Polarity of Molecules: Lesson 1

# Marian College of Baliuag, Inc. ## Lesson 1: Exploring Polarity of Molecules and Its Properties ### Objectives: - Differentiate polar and nonpolar bonds. - Determine the polarity based on electronegativity difference. - Describe how polarity of bonds and molecular geometry affects the polarity o...

# Marian College of Baliuag, Inc. ## Lesson 1: Exploring Polarity of Molecules and Its Properties ### Objectives: - Differentiate polar and nonpolar bonds. - Determine the polarity based on electronegativity difference. - Describe how polarity of bonds and molecular geometry affects the polarity of molecules. ## Molecules A molecule is a group of two or more atoms held together by a chemical bond. ### Example of molecules - Water - Salt - Earth - Oxygen ## Polarity It refers to having a dipole, that is, a positive and a negative end. Polarity is dictated by the distribution of electrons in the molecule; either the electrons are equally distributed or unevenly scattered. ### Key Points: - Molecules can be classified as POLAR and NONPOLAR. - The polarity of molecules can be predicted from its shape. - The polarity of the bonds between atoms which can be studied based on electronegativity. - The geometrical shape of the molecules which can be predicted via the valence shell electron pair repulsion (VSEPR) theory. #### Polarity Table | Polar/Nonpolar | Shape | |---|---| | Polar | Linear | | Polar | Bent or Angular | | Nonpolar | Linear | | Nonpolar | Trigonal Planar | | Nonpolar | Tetrahedral | | Nonpolar | Trigonal Pyramidal | | Nonpolar | Trigonal Bipyramidal | | Nonpolar | Octahedral | ## Polarity of Molecules and Its Properties Properties of different molecules can be attributed to their polarity. ### Solubility Ability of a substance (solute) to dissolve in another substance (solvent). ### Miscibility Ability of two substances, usually liquids, to mix in all proportions. ## Polarity of Molecules All compounds can be classified based on what type of chemical bond formed when the atoms combined. ## Polarity of Molecules The classification of the compound can be used to determine whether a molecule is polar or nonpolar. ## Polarity of Molecules - **POLAR COVALENT** - electrons are shared unequally, the difference in electrons density create a dipole moment. - **NONPOLAR COVALENT** - electrons are shared equally, electrons are distributed equally, so there will be no chance to have a partial positive partial negative end. ## Polarity of Molecules The two classifications of compounds are Covalent and Ionic. ## Ionic vs. Covalent | Type of Bond | Characteristic | |---|---| | Covalent | Sharing of electrons | | Ionic | Transfer of electrons | ## Valence Electron and Lewis Dot Symbol ### Valence Electron They are the "outermost electrons" of the atom involved in chemical bonding. ### Lewis Dot Symbols/Structures Are diagrams that represent the valence electrons of an atom. ## Octet Rule States that atoms tend to form compounds in ways that give them eight valence electrons thus the electron configuration of a noble gas. ### Example of Ionic Bond - Sodium Chloride - 11Na – 1s2 2s2 2p6 3s1 - 17CI – 1s2 2s2 2p6 3s2 3p5 ### Example of Covalent Bond - Carbon Dioxide - 6C - 1s2 2s2 2p2 - 8O – 1s2 2s2 2p4 ## Electronegativity - Is a measure of how strongly atoms attract bonding electrons to themselves. - The higher the electronegativity, the greater an atom's attraction for electrons. #### Table of Electronegativity Values | Element | Electronegativity | |---|---| | H | 2.1 | | Li | 1.0 | | Be | 1.5 | | B | 1.5 | | C | 2.5 | | N | 3.0 | | O | 3.5 | | F | 4.0 | | Na | 0.9 | | Mg | 1.2 | | Al | 1.5 | | Si | 1.8 | | P | 2.1 | | S | 2.5 | | Cl | 3.0 | | K | 0.8 | | Ca | 1.0 | | Sc | 1.3 | | Ti | 1.5 | | V | 1.6 | | Cr | 1.6 | | Mn | 1.5 | | Fe | 1.8 | | Co | 1.9 | | Ni | 1.8 | | Cu | 1.9 | | Zn | 1.6 | | Ga | 1.6 | | Ge | 1.8 | | As | 2.0 | | Se | 2.4 | | Br | 2.8 | | Rb | 0.8 | | Sr | 1.0 | | Y | 1.2 | | Zr | 1.4 | | Nb | 1.6 | | Mo | 1.8 | | Tc | 1.9 | | Ru | 2.2 | | Rh | 2.2 | | Pd | 2.2 | | Ag | 1.9 | | Cd | 1.7 | | In | 1.7 | | Sn | 1.8 | | Sb | 1.9 | | Te | 2.1 | | I | 2.5 | | Cs | 0.7 | | Ba | 0.9 | | Hf | 1.3 | | Ta | 1.5 | | W | 1.7 | | Re | 1.9 | | Os | 2.2 | | Ir | 2.2 | | Pt | 2.2 | | Au | 2.4 | | Hg | 1.9 | | Tl | 1.8 | | Pb | 1.9 | | Bi | 1.9 | | Po | 2.0 | | At | 2.2 | | Fr | 0.7 | | Ra | 0.9 | ## Electronegativity Difference - If the electronegativity difference is less than or equal to 0.4 the bond is nonpolar covalent. - If the electronegativity is greater than 0.4 but less than 1.9 the bond is polar covalent. - If the electronegativity is greater than 1.9 then the bond is ionic. ### Examples 1. C and Cl 2. Mg and O 3. H and Cl 4. N and N 5. K and F ## Molecular Shape - Linear - Trigonal Planar - Bent or Angular - Tetrahedral - Trigonal Pyramidal - Trigonal Bipyramidal - Octahedral ## Molecular Shape Electron group pertains to a number of electrons that occupy a specific region around the atom; it might be a lone pair, single bond, double bond or triple bond. ## VSEPR: Predicting the shape of the molecule 1. Identify the central atom 2. Draw the lewis structure for the molecule 3. Count the number of bonding pairs of electrons and lone pair. 4. Arrange them in a way hat minimizes repulsion (as far as possible) 5. Determine the name of the molecular structure from a position of the atom. ### Example 1 - BeCl2 - Central atom is Be. - Valence electrons - 2 bonding pairs; no lone pairs - The arrangement is linear. - Shape is called LINEAR. ### Example 2 - BCI3 - Central atom is B. - Number of valence electrons - 3 bonding pairs; no lone pairs - Arrangement is trigonal planar. - Shape is called TRIGONAL PLANAR.