Ionic and Metallic Bonding

With Help from Paul Surko New Dimensions High School Poinciana, FL

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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.

Gains or loses electrons

Shares electrons

Positive charge Negative charge

Metallic

Metals

Valence Electrons Valence electrons :

the electrons in the highest occupied energy level of an atoms

The number determines the chemical properties of an element

The number of valence electrons can be found by looking at its group number

Group 1A - 1 ve-

Group 2A – 2 ve-

Group 4A – 4 ve-

Electron Dot Structures This diagram shows the valence electrons as dots

Octet Rule When compounds form: atoms tend to achieve the

electron configuration of a noble gas (full valence shell)

ns2np6

Atoms of metals tend to lose their valence electrons leaving a complete octet in the next lowest energy level

Atoms of non-metals tend to gain electrons or to share electrons with another non-metal to achieve a complete octet

Cation Atom loses valence electrons

Positively charged ion

Sodium Electron loss or ionization of sodium atom

Na 1s22s22p63s1 → Na+ 1s22s22p6

-e- -e-

-e-

octet

Magnesium Magnesium atom attains the electron configuration of

neon by losing 2 valence electrons

Cations: Group 1A has a charge of 1+

Group 2A has a charge of 2+

Transition Metals

Charges of cations may vary

Ex: Pb2+ or Pb3+ This looks like lead (II) or lead (III)

Exceptions: Silver 1+

Zinc 2+ Aluminum 3+

**** write these on your Pd table!!

Anions Atom gains valence electrons

Negatively charged ion

Chlorine

A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion. It has the same electron configuration as argon

[[ ]-

Gain of valence electrons

Oxygen atom attains the electron configuration of neon by gaining 2 valence electrons

Gain of valence electrons

Ionic compounds Chemically combined two or more ions

Composed of cation and anion ‏

(usually metal) (usually non-metal)

Example:

Na+ + Cl- NaCl

•Ionic compounds are electrically neutral total + charge = total - charge of cations of anions

Ex 1: Na+ + Cl-

NaCl

Ex 2: Ca+2 + 2Cl-

CaCl2

Ionic bonds are held together by electrostatic forces

(cation and anion have opposite charges)

Chemical formula: shows the kinds and numbers of atoms in the smallest unit of a substance AlBr3 or H2O Formula Unit: lowest whole number ratio of ions in an ionic compound AlBr3

Predicting Formulas of Ionic Compounds: Use electron dot structures to predict the formula

ex 1: Potassium and chlorine:

a. Start with the Lewis structure of each atom:

K And Cl

b. To have a completely filled valence shell, K loses its 1 e- and Cl gains one e-

c. The electron moves from K to Cl creating cation and anion

d. The + charged K is now attracted to the – charged Cl

e. They join, and are bonded to each other by electrostatic forces.

f. Electrons lost equals electrons gained

g. The formula of the new ionic compound is KCl

ex 2: Potassium and oxygen

Electrons lost equals electrons gained. New chemical formula (formula unit) is: K2O

Ex 3: Magnesium and nitrogen

1. High melting points

2. Most ionic compounds are crystalline solids at room temperature

2. CONTINUED crystalline solids

3. Can conduct an electric current when melted or dissolved in water

Anion / Cation Lab Quiz Take out a blank sheet of paper and your lab notebook.

1. What happened when the Na3PO4 and AgNO3 combined?

2. What is the identity of the unknown anion?

3. How did you know the identity of the cation?

4. What is the answer to question #3 in your analysis.

5. What happened in when you combined KSCN and FeCl3?

1.

2.

Metallic Bonding

Metal atoms are arranged in a very compact and orderly pattern

The valence electrons of metal atoms can be modeled as a sea of electrons

Metallic bonds: attraction of free floating valence electrons for the positively charged metal ions

These bonds are the forces of attraction that hold metals together

Valence electrons are mobile and drift about the metallic bonds that is why metals are ductile and malleable

Alloys Mixtures composed of two or more elements one of

which must be a metal

Why are they important?

More durable

Cost

Examples:

Sterling silver:

Brass

coins

Chrysler Building New York City Completed in 1930, the steel-frame high rise stands 319 meters tall. The spire is covered in shiny stainless steel.

Nomenclature!! How to name chemical compounds.

Practice!! Homework: Page 199 # 14 - 22