Atomic and Molecular Structure Lecture Notes PDF

Lec.1 Atomic and molecular structure  Topics to be covered 1. Atomic and molecular structure/ Complexation. 2. Essential and trace ions: Iron, copper, sulfur, iodine. 3. Non essential ions: Fluoride, bromide, lithium, gold, silver and mercury. 4. Gastrointestinal agents: Acidifyin...

Lec.1 Atomic and molecular structure  Topics to be covered 1. Atomic and molecular structure/ Complexation. 2. Essential and trace ions: Iron, copper, sulfur, iodine. 3. Non essential ions: Fluoride, bromide, lithium, gold, silver and mercury. 4. Gastrointestinal agents: Acidifying agents. 5. Protective adsorbents. 6. Topical agents. 7. Dental agents. 2  Electronic Structure of Atoms  The fundamental unit of all matter is the atom.  The various chemical and physical properties of matter are determined by its elemental composition.  Elements are composed of like atoms and their isotopes.  To predict the properties of matter, molecules, or elements, it is important to understand the structure of atoms. 3  Subatomic Particles  Atoms are composed of a central nucleus surrounded by electrons which occupy discrete regions of space.  The nucleus is considered to contain two types of stable particles which comprise most of the mass of the atom.  These particles are "held" within the nucleus by various "nuclear forces." 4 Subatomic Particles 5  Subatomic Particles  One of these particles is called a neutron. It is an uncharged species with a mass of 1.675 X 10 - 24 g or approximately 1.009 atomic mass units (a.m.u.)  (Avogadro's number 6.022×1023 atom/mol × 1.675 X 10 - 24 g/atom = 1.009 g/mol or a.m.u.).  Another particle is termed a proton which has a positive charge of essentially one electrostatic unit (e.s.u.). Its mass is close to that of the neutron at 1.672 X 10 - 24 g or approximately 1.008 a.m.u.  A third subatomic particle is the electron, which has a negative charge of one electrostatic unit (e.s.u.) and a mass of 9.107×10-28 g or approximately 0.0006 a.m.u. 6  Subatomic Particles  The sum of the masses of the protons and neutrons accounts for most of the atomic mass “weight” of the element, and the number of protons is equal to the atomic number. Atomic number Electronic distribution Atomic mass 7  Subatomic Particles: Isotopic forms of a particular element differ in the number of neutrons, and, therefore, in the atomic mass. Do isotopes have the same atomic number? 8  Atomic Orbitals  Atomic orbitals are defined as discrete volumes of space about the nucleus that the electrons are placed in.  The electrons (contained within the boundaries of these orbitals) are described by a set of four numbers called quantum numbers.  The four quantum numbers set the probability limits within which an electron can be found.  The first three quantum numbers refer to some property of the space or orbital, while the fourth quantum number describes the spin of the electron. 9  The four quantum numbers 1. The Principal Quantum Number (n). 2. The Suborbital Quantum Number (l). 3. The Magnetic Quantum Number (mℓ). 4. The Spin Quantum Number (ms). 10  The Principal Quantum Number (n)  Quantum theory states that electrons in atoms exist in discrete energy levels.  The energy associated with the electron increases as it location farther from the nucleus.  The principal quantum number describes the relative positions of these energy levels and their distance from the nucleus.  The values of this number are integers n = 1, 2, 3,...  When n = 1 the electron is found in the energy level closest to the nucleus. 11  The Suborbital Quantum Number(l)  Also called the "angular quantum number," can be any value in the range 0 , 1, 2 ,... n - 1.  The secondary quantum number divides the shells into smaller groups of orbitals called sub shells (sublevels).  Usually, a letter code is used to identify (l) to avoid confusion with (n). 12  The Suborbital Quantum Number(l)  For example: when n = 1, (l) can only equal 0; meaning that shell n = 1 has only an s orbital (l = 0). when n = 3, (l) can equal 0, 1, or 2; meaning that shell n = 3 has s, p, and d orbitals.  Another example : the sub shell with n=2 and (l)=1 is the 2p subshell; if n=3 and l=0, it is the 3s subshell, and so on.  The following figure shows the shapes of the s, p, and d orbitals. 13 The Suborbital Quantum Number(l) 14  The Magnetic Quantum Number (mℓ)  Basically, this number describes the spatial orientation of the orbital.  The allowed values are restricted by the value of (l) and can be positive or negative integer:  (l) = 0, 1, 2, 3 Where s=0, p=1, d=2, f=3  mℓ = (-3, -2, -1, 0, +1,+2, +3)  s= 0  p= (-1, 0, +1) e.g. mℓ for oxygen = -1  d= (-2, -1, 0, +1, +2)  f= (-3, -2, -1, 0, +1,+2, +3) 20/02/2021 15  The Spin Quantum Number (ms)  Specifies the orientation of the spin axis of an electron.  The spin quantum number describes the direction the electron is spinning in a magnetic field either clockwise or counter clockwise.  Only two values are allowed: +1/2 or -1/2.  For each subshell, there can be only two electrons, one with a spin of +1/2 and another with a spin of –1/2. 16