Chemistry H - 8.3 and 8.4

Covalent Bond

A bond formed by the sharing of electrons between atoms.

Molecule

A neutral group of atoms joined together by covalent bonds.

Diatomic Molecule

A molecule consisting of two atoms.

Molecular Compound

A compound that is composed of molecules.

Molecular Formula

A chemical formula that shows how many atoms of each element are in a molecule.

What does a molecular formula tell you?

It tells how many atoms of each element are present in a compound.

How is a molecule different from a formula unit?

A molecule is the representative unit of a molecular compound; a formula unit is for an ionic compound.

Which elements exist as single atoms in nature?

Noble gases. They're called monatomic.

How is NO different from N2O?

NO has 1 nitrogen and 1 oxygen; N2O has 2 nitrogen and 1 oxygen.

Example of a diatomic molecule in the atmosphere?

Oxygen (O2).

What is molecular structure?

The 3D arrangement of atoms in a molecule.

Single Covalent Bond

Two atoms share one pair of electrons.

Structural Formula

Shows how atoms are arranged in a molecule using lines.

Unshared Pair

Valence electrons not shared between atoms.

Double Covalent Bond

Two atoms share two pairs of electrons.

Triple Covalent Bond

Two atoms share three pairs of electrons.

Coordinate Covalent Bond

One atom donates both electrons in the bond.

Polyatomic Ion

A tightly bonded group of atoms with a charge.

Bond Dissociation Energy

Energy required to break a covalent bond (usually in kJ/mol).

Resonance Structure

One of two or more valid Lewis structures for a molecule.

Molecular Orbital

Orbital that applies to the entire molecule.

Bonding Orbital

A molecular orbital with electrons forming a covalent bond.

Sigma Bond

A bond symmetrical around the axis between nuclei.

Pi Bond

A bond with electron regions above and below the bonding axis.

Tetrahedral Angle

A 109.5° angle when 4 atoms are bonded to a central atom.

VSEPR Theory

Electron pairs repel, so molecules shape themselves to minimize that repulsion.

Hybridization

Orbitals mix to form new hybrid orbitals for bonding.

How are atomic and molecular orbitals related?

Atomic orbitals are from single atoms; molecular orbitals span whole molecules.

What is VSEPR used for?

To predict molecular shapes.

Why is hybridization useful?

It explains bond types and molecular shapes.

Shapes from hybridization: sp2, sp3, sp

sp2 = trigonal planar, sp3 = tetrahedral, sp = linear.

What is a sigma bond?

The first covalent bond formed, lying between the atoms.

Predict bond angles with VSEPR: Methane, Ammonia, Water

Methane = 109.5°, Ammonia = 107°, Water = 104°.

How many sigma and pi bonds in C2H2?

3 sigma, 2 pi bonds.

Shape of BF4

ion?

Nonpolar Covalent Bond

Electrons are shared equally.

Polar Covalent Bond

Electrons are shared unequally.

Van der Waals Forces

Weak attractions between molecules (dispersion + dipole).

Dipole Interactions

Attraction between opposite ends of polar molecules.

Dispersion Forces

Temporary attractions due to moving electrons.

Hydrogen Bond

Strong dipole force where H bonds with N, O, or F.

Network Solid

All atoms are covalently bonded in a large structure.

How does electronegativity affect polarity?

More electronegative atoms pull electrons and become slightly negative.

IMF vs. Ionic/Covalent Bond Strength

IMFs are much weaker than covalent or ionic bonds.

Why are covalent compound properties so varied?

Because intermolecular forces vary widely.

Can a molecule have polar bonds but be nonpolar?

Yes—if it's symmetrical like CCl4.

Draw dot structures & identify polar bonds: HOOH, BrCl, HBr, H2O

H–O–O–H; Br–Cl; H–Br; H–O–H (O/Cl/Br = δ⁻, H = δ⁺).

How is a network solid different?

It’s one huge covalent structure, not separate molecules.

What happens to polar molecules between charged plates?

They align with the charges.

Dipole vs. Dispersion Forces

Dipole = from permanent polarity; Dispersion = from temporary shifts in electrons.