Chp 19.1

Bonding and Molecules

Bonding and Molecules Most pure elements, except ______

____, will eventually react with another substance to become something else.

A molecule is made up of more than one different type of atoms.

A _______ bond is the force that binds two or more atoms together.

Valence Electrons ________ are located in

energy levels around the nucleus. The outermost energy level contains the valence electrons.

Stable elements have __ valence electrons. Unstable elements have ___ than 8.

Octet Rule Chemically stable atoms

have 8 valence electrons (2 for 1st E.L. only).

Atoms form bonds to complete their octet and become stable.

Known as _____ ____.

Exceptions to the Octet Rule Most energy levels need 8 electrons

to complete the level. The first energy level is unique because it only needs 2 electrons.

_______ and ______ need only two electrons to fill its valence electrons.

Since Helium already has two electrons it is stable.

Energy Levels

First E.L. can hold ___ __ 2 e-.

What is this element?

Second E.L. can hold up to 8 e-.

What is this element?

Third E.L. can hold up to 8 valence shell e-.

How many more e- can this atom hold in its valence shell?

Complete outer level During bonding, atoms will ____ or ____

electrons to complete their outer levels. The _____ number on the periodic table

tells you how many valance electrons. Lithium has only __ valence electron.

It would be easier to lose that one electron than to gain ___ more.

Fluorine has 7 valence electrons. It would be easier to gain one electron than to lose all 7.

Use the PT to find # of valence e-.

Column (______ / family) tells how many valence e- .

All atoms in a group have same # of valence e-, with exception of transition metals.

Complete this chart:

Dot Diagrams

_____ ________ are used to represent valence e-.Element symbol represents nucleus & all e- except for valence e-.

Dot Diagrams, cont.

– Dots around symbol = valence e-.

– Place one dot for each valence e- on each side of the symbol ______ pairing up the e-.

Dot diagrams Dot diagrams is a system to show the

number of valence electrons of an element.

The location of the dots ___ _____matter. Traditionally dots are shown as pairs around the four sides of the symbol.

Ionization When an atom loses or gains electrons

they become _____ – or atoms with an electrical charge.

If an atom _______ an electron, it becomes an ion with a +1 charge.

If an atom _______ an electron, it becomes an ion with a –1 charge.

Opposite Attract When a positively charged ion

comes in contact with a negatively charged ion, the two ______.

The compound will be _____ as long as the two ions stay together.

+

______ _____ - formed when atoms gain or lose electrons.

Ex: Na has 1 valence e-

=

When Na loses that electron, its 2nd E.L. becomes full and stable with 8 e-.

Atoms with an electrical charge are called _____.

sodium ionsodium atom

Chlorine has 7 valence electrons. If Cl gains 1 electron, its valence

shell will be full and stable.

chlorine atom

chlorine ion

Opposites attract, so…

Are these two ions likely to bond?

Covalent Bonds

Most atoms ______ electrons to gain an octet.

________ ______ are formed when e- are shared.

Covalent Bonds, cont.

Covalent bonds can form between 2 different types of atoms or between 2 or more atoms of the same type.

Diatomic molecules:

– covalently bonded atoms of the same type.

Exs: H2 Cl2 F2 I2

O2 Br2 N2

How can you tell whether a bond is ionic or covalent?

In GENERAL: Ionic – metal / nonmetal Covalent – 2 nonmetals

Types of Bonds Review Ionic bonds are formed when atoms

gain or lose electrons resulting in an attraction between two oppositely charged particles.

Covalent bonds are formed when atoms share electrons.

In general bonds between a metal and a nonmetal are ionic. While bonds between two nonmetals are covalent.

Electronegativity The attraction an atom has to gain

additional electrons is called _____________. The closer an atom is to having a complete

valence shell, the _____ the electronegativity.

Elements in group 7 (with 7 valence electrons) have the highest electronegativity. While electrons in group 1 have the _______ electronegativity.

Paper or Plastic _______ Poly- “many” mer-

“unit” Large molecule that is

composed of repeating smaller molecules.

Biodegradable plastics microoganisms