Lesson 1 Intro to Chemical Bonding

Covalent Bonding Unit

Lesson 1: Introduction to Chemical Bonding

TargetsI can define chemical bond.I can describe covalent bonding.I can classify bonding type

according to electronegativity differences.

DefinitionsChemical Bond – mutual electrical

attraction between the nuclei and valence electrons of different atoms that bind the atoms together

Valence electrons – outermost electrons that are available to be lost, gained, or shared to form a chemical bond

Chemical Bond

A force that holds groups of 2 or more atoms together and makes them function as a unitAtom – smallest unit of an elementMolecule – Group of covalently bonded

atomsAtoms

Molecule

Types of Chemical BondsIonic Bonding – (covered in next chapter)

a type of bond in which a metal and a nonmetal transfer electrons

Covalent Bonding – type of bond in which 2 or more nonmetal atoms share electrons

Periodic TableIONIC – Metal + nonmetalCOVALENT – 2 nonmetals

Types of Covalent BondsNonpolar covalent bond – electrons are

shared equally

Types of Chemical BondsPolar covalent – electrons are not shared

equally because one atom attracts the shared electrons more than the other atom

Bond Types Video

Electronegativity

Electronegativity - measure of an atom’s ability to attract electrons.

Electronegativities tend to increase across a period and decrease down a group

Classifying Chemical BondsThe polarity of a bond depends on the

difference between the electronegativity values of the atoms forming the bonds.

Nonpolar covalent – 0 to 0.3Polar covalent – 0.4 to 1.7Ionic – greater than 1.8

Increases from left to right across a period Decreases down a group of representative

elements

Electronegativity Values

PracticeUse electronegativity values to classify the

following bonds:a. Sulfur and Hydrogenb. Lithium and Fluorinec. Potassium and Chlorined. Iodine and Brominee. Carbon and Hydrogen

PracticeUse electronegativity values to classify the

following bonds:a. Sulfur and Hydrogen 2.5 – 2.1 = 0.4;

polar covalentb. Lithium and Fluorine 4.0 – 1.0 = 3.0;

Ionicc. Potassium and Chlorine 3.0 – 0.8 =

2.2; Ionicd. Iodine and Bromine 2.8 – 2.5 = 0.3;

Nonpolar covalente. Carbon and Hydrogen 2.5 – 2.1 = 0.4 ;

polar covalent

Covalent Bonding and Molecular Compounds

Covalent Bonding

TargetsI can explain why most atoms form

chemical bonds.I can explain the relationships among

potential energy, distance between approaching atoms, bond length and bond energy.

I can state the octet rule.I can determine the number of valence

electrons for a given atom.

Nature favors chemical bonding because most atoms have lower potential energy when they are bonded to other atoms.

Formation of a Covalent Bond

Each atom has a positive nucleus in the center and negative electrons surrounding the nucleus in a spherical pattern.

The positively charged nuclei are attracted to the negatively charged electrons.

Formation of a Covalent Bond

As the atoms approach each other, the charged particles interact: nucleus on one atom attracts electrons on the other atom.

Formation of a Covalent Bond

As the atoms approach one another, the potential energy decreases.

A bond forms when the potential energy is at a minimum.

Formation of a Covalent Bond

If the atoms continue to approach one another once the bond forms, the nuclei will begin to repel one another and the potential energy will start to increase.

Formation of a Covalent Bond

Characteristics of the Covalent Bond

Bond length – distance between two bonded atoms at their minimum potential energy or the average distance between two bonded atoms

Bond energy – energy required to break a chemical bond and form neutral isolated atoms

- kilojoules per mole (kJ/mol)Bond lengths and bond energies vary with

the types of atoms that have combined

The octet rule states that atoms tend to lose, gain or share electrons until they are surrounded by 8 electrons in their valence shell.

The number of valence electrons is equal to the group number. (Groups 13-18; Group # -10)

LABEL YOUR PERIODIC TABLE

The Octet Rule

1A2A 3A4A5A6A7A

8A

PracticeWhat is the relationship between bond

energy and bond length?

PracticeWhat is the relationship between bond

energy and bond length? The bond length decreases as the

strength of the bond increases.

PracticeArrange the following in order of increasing

bond strength: C–Cl, C–I, H–F, and I–ISKIP

PracticeArrange the following in order of increasing

bond strength: C–Cl, C–I, H–F, and I–II-I, C-I, C-Cl, H-F

Which pair of bonded atoms has the strongest bond?

Practice Problems

Which pair of bonded atoms has the strongest bond?H – F

Practice Problems

Which pair of bonded atoms has the weakest bond?

Practice Problems

Which pair of bonded atoms has the weakest bond?I – I

Practice Problems

Arrange the following bond lengths in order of increasing bond strength: 72 pm, 149 pm, 53 pm, and 398 pm

SKIP

Practice Problems

Arrange the following bond lengths in order of increasing bond strength: 72 pm, 149 pm, 53 pm, and 398 pm 398 pm, 149 pm, 72 pm, 53 pm

Practice Problems

Determine the number of valence electrons in each of the following atoms.LithiumSulfurCarbonNeon

Practice Problems

Determine the number of valence electrons in each of the following atoms.Lithium - 1Sulfur - 6Carbon -4Neon - 8

Practice Problems