CRYSTALLINE SOLIDS

Energy - the ability to do work and heat

Work - directed energy change resulting from a process

Potential Energy -

Kinetic Energy -

UNITS OF ENERGY

joule (J)

calorie (cal)

Calorie (Cal) 1 Cal = 1000 cal = 1kcal

British Thermal Unit (BTU) 1 BTU = 1055 J

Heat - transfer of thermal energy between two bodies that are different temperature

Endothermic - heat supplied to the system by the surroundings

Exothermic - gives off heat or transfers thermal energy to the surroundings

First Law of Thermodynamics - energy cannot be created or destroyed

Specific Heat Capacity - amount of heat required to raise the temperature of 1g of a substance by 1 °C.

Formula: 𝑄=𝑚CpΔ𝑇

Calorimetry - measurement of heat flow

Calorimeter - apparatus that measures heat flow

Constant-Pressure Calorimetry

  • ΔH measurement

  • carried out in a coffee-cup calorimeter

Constant-Volume/Bomb Calorimetry

  • carried out in a bomb calorimeter

  • combustion reaction

  • ΔE measurement

Thermochemical Equations - represents chemical reactions and the heat involved in it consists of balanced chemical equation (with physical states) and value of ΔH (constant-pressure reaction) or ΔE (constant-volume reaction)

  • enthalpy is an extensive property

ELECTROCHEMISTRY

Redox Reactions - reduction and oxidation half-reactions occurring for electron transfer

Voltaic Cell - generate electricity from chemical reaction

Electrolytic Cell - consumes electricity to cause a chemical reaction

Electrochemical Cell Parts:

Circuit - where electrons flow

Anode - electrode that oxidizes

Cathode - electrode that reduces

Anode Half-Cell - where oxidation takes place

Cathode Half-Cell - where reduction takes place

Salt Bridge - keeps solutions electrically neutral

Electrical UNITS:

Electrical Charge - coulombs. C Faraday’s constant: 1mol e- = 9.65×10^4 C

Current - ampere, A 1A = 1 C/s

Electrical Energy - joule, J and kilowatt-hour, kWh 1J = 1V * C

Power - watt, W

Electrolysis - aids in separation of elements of a compound in a solution

Electroplating - technique of allowing metal ions to deposit as solids to form a coating

CRYSTALLINE SOLIDS

Solid

  • has definite mass, volume, and shape

  • intermolecular distances are short        

  • intermolecular forces are strong

  • incompressible and rigid

Crystalline Solids

  • regular arrangement of particles

  • long range order

  • sharp melting points

  • anisotropy ( polarizes light)

  • when cut, new surfaces are plain and smooth

Examples:

diamond, graphite, NaCl, sugar

Classification of Crystalline Solids

Molecular:

  • orderly collection of molecules held together by van der Waals force

  • gases solidify only at low temperatures

  • easy to deform and compress

  • poor conductors

Covalent-Network:

  • 3D collection of atoms bound by shared valence electrons

  • difficult to deform because bonds are directional

  • high melting point

  • poor electrical conductor

  • opaque

Ionic:

  • individual atoms act like closed-shell

  • commonly salts that are held together by the strong force of attraction between ions of opposite charge

  • tight packed arrangement

  • poor electrical conductors

  • hard and high melting points

Metallic:

  • constructed of atoms that have very weakly bounded outer electrons

  • large number of vacancies in orbitals

  • electrons aren't tightly bound to individual atoms and are free to migrate through the metal.

  • good conductor of electricity and heat

Amorphous Solids

  • random arrangement of particles

  • only short-range order

  • broad melting points

  • isotropic (does not polarize light)

  • when cut, new surfaces have an irregular surface

Examples:

coal, coke, glass, plastic, rubber

Allotropes - one or more forms of a chemical element that

occur in the same physical state.

CRYSTALLINE STRUCTURES

Crystalline lattice - atoms in a crystal are in a regular repeating

pattern (unit cell)

Simple Cubic (SC)

  • very inefficient and rarely seen in nature due to low packing density,

  • atoms touch each other along the cube edge

Body-Centered Cubic (BCC)

  • atoms touch each other along cube diagonals

  • contains 1 center atoms in contact with 8 corner atoms

Face-Centered Cubic (FCC)

  • atoms touch each other along face diagonals

  • contains 6 face atoms and 8 corner atoms

Coordination Number – the number of atoms touching a particular atom, or the number of nearest neighbors

Number of atoms in a unit cell – based on the total contribution of the atoms composing the unit cell

Atomic Radius - ½ of edge length

Atomic Packing Factor (APF) - the fraction of space occupied by atoms assuming that atoms are hard spheres

Note: density of a crystal lattice is equal to the density of its unit cell

Metals - close packing, often large atomic masses

Ceramics - less dense packing, often lighter elements

Polymers - low packing density (often amorphous)

Composite - intermediate values

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