Chapter 5. Chemical Bonding and Structure

Compound

Substance made up of two or more different elements combined together chemically

Chemical Bonds

When elements combine to form compounds, these attractive forces hold the atoms together

Octet Rule

When bonding occurs, atoms tend to reach electron arrangement with 8 electrons in outermost energy level

Exceptions to the octet rule

• Transition metals, they can have more or fewer than 8 electrons in their outermost energy level

• Helium and other elements nearby such as lithium and hydrogen, they tend to achieve the same electron arrangement as helium.

Ion

Charged atom/group of atoms

Ionic bond

Force of attraction between oppositely charged ions in a compound. Bonds are always formed by complete transfer of electrons from one atom to another

Cation

Positive ion

Anion

Negative ion

Crystal lattice

The three-dimensional arrangement of ions

Unit cell

The repeating unit in a crystal lattice

Chemical formula

Way of representing a compound using symbols for the atoms present and numbers to show how many atoms of each element are present.

-ide suffix

A compound that contains just two elements

-ate suffix

Compounds which contain oxygen as well as two other elements

Transition metal

One that forms at least one ion with a partially filled d sublevel

Transition metal properties

• Transition metals have variable valency

• Transition metals usually form coloured compounds

• Transition metals are widely used as catalysts

D-block elements that have exceptions to the transition metals’ properties

• Scandium only forms Sc3+ ions and zinc only forms Zn2+ ions.

• Scandium and zinc only form white compounds

• Scandium and zinc show little catalytic activity

• Neither Sc3+ nor Zn2+ has a partially filled d sublevel

Covalent bond

Chemical bond formed when two atoms share pair(s) of electrons

Molecule

Group of atoms joined together. Smallest particle of an element or compound that can exist independently

Valency

The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.

Sigma bond

Head-on overlap of two orbitals

pi bond

sideways overlap of p orbitals

When is a single bond formed?

When one pair of electrons is shared between two atoms.

When is a double bond formed?

When two pairs of electrons are shared between two atoms.

When is a triple bond formed?

When three pairs of electrons are shared between two atoms.

Differences between sigma and pi bonds

• Sigma bonds are formed by head-on overlap of two orbitals

• Pi orbitals cannot involve s orbitals

• Sigma bonds have a stronger bond which is not easily broken

• Pi bonds are associated with double and triple covalent bonds

• Pi bonds are only formed after a sigma bond is formed and cannot exist on its own

VSEPR Theory Full Name

Valence Shell Electron Pair Repulsion Theory

VESPR Theory explanation

States that the shape of a molecule depends on the number of pairs of electrons around the central atom. Since electrons are negatively charged, electron pairs repel each other and arrange themselves in space so that they are as far apart as possible

What is the shape of an atom with two pairs of electrons around the central atom

linear, 180 degrees

What is the shape of an atom with three pairs of electrons around the central atom

triangular planar, 120 degrees

What is the shape of an atom with fours pairs of electrons around the central atom

Tetrahedral, 109.5 degrees

Lone pair presence effect on the bond angle

decreases it by 2.5 degrees for every lone pair

Why do lone pairs affect the bond angles?

Because lone pairs are closer to the nucleus, they exert a greater force of repulsion on each other than bond pairs do.

Order of the repulsions’ strengths for the VESPR theory

Repulsion between two lone pairs > repulsion between a lone pair and a bond pair > repulsion between two bond pairs

Qualitative analysis

Determining the presence of a result(substance) rather than determining how much of a result(substance) is present.

Precipitation reaction

Reaction in which an insoluble substance is produced from soluble substances in solution.

Precipitate

The insoluble substance formed in a precipitation reaction