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...

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 structural and geometrical differences. One of the ways to classify molecules is through their POLARITY. EXPERIMENT !!! Observe how water and dish washing liquid behave when they are mixed with a cooking oil.  Oils and fats do not dissolve in water Dish washing liquid breaks the bonds of atoms in oil. POLARITY Equal or unequal sharing of electrons among the atoms of a molecule.  Water and Oil  Polar Molecule There is unequal or asymmetrical distribution of electrons among the atoms of a molecule. H 2O Electron Configuration of Oxygen The atomic number of oxygen is 8, implying that an oxygen atom holds 8 electrons. Its electrons are filled in the following order: K shell – 2 electrons L shell – 6 electrons Therefore, the electron configuration of oxygen is 1s2 2s2 2p4, as shown in the illustration provided below.  States that atoms tend to gain, share Octet or transfer electrons to attain Rule a stable 8 valence electron configuration. Chlorine Electronic Configuration Chlorine has an atomic number of 17. Therefore, its 17 electrons are distributed in the following manner: K shell – 2 electrons L shell – 8 electrons M shell – 7 electrons The electron configuration of chlorine is illustrated below. It can be written as 1s22s22p63s23p5 or as [Ne]3s23p5 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 PAULING, an American chemist. 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 to attract electrons towards itself.  Nonpolar molecule There is equal or symmetrical distribution of electrons among the atoms in a molecule. 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 bond have unequal sharing of electrons. NONPOLAR COVALENT BOND E.N. difference 0.4 or less Forms a bond where electrons are equally shared indicating a balanced distribution of electrical charge. IONIC BOND E.N. difference 1.7 An ionic bond is formed when there is a transfer of electrons from a metal to a non- metal, forming oppositely charged particles.  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 electrons involved in chemical bonding. 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 was an American physical chemist who proposed the idea of 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  Lewis Dot Structure of Carbon : : : : Dioxide O: :C: :O : : : : 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.. (NH3) H H : :N.. H Lewis Dot Structure of Ammonia (NH3) H H.. :.... N H Lewis Dot Structure of Ammonia (NH3) H H : N 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 of atoms in a molecule. In VSEPR theory, the atoms are spatially arranged in molecules generally in angles of 90°, 109.5°, 120°, and 180°. THE BASIC MOLECULAR GEOMETRIES Symmetr ical Molecula r  THE BASIC MOLECULAR GEOMETRIES LINEAR  THE BASIC MOLECULAR GEOMETRIES TETRAHEDRA L  THE BASIC MOLECULAR GEOMETRIES TRIGONAL PLANAR  THE BASIC MOLECULAR GEOMETRIES TRIGONAL BIPYRAMIDAL  THE BASIC MOLECULAR GEOMETRIES OCTAHEDRAL THE BASIC MOLECULAR GEOMETRIES Non- Symmetrical Molecular Structures THE BASIC MOLECULAR GEOMETRIES BENT  THE BASIC MOLECULAR GEOMETRIES TRIGONAL PYRAMIDAL  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).