Chapter 19: Chemical Bonding

“Isn’t It Ionic?”

Questions for Review

What atomic particle

determines the chemical

properties of an element?

a. protons b. neutrons c. electrons d. morons

What atomic particle

determines the chemical

properties of an element?

a. protons b. neutrons c. electrons d. morons

Which electrons determine an

element’s chemical properties?

a. electrons near the nucleus of the atom

b. middle energy level(s) c. valence electrons

Which electrons determine an

element’s chemical properties?

a. electrons near the nucleus of the atom

b. middle energy level(s)

c. valence electrons

How many valence electrons do most atoms need to become chemically stable?

a.1b.4c.8d.10

How many valence electrons do most atoms need to become chemically stable?

a.1b.4c.8d.10

Atoms are chemically stable (or resistant to change) when their valence shells are completely filled with electrons.

For most atoms, 8 electrons are needed to be chemically stable.

Why do the Noble Gases not form

compounds easily?

The valence shells of the Noble gases are already completely filled with electrons.

All of the Noble Gases, with the exception of helium, have 8 valence electrons. Helium has only two electrons.Therefore, the first energy level is full, making it stable with its two valence electrons.

How are electrons in an atom

represented?

a. Bohr Models b. Lewis Dot Diagrams c. both of these

How are electrons in an atom

represented?

a. Bohr Models b. Lewis Dot Diagrams c. both of these

Bohr Model of the Atom

Sodium atom Chlorine atom

How are valence electrons in an

atom represented?

a. Bohr Models b. Lewis Dot Diagrams c. both of these

How are valence electrons in an

atom represented?

a. Bohr Models b. Lewis Dot Diagrams c. both of these

See http://www.ausetute.com.au/lewisstr.html

Lewis Dot Diagrams

Why do chemical bonds

form?

Stability is achieved when the atoms…

have achieved a Noble Gas configuration (which have a complete set of valence electrons)

(In other words, atoms are stable when they have bonded with other atoms to completely fill their outer-level electron shells).

Chapter 19: Types of

Chemical Bonds1.Ionic Bonds = usually metal + nonmetal2. Covalent Bonds = nonmetal + nonmetal

What are ions?

How do ions form?

Ion

an atom that has gained or lost one or more electrons, therefore it has a positive or negative charge

Ionic BondUsually forms between a metal and a nonmetal

Is the force of electrostatic attraction between positively and negatively charged ions

Demonstration of Ionic Bonding

A transfer of electrons takes

place

If an atom loses electrons it becomes ____ charged.

If an atom gains electrons, it becomes ____ charged.

A transfer of electrons takes

place

If an atom loses electrons it becomes _positively_ charged.

If an atom gains electrons, it becomes _negatively_ charged.

Metals tend to lose electrons, becoming a positive ion (cation).

Nonmetals tend to gain electrons & become negative ions (anion).

Classify the following

compounds as covalent or ionic:

1.NaCl2.CO2

3.H2O

4.MgCl2

5.C4H10

Classify the following

compounds as covalent or ionic:

1.NaCl (ionic)2.CO2 (covalent)

3.H2O (covalent)

4.MgCl2 (ionic)

5.C4H10 (covalent)

Ionic Charges are indicated by a

Superscript

superscript -“written above”

Examples: Na+, Mg2+, Cl-, O2-

Chemical Formula Indicates the elements in a compound and the ratio of the atoms of those elements in one unit of the compound.

Chemical Formula• Examples: NaCl; H2O• The “2” in H2O is a subscript.

• Subscript (“written below”)indicates the number of atoms of an element in a unit of that compound.

• What is the ratio of sodium to chlorine in NaCl?

• What is the ratio of hydrogen to oxygen in H2O?

• What is the ratio of sodium to chlorine in NaCl? 1:1

• What is the ratio of hydrogen to oxygen in H2O? 2:1

Writing Formulas for Binary Ionic

Compounds Determine the oxidation number of

each ion (the number of electrons an atom gains or loses)

Oxidation numbers for the representative elements can be determined from its position on the periodic table. Oxidation Numbers for transition elements are determined from their negative ions.

Oxidation StateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound.

The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic.

Oxidation states are typically represented by integers, which can be positive, negative, or zero. http://en.wikipedia.org/wiki/Oxidation_state

Oxidation State In some cases the average oxidation state of an element is a fraction, such as 8/3 for iron in magnetite (Fe3O4).

The increase in oxidation state of an atom through a chemical reaction is known as an oxidation; a decrease in oxidation state is known as a reduction. Such reactions involve the formal transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation.

For pure elements, the oxidation state is zero.

http://en.wikipedia.org/wiki/Oxidation_state

Oxidation Numbers can be predicted from the

element’s position on the periodic table.

Writing Formulas for Binary Ionic

Compounds1. Write the symbol of the positive

ion first.2. Write the symbol of the negative

ion.3. Add the superscripts. Is the sum

zero?4. If the sum does NOT equal zero,

criss-cross the ionic charges.

Writing Names for Binary Ionic

Compounds

1.Write the name of the positive ion first.

2.Write the root of the negative ion’s name.

3.Change the ending to -ide.

Use the ion cards to write formulas

for and name binary ionic

compounds

1. sodium and chlorine2. calcium and chlorine3. aluminum and chlorine

Na 1+ Cl 1-

Formula: NaCl

Name of compound: sodium chloride

sodium ion chloride ion

Ca 2+

Cl 1-

Cl 1-

Formula: CaCl2

Name: Calcium Chloride

Al 3+

Cl 1-

Cl 1-

Formula: AlCl3

Name: Aluminum Chloride

Cl 1-

Polyatomic IonsA group of atoms that shares a common ionic charge.

Polyatomic ions must be memorized --- there’s no way around it!

See the chart of common ions.

Examples of some polyatomic ions:

Ammonium ion: NH41+

Nitrate ion: NO31-

Nitrite ion: NO31-

Hydroxide ion: OH1-

Sulfate ion: SO42-

Carbonate ion: CO32-

Phosphate ion: PO43-

Using the Ion Cards with

Polyatomic Ions

Na 1+NO3

1-

Sodium ion Nitrate ion

Chemical Name: sodium nitrate

Chemical Formula: NaNO3

NH4 1+

Ammonium ion

NH4 1+

Ammonium ion

SO42-

Sulfate ion

Chemical Name: ammonium sulfate

Chemical Formula: (NH4)2SO4

NH4 1+

Ammonium ion

NH4 1+

Ammonium ion

PO43-

Phosphate ion

Chemical Name: ammonium phosphate

Chemical Formula: (NH4)3PO4

NH4 1+

Ammonium ion

Ca 2+

calcium ionNO3 1-

Nitrate ion

NO3 1-

Nitrate ion

Chemical Name: calcium nitrate

Chemical Formula: Ca(NO3)2

Roman Numerals are used with elements

that have more than one common

oxidation number. (This includes most of the transition elements)

Examples:

CuBr2 is named Copper (II) bromide

PbCl2 is named Lead (II) chloride

EXCEPTIONS: Roman Numerals are NOT

needed for silver, cadmium, and zinc:

These transition elements ALWAYS have the following

oxidation numbers: Ag+ Cd2+, Zn2+

Examples:AgBr is named silver bromide, and NOT silver (I) bromide, because silver always has a 1+ oxidation number.

The same is true for compounds containing Cadmium or Zinc. (Cd and Zn are always 2+)

Some Special Ions:Copper (I) and (II) = Cu+ and Cu2+

Iron (II) and (III) = Fe2+ and Fe3+

Chromium (II) and (III) = Cr2+ and Cr3+

Lead (II) and (IV) = Pb2+ and Pb4+

Write names for:

1.FeS

2.CuCl

3. PbBr4

Check your work:

1.Iron (II) sulfide2.Copper (I) chloride

3.Lead (IV) bromide

Write formulas from the following

names:

1.Lead (II) bromide2.Chromium (II) sulfide3.CuI copper (II) iodide

Check your work:

4.PbBr2

5.CrS6.CuI2

Ionic CompoundsResult from the formation of ionic bonds.

Exist usually between a metal and a nonmetal

Are fun to name and write formulas for once you know the rules!