Bonding and Properties of Matter

Properties of Matter & Bonds

  • The purpose is to connect bonding concepts to properties of matter (gases, liquids, solids, metals, nonmetals, alloys, mixtures, pure substances).

  • Focus on forces of attraction and how they determine properties.

Types of Bonding

  • Molecular substances: Polar and nonpolar covalent bonds.

    • Polar covalent bonds: Electronegativity difference between 0.4 and 1.8.

    • Nonpolar covalent bonds: Electronegativity difference below 0.3 (down to zero).

  • Ionic substances: Metal + nonmetal or substances containing polyatomic ions.

  • Metallic substances.

  • Network substances (to be covered later).

Molecular Substances

  • Covalent bonds lead to the formation of molecules, which are neutral particles made of two or more atoms covalently bonded.

  • Key terms: electron sharing, Lewis structures.

  • Molecules can be polar or nonpolar, influencing the forces of attraction.

  • Force of attraction influences the properties of the substance.

Ionic Substances

  • Often consist of a metal and a nonmetal or include polyatomic ions.

  • Salts are ionic substances that form crystalline lattices.

  • Bond type: Ionic.

  • Defined as an electrostatic attraction between a cation (positive ion) and an anion (negative ion).

  • No discrete particles; instead, they form a lattice.

  • Simplest unit of a salt: Formula unit - a neutral particle composed of the simplest ratio of ions in a salt. It relates to the empirical formula of a salt.

Covalent Bonds

  • Electrostatic sharing of electrons between two nuclei.

Identifying Bond Types

  • Molecular: Nonmetal + nonmetal.

  • Ionic: Usually metal + nonmetal or containing polyatomic ions.

Discrete Particle

  • A particle with defined boundaries that retains the properties of the substance.

  • Water molecules are discrete; a sample of salt is not, because the boundaries between the formula units aren't definable in the same way.

  • Ionic lattices have no discrete particles; the simplest unit to discuss is a formula unit.

    • A formula unit is composed of the simplest ratio of ions in a salt.

Metallic Substances

  • Metallic bonds.

    • An electrostatic attraction between a lattice of cations and delocalized valence electrons.

  • How to identify:

    • A single metal element (pure substance).

    • An alloy (mixture of metals).

  • Delocalized electrons: Electrons are loosely held and can move freely within the metal structure.

    • Like a dislocated shoulder, the electrons are still there, but not firmly attached.

Metallic Bonds

  • Sharing electrons.

  • Transfer of electrons.

  • Delocalized electrons.

Molecular Polarity

  • Polarity describes the distribution of electrons (even vs. uneven, symmetrical vs. asymmetrical).

  • Polarity applies to both bonds and molecules.

Bond Polarity

  • Focuses on the distribution of electrons between two atoms in a bond.

  • Even distribution: Nonpolar.

  • Uneven distribution: Polar, resulting in partial positive and partial negative charges.

  • Determined by the difference in electronegativity between the two atoms.

Molecular Polarity

  • Focuses on the overall distribution of electrons in the molecule.

  • Requires the ability to:

    • Draw Lewis structures correctly.

    • Identify the geometry of the molecule.

    • Identify the bond polarity.

  • Assessment:

    • Examine electron distribution around the central atom, symmetry, and overall charge.

    • Symmetrical distribution = nonpolar molecule (no charges).

    • Asymmetrical distribution = polar molecule (positive and negative ends).

Models in Chemistry

  • Used because chemistry is difficult to visualize directly.

  • Models simplify and make assumptions, illustrating only certain features.

Types

  • Ball and stick models: Represent nuclei as balls and electron sharing as sticks.

    • Limitation: Show sharing but don't accurately depict electron transfer in ionic bonds.

  • Cross test: Assessing symmetry by putting a cross through the molecule.

    • Symmetrical molecules are nonpolar.

    • Asymmetrical molecules are polar.

  • Space-fill models: Show overlapping orbitals to represent electron clouds.

  • False-color models: Use colors to represent electron density (e.g., red for high density, blue for low density).

Intermolecular Forces

  • Forces of attraction between particles that determine properties like melting and boiling points.

  • Stronger forces require more energy to separate particles, resulting in higher melting/boiling points.

Describing Intermolecular Force

  • An intermolecular force is between particles, not inside a particle.

  • Breaking intermolecular forces changes the phase but not the substance itself.

Dipole-Dipole Forces and Hydrogen Bonding

  • Dipole-dipole forces:

    • Attraction between permanent dipoles in polar molecules.

    • Polar molecules act like magnets.

  • Hydrogen bonding:

    • A special type of dipole-dipole force.

    • Occurs when hydrogen is directly bonded to oxygen, nitrogen, or fluorine.

    • Requires another oxygen, nitrogen, or fluorine on a different molecule.

    • Strong dipole-dipole force.

Criteria for Hydrogen Bonding

  1. Must be a polar molecule.

  2. Must have hydrogen bonded directly to nitrogen, oxygen, or fluorine.

  3. The nitrogen, oxygen, or fluorine must have a lone pair.

London Dispersion Forces

  • Occur in nonpolar molecules.

  • The predominant intermolecular force of nonpolar molecules (all molecules have dispersion).

  • Weakest intermolecular force.

    1. Temporary.

  • Temporary dipoles: Electrons repel each other, creating temporary charge imbalances.

    • An induced dipole means it was temporarily forced to become a dipole.

    • Causes temporary slight charges.

Attractive force-

any natural force in the Universe that draws one mass towards another

Here's a breakdown of formula units and attractive forces for each type of solid:

  • Ionic Solids:

  • m+nm

  • Composed of metal ions (m) and nonmetal ions (nm), these solids are characterized by high melting points and strong electrostatic attractions between oppositely charged ions.

    • Attractive Forces: Electrostatic attractions between oppositely charged ions (cations and anions). These are strong and long-range, leading to high melting and boiling points.

    • Formula Units: Yes. Ionic solids don't have discrete molecules. The formula unit represents the simplest ratio of ions in the crystal lattice (e.g., NaCl).

  • Molecular Solids:

  • molecule+molecule

    • Attractive Forces: Intermolecular forces (IMFs) such as dipole-dipole forces, hydrogen bonding (if applicable), and London dispersion forces. These forces are weaker than ionic or covalent bonds.

    • Formula Units: No. Molecular solids are made of individual molecules (e.g., H2O, CO2). We refer to individual molecules, not formula units.

  • Network Covalent Solids:

  • nm+nm

    • Attractive Forces: Covalent bonds form a continuous network throughout the entire solid. These are strong and give the solid its hardness and high melting points.

    • Formula Units: No. Network covalent solids don't have discrete molecules or ionic units. The entire crystal is essentially one giant molecule. We would describe it in terms of atoms (e.g. C for diamond).

  • Metallic Solids:

  • m+m

    • Attractive Forces: Metallic bonds, which are electrostatic attractions between a lattice of positive metal cations and a "sea" of delocalized valence electrons. These forces vary in strength.

    • Formula Units: No, typically. We refer to individual metal atoms (e.g. Fe)