Chemical Bonding Notes

Chemical Bonding Notes

Valence Electrons

• Recall: valence electrons are the electrons in the outermost energy level

• MOST IMPORTANT FOR BONDING

• Hydrogen and Helium only need 2 valence electrons in order to be stable

• The rest of the elements need 8

Why do elements bond?

• Full outer energy levels mean they are stable

• If the atoms of elements do not have full energy levels, they will seek out other atoms with whom they can join

• Elements will gain, lose, or share electrons to fill up the outer energy level (8 is the magic number) and become chemically stable.

Multiple Choice

Why do elements bond together?

• Because it is easier to survive in the world if they are bonded

• They share or transfer electrons to get a full outer shell to be happy

• They like to have a partner element to make them stronger

Noble Gases (Group 18)

• The Noble Gases already have full outer energy levels

• They are chemically stable and very rarely form compounds

Other Elements

• Other elements do not have 8 valence electrons

• They will form chemical bonds in order to become chemically stable.

Multiple Choice

Which elements on the periodic table do NOT bond?

• Group 1 Alkali metals

• All metals

• All nonmetals

• Noble Gases

Oxidation Numbers

• Oxidation numbers tell how many electrons an atom gains, loses, or shares to become stable

• Valence electrons determine the number in oxidation numbers

• During ionic bonding, metals will lose those valence electrons because they will be transferred to the nonmetals

• So metals lose those electrons and nonmetals gain them.

Oxidation Numbers

• In covalent bonding, one nonmetal will be assigned a positive number and the other one(s) will be assigned a negative number

• Examples of Oxidation Numbers:

  Lithium:

  Chloride:

  
  

Chemical Bond

• A chemical bond is the force of attraction between two different atoms

• Sometimes it can occur between two of the same atoms

Types of Bonds

• There are three types of chemical bonds:

• Ionic

• Covalent

• Metallic

• We will only concentrate on ionic and covalent bonds

Ionic Bonds

• A transfer of electrons from metals to nonmetals

• The smallest unit of the compound is the ion

• The bond occurs because of the attraction between the positive ion and the negative ion

• The compounds conduct electricity when dissolved in water

Covalent Bonds

• Sharing of electrons between nonmetals and metalloids

• The smallest unit of the compound is a molecule

• The bond occurs because the atoms must stay close together to share electrons

• The compounds do not conduct electricity well when dissolved in water

Ions

• Charged particles resulting from a gain or loss of electrons

• Write the symbol of the element followed by a superscript indicating the oxidation number

Ionic Bonding

• Metals give up valence electrons so that the remaining energy level is full – they become positive ions (cations)

• Nonmetals gain valence electrons so that their outer energy level is full – they become negative ions (anions)

Compounds are neutral!

• The number of electrons lost by the metal must equal the number of electrons gained by the nonmetal

• The positive charge must equal the negative charge so that they cancel each other out

Covalent Bonding

• Formed when atoms share electrons

• Occurs between two or more nonmetals or metalloids neither of which will easily give up electrons

• A molecule is a particle that forms from electron sharing.

Types of Covalent Compounds

• Polar compounds result from unequal sharing between atoms – one end of the molecule is slightly positive while the other end is slightly negative

• Made up of two atoms of unequal size

• Nonpolar compounds result from equal sharing between atoms – they have no electric charge

• Made up of two identical atoms or a symmetrical arrangement

Types of Covalent Bonds

• Single bonds: Two shared electrons Represented by a single line

• Double bonds: Four shared electrons Represented by two lines

• Triple bonds: Six shared electrons Represented by three lines

Multiple Choice

How many electrons do double bonds share?

• 2

• 4

• 6

• 8