoms around it

CH

H

H

H

Step 4 – Methane (CHStep 4 – Methane (CH44))► Complete the octet for all atoms by Complete the octet for all atoms by

pairing up unpaired epairing up unpaired e-- between atoms. between atoms. Each pairing represents 1 bond.Each pairing represents 1 bond.

CH

H

H

Hdraw

CH

H

H

H

Step 5 – Methane (CHStep 5 – Methane (CH44))► Check your structure by counting the Check your structure by counting the

number of valence enumber of valence e-- around each around each atom.atom.

CH

H

H

H

Remember, each bond is worth two electrons to each element it touches.

C = 2 +2+2+2 = 8

H = 2

H = 2

H = 2

H = 2

2e-

Try CClTry CCl44

C Cl

Cl

Cl

Cl

Try CClTry CCl44

C Cl

Cl

Cl

Cl

Cl = 3 lone pairs + 1 bond

Cl = 3 x 2 + 1 x 2

Cl = 6 +2

Cl = 8

C = 4 bonds

C = 4 x 2

C = 8

Try ITry I22

I I

Try ITry I22

I I

I = 3 lone pairs + 1 bondI = 3 x 2 + 1 x 2I = 6 +2I = 8

Practice ProblemsPractice Problems

►P. 76 # 3P. 76 # 3►P. 78 # 5P. 78 # 5►P. 81 # 6, 7P. 81 # 6, 7►P. 84 # 1P. 84 # 1