14.2 Chemical Bonding & States of Matter

14.2 Chemical Bonding & States of Matter

Quick Answer: Atoms bond to reach stable valence configurations (octet rule). Ionic bonds transfer electrons (metal ↔ nonmetal); covalent bonds share electrons (nonmetals). Polar covalent sharing in water creates a polar solvent that dissolves electrolytes and many drugs. Solids, liquids, and gases differ in particle motion and spacing (kinetic molecular theory at intro level). Physical changes rearrange form; chemical changes make new substances.

Bonding explains why NaCl dissolves in water, why O₂ is a gas at room temperature, and why breaking a tablet is not the same as metabolizing a drug. Stay conceptual—no kinematics, optics, or circuit problems.

The Octet Rule

Many main-group atoms are most stable with eight valence electrons—the electron configuration of a noble gas. They achieve this by:

• Losing electrons (metals → cations)
• Gaining electrons (nonmetals → anions)
• Sharing electrons (covalent bonds)

Hydrogen is an exception: it needs two electrons (a duet) to match helium’s configuration. Atoms already with full octets (noble gases) rarely bond under ordinary conditions.

The octet rule is a useful HS/intro-college guide, not an absolute law (transition metals and expanded octets exist), but it is exactly the level NEX Chemistry expects.

Ionic Bonding

An ionic bond forms when electrons are transferred from one atom to another, creating oppositely charged ions that attract electrostatically.

Typical pattern:

1. A metal atom with few valence electrons loses them → cation
2. A nonmetal atom with nearly full valence shell gains them → anion
3. Electrostatic attraction holds the ions in a crystal lattice (e.g., NaCl)

Example: Na (1 valence e⁻) + Cl (7 valence e⁻) → Na⁺ + Cl⁻ → ionic compound sodium chloride.

Properties of many ionic compounds (exam-level):

• High melting/boiling points (strong lattice attractions)
• Often crystalline solids at room temperature
• Conduct electricity when molten or dissolved in water (mobile ions)—not as dry solids
• Many are water-soluble (especially Group 1 salts)

Nursing link: IV saline is aqueous Na⁺ and Cl⁻; serum electrolytes are free ions in water, not dry salt crystals.

Covalent Bonding

A covalent bond forms when atoms share one or more pairs of electrons—typically between nonmetals.

Molecules are the discrete units of many covalent substances (H₂O, O₂, CO₂, glucose). Molecular compounds generally have lower melting/boiling points than ionic lattices and do not conduct as solids; whether a solution conducts depends on whether molecules ionize (acids) or stay molecular.

Polar vs Nonpolar Covalent Bonds

Atoms do not always share equally.

• Electronegativity is an atom’s attraction for shared electrons.
• Nonpolar covalent: equal (or nearly equal) sharing—e.g., O₂, H₂, Cl₂, or C–H roughly.
• Polar covalent: unequal sharing—one end of the bond is slightly negative (δ−), the other slightly positive (δ+). Classic example: O–H in water (oxygen pulls electrons more strongly).

Water: The Body’s Polar Solvent

A water molecule has two polar O–H bonds and a bent shape, so the molecule has a permanent dipole: oxygen side δ−, hydrogen side δ+. That polarity lets water:

• Attract and surround ions (hydration shells) → dissolve NaCl, KCl, many electrolytes
• Dissolve other polar molecules (sugars, alcohols, many drugs)
• Form hydrogen bonds between water molecules—explaining high boiling point for such a small molecule, surface tension, and cohesion

“Like dissolves like”: polar/ionic solutes dissolve well in polar solvents (water); nonpolar solutes (oils, many lipid-soluble drugs) prefer nonpolar environments (lipid bilayers, fat tissue). This single idea connects bonding to pharmacokinetics and IV compatibility at the conceptual level.

States of Matter

Matter commonly exists in three states on the NEX:

Plasma (ionized gas) appears in advanced contexts; NEX focus is solid/liquid/gas.

Phase changes (melting, freezing, vaporization, condensation, sublimation) are usually physical—the substance remains chemically the same (ice ↔ liquid water ↔ steam are all H₂O).

Kinetic Molecular Theory (Intro Level)

Kinetic molecular theory (KMT) explains states and gas behavior with particle motion—not physics problem-solving:

• Particles are in constant motion; temperature reflects average kinetic energy.
• In gases, particles are far apart, collide elastically (idealized), and pressure arises from collisions with container walls.
• Heating a gas (at fixed volume) increases collision force/frequency → higher pressure; more gas particles → higher pressure; smaller volume → higher pressure (qualitative Gas Law relationships).

Clinical flavor without calculation drills: sealed containers, oxygen tanks, and vapor pressure of volatile liquids matter for safety—but the NEX wants the idea that gases are fast-moving, widely spaced particles, not algebra contests.

Physical vs Chemical Change

Dissolving ionic compounds in water is often taught as physical (ions disperse; recovery by evaporation), though ion–water interactions are chemical in a deeper sense—for NEX, treat typical dissolving/melting as physical unless a reaction clearly produces a new compound.

Nursing link: crushing a tablet (physical) vs the drug undergoing metabolism (chemical). Mixing two compatible IV fluids without reaction is physical blending; incompatible mixtures that precipitate are chemical/physical red flags.

Bonding and Matter at a Glance

Exam Traps

• Ionic vs covalent: Transfer vs share—not “metals always covalent.”
• Water conductivity: Pure water is a poor conductor; dissolved ions make solutions conductive.
• Polar ≠ ionic: Polar covalent molecules have partial charges; ionic compounds have full ion charges.
• Boiling water: Physical change—steam is still H₂O.
• Noble gases: Full octets already—do not invent bonds they do not form under ordinary conditions.
• Gas theory on NEX: Qualitative particle picture—not projectile motion or optics.

Master bonding type first, then ask: Will this dissolve in water? Will it conduct when dissolved? Is the change physical or chemical? Those three questions solve most Section 14.2 items and set up mixtures and reactions next.