Ch. 3 - Bonding and Chemical Interactions

12% of MCAT Chemistry content

What are the two main types of chemical bonds?

Ionic and covalent bonds.

Why do elements form chemical bonds?

To attain a noble gas-like electron configuration.

What is the octet rule?

Elements are most stable with eight valence electrons.

What are the exceptions to the octet rule?

1. Incomplete octet: Stable with fewer than eight electrons (H, He, Li, Be, B).

2. Expanded octet: Stable with more than eight electrons (elements in period 3 or greater).

3. Odd number of electrons: Cannot have eight electrons on each element.

How is an ionic bond formed?

By transferring electrons from an element with low ionization energy to one with high electron affinity.

Between what types of elements do ionic bonds usually form?

Metals and nonmetals with large differences in electronegativity (ΔEN>1.7)

What are cations and anions?

• Cations: Positively charged ions.

• Anions: Negatively charged ions.

What structure do ionic compounds form, and what are their properties?

• Form crystalline lattices.

• Dissociate in water and polar solvents.

• Have high melting points.

How is a covalent bond formed?

By sharing electrons between two elements with similar electronegativities.

What is bond order?

Refers to single, double, or triple bonds; as bond order increases:

• Bond strength and energy increase.

• Bond length decreases.

What are nonpolar and polar covalent bonds?

• Nonpolar: Equal sharing of electrons (ΔEN < 0.5)

• Polar: Unequal sharing of electrons (0.5 ≤ ΔEN ≤ 1.7)

What is a coordinate covalent bond?

A bond where one atom provides both bonding electrons, often seen in Lewis acid-base interactions.

What is a Lewis dot symbol?

A representation of an atom's valence electrons.

What are resonance structures?

Representations of all possible electron configurations (stable and unstable) in a molecule.

What is formal charge?

Difference between the valence electrons an atom has in its neutral state and those in a molecule.

What does VSEPR theory predict?

The 3D molecular geometry of covalently bonded molecules, arranging electrons as far apart as possible.

What is the difference between electronic and molecular geometry?

• Electronic geometry: Position of all electrons (bonding and nonbonding).

• Molecular geometry: Position of bonding pairs only.

What determines molecular polarity?

The sum of dipole moments in the structure;

• polar molecules contain polar bonds

• nonpolar molecules may have nonpolar bonds or canceling dipole moments.

What is the difference between sigma (σ\sigmaσ) and pi (π\piπ) bonds?

• Sigma bonds: Head-to-head overlap.

• Pi bonds: Parallel overlap of electron cloud densities.

What are intermolecular forces, and how do they rank in strength?

Electrostatic attractions between molecules; weaker than covalent bonds, which are weaker than ionic bonds.

What are London dispersion forces?

The weakest interactions, present in all atoms and molecules, increasing with the size of the atom or molecule.

What are dipole–dipole interactions?

attractions between oppositely charged ends of polar molecules; stronger than London forces but negligible in the gas phase.

What are hydrogen bonds?

A subset of dipole–dipole interactions

when hydrogen bonds with fluorine, oxygen, or nitrogen, creating strong intra- and intermolecular attractions.