Formation of Compounds

Chapter 4

Objectives 4.1

• Distinguish the properties of compounds

from those of the elements which they are

composed of.

• Compare and contrast the properties of an

ionic compound and covalent compound

• Analyze evidence to conclude that

differences exist in the ways compound

form

Salt and its Elements

• Sodium and Chlorine

– What are the physical and chemical

properties of these two elements?

– What are the physical and chemical

properties of salt?

Carbon Dioxide

• Carbon and Oxygen

– What are the physical and chemical

properties of these two elements?

– What are the physical and chemical

properties of carbon dioxide?

Water

• Hydrogen and Oxygen

– What are the physical and chemical

properties of these two elements?

– What are the physical and chemical

properties of Water?

• Why do compounds have different

properties than the elements that make

them up?

• How do we know that the elements have

even bonded?

Self Quiz 4.1

• 3 Compounds

– 1 Physical Property of each element that is

different from the compound

– 1 Chemical Property of each element that is

different from the compound

– Compounds can share elements but must

have different properties listed

Objectives 4.2

• Model two types of compound formation:

Ionic and covalent at the atomic level.

– Metallic as well

• Demonstrate how and why atoms achieve

chemical stability by bonding.

• Compare, using examples, the effect of

covalent and ionic bonding on the physical

and chemical properties

Key Terms 4.2

• Octet Rule

• Noble gas

configuration

• Ion

• Ionic compound

• Ionic bond

• Crystal

• Covalent Bond

• Covalent Compound

• Molecule

• Electrolyte

• Intermolecular Force

• Intramolecular Force

– Interparticle Force

Chemical Properties

– Dictated by valence electrons (outermost

electrons)

• Octet Rule: Outermost shell can hold 8

electrons. • Will discuss expanded outer shells later courses

• A full outer shell is associated with

stability, being unreactive

• Full outer shell = Noble Gas Configuration

Attaining the Octet

• Electron Transfer (Steal or Lose)

• Elements which have not lost or gained

electrons are neutrally charged: 1 Proton

for 1 Electron

• Gaining or losing changes this

Review

• How many valence electrons do the following atoms have?

• Ar

• K

• O

• N

• F with a -1 charge

• Mg with a +2 charge

Terminology

• Ion = Atom that has a positive or negative

charge

• Cation = Atom that has a positive charge

– Has lost an electron

• Anion = Atom that has a negative charge

– Has gained an electron

• Electrolyte = An ion in a water solution

Ionic Bonding

• When we say Ionic Bonding, there really is no “Actual” bond.

• Instead, two atoms are electromagnetically attracted to one another by having different charges

• This “Bond” is actually very strong

– (The electromagnetic repulsion between two electrons is roughly 43 powers of 10 times larger than gravitational attraction)

http://images.google.com/imgres?imgurl=http://www.firehouse.com/training/hazmat/chemist/2002/1_chemist1.jpg&imgrefurl=http://www.firehouse.com/training/hazmat/chemist/2002/1_chemist.html&h=225&w=300&sz=23&hl=en&start=9&usg=__zNkBjqgUoVxhxWF-W9ZqHQ-tycw=&tbnid=pGzSQH6SG9oSZM:&tbnh=87&tbnw=116&prev=/images%3Fq%3DIonic%2BBonding%26gbv%3D2%26hl%3Den

Formation of Ionic Bonding

• Three processes (Endothermic and

Exothermic)

• The loss of an electron from one atom

(always endothermic)

• The gain of an electron from one atom

(first electron is usually exothermic)

• The “Attractive Bond” formed (always

exothermic)

Cl–Na+ Cl–

Ionic bonding• Ionic bonding involves 3 steps (3 energies)

• 1) loss of an electron(s) by one element, 2)

gain of electron(s) by a second element, 3)

attraction between positive and negative

Na Cl

e–1) 2)

3)

Na+

Formation of the Bond

• Consider Mg and O forming an Ionic

Bonding

– Magnesium needs to lose 2 electrons, taking

the 2nd electron away is very endothermic

– Oxygen needs to gain 2 electrons, adding a

2nd electron is always endothermic

• The only way this could happen is if the

final bond formed is very strong

(Electromagnetic Forces)

Formation of the Bond

• The bond between Mg and O is very

strong, much stronger than the bond

formed between Na and Cl.

• The reason is the larger charges

– The bigger the magnet, the harder to pull

apart, which also means

– The more energy released when forming the

bond

Ionic bonding: Mg + O

Mg + O [Mg]2+[O]2–

12p+

12n02e- 8e- 2e-

1e-

[ O ]2–[Mg]2+

6e- 2e-

8n08p+

1e-

8e- 2e-

8n08p+12p+

12n02e- 8e-

OMg

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1e-

17p+

18n07e- 8e- 2e-

13p+

14n0 2e- 8e-3e-

17p+

18n07e- 8e- 2e-

17p+

18n07e- 8e- 2e-

Ionic bonding: Al + Cl

1e-

1e-17p+

18n08e- 8e- 2e-

17p+

18n08e- 8e- 2e-

17p+

18n08e- 8e- 2e-13p+

14n0 2e- 8e-

Ionic bonding: Al + Cl

[ Cl ]3–[Al]3+

Al + 3Cl [Al]3+[Cl]3–

Cl

Al Cl

Cl

Ionic Compound

• Composed of Ions

• Ions organized into crystal patterns

How the atoms arrange themselves

• Crystal structure is dependent upon

– Size of atoms

– Ratio of Charges

• Beyond the scope of this course to go into great

detail about this, but there are many different ways

the atoms rearrange themselves

Melting Points/Boiling Points

• MgF2 1534 K Melting 2512 K BP

• NaCl 1074 K 1686 K

• CaI2 1057 K 1373 K

• Water 273 K 373 K

• Ionic compounds in general have higher

melting and boiling points than covalent

bonds. (Strong EMF)

You don’t need to know this but

may find it interesting

• The larger the charges, the higher the

MP/BP

• The smaller the atoms, the higher the

MP/BP

• LiF will have a higher MP than NaCl

+1+2 General Ionic Charges -1-2-3

Covalent bonding

• Thus far we have looked at when atoms

bond due to the transfer of electrons

• An ionic bond forms when an atom has a

greater attraction for e–s than a second atom

• However, if two atoms have approximately

the same pull on electrons, they share the

electrons (forming a “covalent” bond)

• Atoms bonded like this are called Molecules

Covalent Compounds

• Formed from atoms covalently bonded to

one another.

• Boiling point/Melting point much lower

than Ionic

Covalent bonding

CCl4 - Covalent

C

Cl

Cl

Cl

Cl

HCl - Covalent

H Cl

MgF2 - Ionic

[ F ]2–[Mg]2+

H2O - Covalent

H O H

NH3 - Covalent

H N H

H

NaCl - Ionic

[ Cl ]–[Na] +

OH– - Covalent

O H

H2 - Covalent

H H

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Multiple bondsHCl - Covalent

H Cl H Cl

CO2 - Covalent

C OO

Na2O - Ionic

[ O ]2–[Na]2+

H N H

H

H N H

H

OO

OO

O2 - Covalent

OO C

II

II

I2 - Covalent

[ O ]32–[Al]2

3+

Al2O3 - Ionic

NH3 - Covalent

OO O

O OO

O3 - Covalent

H C H

H

H

H C H

H

H

How many bonds?

• For non-metals, who form bonds, the

number of bonds is equal to the number of

electrons they still need (their would be

ionic charge)

– F = 1

– O = 2

– N = 3

– C = 4

Comparing Ionic and Covalent

– Ionic

• Solid at room

Temperature

• Charged Particles

• Strong IMF’s

– Intermolecular forces

– Covalent

• Gas or Liquid at room

Temperature

• Neutrally Charged

Molecules

• Weak IMF’s

• Strong Intramolecular

forces

Ionic or Covalent Substance?

• Metal + Nonmetal = Ionic Properties

• Nonmetal + Nonmetal = Covalent Prop’s

• Metal+ Metal = Metallic Properties

• Spectrum: The bigger the electronegative

differences, the larger % of ionic character

– But we will use the three rules above

The quiz

• 25 Questions

– 4 Metallic, Ionic, or Covalent Bond

• Na and Fr, Mg and Cl, F and N

– 3 how many electrons do they need gain/lose

• Na 1, Mg 2, O 2, F 1

– 3 Different properties of ionic v covalent

– 4 Questions ionic charge or amount of bonds

• Na +1, Mg + 2, O -2 or two bonds, F – 1 or 1 bond

– Other questions: General terms/process of

forming the bonds