Unit 3Chemical Bonding

Agenda: 1/23 & 1/24

● Lecture: Covalent Bonding● Crash Course Video: Lewis Structures● Board Notes: Lewis Structures● Practice

Covalent Bonds

✘ We have previously learned that noble gases have a very stable electron configuration.

✘ This stable arrangement consists of a full outer energy level

✘ A full outer energy level consist of two valence electrons for helium and eight valence electrons for all noble gases

✘ Because of this stability, noble gases don’t tend to react with other elements to form compounds

Covalent Bonds✘ With ionic compounds metals and nonmetals react to form:✘ Binary ionic compounds✘ Electrons are transferred and ions are created✘ The ions in the ionic compound are now in a noble gas configuration✘ But… sometimes two atoms both need to gain valence electrons to

become stable and have a similar attraction for electrons… what do they do?

Covalent Bonds✘ THEY SHARE!✘ Sharing electrons is another way that these atoms can acquire the electron

configuration of a noble gas.✘ The octet rule states that atoms lose, gain or SHARE electrons to achieve a

stable configuration of eight valence electrons, or an octet.✘ Although exceptions to the octet rule exist, the rule provides a useful

framework for understanding chemical bonds

Covalent Bonds

● A Covalent Bond is when atoms share electrons in order to fill their valence (outer) shell○ Covalent bonds can be single, double, or triple○ A filled valence shell is a stable electron

configuration○ Bonds are between Non-Metal Elements

Properties of Covalent Compounds

● Covalent compounds are materials that are made up of covalently bonded molecules

● In General, they have the following properties:○ Low boiling point○ Low melting point○ Do not conduct electricity

● Some are soluble in water○ Depends on polarity (to be explained later)○ Un-equal sharing of electrons

Rules for Determining Lewis Structure

1. Predict the location of certain atoms:a. Hydrogen is always a terminal, or end, atom. Because it can only share one pair of electrons,

hydrogen can be connected only to one other atomsb. The atom with the least attraction for shared electrons in the molecule is the central atom. This

element usually is the one closer to the left on the periodic table. Find the total number of electrons available for bonding. This total is the number of valence electrons in the atoms in the molecule

2. Find the total number of electrons available for bonding. This total is the number of valence electrons in the atoms of the molecule

3. Determine the number of bonding pairs by dividing the number of electrons available for binding by two

4. Place one bonding pair (single bond) between the central atom and each of the terminal atoms5. Subtract the number of pairs you used in step 4 from the number of bonding pairs in step 3, place the

electrons around the terminal atoms first, and the remaining pairs to the central atom6. If the central atoms in not surrounded by four electron pairs, it doesn’t have an octet, you must convert

one or two of the lone pairs on the terminal atoms to a double bond as needed

Board Notes

Br2 CO2

CH4 AlCl3

NH3 PO43-

This is the end of the lecture

Agenda: 1/25 & 1/28

● Lecture: Double and Triple Bonds● Board Notes: Double and Triple Bonds● Lab: Making Molecules● Practice

Lecture: Double and Triple Bonds

● In many molecules, atoms attain a noble gas configuration by sharing more than one pair of electrons between two atoms, forming multiple covalent bonds.

● Atoms of the elements carbon, nitrogen, oxygen and sulfur most often form multiple bonds

● A double bond two electron pairs are shared● A triple bond, three electron pairs are shared

Board Notes: Double and Triple Bonds

.

C2H2 N2

O2 C2H2

C3H6O (CH3COCH3) HCN

This is the end of the lecture

Agenda: 1/29 & 1/30

● Quiz: Covalent Bonding and Lewis Structures● Lecture: Naming Covalent Compounds● Activity: Molecule Name Game● Practice

Naming Binary Covalent Compounds1. The naming system is for

compounds consisting of two non-metallic elements

2. The first element keeps its namea. The first element gets a PREFIX

only if there is more than one atom in the formula (compound)

3. The second element gets the -ide suffixa. The second element ALWAYS gets a

PREFIX

Prefixes:1. Mono

2. Di3. Tri4. Tetra5. Penta6. Hexa7. Hepta

Naming Binary Compounds

.

Carbon Dioxide

Dinitrogen Monoxide

Diphosphorus Pentoxide

H2O

CCl4

This is the end of the lecture

Agenda: 1/31 & 2/1

● Lecture: VSEPR Models and Shapes● Board Notes● Practice

Molecular Shapes

● The shape of a molecule determines many of its physical and chemical properties.

● Molecular shape, in turn, is determined by the overlap of orbitals that share electrons

● Theories have been developed to explain the overlap of orbitals and are used to predict the shape of the molecule

VSEPR Models

✘ Many chemical reactions, especially those in living things, depend on the ability of two compounds to contact each other

✘ The shape of the molecule determines whether or not molecule can get close enough to react

✘ Once a Lewis structure is drawn, you can determine the molecular geometry, or shape, of the molecule

VSEPR Models

✘ The model used to determine the molecular shape is referred to as the Valence Shell Electron Pair Repulsion or VSEPR

✘ This model is based on an arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom

VSEPR Models

● In short, the repulsion between electrons makes them want to be as far part from each other as possible.

● This repulsion makes it so molecules form predictable shapes● The bond angle between electrons changes with the number of

electrons present● We are going to learn the different shapes

Covalent Compounds

Compound Name Drawing Shape

SiO2

PF3

SiH4

SeBr2

Name the compound, draw the lewis structure, and determine the geometry : Linear, Trigonal Pyramidal, Tetrahedral or Bent

This is the end of the lecture

Agenda: 2/4 & 2/5

● Quiz: Names and Shapes● Crash Course: Polar vs Nonpolar Molecules● Lecture: Electronegativity and Polarity● Practice

Electronegativity and Polarity

● Electron affinity is a measure of the tendency of an atom to accept an electron.

● Excluding noble gases, electron affinity increases as the atomic number increases within a given period and decreases with an increase in atomic number within a group.

● The scale of electronegativities allows a chemistry to evaluate the electron affinity of specific atoms when they are incorporated into a compound

Electronegativity and Polarity

● Look at the electronegativity trends on the periodic table. Fluorine has the highest electronegativity value of 3.98, while francium has the lowest, 0.7.

● Because noble gases do not generally form compounds, individual electronegativities for noble gases like helium are not given

Electronegativity and Polarity

Which element is the higher electronegativity?

Sulfur or Aluminum Fluorine or Magnesium

Gold or Silver Bromine or Calcium

Oxygen or Nitrogen Boron or Beryllium

Electronegativity and Polarity

● The character and type of a chemical bond can be predicted using the electronegativity difference of the elements that are bonded.

Example: Electronegativity of chlorine is 3.16, and hydrogen is 2.20.3.16 - 2.20 = 0.96

Electronegativity and Polarity

● Unequal sharing of electrons results in a polar covalent bond (majority of bonds are unequal)○ When the electronegativity is equal, the bond is said to be

nonpolar○ When the electronegativity is unequal, the bond is said to be

polar● Molecules are either nonpolar or polar, depending on the location

and nature of the covalent bonds they contain.● In addition to the electronegativity numbers, shape is really

important in deciding polarity

Polar or Nonpolar? Draw each structure, and identify the electronegativity if needed to determine if the molecule is polar or non-polar.

HCl NH3

O2 H2O

CH4 C2H4

This is the end of the lecture

Agenda 2/6 & 2/7

● Lab: Properties of Water● Notes: Take notes from the lab sheet

Agenda: 2/8 & 2/11

● Finish Water Lab● Quiz: Electronegativity, Polarity and Properties

of Water

Agenda: 2/12 & 2/13

● Review● Practice Test● Correct Previous Quizzes

Agenda: 2/14 & 2/15

Test: Covalent Bonds and Properties of Water