PHY1039 Properties of Matter Introduction to Matter 6 February, 2012 Lecture 1

Why Study Matter? Understanding Gases Meteorology: high and low pressure Measuring Lung Capacity capacity-7810.jpg Ideal Gas : Pressure, Volume, Temperature relationships Atmospheres of Planets

Thermal expansion of girders was restricted by frictional forces. They could not expand lengthwise, so they buckled! Joints in bridges are used to enable thermal expansion. Why Study the Properties of Matter? Thermal Expansion Pressure, volume and temperature are interrelated in solids.

Why Study the Properties of Matter? Heat Dissipation Heat sinks, heat spreaders, and fans remove heat from the CPU of a laptop computer. (The objective is to do electrical work, but heat is also given off in the process.)

Double-walled Multi-walled Single-walled Carbon Nanotubes Why Study the Properties of Matter? Underlies (Nano)Technology

Electron microscope image of multi- walled carbon nanotubes S. Iijima, Nature 354 (1991) 56. Is it possible to construct a lift to satellites orbiting the Earth?

What Happens when Thermal Properties Go Wrong? A failed O-ring allowed the escape of H 2 gas. The result was an explosion = sudden release of heat Challenger Space Shuttle Disaster Columbia Space Shuttle Disaster Damage to the wing caused over-heating on re-entry into the atmosphere

Thermodynamics Provides Equations to Describe Properties of Matter Properties are inter-related: Mechanical (elastic modulus and compressibility) Thermo-mechanical (expansivity) Thermal (heat capacity) Flow (viscosity)

A Typical Phase Diagram for the Three States of Matter Figure from “Understanding Properties of Matter” by M. de Podesta Solid  Liquid: Melting (heat in) Liquid  Solid: Freezing (heat out) Liquid  Gas: Boiling (heat in) Gas  Liquid: Condensation (heat out) Solid  Gas: Sublimation (heat in) Gas  Solid: Deposition (heat out) Phase Transitions Lines represent conditions where two phases co-exist. Three phases co-exist at the triple point.

Importance of Phase Transitions: Laser Annealing Laser annealing to create metal nanoparticles Intense laser beam can melt metals. The liquid metal flows and makes small droplets on the surface. If the metal liquid is hot enough, it evaporates into the air where it forms nm-sized solid particles when cooled.

I mage: Phase Diagram for Carbon Dioxide atm = atmospheres (a unit of pressure) For a video of supercritical CO 2, see:

Image: Phase Diagram for Water

States of Matter Gas Atoms/molecules randomly distributed throughout their container. Have a distribution of mean speeds. Travel in all directions. Low density: the mean free path is about = 3 nm in air under standard conditions. Liquids Atoms/molecules randomly distributed throughout their container (like gas). Have a distribution of mean speeds. Vibrate in all directions. Density is higher than in a gas. Separated from gas by a meniscus. Crystalline Solids Atoms/molecules arranged on a periodic array in three dimensions (a lattice) Vibrate in all directions Density is usually higher than the liquid’s. Atoms are in close contact. Figures from “Understanding Properties of Matter” by M. de Podesta

Mean Free Path of Gas Molecules Molecules travel a distance of in between collisions. Figure from “Understanding Properties of Matter” by M. de Podesta

Bonds in Solids In simple cubic packing, each atom has six nearest neighbours. The bond between two atoms with a mass of m can be modelled as springs, with a spring constant, K, showing simple harmonic motion with a resonant frequency of f 0 : When the atoms vibrate and stretch the springs, the potential energy rises. The kinetic energy also oscillates as the velocity changes during the vibrations. Figures from “Understanding Properties of Matter” by M. de Podesta

H = blue O = red One of the Crystal Structures of Ice “Open” arrangement of molecules on a hexagonal lattice. Under pressure, the molecules can be moved closer together in the liquid state.

“Sea of electrons”: electrons are shared between all atoms, i.e. delocalised Ionic bonds: Coulombic attraction between cations (+ve) and anions (-ve) Weak van der Waals’ attraction between individual charge- neutral molecules; No sharing of electrons Classification of Solids (2) Ionic (1) Molecular (4) Meta l (3) Covalent Electrons are shared in bonds between neighbouring atoms; Bonds extend in prescribed directions Figure from “Understanding Properties of Matter” by M. de Podesta e.g. Ar; CO 2 e.g. NaCl; CaF 2 e.g. Au; Cu e.g. Si; C in diamond and nanotubes

Potential Energy, u, between Ions For a singly-charged cation (+ve) and an anion (-ve) at a distance of r o, the potential energy is: In an ionic solid, there are interactions between ions in three dimensions and at regularly spaced distances. Figure from “Understanding Properties of Matter” by M. de Podesta e = charge on the electron: x C  o = permittivity of free space: x Fm -1

Potential Energy, u, between Neutral Atoms Averaged over time, electrons are uniformly distributed around an atom’s nucleus. But at any given instant, the electron charge distribution is non-uniform. There is an attraction between the oppositely-charged sides of atoms: Electron distribution at intervals of seconds Potential energy: r Figures from “Understanding Properties of Matter” by M. de Podesta

Potential Energy for Non-Charged Atoms/Molecules r  r  Potential Energy Potential Energy varies with the separation distance, r. There is also kinetic energy, which is the energy of motion. Figure from “Understanding Properties of Matter” by M. de Podesta ~ r -6 Relevant to gases, liquids and solids (e.g. Ar, Xe, CO 2 )