2.2 Intramolecular force and Potential Energy

Covalent bonds are the bonds between ______ when they ______

two nonmetals; share valence electrons.

Different types of covalent bonds:

Polar or nonpolar

In polar covalent bonds, electrons are shared equally/unequally

unequally

In nonpolar covalent bonds, electrons are shared equally/unequally

equally

Covalent bonds can what three types of bonds?

single, double, triple bonds

What type of bond do covalent bonds have if there are resonance structures?

Average of single, double, triple bonds

Covalent bonds occur at the highest/lowest energy state.

lowest

The low energy state of covalent bonds happens when:

the attraction between the nuclei is greatest for the shared electrons, but the repulsions between electrons and between the nuclei is the least.

What happens when atoms in covalent bonds are too close together?

The nuclei will repel each other

What happens when atoms in covalent bonds are too far apart?

the attraction will not be enough to hold them together

Bond energy is the energy required when:

breaking a bond

the energy released when a bond is formed

bond energy

Compare the magnitude and sign of energy required when breaking a bond vs energy released when forming a bond:

Same magnitude but different sign

Larger atomic radii increase/decreases the bond length.

increases

Longer bond length increases/decreases the bond energy

decreases

Increasing the bond order increases/decreases the bond energy

increases

Why does increasing the bond order increase the bond energy?

there are more electrons involved and therefore greater coulombic attraction and the bond length has decreased.

The energy to separate ions in ionic compounds is their:

lattice energy

The change in energy that takes place when gaseous ions are combined to form an ionic solid.

Lattice energy

Combining ions will absorb/release energy.

release

Lattice energy can be represented using:

a modification of Coulomb’s law where the energy is proportional to the charges and inversely proportional to the distances between the nuclei.

Why is energy proportional to the charges in terms of lattice energy?

Larger charges = more attraction = more energy required to separate the ions

Why is energy inversely proportional to distance between the nuclei in terms of lattice energy?

Smaller radii = more attraction = more energy required to separate the ions

What is a useful representation for describing the interactions between atoms?

A graph of potential energy vs distance between atoms

Graphs of potential energy vs distance between atoms illustrate:

Equilibrium bond length and bond energy

The separation between atoms at which the potential energy is lowest:

Equilibrium bond length

The energy required to separate the atoms:

Bond energy

In a covalent bond, the bond length is influenced by:

Size of the atom’s core and the bond order

Examples of bond order:

Single, double, triple

Bonds with a higher bond order are longer/shorter

Shorter

Shorter bond have larger/smaller bond energies

Larger

What can be used to understand the strength of interactions between cations and anions?

Coulomb’s law

Larger charges lead to stronger/weaker interactions

Stronger

Why do larger charges lead to stronger interactions?

Interaction strength is proportional to the charge on each ion

Smaller ions lead to stronger/weaker interactions

Stronger

Why do smaller ions lead to stronger interactions?

The interaction strength increases as the distance between the centers of the ions (nuclei) decreases

A chemical bond involves a balance between:

Attractions and repulsions

Is this a covalent bond?

No

Why is this not a covalent bond?

The atoms are too far apart and they do not interact with each other

The potential energy between the atoms is equal to:

Zero

This is a ______ bond

Stable covalent

There is a balance between:

Attractions between the proton of one atom and the electron of the other atom, repulsions between protons, and repulsions between electrons

Is this a stable arrangement?

No

Why is this not a stable arangement?

The atoms are too close together, so there is too much repulsion between the protons of each atom

The potential energy between the atoms is very high/low

High

Internuclear distance vs potential energy graph with atoms that are far apart, touching, and overlapping:

Label bond length on internuclear distance vs potential energy graph:

Label bond energy on internuclear distance vs potential energy graph:

The bond energy represents the energy that is:

Released when the bond is formed and absorbed when the bond is broken

The number of bonds that are formed between two atoms affect the:

Bond length and bond energy

The number of electron pairs that are shared between two atoms

Bond order

A double bond is shorter/longer than a single bond

Shorter

A double bond is weaker/stronger than a single bond

Stronger

A triple bond is shorter/longer than a double bond

Shorter

A triple bond is weaker/stronger than a double bond

Stronger

As the bond order increases, the bond length increases/decreases

Decreases

As the bond order increases, the bond energy increases/decreases

Increases

Ionic compounds have relatively high/low melting points

High

Why do ionic compounds have relatively high melting points?

The attractions between the ions in the solid crystal are very strong

Measure of the strength of the attractions between ions

Lattice energy

The energy required to separate one mole of a solid ionic compound into its gaseous ions

Lattice energy

The energy released when gaseous ions combine to form one mole of a solid ionic compound

Lattice energy

The greater the magnitude of the lattice energy, the stronger/weaker the attraction between the ions in the crystal lattice of an ionic compound

Stronger

Coulomb’s law describes the:

Attractive (or repulsive) force between two charged particles

Coulomb’s law:

F is proportional to q1q2/r²

The magnitude of the lattice energy of an ionic solid depends on:

Magnitude of the charges on the ions and the distance between the ions in the crystal lattice

The magnitude of the lattice energy of an ionic compound tends to increases as the magnitude of the charges on the ions increases/decreases

Increases

The magnitude of the lattice energy of an ionic compound tends to increases as the distance between the ions in the crystal lattice increases/decreases

Decreases

From bond length of 0 to 74 pm, is repulsion less than, greater than, or equal to attraction?

Greater than

At bond length of 74 pm, is attraction less than, greater than, or equal to repulsion?

Equal to

From bond length of 74 to 250 pm, is attraction greater than, less than, or equal to repulsion

Greater than

Energy released is exothermic/endothermic

Exothermic

Energy gained is exothermic/endothermic

Endothermic

Bond length is directly/inversely proportional to bond energy

Inversely