Chemical Bonding and Nomenclature Chemical Bonding and Nomenclature.

Chemical Bonding and Nomenclature

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8

I want you to meet a friend of mine?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.

5.1 What are Molecules?

Molecules are a combination of atoms

bonded together. Bonding determines the chemical

properties of the molecule (compound).

VALENCE ELECTRONS

The number of valence electrons determines the chemical properties of an element

Electrons that engage in bonding to form molecules and compounds

Groups - Review

• Each column is called a “group”

• Each element in a group has the same number of electrons in their outer orbital, also known as “shells”.

Group 1 = 1 electron

Group 2 = 2 electrons

Group 8 = 8 electrons

Except for He, it has 2 electrons

• The electrons in the outer shell are called “valence electrons”

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3, 4, 5, 6, 7

VALENCE ELECTRONS

B = 1S22S22P1

Octet rule

Group 8 – noble gasesHave 8 valence electronsStable and unreactive in chemical reactionsAtoms will react with each other in order to

attain 8 valence electrons ( octet=8)Gain or lose electrons – ionsShare electrons

Lewis Structures – visually show valence electrons

1) Find your element on the periodic table.

2) Determine the number of valence electrons.

3) This is how many electrons you will draw.

Lewis Structures

1) Write the element symbol.

2) Carbon is in the 4th group, so it has 4 valence electrons.

3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol.

C

IONIC BONDING FORMING CATIONS AND ANIONS

• Atoms are electrically neutral due to equal numbers of electrons and protons

• Ions which are charged particles form when atoms or groups of atoms gain or lose electrons to form compounds

• Want to have an octet or be like the noble gases

• Oxidation numbers are assigned to keep track of electrons that are lost or gained

IONIC BONDING FORMING CATIONS AND ANIONS

ANION = O becomes O-2 is an oxygen ion

Oxidation number is -2 O will gain 2, (valence = 6) has more electrons that protons = negative

overall

CATION = Na becomes Na+ - Na ion

Oxidation number is +1 Na will give up 1, will never gain 7Has more protons than electrons = positive

overall

The positive and negative ions are attracted to each other electrostatically.

Opposites Attract!

Formation of Ionic Compounds

Formula UnitsA chemical formula shows the kinds and numbers

of atoms in the smallest representative unit of a substance.

EX. NaCl, MgCl2

A formula unit is the lowest whole-number ratio of ions in an ionic compound.

NaCl ( 1:1), MgCl2 (1:2)

7.2

Conceptual Problem 7.2

REVIEW QUIZ

How many valence electrons are in K ( potassium) Mg (magnesium)

Draw the lewis dot structure for the above

3 points each1 = formula1 = correct symbol1= lewis dot and correct depiction of bonding

Al + Br

Review

Na + and O2-?

Write chemical formula?

Name the compound

NAMING IONS

Compounds have a positive metal ion and a negative nonmetal ion combined together to form a neutral compound

Monatomic ions = single atom with a positive or negative charge resulting from a loss or gain of valence electrons

NAMING CATIONS

The names of cations are the same as the metal followed by the word ion or cationEx. Na + = sodium cation (ion)Al 3+ = aluminum cation (ion)

NAMING ANIONS

Nonmetals gain electrons forming anionsNaming

Start with the stem of the element nameAdd –ide

Ex. Chlorine = Chloride ionSulfur = Sulfide ion

Diatomic Compounds

Use the full name of the cation (metal) written first

The anion (nonmetal) comes last and change ending to –ide

Sodium Chloride Potassium Nitride

TRANSITION METAL IONS

Can form more than 1 cationEx. Fe can lose 2 e- or it can lose 3 e-These metals are designated by a roman

numeral in parenthesis Fe (II) ionIf the metal has only one ionic charge you

would not use a (I).

Writing Formulas From Names Identify the charge of the cation Identify the charge of the anionCriss Cross oxidation numbers to become

the subscripts in the formula

Aluminum Sulfide Al3+ S2-

Al2S3

POLYATOMIC IONS

Group of atoms that stay together and have a charge.

ex. Sulfate anion = SO4 2-

Different endings depending on the number of o (oxygen) in the atom

ex. NO2 – = nitrite NO3 - = nitrate

POLYATOMIC IONS

Create a notecard the lists the names of polyatomic ions

This may be used on tests-if you forget it, you are out of luck !!!

Page 257 table 9.3

Review Quiz

Using correct oxidation numbers write the chemical formula of the followingAluminum OxideZinc Nitrate

Correctly name the following compoundsCu3 P

Mn2(SO3)3

PROPERTIES OF IONIC COMPOUNDS

Most are crystalline solids at room temperatureArranged in repeating 3-D patterns

MELTING POINTS

Generally very high melting points

Due to very large attractive forces between ions and crystal formation

CONDUCTIVITY Ionic compounds can conduct an electric

current when dissolved in water

Review Quiz

Write the following formulasMagnesium oxideSodium sulfideTin (II) flouride

Name the following compoundsMnO2

CuCl2Li3N

METALLIC BONDS/PROPERTIES

Occur between two metalsGood conductors because electrons can

flow freely Crystalline structureMetals are arranged in a very compact

and orderly fashion

ALLOYS

Most metals are alloys - mixture of two or more elements with at least one being a metalEx. Brass, sterling silver, stainless steel, cast

ironUsually more durable, harder ect..

Review Problems

Do 7.3 section assessment