Unit 4: Solids & Liquids

Types of Motion and how much energy do they require:

1. Translational (Require the most)

2. Rotational

3. Vibration (Require the least)

Polar bond:

One between atoms with different electronegativities

Electronegativity:

The attraction an atom has for electrons in a chemical bond.

One atom acquires a partial positive charge and the other a partial negative charge.

Dipole:

A separation of charge.

Dipole moment:

The magnitude of a dipole

Ionic bond:

Between two atoms with a large difference in electronegativity.

If the difference in electronegativity between two atoms is 1.7 Paulings or greater, the bond is ionic.

Polar covalent bond:

unequal sharing of electrons by atoms that creates a small dipole. (between 0.4

and 1.7 Paulings)

Non-polar covalent bond:

an equal sharing of electrons.

no dipole created since the electrons are shared equally

differences that are 0.4 Paulings or less

This bond forms between atoms with similar (or the

same) electronegativities

The average distance between particles of molecules in Solids & Liquids:

Very close

Less than one molecular diameter

The average distance between particles of molecules in Gas:

Very far apart

The average distance between particles is about 10 molecular diameters

Intermolecular Forces:

Forces of attraction between molecules or atoms

When a molecular substance changes, states the atoms within the molecule are ___:

unchanged

Why does the strength of the intermolecular forces determines the physical properties of the substance:

The temperature at which a liquid boils reflects the kinetic energy needed to overcome the attractive intermolecular forces

Electrostatic Force/Coulomb’s Law:

Ion-Dipole Interactions:

Types of Intermolecular Forces

Between an ion and a polar molecule

Three factors that effect the Ion-Dipole Interactions:

The magnitude of the ion’s charge

The magnitude of the dipole

The distance between the ion and the dipole

Hydration of an ion in water:

1. Each ion becomes “hydrated” - surrounded by polar water molecules.

2. As the ions are surrounded, energy is released. (Exothermic process)

Dipole-Dipole Interactions:

Between polar molecules

Require close proximity of molecules

More polar molecules = stronger dipole-dipole interactions

Hydrogen Bonding:

Dipole-dipole type interactions

Occur between molecules with extremely polar bonds, where a partially positive hydrogen atom is strongly attracted to the lone pair of a nearby electronegative atom (N, O, or F)

Hydrogen Bonding in Water:

London Dispersion Forces/Van der Waals forces:

Temporary intermolecular forces present in all molecules (polar and nonpolar), caused by uneven electron distribution that creates temporary dipoles

Why are noble gases (e.g., Helium, Neon) able to form liquids:

Because of London Dispersion Forces, which become strong enough to hold atoms together at very low temperatures

Properties of Liquids:

Very low compressibility

Fixed volume, assumes shape of container

High density (comp. to gases)

Particles close together, touching

Translational, rotational, & vibrational

Properties of Gas:

Assumes shape & volume of container

Particles very far apart

High-speed translational, rotational, & vibrational

Low density

Properties of Solid:

Fixed volume & shape

Particles tightly packed in fixed positions

Vibrational only

Cohesive forces:

The forces between molecules within the liquid

Strong cohesive forces = Strong intermolecular forces = High surface tension = High viscosity (độ nhớt)

Viscosity decreases with increased temperature in liquids because:

Higher temperatures increase molecular kinetic energy → molecules overcome intermolecular attractive forces and move more freely

Adhesive forces:

The forces between liquid molecules and their container

These forces are strong if the liquid is polar and the surface is polar (or if the liquid is non-polar and the

surface is non-polar)

A liquid will WET a surface if there are strong adhesive forces

Capillary action:

Explained by strong adhesive forces between the liquid and the tube’s surface and the strong cohesive forces between liquid molecules

Crystal Lattice:

A 3D, regular, periodic arrangement of particles (atoms, ions, or molecules).

Unit Cell:

The smallest, repeating unit of a crystal lattice

Three common cubic unit cells:

Simple Cubic (sc)

Body-Centered Cubic (bcc)

Face-Centered Cubic (fcc)

BXH bond:

Stronger IMFs mean:

Higher boiling point / melting point

Higher viscosity

Higher surface tension

Lower vapor pressure

Define Crystalline vs. Amorphous solids

Crystalline: Regular, repeating 3D geometric arrangement

Amorphous: Considerable disorder and no repeating pattern

Density of a unit cell:

Z = number of atoms inside 1 unit cell

M = molar mass

N_a = Avogadro Number

a³ = Volume

Why do Ionic Solids conduct electricity when melted/aqueous, but not when solid?

As a solid, ions are locked in a rigid lattice. When melted or dissolved, the ions are free to move and carry an electrical current.

Difference between a Substitutional and an Interstitial alloy?

Substitutional: Atoms are replaced by other metal atoms of similar size

Interstitial: Small gaps in the lattice are filled by much smaller atoms

What are the 4 main classifications of solids:

1. Ionic solids

2. Molecular solids

3. Atomic solids (Metallic, Network, Group 18)

4. Amorphous solids

Ionic Solid:

Cations + anions

Strong electrostatic ionic bonds

Examples: NaCl

High melting point

Molecular Solid:

Nonmetal atoms covalently bonded to each other inside the molecule

Weak Intermolecular Forces (LDF, Dipole-Dipole, or H-bonding)

Low melting point

3 sub-categories of Atomic Solids:

1. Metallic solids

2. Network Covalent solids

3. Group 18 (Noble Gas) solids

Network Covalent Atomic Solid:

A continuous network of strong, directional covalent bonds

High melting point

Eg: Diamond