Unit 3
Characteristics of Chemical Bonds
Characteristics of Ionic Compounds
Lewis Structures
Structures of Molecules
click to edit
Hold groups of atoms together.
Either ionic or covalent.
Electronegativity: Ability of an atom to attract the electrons shared with another atom in a bond.
Differences in electronegativity control bond polarity.
Stable compounds: Atoms assort to the electron configuration of nearest noble gas atom.
Ionic compounds: Nonmetals gain atoms to reach nearest noble gas, metals lose atoms to achieve the same.
Ions clump to form electrically neutral compounds.
Represent valance electron assignments of atom in a compound.
Some molecules have multiple valid Lewis structures - resonance.
Some molecules (e.g. BF3, NO2, and NO) violate octet rule.
Molecules are structured based on how atoms occupy space.
Molecular structure can be predicted via VESPR.
Energy, Temperature and Heat
Energy is neither created nor is it destroyed.
Energy can change form, but energy cannot be gained or lost.
Thermodynamics: Study of energy and relation to temperature.
Energy is kinetic (derived from motion), or potential.
State functions:
Flow of Energy
Internal energy is a combination of potential and kinetic energy in an object.
Internal energy (also E) can be changed by heat (q) and work (w).
delta E = q+w
Specific heat capacity: Energy required to change the temperature of a 1g sample of an object by 1degrC.
Energy and Chemical Reactions
@ constant pressure, the change in enthalpy (or delta H) is equal to heat.
Hess' Law: Allows calculation of reaction heat by the heats of related reactions.
Calorimeter: Measures heat of a chemical reaction.
Uses of Energy
Energy quality reduces per cycle.
Natural processes push for greater empathy.
Our use of energy sources has impacts on the world.
Atoms and Energy
Rutherford model: Dense nucleus, with electrons consuming the vast majority of the molecule's volume.
Electromagnetic radiation catergorized by wavelength, frequency. Stream of energy subdivided into 'packets'.
Hydrogen
Hydrogen atoms emit different amounts of energy as they shift levels.
Had quantized energy levels -> finite amt..
Atomic Orbitals
Bohr Model: Assumed that electrons travel around nucleus in a circular orbit.
Wave mechanical model: Electrons particles in a wave.
Electron Configurations and Atomic Properties
Atomic levels broken into principal levels (n), then to sublevels.
Number of protons equals number of electrons.
Electrons occupy lowest level (open) orbitals first.
Pauli exclusion principle states that one orbital can only hold two electrons with opposite spins.
Highest level orbitals' electrons are valance electrons.
Electron arrangement decides position on periodic table.
Atomic size increases down groups, decreases across period.
Ionization energy (generally) decreases down group and increases over period.