Chapter 6: Bonding Basics

• OBJECTIVES:

–Determine the number of valence electrons in an atom of a representative element.

–Explain how the octet rule applies to atoms of metallic and nonmetallic elements.

• OBJECTIVES:

–Describe how cations form.

–Explain how anions form.

–Explain the electrical charge of an ionic compound.

• OBJECTIVES:

–Describe how cations form.

–Explain how anions form.

–Explain the electrical charge of an ionic compound.

• OBJECTIVES:

–Explain the electrical charge of an ionic compound.

–Describe three properties of ionic compounds.

• OBJECTIVES:

–Describe the arrangement of atoms in a metal.

–Explain the importance of alloys.

The Octet Rule We learned that noble gases are unreactive in

chemical reactions In 1916, Gilbert Lewis used this fact to

explain why atoms form certain kinds of ions and molecules

The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stable Each noble gas (except He, which has 2)

has 8 electrons in the outer level

Formation of Cations• Metals lose electrons to attain a noble gas

configuration.

• They make positive ions (cations)

Electron Dots For Cations• Metals will have few valence electrons

(usually 3 or less); calcium has only 2 valence electrons

Ca

Electron Dots For Cations• Metals will have few valence electrons

• Metals will lose the valence electrons

Ca

Electron Dots For Cations• Metals will have few valence electrons

• Metals will lose the valence electrons

• Forming positive ions

Ca2+NO DOTS are now shown for the cation.

This is named the “calcium ion”.

Electron Configurations: Anions• Nonmetals gain electrons to attain noble

gas configuration.• They make negative ions (anions)

Electron Dots For Anions• Nonmetals will have many valence electrons

(usually 5 or more)

• They will gain electrons to fill outer shell.

P 3-(This is called the “phosphide ion”, and should show dots)

Stable Electron Configurations• All atoms react to try and achieve a noble

gas configuration.• 8 valence electrons = already stable!• This is the octet rule (8 in the outer level is

particularly stable).

Ar

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

Learning Check

A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot formula

1) B 2) N 3) P

Chemical bonds: an attempt to fill electron shells

1. Ionic bonds –

2. Covalent bonds –

3. Metallic bonds

IONIC BONDbond formed between

two ions by the transfer of electrons

Ionic Bonding —Ionic Compounds

• Anions and cations are held together by opposite charges (+ and -)

• Ionic compounds are called salts.• The bond is formed through the transfer

of electrons (lose and gain)• Electrons are transferred to achieve noble

gas configuration.

Ionic Bonding

Na ClThe metal (sodium) tends to lose its one electron from the outer level.

The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

Ionic Bonding

Na+ Cl -

Note: Remember that NO DOTS are now shown for the cation!

Ionic Bonding

• All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).

Ca P

Lets do an example by combining calcium and phosphorus:

Ionic Bonding

Ca P

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca

Ionic Bonding

Ca2+ P 3-

Ca P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+P

3-

Ca2+

Ionic Bonding

= Ca3P2Formula Unit

This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.

For an ionic compound, the smallest representative particle is called a: Formula Unit

Properties of Ionic Compounds1. Crystalline solids - a regular repeating

arrangement of ions in the solid: Fig. 5, page 162

– Ions are strongly bonded together.

– Structure is rigid.

2. High melting points

• Coordination number- number of ions of opposite charge surrounding it

- Page 162

Coordination Numbers:

Both the sodium and chlorine have 6

Both the cesium and chlorine have 8

Each titanium has 6, and each oxygen has 3

NaCl

CsCl

TiO2

Do they Conduct?• Conducting electricity means allowing

charges to move.• In a solid, the ions are locked in place.• Ionic solids are insulators.• When melted, the ions can move around.3. Melted ionic compounds conduct.

– NaCl: must get to about 800 ºC.– Dissolved in water, they also conduct (free to

move in aqueous solutions)

Formation of Ions from Metals

Ionic compounds result when metals react with nonmetals

Metals lose electrons to match the number of valence

electrons of their nearest noble gas

Positive ions form when the number of electrons are

less than the number of protons

Group 1 metals ion 1+

Group 2 metals ion 2+

• Group 13 metals ion 3+

Formation of Sodium Ion

Sodium atom Sodium ion

Na – e Na +

2-8-1 2-8 ( = Ne)

11 p+ 11 p+

11 e- 10 e-

0 1+

Formation of Magnesium Ion

Magnesium atom Magnesium ion

Mg – 2e Mg2+

2-8-2 2-8 (=Ne)

12 p+ 12 p+

12 e- 10 e-

0 2+

Some Typical Ions with Positive Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

Learning Check

A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5 e-

C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Solution

A. Number of valence electrons in aluminum3) 3 e-

B. Change in electrons for octet1) lose 3e-

C. Ionic charge of aluminum 3) 3+

Learning Check

Give the ionic charge for each of the following:A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-

Ions from Nonmetal Ions

In ionic compounds, nonmetals in 5A, 6A, and

7A gain electrons from metals

Nonmetals add electrons to achieve the octet

arrangement

Nonmetal ionic charge:

3-, 2-, or 1-

Fluoride Ion

unpaired electron octet

1 -

: F + e : F :

2-7 2-8 (= Ne)

9 p+ 9 p+

9 e- 10 e- 0 1 -

ionic charge

Ionic Bond

• Between atoms of metals and nonmetals with very different electronegativity

• Bond formed by transfer of electrons

• Produce charged ions all states. Conductors and have high melting point.

• Examples; NaCl, CaCl2, K2O

Ionic Bonds: One Big Greedy Thief Dog!

Naming Ionic Compound

• All names have a predictable pattern.• Name of the cation first, then the anion.

• Cation name remains the same• Anion name will end in –ide.• EXAMPLE: Sodium Chloride

• COMMON ANIONS• Fluorine Fluoride• Chlorine Chloride• Bromine Bromide• Iodine Iodide• Oxygen Oxide• Sulfur Sulfide• Nitrogen Nitride• Phosphorus Phosphide

Section A: Complete the chart using a periodic table to help you.

Answer these questions:

An atom that gains one or more electrons will have a ____________________ charge.

An atom that loses one or more electrons will have a ____________________ charge.

An atom that gains or loses one or more electrons is called an ____________.

A positive ion is called a ______________ and a negative ion is called an _______________.

POSITIVE

NEGATIVE

ION

CATIONANION

“An-Eye-On”

“Cat-Eye-On”

What is an ionic bond?

Atoms will transfer one or more ________________ to another to form the bond.

Each atom is left with a ________________ outer shell.

An ionic bond forms between a ___________ ion with a positive charge and a ________________ ion with a negative charge.

Example B1: Sodium + Chlorine Example B2: Magnesium + Iodine

ELECTRONS

COMPLETE

METALNONMETAL

Example B3: Potassium + Iodine Example B4: Sodium + Oxygen

Example B5: Calcium + Chlorine Example B6: Aluminum + Chlorine

COVALENT BONDbond formed by the sharing of electrons

Covalent Bond

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electron pairs

• Stable non-ionizing particles, they are not conductors at any state

• Examples; O2, CO2, C2H6, H2O, SiC

Bonds in all the polyatomic ions

and diatomics are all covalent bonds

when electrons are shared equally

NONPOLAR COVALENT BONDS

H2 or Cl2

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.

Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom

Oxygen Molecule (O2)

when electrons are shared but shared

unequally

POLAR COVALENT BONDS

H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Polyatomic Ions

• Covalently bonded group of atoms that has a positive or negative charge and acts as a unit.

COMMON POLYATOMIC IONS

• Ammonium -- NH4

• Hydroxide -- OH• Nitrate -- NO3

• Sulfate -- SO4

• Carbonate -- CO3

• Phosphate -- PO4

• Chromate -- CrO4

• Silicate -- SiO3

• Acetate -- C2H3O2

• Peroxide -- O2

What is a covalent bond?

Atoms ___________ one or more electrons with each other to form the bond.

Each atom is left with a ________________ outer shell.

A covalent bond forms between two _________________.

Example C1: Hydrogen + Hydrogen Example C2: 2 Hydrogen + Oxygen

SHARE

COMPLETE

NONMETAL

Example C3: Chlorine + Chlorine Example C4: Oxygen + Oxygen

Example C5: Carbon + 2 Oxygen Example C6: Carbon + 4 Hydrogen

METALLIC BONDbond found in

metals; holds metal atoms together very strongly

Metallic Bonds are…• How metal atoms are held together

in the solid.

• Metals hold on to their valence electrons very weakly.

• Think of them as positive ions (cations) floating in a sea of electrons

Sea of Electrons

+ + + ++ + + +

+ + + +

• Electrons are free to move through the solid.

• Metals conduct electricity.

Metals are Malleable• Hammered into shape (bend).

• Also ductile - drawn into wires.

• Both malleability and ductility explained in terms of the mobility of the valence electrons

1) Ductility 2) Malleability

Due to the mobility of the valence electrons, metals have:

and

Notice that the ionic crystal breaks due to ion repulsion!

Malleable

+ + + ++ + + +

+ + + +

Force

Malleable

+ + + +

+ + + ++ + + +

• Mobile electrons allow atoms to slide by, sort of like ball bearings in oil.

Force

Ionic solids are brittle

+ - + -+- +-

+ - + -+- +-

Force

Ionic solids are brittle

+ - + -

+- +-+ - + -

+- +-

• Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.

Force

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Ionic Bond, A Sea of Electrons

Alloys• We use lots of metals every day, but

few are pure metals

• Alloys are mixtures of 2 or more elements, at least 1 is a metal

• made by melting a mixture of the ingredients, then cooling

• Brass: an alloy of Cu and Zn

• Bronze: Cu and Sn

Why use alloys?• Properties are often superior to the pure

element

• Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware

• Steels are very important alloys– corrosion resistant, ductility, hardness, toughness,

cost

Metals Form Alloys

Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.