محاضرة 1-2-1: الكيمياء PDF

Chapter one Learning objective: After going through this chapter, students will be able to; 1) Describe the purpose of studying chemistry, what chemical engineers do, and why it is useful to learn chemistry. 2) Understand what is meant by electronic configuration and its im...

Chapter one Learning objective: After going through this chapter, students will be able to; 1) Describe the purpose of studying chemistry, what chemical engineers do, and why it is useful to learn chemistry. 2) Understand what is meant by electronic configuration and its importance. 3) Differentiate between polar and non-polar compounds? 4) Draw organic molecules. 5) Learn the geometrical shape based on the type of hybridization 6) Explain the difference between the types of interactions between molecules. 7) Relate the properties of matter to its composition 8) Know the importance of studying the intermolecular attraction forces and their impact on the different properties of matter such as: state of matter, boiling point, the degree of solubility in various solvents 1 Introduction Matter on the Macroscopic Scale is anything that has mass and occupies space.  The substance may be pure or in the form of mixtures.  Matter in its pure form may be either in the form of elements or compounds.  Each element is composed of a unique kind of atom. These atoms combine with each other through certain bonds called intramolecular attraction forces to form molecules  Each element is composed of only one kind of atom e.g. Figure 1. Hydrogen and oxygen. Compounds are substances composed of two or more elements; they contain two or more kinds of atoms e.g. Water 2 Figure 1. Examples of some elements Figure 2. Examples of some compounds 3 4  The forces that hold atoms together within a molecule are known as intramolecular forces. The forces that exist between molecules are referred to as intermolecular forces. Ionic bonds Ionic bonds are a result of the attraction between ions. Ions are formed when an atom loses or gains an electron. These types of bonds are commonly formed between a metal and a nonmetal Examples  Sodium (Na) and chlorine (Cl) combine to form stable crystals of sodium chloride (NaCl), also known as common salt. Properties of ionic compounds  The cations and anions in ionic compounds are held together by electrostatic forces of attraction.  These compounds are polar and soluble in polar solvents like water, ammonia, etc.  Ionic compounds are ionizable in solution or in fused state. 5  The solution of ionic compounds is a good conductor of electricity.  They possess high melting points and boiling points. Covalent bond In this case, an atom shares one or more pairs of electrons with another atom and forms a bond. This sharing of electrons happens because the atoms must satisfy the octet (noble gas configuration) rule while bonding. Such a type of bonding is common between two nonmetals. A covalent bond can be divided into a nonpolar covalent bond and a polar covalent bond. Non-Polar (pure) Covalent Bond  In the case of a nonpolar covalent bond, the electrons are equally shared between the two atoms.  ∆EN between the atoms = zero Example  Two atoms of clorine (Cl) combine to form chlorine (Cl2) gas. 6 Polar Covalent Bond  This type of covalent bond exists where the unequal sharing of electrons occurs due to the difference in the electronegativity of combining atoms.  More electronegative atoms will have a stronger pull for electrons.  ∆EN between the atoms is greater than zero and less than 1.8. Examples  One atom of carbon (C) combines with two atoms of oxygen (O) to form a double covalent bond in carbon dioxide (CO2).  Two atoms of hydrogen (H) combine with one atom of oxygen (O) to form a polar molecule of water (H2O). N.B. The presence of a bond between two elements can be determined by calculating the electronegative value between two atoms. 7  Bond Type Electronegativity Value Polar Covalent Bond 0.5 to 1.9 Non-polar Covalent Bond 0 to 0.4 Ionic Bond 2.4 to 4.0 Prop e rt ie s of co va le nt co mp o un ds  The melting and boiling point of covalent compounds are low.  Covalent compounds are generally soft, easily fusible, and volatile in nature. Metalic bond A metallic bond is a force that holds atoms together in a metallic substance. Metals react primarily by donating one or more electrons (their valence electrons). 8  Metalic solid consists of tightly packed atoms, where the outermost electron shell of each metal atom overlaps with a large number of neighboring atoms (see Figure ). As a consequence, the valence electrons move freely from one atom to another. They are not associated with any specific pair of atoms. This behavior is called non- localization. Metals can be pictured as: a lattice of fixed positive ions in a 'sea' of electrons. 9 Properties of Metalic compounds Hardness: Metallic bonds are strong and require a great deal of energy to break, and therefore metals have high melting and boiling points. Density: The atoms in metals are closely packed and so metals have high density. Electrical and thermal conductivity: The electron sea model in the metallic bonding can easily explain the conductance and conduction of heat in the metal compounds. Metallic lustre: the delocalised electrons are good at reflecting (or re-emitting) light that strikes the metal surface and so metals are shiny (lustrous). 11 11 Polarity of Bonds  Polar molecules have a negative “end” and a positive “end.” They tend to associate because the positive end of one molecule attracts the negative end of another molecule. ‫الرابطه القطبيه تتكون من ذرات مختلفة في السالبية الكهربية و بذلك يكون‬ ‫تركيز الشحنات مختلفا ً عبر أطراف الجزيء مثل الرابطه في جزئ حمض‬ ‫الهيدروكلوريك حيث تنجدذب االكترونات نحو الكلور وتبعد عن الهيدروجين‬  The polarity of a bond depends on the electronegativities of the bonded atoms. ‫تعتمد القطبيه علي قيمة السالبيه للذرات في الرابطه‬  Large differences between the electronegativities of the bonded atoms increase the polarity of bonds. 12  ‫‪ The magnitude of the polarity of a bond is the dipole‬‬ ‫‪moment, μ.‬‬ ‫قيمة القطبيه يعبر عنها بعزم القطب ‪ μ‬وهذا العزم له اتجاه يعبر عنه بسهم‬ ‫يتجه نحو الذره االعلي في السالبيه‬ ‫‪Molecular polarity‬‬ ‫المواد القطبية ‪polar materials‬هي التي تتكون جزيئاتها من ذرات مختلفة‬ ‫في السالبية الكهربية و بذلك يكون تركيز الشحنات مختلفا ً عبر أطراف‬ ‫الجزيء مثل الماء‪ ،‬له قطب سالب ناحية األكسجين حيث تتركز اإلليكترونات‬ ‫و له قطب موجب ناحية الهيدروجين لذلك يسمى قطبياً‪.‬‬ ‫‪A water H-O-H molecule is polar because‬‬ ‫‪(1) its O-H bonds are significantly polar,‬‬ ‫‪(2) its bent geometry makes the distribution of those polar‬‬ ‫‪bonds asymmetrical.‬‬ ‫المواد الال قطبية‪non- polar materials‬هي فهي التي تتكون جزيئاتها من‬ ‫‪ )1‬ذرات متماثلة‬ ‫‪ )2‬قريبه جدا جدا جدا في السالبية الكهربية مثل ‪C & H‬‬ ‫و بذلك يكون تركيز الشحنات ثابتا ً عبر جميع أطراف الجزيء‬ ‫‪13‬‬  Hydrogen and carbon have similar electronegativity values, so the C—H bond is not normally considered a polar covalent bond. Thus ethane, ethylene, and acetylene have nonpolar covalent bonds, and the compounds are nonpolar.  All polar compounds contain polar bonds. But having polar bonds does not necessarily result in a polar compound. ‫قد يحتوي المركب علي روابط قطبيه ولكن محصلة العزم لكل الروابط تساوي‬ ‫صفرعندما يكون المركب متماثل‬ ‫قد تكون الرابطه قطبيه لكن محصلة الجزئ غير قطبي ولذلك تعتمد القطبيه‬ ‫ لكل الجزئ وليس فقط الروابط‬stereochemistry ‫علي الشكل الفراغي‬ ‫الموجوده به‬ If the polar bonds are evenly (or symmetrically ‫)متماثل‬ distributed, the bond dipoles cancel and do not create a molecular dipole (eg. BF3). 14  Example: Decide whether the molecules represented by the following formulas are polar or nonpolar. Solution BCl3, PF5, CCl4 and SF4 are symmetrical molecules therefore they are nonpolar compounds μ=0 Ammonia (NH3) is a polar molecule is due to its uneven distribution of charges. The nitrogen atom in ammonia has higher electronegativity than hydrogen atoms, which leaves it with an uneven distribution of charges. This causes the molecule to be electrically polarized, which means that there is an unequal distribution of electrical charge throughout the molecule. 15  Intermolecular Forces (IMF) Intermolecular forces are the forces that act between molecules. Importance of Intermolecular forces  Intermolecular forces are responsible for most of the physical and chemical properties of matter. 1) Effect of IMF on physical state  The differences in the properties of a solid, liquid, or gas reflect the strengths of the attractive forces between the atoms, molecules, or ions that make up each phase.  Viscosity is the resistance to flow of a liquid. Substances that are very viscous have larger molecules and stronger intermolecular forces than substances with smaller molecules. 2) Effect of IMF on boiling points  The boiling point of a substance is proportional to the strength of its intermolecular forces – the stronger the intermolecular forces, the higher the boiling point. 3) Effect of IMF on solubility  In general, having similar interactions to the solvent will allow better compatibility. More commonly this is expressed as like dissolves like. ‫ " ُكل يذيب مثيله" أي أن القطبي يذيب القطبي و الال‬:‫يوجد قاعدة في الكيمياء‬ ‫قطبي يذيب الال قطبي المذيبات القطبية تستطيع اذابة الجزيئات القطبية فقط‬ ‫مثل ملح الطعام مع الماء المذيب الغير قطبي ال يمكنه اإلختالط بالمركبات‬ ‫القطبية مثل الماء و لكن يمكنه فقط اإلختالط بالجزيئات الغير قطبية مثل‬ ‫الزيوت‬ 16 Types of Intermolecular forces Hydrogen Bonding forces  Hydrogen bonding results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom and another very electronegative atom.  Examples of hydrogen bonds include HF⋯HF, H2O⋯HOH, and H3N⋯HNH2, in which the hydrogen bonds are denoted by dots. Dispersion // London // Van der Waals forces  The weakest intermolecular force  Exists between non-polar molecules  Dispersion interactions are stronger in molecules with larger masses. 17 Substance Formula Molar mass g mol–1 Boiling Pt. (°C) Iodine I2 254 457 Chlorine Cl2 71 238 Fluorine F2 38 85 Dipole-Dipole Interactions  Dipole-dipole interactions are attractive forces among polar molecules.  Polar molecules have permanent dipoles that are formed due to differences in the electronegativities of the atoms that are associated with a covalent bond.  The partially positive portion of one molecule is attracted to the partially negative portion of another molecule. Figure – Example of a Dipole-Dipole Interaction 18