1Elements, Element Association, Bonding, and Element Fractionation1- The Atomic StructureThe energy levels K, L, M and NThe orbitals: s, p, d & fThe four quantum numbers: (Table 1)(1) the principal quantum number "n" which determines the energy andoverall size of the orbital.(2) the orbital quantum number, "l" which determines the angularmomentum and configuration of the orbital(3) the magnetic quantum number, "m" which describes the shape andorientation of the orbital relative to an externally applied magnetic field(4) the spin quantum number "s" which determines the direction of spin ofan electron within this orbital.Each energy level or shell has a unique principal quantum number: for shell K, n = 1,for L, n = 2, ... etc. n is related to the orbital number l by the relation: n l + 1. Thus for n = 2, l = 0 or1, ... etc. The orbitals s, p, d and f, correspond to the l values 0, 1, 2, and 3 respectively, withthe s orbitals having the lowest energies, and the f ones the highest. The maximumnumber of orbitals in a given shell is equal to n2..For each value of l, the number of orbitals is given by the relationship: 2l+1. Orbitalswhich have the same value of l have the same "energy level", and are thereforeconsidered degenerate, even though they have different values of m which describetheir different shapes and orientations. The fourth quantum number "s" has a value of 1/2 or -1/2, representing the directionof spin (or rotation) of an electron around itself in a given orbital. The maximum # of electrons in a shell = 2n2Pauli's Exclusion Principle: "No two electrons can be described by exactly the same setof quantum numbers" Therefore, when two electrons share the same orbital (i.e. n, l, andm are the same), they must have different directions of spin (i.e. different s). Because themaximum number of electrons in any orbital is 2, every electron in an atom will have aunique set of quantum number values. The Aufbau Principle: Electrons will tend to occupy the lower energy shells and orbitalsbefore the higher energy ones. Therefore, the orbitals are filled in the order s, p, d then fin one shell before going to the next shell and following the same order. However, it wasfound that the energy value of 4s is less than that of 3d. Similarly, 5s < 4d, ... and so on.So the sequence of filling up orbitals will be: 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s.....and so on. Valency: Valency of an element is generally a measure of its ability to combine withanother element. Electrons in the last or outermost shell of an atom are known as thevalence electrons. These play a crucial role in determining the chemical properties of2most elements. Elements in which all orbitals are completely filled with electrons are themost inert or stable from a chemical point of view (e.g. the inert gases He, Ne, Ar, ...etc.). Atoms of all other elements will be chemically reactive, and will attempt to reachthe stable configuration of the inert gas with the atomic number closest to its own. Theydo so either by transfer of electrons to the orbitals of another atom, resulting in ionicvalency, or by modification of shapes of orbitals and sharing electrons between twoatoms (covalency). The type of valency is determined by the ionization potentials,electron affinities and electronegativities of the atoms. Ionization Potential: Is the energy (in eV) required to cause any atom to lose an electronand thus become a cation. Ionization potentials for all atoms are always positive. Electron Affinity: is the energy required to convert an atom to an anion. Electronaffinities may be positive or negative. Electronegativity, as defined by Nobel prize winner Linus Pauling, is a measure of theability of an atom in a molecule to attract electrons to itself. Pauling devised an empiricalscale for the electronegativities of elements, where Cs, the most electropositive element,was assigned a value of 0.7, whereas F, the most electronegative element, was given avalue of 4. Table 2 lists the electronegativity values of Pauling for some commonelements of geologic interest. A similar scale can be derived based on the relationship:Electronegativity = 1/2 (Ionization potential + Electron affinity).The difference between the values of electronegativities of two elements will determinethe type of bond that these two elements will form in a compound.2- The Periodic Table: (Fig. 1)Periods and GroupsPeriod # = Principal quantum # (n), or # of energy levels that are being filled with electrons.Group #: # of electrons in the outermost shell (valence electrons)Metallic Character: decreases from groups I to VIII, but increases going down each group (i.e. from one period to the next), although the latter is less pronounced! Ionic Radii: The largest ions within a period occur at the beginning and end of that period. On the other hand, ionic radii increase systematically down each group. For elements with more than one oxidation state, the higher the oxidation state, the smaller the ion (Fe3+ is smaller than Fe2+). Note that ionic radii vary as a function of coordination #; the larger the C.N., the larger the radius (even for the same element; Fig. 3).3- Types of Elements:a) Alkali metalsb) Alkaline Earth elementsc) Halogens: all gases; strongly electronegative.d) Inert (noble) gases: unreactivee) Transition elements:3incompletely filled d orbitalsAll are metalsMany oxidation states; d- electrons often serving as valence electrons.properties not easy to predict from the periodic table.f) Platinum Group elements:- A subgroup of transition elements that includes the elements: Ru, Rh, Pd, Os, Ir, and Pt.- Can occur in the native state, or with many valencies (+2, +3, +4, +6).- Are mostly associated with Fe in nature. g) Lanthanides and Actinides:All have 3 valence electrons.Incompletely filled f orbitals; with increasing Z, filling of the f located two orbitals below the ultimate orbital or shell.Lanthanide contraction: progressive decrease of ionic radius with increasing atomic number.Outer electronic structure for these elements is so similar that they have almost identical chemical properties.Eu & Yb: Oxidation of state of +2 is actually preferred (unlike the other REE), but the +3 oxidation state is also possible and common.4- Goldschmidt's classification of elements: (Fig. 2; Table 3)A qualitative classification based on element