Lecture No. 2 Pharmaceutical Analytical Chemistry PDF

10/5/2024 Lecture No. 2 Presented by Prof. Dr. Samia El-Gizawy Dr. Noha Mostafa Hosny Group A & B Group C Pharmaceutical Analytical...

10/5/2024 Lecture No. 2 Presented by Prof. Dr. Samia El-Gizawy Dr. Noha Mostafa Hosny Group A & B Group C Pharmaceutical Analytical Chemistry Department Faculty of Pharmacy Assiut University 2024-2025 1 2 2 1  10/5/2024 History of Atomic Structure ✓ The term "atom" comes from the Greek word “Atomos” for indivisible, it means not divided; not separable into parts. ✓ The idea of an indivisible particle was explained by a number of philosophers and scientists such as Galileo, Dalton, Newton, Boyle and Lavoisier. ✓ John Dalton is the first chemist that suggests the modern atomic theory based on his experiments on gases. ✓ ATOM is smallest constituent of matter and consists of nucleus and surrounding electrons. We now know that atoms are made up of three particles: protons, neutrons and electrons. 3 3 Dalton’s Atomic Theory ❑ Every atom is composed of a nucleus and one or more electrons bound to the nucleus. ❑ The nucleus is made of one or more protons and typically a similar number of neutrons. ❑ Protons and neutrons are called nucleus. More than 99.94% of an atom's mass is in the nucleus. ❑ The protons have a positive electric charge, the neutrons have no electric charge while the electrons have a negative electric charge. ❑ If the number of protons and electrons are equal, that atom is electrically neutral. ❑ If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion. 4 4 2  10/5/2024 Dalton’s Atomic Theory ✓ These ideas based on his studies on gases: A. All atoms of a given element are identical. B. Atoms of different elements vary in size and mass. C. Compounds are combinations of two or more different types of atoms. D. Atoms are indivisible and the chemical reaction leads to rearrangement of atoms not to their creation or destruction. ❑ Dalton outlined law of multiple proportions that describes how reactants combine in set ratio. e.g. The element carbon forms two oxides by combining with oxygen in different proportions carbon monoxide (CO) and carbon dioxide (CO2). 5 5 Periodic Table 6 6 3  10/5/2024 Periodic Table ▪ Periodic table is a tabular arrangement of the chemical elements. ▪ The periodic table is arranged by atomic weight and valence electrons. These variables allowed Mendeleev to place each element in a certain row (called a period) and column (called a group). ▪ It consists of periods (horizontal) and groups (vertical). ▪ Atomic number is number of protons in the atom and determines its chemical properties. ▪ Atomic weight is the average mass of atoms of a chemical element. ▪ The periodic table is an organized arrangement of the 118 known chemical elements. ▪ The chemical elements are arranged from left to right and top to bottom in order of increasing atomic number. 7 7 Periodic Table ❑ The vertical columns of the periodic table are called groups. Members of the same group in the table have the same number of electrons in the outermost shells of their atoms and form bonds of the same type. ❑ The horizontal rows on the periodic table are called periods, where each period number indicates the number of orbitals for the elements in that row. For example, period 1 includes elements that have one atomic orbital; period 2 has two atomic orbitals, period 3 has three and so on. (7 rows) 8 (18 column) 8 4  10/5/2024 Periodic Table Hydrogen: Group 1, Period 1 From the electronic configuration of Mg12, O8, sodium (Na = 11 = 2, 8, 1), There is one electron in its outermost He2, Cl17 shell (third shell). Therefore, sodium is an element of group 1 and period 3. 9 9 Classification of Matter 10 10 5  10/5/2024 Atoms, Molecules & Ions 11 11 Pure Substance (Element) WHAT ARE ELEMENTS ? ELEMENT : is a substance made up of only one kind of atoms. cannot be broken down into simple substances by physical or chemical means. Have same atomic number. 118 elements are known. Are represented by symbols. Examples: Iron metal, Fe Copper, Cu Gold, Au 12 12 6  10/5/2024 IONS ❑Ions are atoms or molecules have non-zero net electrical charge. (Its total number of electrons is not equal to its total number of protons) ❑Types of ions are: 1. Cations: number of protons more than electrons and so, have positive charge; e.g. Na+, K+ 2. Anions: number of electrons more than protons and so, have negative charge; e.g. Cl- 3. Zewitter ion: Neutral molecules although it has positive and negative ions at different positions; e.g. amino acids +NH -CH -COO- 3 2 13 13 IONS 14 14 7  10/5/2024 MOLECULES Molecules are neutrally charged species Homonuclear Heteronuclear and has no charge e.g. HCl. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. A molecule may be: 1- Homonuclear, it consists of atoms of one chemical element like oxygen (O2); or 2- Heteronuclear, a chemical compound composed of more than one element, like water 15 (H2O). 15 Pure Substance (Compound) 16 16 8  10/5/2024 Mixtures Mixture is impure substance made up of two or more elements combined together by physical forces. It can be broken by physical means. No chemical changes occur. Has no formula. 17 17 Compound vs Mixture 18 WHY water is a compound and air is a mixture?!! 18 9  10/5/2024 Isotopes 19 19 What are Isotopes? ✓ Isotopes are atoms of the same element that contain identical numbers of proton and different numbers of neutrons. ✓ For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14, respectively. ✓ The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8, respectively. Calculate the neutron numbers in O816 & O818 20 20 10  10/5/2024 What are Isotopes? ▪ Isotopes of the same element have very similar physical properties. ▪ Some isotopes are unstable and will undergo radioactive decay to be other element. ▪ 14C is a radioactive form of carbon, whereas 12C and 13C are stable isotopes. ▪ The predictable half-lives of isotopes allows scientist to date materials based on its isotopic composition such as dating with 14C (The longest- lived radioisotope with a half-life of 5,700 years). ▪ Half-life of isotope: is the time it takes for half of original concentration of an isotope to decay back to its more stable form. 21 21 Isotopes of Hydrogen The isotopes of hydrogen are: a. Protium (1H) with zero neutrons, b. Deuterium (2H) with one neutron, and c. Tritium (3H) with two neutrons. 22 22 11  10/5/2024 Isomers ▪ Isomers are molecules with the same number of molecular formula (same number of atoms) but different configuration (orientation). ▪ Isomers differ from each other by the way in which the atoms are arranged. 23 23 24 12  10/5/2024 Introduction to Chemical Bonds ❖ Chemical bonds join atoms together to form more complex structures (like molecules or crystals). ❖ Bonds can form between atoms of the same element, or between atoms of different elements. ❖ There are several types of chemical bonds which have different properties and give rise to different structure. ❖ These types include: ionic, covalent, hydrogen, metallic and co-ordination bonds. 25 25 Types of Chemical Bonds 26 26 13  10/5/2024 1- Ionic Bonds It is formed between positive ions (cations) and negative ions (anions). In an ionic solid, the ions arrange themselves into a rigid crystal lattice. NaCl (common salt) is an example of an ionic substance. When ionic bonds form, there is an attractive force established between the positive cation and the negative anion. This attraction between oppositely-charged ions is the ionic bond. Generally, when metals react with non- metals, electrons are transferred from the metals to the non-metals. The metals form +ve ions and the non-metals form -ve ions. 27 27 1- Ionic Bonds ❑ Characteristics of ionic bonds are: 1. High melting point (solid at room temperature). 2. Hard but brittle. 3. Many dissolve in water. 4. Conductors of electricity when dissolved or melted. ❑ How ionic bond formed? ▪ Ionic bonds form when metals and non-metals chemically react. By definition, a metal is relatively stable if it loses electrons to form a complete valence shell and becomes positively charged. 28 28 14  10/5/2024 1- Ionic Bonds ❑ How ionic bond formed? ▪ A non-metal becomes stable by gaining electrons to complete its valence shell and becomes negatively charged. When metals and non-metals react, the metals lose electrons by transferring them to the non-metals, which gain them. Consequently, ions are formed, which instantly attract each other—ionic bonding. ▪ For instance, in the reaction of Na (sodium) and Cl (chlorine), each Cl atom takes one electron from Na atom. Therefore, each Na becomes an Na+ cation and each Cl atom becomes a Cl- anion. It should also be noted that some atoms can form more than one ion. This usually happens with the transition metals. For example, Fe (iron) can become either Fe2+ (called iron (II) or ferrous) 29 or Fe3+ (called iron (III) or ferric). 29 1- Ionic Bonds Ex1: NaCl Ex2: MgCl2 Ex3: PCl3 The ions are in a very strong 30 CRYSTAL LATTICE pattern. 30 15  10/5/2024 2- Covalent Bonds Covalent bonding is a common type of bonding, in which two or more atoms share valence electrons more or less equally. The simplest and most common type is a single bond in which two atoms share two electrons. Other types include the double bond, the triple bond. Diagram of a covalent bond between hydrogen atoms 31 31 2- Covalent Bonds Covalent bonding most occurs between a non-metal and a non- metal, or between metalloids and non-metals. Properties: ▪ Lower MP & BP ▪ Tend to be volatile gases or liquids ▪ Softer substances and crush easily ▪ Poor conductors of electricity 32 32 16  10/5/2024 Types of Covalent Bonds 33 33 Types of Covalent Bonds I- Based on the number of shared electron pairs, there are three types of covalent bonds: A. Single Covalent Bond When one pair of electrons, or two electrons, are shared between the atoms, it is known as a single bond. Examples: H2, Cl2, Br2, I2, HCl, NH3, CH4, and C2H6 B. Double Covalent bond When two pairs of electrons, or four electrons, are shared between the atoms, it is known as a double bond. Examples: O2, CO2, SO2, and C2H4 http://4.bp.blogspot.com/-3OzUYYt33JY/VBxGjla9_fI/AAAAAAAAAJA/JgGlbWIViP8/s1600/nitrogen%2Bdot%2Band%2Bcross.gif C. Triple Covalent Bond When three pairs of electrons, or six electrons, are shared between the atoms, it is known as a triple bond. 34 Examples: N2, C2H2, and CN– 34 17  10/5/2024 Single vs Double vs Triple Covalent Bonds Note that: ▪ Double bonds are much stronger than single bonds, so the bond length is shorter, and the bond energy is higher. ▪ Triple bonds are stronger than double bonds. They have the shortest bond lengths and highest bond energies. ▪ Triple bonds more strong than double than single and so triple bonds requires more energy than others to be destroyed. 35 35 Covalent Bonds and Electronegativity Electronegativity is the property of an atom by which an atom attracts the shared electron pair towards it. The electronegativity values of the atoms are taken from the Pauling scale. If the electronegativity difference between two atoms in a chemical bond is greater than 2.0, then the chemical bond is considered an Ionic bond. However, if this difference is less than 2.0 on the Pauling scale, then there is a covalent bond. 36 36 18  10/5/2024 Types of Covalent Bonds II- Based on the polarity of the bond and the coordination of the atoms, there can be three other types of covalent bonds: A. Polar Covalent Bond A covalent bond in which the atoms have an unequal attraction for electrons and so the sharing is unequal. A covalent bond is likely to be polar when the atoms sharing the electrons have a significant difference in their electronegativities, i.e., between 0.1 to 2. As a result, the bonded pair is attracted toward the more electronegative atom making that atom slightly negative, and the other atom becomes slightly positive. Examples: H2O, CHCl3, CH3OH, HF, HCl, and NH3 37 37 Types of Covalent Bonds B. Non-Polar Covalent Bond A covalent bond in which the bonding electrons are shared equally between the two atoms. When the electronegativity difference between the atoms is zero, then electrons are equally shared between the atoms. In this case, the covalent bond is non-polar. Examples: H2, O2, N2, CO2, and CH4 38 38 19  10/5/2024 Types of Covalent Bonds C. Coordinate Covalent Bond Coordinate bond is a sharing of lone pair of electrons from one atom called donor (Lewis base) to another atom called acceptor (Lewis acid). ▪ Lewis acid (Metal): electron pair acceptor e.g. H+, AlCl3, FeBr3, BF3. ▪ Lewis base (Ligand): electron pair donor e.g. compounds containing heteroatoms (O, S, N) e.g. NH3, H2O 39 39 40 40 20