Chemical BondingChapter 5

Electron Cloud

Electrons are located around the nucleus in the electron cloud.

The cloud is arranged into levels called shells or energy levels.

The elements in a period have the same number of levels or shells.

1st Period = 1 Shell

2nd Period = 2 Shells

3rd Period = 3 Shells

4th Period = 4 Shells

Electrons

Remember from Chapter 4- each column is called a group.

Each element in a group has the same number of electrons in their outer orbital, or “shell”.

Each shell can hold a specific number of electrons 1st= 2 electrons 2nd= 8 electrons 3rd= 8 electrons

A shell must be filled before moving to the next level

The electrons in the outer shell are called “valence electrons”

Turn to your periodic table and label…

Group 1 = 1 electronGroup 2 = 2

electrons

Group 8 = 8 electronsExcept for He, it has 2 electrons

3 4 5 6 7

Determine the number of shells and the number of valence electrons to create Bohr Diagram for:

Carbon - C2nd Period = 2 shells

4th Group = 4 valence electrons

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Now you try:

Ne

8th Group = 8 valence electrons

2nd Period = 2 shells

NeonName the element. Number of shells ?Valence electrons ?

Try another:

Be

2nd Group = 2 valence electrons

2nd Period = 2 shells

BerylliumName the element. Number of shells ?Valence electrons ?

Last one:

S

6th Group = 6 valence electrons

3rd Period = 3 shells

SulfurName the element. Number of shells ?Valence electrons ?

Electron Dot Diagrams & Chemical Bonding

The goal of an atom

The goal of an atom is to be “happy.”

An atom is happy when it has a full outer energy level

How many valence electrons does this need to be “happy?”

A. B.

How many valence electrons does this need to be “happy?”

C. D.

How many valence electrons does this need to be “happy?”

E. F.

How to draw Electron Dot Diagram

Step 1: Write down Element symbolStep 2: Find out how many valence

electrons there are Step 3: Place electrons around the

symbol one at a time and if there is enough double up

O= 6 ValenceElectrons

Some common Examples

1.SodiumNa1 valence electron

2. Argon Ar 8 valence electrons

Practice Problems

Use your periodic table to find the number of valence electrons for each of the following. Then, draw an Electron Dot Diagram for each.1. Carbon2. Lithium3. Krypton4. Boron5. Neon6. Nitrogen7. Flourine8. Helium9. Aluminum10.Calcium

Chemical Bonding

Chemical Bonding- combining of atoms to form molecules or ionic compounds

Chemical Bond- what holds the atoms together

Periodic Table

Remember from last week, the periodic table tells you how many valence electrons an atom has.

If we know the number of valence electrons, we can figure out which atoms combine and how.

Noble Gases

All have 8 valence electrons except Helium which has 2

All of these atoms are happy because their outer shell is full.

Since they are happy, they are not likely to form compounds.

Three types of Bonding

Ionic- between metal/nonmetalCovalent- between nonmetalsMetallic- between metals

Ionic Bonding

Ionic Bonding- bond that forms when electrons are transferred from one atom to another

Ions- charged particles that form when an atom gains or loses electrons

This occurs between a metal and a nonmetal

Polyatomic ion- ionic bond with more than one bond NaOH and NO3

These are both the same element. How?

What is the element for A?How many valence electrons are missing from A to make it happy?Is it easier to gain 5 electrons or lose 3 electrons?What is the name for B?

A B.

Gain or Lose

• If you lose electrons, the charge becomes a positive• If you gain electrons, the charge becomes a negative

What bonds with what?

Positive charges bond with negative charges

Positive always is written firstYou may have to increase the number of atoms to balance the bond

Cheat

Ionic Bonding Steps

Using 2 different colors, draw the electron dot diagram for each atom

Decide whether each will gain or lose electrons

Draw arrows to show where the electrons are transferred

Write in the new charge for each molecule

Ionic Bonding

Bond Sodium(Na) with Fluorine(F).Bond Beryllium(Be) with

Oxygen(O).Bond Aluminum(Al) with

Phosphorus(P).Bond Magnesium(Mg) with

Sulfur(S).

Cross Bonding

Good when charges are not equal Bond Aluminum with sulfur Top number loses charge and goes to

bottom number Al+3 S-2

Al2 S3

Answer=Al2S3

Now try cross bonding yourself

Bond Fluorine with BoronBond Aluminum with Selenium

Bond Chlorine with GalliumBond Silicon with Sulfur.

Covalent Bonds

Covalent bond- formed when atoms share one or more pairs of electrons these form molecules

Shared Electrons

H H

2 different types of covalent bonds

Polar bonds- electrons are shared unequally

Nonpolar bonds- electrons are shared equally

Covalent Bond

H2

O

Steps for Covalent Bonding

Draw the EDD for all elements Look for ways to make the “puzzle

pieces” fit together If two elements are sharing an

electron it will be on the same side

Water is made of covalent bonds

Charge vs. Number

B+3O-

2

B2O3

chargeTOP

how manyBOTTOM

Now try drawing some on your own!

NH3

H2S CH4

Cl2 CO2

Metallic Bond

• Metallic bond- attraction between a positive metal ion and the electrons surrounding it

• Alloy- has two or more metals that are bonding together

Alloy Properties

▪ Resist rust▪ Ductile-put into a wire▪ Malleable- flattened into sheets

Properties of Covalent bondsLow melting pointsPoor conductivityDo not break up into ions

Properties of Ionic

Forms ionic crystalsHas high melting pointsBonds are broken by electricity

Make the following molecules using puzzle pieces:

H2F2H2ON2NH3CH4

CO2C2H6

O2Br2PCl3SiO2

C2H4Cl2C2H2I2