Polarity.pptx

POL ARITY OF MOLECULES Learning Objectives D e fi n e e l e c t ro n e g a t i v i t y a n d c o m p a re t h e e l e c t ro n e g a t i v i t y o f d i ff e re n t e l e m e n t s D e t e rm i n e if a molecule is polar or n o n p o l a r g i v e n i t s s t r u c t u re Re l a t e t h e p o l a r...

POL ARITY OF MOLECULES Learning Objectives D e fi n e e l e c t ro n e g a t i v i t y a n d c o m p a re t h e e l e c t ro n e g a t i v i t y o f d i ff e re n t e l e m e n t s D e t e rm i n e if a molecule is polar or n o n p o l a r g i v e n i t s s t r u c t u re Re l a t e t h e p o l a r i t y o f a m o l e c u l e t o i t s p ro p e r t i e s MOLECULES A group of two or more atom held together by chemical bonds. ATOM MOLECULE Some molecules that are present in nature: Ozone (O 3 ) Nitrogen (N 2 ) Water (H 2 O) Some molecules which comprises the structure of our favorite food: Sucrose (C 1 2 H 2 2 O 1 1 ) Caff eine (C 8 H 1 0 N 4 O 2 ) Theobromine (C 7 H 8 N 4 O 2 ) Capsaicin (C 1 8 H 2 7 NO 3 ) Menthol (C 1 0 H 2 0 O) Some molecules that make up medicines and supplements: Aspirin (C 9 H 8 O 4 ) Paracetamol (C 8 H 9 NO 2 ) Vitamin C (C 6 H 8 O 6 ) The properties of molecules highly depend on the structure and arrangement of their atoms. Because of this, their classification also varies due to their differences. structural and geometrical One of the ways to classify molecules is through their POLARITY. POLARITY This refers to the distribution of electric charge around atoms, chemical groups, or molecules. ELECTRONEGATIVITY This is the atom's tendency to attract electrons to itself in a chemical bond. The concept was first introduced in 1932 by LINUS chemist. PAULING, an American The electronegativity value increases in a period from LEFT TO RIGHT and decreases in a group from TOP TO BOTTOM. The higher the electronegativity the more it tends towards itself. to attract electrons Determining the polarity of molecules: Electronegativity difference Geometrical shape of the molecules based on the Valence Shell Electron Pair Repulsion (VSEPR) Theory and/or Lewis Dot Structure POLAR COVALENT BOND E.N. difference 0.5-1.7 Atoms in polar covalent unequal sharing of electrons. bond have NONPOLAR COVALENT BOND E.N. difference 0.4 or less Forms a bond where electrons are equally shared indicating a balanced distribution electrical charge. of IONIC BOND E.N. difference 1.7 An ionic bond is formed when there is a transfer of electrons from a metal to a nonmetal, particles. forming oppositely charged S H A PE S AND STR U CTU R E S O F M OL E CU L E S Molecules are held together by shared electron pairs. Such bonds are directional, meaning that the atoms adopt specific positions relative to one another so as to maximize the bond strengths. As a result, each molecule has a definite, fairly rigid structure, or spatial LEWIS SYMBOL An element’s Lewis symbol is basically the element’s chemical symbol surrounded by dots, which represent the element’s valence electrons. Chlorin e Valence Electrons These are the electrons located at the outermost shell of the atom of a given element. These are the involved in chemical bonding. electrons LEWIS STRUCTURE This is the graphic representation of the electron distribution around the atom of a compound. Lewis structure of chlorine (Cl2) molecule Lewis Structure of Chlorine Lewis Structure of Chlorine Lewis Structure of Chlorine Lone pair: the pair of electrons that do not take part in bonding (nonbonding electrons) Bonding pair: the pair of electrons that forms the bond (bonding Lewis Structure of Chlorine Gilbert Newton Lewis American physical proposed the idea was chemist of an who covalent bonding and the importance of the electron pairs in bonding. Tips in drawing Lewis Structure of a 1. Determine the number of valence Compound electrons in each constituent element of the compound. 2. Draw the Lewis symbol of each element. Tips in drawing Lewis Structure of a Compound 3. Determine the central atom. *The central atom must have the least electronegativity value. 4. Determine the number of bonding pair(s). Let’s draw the Lewis Structure of Carbon Dioxide! What is the chemical formula of Carbon Dioxide? Good Job! CO2 How many valence electrons are there in Carbon? In Oxygen? Great! C=4 ; O= What element must be in the center? Nice! Carbon : : :O :C: : : O: Dioxide : : : : Lewis Dot Structure of Carbon O::C::O Lewis Dot Structure of Carbon Dioxide Multiple bonds If two bonding electrons can be represented by single line, how about four bonding electrons? Lewis Dot Structure of Carbon Dioxide Let’s draw the Lewis Structure of Ammonia(NH3)! Lewis Dot Structure of Ammonia (NH3)... :. :N H H H Lewis Dot Structure of Ammonia : H. :N.. H (NH3). H Lewis Dot Structure of Ammonia H.. :.... H (NH3) N H Lewis Dot Structure of Ammonia : H (NH3) N H H Try this! (10-minute activity) Determine the Lewis Structure of Carbon Tetrachloride(CCl4)! Valence-Shell Electron Pair Repulsion Theory The VSEPR theory represents a model used to predict molecular geometry of a compound based on the number of valence shell electron bond pairs among the atoms in a molecule. Valence-Shell Electron Pair Repulsion Theory The VSEPR model is also referred to as the electron domain (ED) model. Molecular Geometry This is the three-dimensional structure or arrangement atoms in a molecule. of In VSEPR theory, the atoms are spatially arranged in molecules generally in angles of 90°, 109.5°, 120°, and 180°. THE BASIC GEOMETRIES MOLECULAR Symmetr ical Molecula r THE BASIC GEOMETRIES LINEAR MOLECULAR THE BASIC GEOMETRIES TETRAHEDRA L MOLECULAR THE BASIC GEOMETRIES TRIGONAL PLANAR MOLECULAR THE BASIC GEOMETRIES TRIGONAL BIPYRAMIDAL MOLECULAR THE BASIC GEOMETRIES OCTAHEDRAL MOLECULAR THE BASIC MOLECULAR GEOMETRIES NonSymmetrical Molecular Structures THE BASIC GEOMETRIES BENT MOLECULAR THE BASIC GEOMETRIES TRIGONAL PYRAMIDAL MOLECULAR The three-dimensional shape of a molecule can be predicted using its Lewis structure. DETERMINING THE ACTUAL GEOMETRY OF A MOLECULE Step 1. Draw the Lewis structure of the molecule. Take Ammonia for example Step 2. Count the total number of electron domains of the central atom. Electron Domain The region in which electrons are most likely to be found (bonding and nonbonding). A lone pair, single, double, or triple bond represents one region of an electron domain. Step 2. Count the total number of electron domains of the central atom. Step 2. Count the total number of electron domains of the central atom. Electron domains: 1 lone pair 3 bonding pairs Total: 4 electron domains Step 3. Identify the electron pair arrangement. The electron pair arrangement of ammonia is TRIGONAL PYRAMID Step 4. Identify the molecular geometry and approximate bond angle(s).