Phases of Matter Flashcards
Topic 1, Lecture 1 - Colan Hughes
Macroscopic properties
Properties that can be observed and measured at a large scale and are visible to the eye. E.g., mass, volume, temperature
Microscopic properties
Properties on an atomic/molecular scale. Not directly observable, e.g., arrangement of atoms, vibrations and forces.
Macroscopic:
Condensed - difficult to compress (S, L)
Fluid - flows easily (L, G)
Microscopic:
Particle separation - distance between particles in different states of matter. (G>L>S)
Particle motion - The number of ways particles move in different states of matter (G>L>S)
How macro and micro properties are related
A phase with large particle separation can be easily compressed.
A phase with more particle movement can flow.
Types of particle motion
Translational, rotational and vibrational
Atomic gas
Translational
Molecular gas
Translational, Rotational , Vibrational
Atomic liquid
T
Molecular liquid
T, R , V
Atomic/ionic solid
V
Molecular solid
V, (R) sometimes
Detecting motion: spectroscopy
Different types of motion have quantised energy levels, meaning specific frequencies of light are absorbed or emitted depending on the type of motion.
Detecting motion: thermal energy
Measured using heat capacity. The more energy needed to increase temperature, (higher heat capacity) the more forms of motion present.
Order
If material is ordered, it has a regular and repeating structure (crystalline solids). Gases are always disordered, but solids and liquids can exist in ordered and disordered states.
How order is detected
Diffraction: if an x-ray is passed through ordered material, some of them will be diffracted by a precise angle defined by the repeating structure. The diffraction pattern can thus be used to determine the structure and order.
Properties influenced by order
Many crystalline materials have birefringence, where they split a ray of light in two when passing through.
Interparticle interactions
Dependent on separation and chemical nature of particles. In gases, there is large separation; therefore, there are minimal forces between particles.
Electrostatic interactions
When charged atoms or molecules are present, an electric force will exist between them. Like charges repel and opposites attract, which is responsible for bonding in simple salts, e.g. NaCl.
Van der Waals interactions
Neutral molecules interact with one another through non-uniform charge distributions that occur as a result of orbiting electrons. A dipole on one molecule can induce a dipole in another, resulting in attractive force.
Hydrogen bonding
Interaction between a ydrogen atom and an electronegative atom in another molecule. Strong and directional bonds (influenced by molecular geometry)
Repulsive interactions
All molecules and atoms experience attractive and repulsive interactions. R dominates when they are too close and A dominates when they are too far apart.
Phase transitions
Phases can transition between one another at different temperatures and pressures. In a phase diagram, the triple point is the unique combination of pressure and temperature at which all phases are stable.
