Chapter 4

Atoms and Chemical Bonding

Chapter 7Ionic and Metallic Bonding

Valence Electrons

• Highest energy level

• Determine chemical properties

• [Ne]4s2 3d10 4p5 - Bromine

7 valence e-

Representative elements = group #

Valence ElectronsLewis (1916)

Valence electrons are the electrons in the atom’s highest numbered energy level.

1 2 3 4 5 6 7 8

Electron dot Structures

• Lewis dot

• Show electrons as dots •

• Ca• •B•

• Fill in each side with one dot before you double up

Octet Rule

In forming compounds atoms gain, lose, or sharein such a way that they achieve the electron configuration of the

nearest noble gas in the periodic table.Noble gases are stable

have eight electrons in the outermost level

Ionic Bonding Atoms lose or gain electrons to form ions

Cations are positive ions metals generally form cations

Anions are negative ions non-metals generally form anions

Ionic compounds are held together by electrostatics- the positive charge of the cation attracting the negative charge of the anion.

Ionic Bonding Continued

Ionic Compound METAL + NONMETAL Important metal ions

group 1A - loose 1 electron (+1) group 2A - loose 2 electrons (+2) group 3A - loose 3 electrons (+3)

Important non-metal ions group 7A (-1), group 6A (-2), group 5A (-3)

Properties of Ionic bonds

• Most are crystalline solids at Room temp

Stable structures with all of the (+) and (-) attractions

Properties cont.

Stable structures with all of the (+) and (-) attractions

• High melting points

• Conduct electricity – Ions move freely so e- can travel toward (+)– When dissolved in water

Ionic Bonds

• One cation and one anion

• Electrically neutral

• Cation gives e-

• Anion takes e-– Example Aluminum and bromine

Common Ions and Their Position in the Periodic Table

Lewis Structures

• Al • •Cl•

Cl

Cl

[Al] [Cl]3

Names of Common Nonmetallic Ions

Polyatomic IonsPolyatomic means “many-atom” ion

Metallic bonds

• Closely packed cations

• Valence e- are free and can drift from one metal to another

• Meallic bonds consist of the attraction of ther free-floating valence e- for the positively charged metal ions

Metallic bonds (e-)

• they do not "belong" to any one atom • are part of the whole metal crystal • *Metallic bonds are best characterized by the

phrase "a sea of electrons"*

Metallic properties

• electrons flow explains characteristics of metals:• - Metals are good conductors of heat and electricity.

– mobility of the electrons.• - The "cement" effect of the electrons determines the

hardness Some• -  Metals are lustrous. 

– due to the uniform way that the valence electrons absorb and re-emit light energy.

• - Metals are malleable (can be flattened) and ductile (can be drawn into wires) – because the metal cations and electrons can "flow" around each

other, without breaking the crystal structure.

http://www.ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/metallicbonding.htm

Alloys

• Mixture of two or more elements, at least one is a metal

• Example: brass = copper and zinc• Properies are better than those of the single

elements• Sterling silver = siler and copper

– Durable /no tarnishSteel is a very important alloy

iron, carbon, boron, chromium, manganese, and more