Chemical Bonds

(Ionic and Covalent

Bonds) Part 1Textbook Pages: 52-63

Chemical Bonds• Chemical Bonds: The forces that attract atoms to each

other in compounds.

o Ionic Bond: The attractive electrostatic force between a negative ion and a positive ion.

o Covalent Bond: The attraction between atoms that results

from the sharing of electrons.

• A filled valence shell makes atoms stable

Therefore, when bonds form between atoms, they do so in a way that gives each atom a filled valance shell (stable octet).

Octet Rule: When bonds form between atoms, the atoms gain, lose, or share electrons in a way that they crate a filled outer shell containing eight (8) electrons.

Ionic vs. CovalentProperty Ionic Compounds Covalent (Molecular)

Compounds

Types of elements involved

Metal and Nonmetal Two Nonmetals

What happens to electrons?

Electrons Transferred Electrons Shared

Type of bond that forms

Ionic Covalent

State at Room Temperature

Solid Solid, Liquid, or Gas

Solubility in Water Soluble Insoluble

Electrical Conductivity in Solution

Conducts Does not conduct

Old Way of Bond Classification

• BEFORE, classification of bond type was easy.o To know us the bond type all we did was look at the types of elements in the

compounds.

o Examples:• NaCl

o (metal + non-metal) IONIC

• CH4

o (nonmetal + non-metal) COVALENT

• Consider the following compound:

o BeH2

• Be is a metal• H is a non-metal• You think it’s going to be an ionic compound, BUT it is in fact a

COVALENT compound!!!• Therefore, our “inspection” method of classifying bond type is no

longer sufficient to predict the classification of bond type.

Electronegativity and Bond Classification

• Electronegativity: A measure of an element’s ability to attract electrons in a chemical bond.

• By comparing the electronegativity values of two elements involved in a chemical bond, we can determine whether they will:o Transfer electrons (IONIC)o Share electrons (COVALENT)

• Unequal sharing of electrons (POLAR COVALENT)• Equal sharing of electrons (COVALENT)

• Examples:o Classify the type of bond present for each of the following compounds:

• CH4

• B2S3

• CaO

• H2O

Electronegativity and Bond Classification

Ionic Compounds• Ionic compounds transfer electrons to produce

positive ions and negative ions.• The oppositely charged ions attract each other.• The attraction is what holds the ions together.

• This attraction is strong.• It is this attraction that give ionic compounds HIGH

melting points and makes them solid at room temperature.

• Since the ions are charged, when they dissolve in water, they can conduct electricity by facilitating the movement of the ions through the liquid.

Rules for Drawing Lewis Structures for

Ionic Compounds• 1. Write the ionization equation of each element.

• Use this to determine the number of electrons transferred by each element.

• Multiply the equations (if necessary) to equalize the number of electrons lost and gained.

• 2. Each ion goes in a set of square brackets [ ] with the charge outside the bracket corresponding to the number of electrons lost or gained.

• 3. Alternate ions of opposite charges.