Lecture 2 - Atoms and Elements

Overview Details

 

A. Bohr model of the atom

B. Quantum numbers

1. The principle quantum number (n) determines the major energy level.  n = 1-7, with each level also designated by a letter: K - Q, with K (n=1) being the lowest energy level and Q (n=7) the highest.

2. The angular momentum quantum number (l) represents 'subshells' or orbitals, within each energy level.  l varies from 0 to n-1, with higher values of l corresponding to higher angular momentum.  The corresponding orbitals are s, p, d, and f for l = 0-3;  these may hold up to 2,6,10 and 14 electrons, respectively.  Electrons fill orbitals from lowest to highest ene

3. The magnetic quantum number (m) relates to the magnetic field generated by an electron with angular momentum; may be –1, 1

4. The spin quantum number relates to the intrinsic magnetism of the electron itself, and may be either -1/2 or +1/2

 

 

C. Modern periodic table

1.         Periods - rows; the number of the period indicates the orbitals occupied by electrons

2.         Groups - columns; have valence electrons in similar orbitals, and hence they have similar chemical properties.

D. Ions

            Anions are formed when atoms gain 1 or more electrons

            Cations are formed when atoms lose 1 or more electrons

Anions are thus generally larger than cations, and crystal structures can be envisaged as large spheres packed around small spheres in such a way that the space between spheres is minimized, and positive and negative charges are balanced. 

 

E. Atomic number and mass

            Atomic number is the number of protons in an element's nucleus (Z) - most important in controlling elemental properties.

            Atomic mass (A) is the number of protons (Z) + number of neutrons (N).  

A mole of an element is defined as the amount of that element that has its weight in grams equal to its atomic weight.  Given by Avogadro's number (N): one mole of an element or compound always has 6.022 x 1023 atoms.

 

F. Bonding in minerals

            Covalent - shared electrons in outer shell  

Ionic -bond between a cation and an anion where complete electron transfer has occurred

Metallic - detached electrons move freely through the structure

            Van der Waals

 

Effects of size - The minimum energy configuration occurs where the distance between centers of ions is equal to the sum of their ionic radii (closest packing).