Chemical bonding

Chemical Bond

A force that forms when atoms rearrange valence electrons to achieve stability

Valence Electrons

Electrons in the outer energy level of an atom that are involved in bonding

Octet Rule

Atoms tend to gain, lose, or share electrons to have 8 valence electrons (stable configuration)

Ionic Bond

A bond formed by the transfer of electrons from one atom to another

Cation

A positively charged ion formed when an atom loses electrons

Anion

A negatively charged ion formed when an atom gains electrons

Ionic Compound

A compound made of oppositely charged ions held together by electrostatic attraction

Crystal Lattice

A repeating 3D arrangement of ions in an ionic compound

Property of Ionic Compounds (Melting Point)

High melting and boiling points due to strong electrostatic forces

Property of Ionic Compounds (Hardness)

Hard and brittle due to rigid crystal lattice

Property of Ionic Compounds (Conductivity)

Conduct electricity when molten or dissolved in water

Covalent Bond

A bond formed when atoms share electrons

Molecule

A neutral group of atoms held together by covalent bonds

Single Bond

A covalent bond where 1 pair of electrons is shared

Double Bond

A covalent bond where 2 pairs of electrons are shared

Triple Bond

A covalent bond where 3 pairs of electrons are shared

Polar Covalent Bond

A covalent bond with unequal sharing of electrons due to electronegativity difference

Nonpolar Covalent Bond

A covalent bond with equal sharing of electrons

Electronegativity

A measure of an atom’s ability to attract electrons in a bond

Electronegativity Difference ≥ 1.7

Indicates an ionic bond

Electronegativity Difference 0.3–1.7

Indicates a polar covalent bond

Electronegativity Difference ≤ 0.3

Indicates a nonpolar covalent bond

Partial Charge (δ+ / δ−)

A slight positive or negative charge due to unequal electron sharing

Metallic Bonding

A bond in metals where valence electrons are delocalized in a “sea of electrons”

Sea of Electrons

Model describing free-moving electrons in metals

Property of Metals (Luster)

Shiny appearance due to electron movement

Property of Metals (Conductivity)

Excellent conduction of heat and electricity

Property of Metals (Malleability)

Ability to be hammered into thin sheets

Property of Metals (Ductility)

Ability to be drawn into wires

Electron Dot Diagram

A representation of valence electrons using dots around an element symbol

Lewis Structure

A diagram showing bonding and lone pairs of electrons in a molecule

Lone Pair

A pair of valence electrons not involved in bonding

Shared Pair

A pair of electrons involved in a covalent bond

Central Atom

The atom in the middle of a Lewis structure (usually least electronegative, never hydrogen)

Rule for Hydrogen in Lewis Structures

Hydrogen forms only 1 bond and needs 2 electrons

Rule for Carbon in Lewis Structures

Carbon typically forms 4 bonds and has no lone pairs

Rule for Nitrogen in Lewis Structures

Nitrogen forms 3 bonds and has 1 lone pair

Rule for Oxygen in Lewis Structures

Oxygen forms 2 bonds and has 2 lone pairs

Rule for Halogens (F, Cl, Br, I)

Form 1 bond and have 3 lone pairs

Polyatomic Ion

A charged group of covalently bonded atoms

Negative Polyatomic Ion

Has extra electrons (add electrons when counting)

Positive Polyatomic Ion

Has fewer electrons (subtract electrons when counting)

Brackets in Polyatomic Ions

Used to show the entire structure carries a charge

VSEPR Theory

Valence Shell Electron Pair Repulsion; electron pairs repel and spread out

Electron Clouds

Regions of electron density (bonding + lone pairs) around central atom

Linear Shape

Molecule shape with 2 atoms or 2 electron groups (180°)

Trigonal Planar Shape

3 electron groups around central atom (120°)

Tetrahedral Shape

4 electron groups around central atom (109.5°)

Bent Shape

Molecule with 2 bonds and 2 lone pairs on central atom

Trigonal Pyramidal Shape

Molecule with 3 bonds and 1 lone pair on central atom

Molecular Geometry

The 3D arrangement of atoms in a molecule

Polar Molecule

A molecule with an uneven distribution of charge (has positive and negative ends)

Nonpolar Molecule

A molecule with even charge distribution or symmetrical shape

Condition for Polar Molecule

Must have polar bonds AND asymmetrical shape

Condition for Nonpolar Molecule

No polar bonds OR symmetrical arrangement cancels charges

Intermolecular Forces

Attractive forces between molecules (weaker than bonds)

Intramolecular Forces

Forces within a molecule (bonds)

Dipole-Dipole Forces

Attraction between polar molecules (strong IMF)

Hydrogen Bonding

A strong dipole-dipole force when H is bonded to N, O, or F

London Dispersion Forces

Weak forces caused by temporary electron movement; present in all molecules

Strongest Intermolecular Force

Hydrogen bonding (special dipole-dipole)

Weakest Intermolecular Force

London dispersion forces

Conductivity Rule for Ionic Compounds

Conduct only when ions are free to move (molten or dissolved)

Conductivity Rule for Covalent Compounds

Do not conduct electricity due to lack of charged particles

Volatile Substance

A substance that evaporates easily (common in covalent compounds)

Bond vs Intermolecular Force

Bond = within molecule; IMF = between molecules