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Bohr Theory - Four Postulates
- 1: Electrons can only travel in special orbits, at a certain discrete set of distances from the nucleus with specific energies
- 2: Electrons of an atom revolve around the nucleus in orbits. These orbits are associated with definite energies and are also called energy shells or energy levels.
- 3: The lowest possible energy level is called the groud state. The electrons can absorb energy and jump to a high energy level. The atoms are said to be in an excited state.
- 4: When an electron falls back to a lower level, energy will be emitted in the form of a quantum of light. E2-E1 = DeltaE = h.v
- Shells, subshells, orbitals
- Each electron of an atom is identified by a combination of four quantum numbers.
- Principle Quantum Number: Identifies the shell (n)
- Subsidiary Quantum Number: Identifies the subshell (l)
- Magnetic Orbital Quantum Number: Identifies the orbital (m)
- Magnetic Spin Orbital Number: Refers to the two possible orientations of the spin axis of an electron. Ms = + 1/2 or - 1/2
Pauli's Exclusion Principle
No two electrons in an atom can have the same for quantum numbers
Hund's Rule - Rule of Maximum Multiplicity
Electrons are distributed among the orbitals of a subshell in a way that gives the maximum number of unpaired electrons with parallel spins
Emphasises the attachment of a noble gas electron configuration on the parts of atoms in covalent bonds.
Acids: electron pair acceptors - BF3
Bases: electron pair donors - NH3
Daltons Atomic Theory - 3 Postulates
- 1: Elements are composed of extremely small particles called atoms. All atoms of the same element are alike, all atoms of different elements are different.
- 2: Separation of atoms and unions occur in chemical reactions. In these reactiond no atom is created or destroyed and no atom of an element is converted to an atom of another element.
- 3: A chemical compound is the result of the combination of atoms of two or more elements. A given compound always contains the same kind of atoms combined in the same proportions.
Law of Conservation of Mass
There is no detectable change in mass during the course of a chemical reaction
The Law of Definite Proportions
A pure compound always contains the same elements combined in the same proportion by mass
The Law of Multiple Proportions
When two elem