Polarity - Bonds and Molecules PDF

# Determining Polarity of Bonds and Molecules ## Table 1: Types of Bonds | Type of Bond | Definition | Electronegativity | Example | |---|---|---|---| | Ionic | Involves transfer of electrons between a metal and non-metal | > 1.7 | NaCl | | Polar Covalent | Involves unequal sharing of electrons...

# Determining Polarity of Bonds and Molecules ## Table 1: Types of Bonds | Type of Bond | Definition | Electronegativity | Example | |---|---|---|---| | Ionic | Involves transfer of electrons between a metal and non-metal | > 1.7 | NaCl | | Polar Covalent | Involves unequal sharing of electrons | 0.4 - 1.7 | H₂O | | Pure Covalent (Non-Polar Covalent) | Involves equal sharing of electrons between two non-metals | 0 | O₂ | ## Electronegativity - Electronegativity (EN) of an atom is a measure of an atom's ability to attract shared electrons in a chemical bond. ## Periodic Trends - Atomic radius increases as you move down a group on the periodic table. - Atomic radius decreases as you move across a period on the periodic table. - Ionization energy decreases as you move down a group. - Ionization energy increases as you move across a period. - Electron affinity decreases as you move down a group. - Electron affinity increases as you move across a period. - Electronegativity decreases as you move down a group. - Electronegativity increases as you move across a period. ## Polar Covalent Bond - A polar covalent bond can be simply referred to as a polar bond - A polar bond is formed when the bonding pair of electrons is unequally shared between two atoms. - Polar covalent bonding occurs because one atom has a stronger affinity for electrons in a bond than the other atom - The affinity for electrons is not enough to pull the electrons away completely and form an ion - The bonding electrons will spend a greater amount of time around the atom that has a stronger affinity for electrons. ## Hydrogen-Oxygen Bond in a Water Molecule - The difference in electronegativity between oxygen (EN = 3.44) and hydrogen (EN = 2.20) is 1.24, indicating that oxygen is more electronegative and thus attracts the bonding electrons more strongly. - The uneven sharing of electrons results in a partial negative charge (δ-) on the oxygen atom and a partial positive charge ( δ+) on the hydrogen atoms. - The result is a dipole moment, which is a measure of the polarity of a molecule. - This dipole moment is responsible for the many unique properties of water, such as its high boiling point and its ability to dissolve many substances. ## Molecular Shapes - Electrons arrange themselves around molecules to maximize the distance between them. - This electron arrangement produces a different shape for different molecules. - There are many different molecular shapes, including linear, bent, tetrahedral, and trigonal planar. - The shape of a molecule affects its polarity because it determines the distribution of electrons. ## Molecular Shapes - **Electron Geometry** describes the arrangement of all electron areas around a central atom, including bonding and lone pairs. - **Molecular Geometry** describes the arrangement of only the bonding electron areas around a central atom. ## Molecular Shape of H₂O - The Lewis structure of water shows two bonding pairs (H atoms) and two lone pairs (non-bonding electrons) in a water molecule. - This gives it a **bent** molecular shape. - The water molecule has a non-linear shape and this contributes to its polarity because the two hydrogen atoms are not directly opposite the oxygen atom. ## Molecule Polarity - Molecules will be polar if they meet the following conditions: - The molecule contains polar bonds - The molecule is asymmetrical ## Flowchart for Determining if a Molecule is Polar or Non-Polar - Start with all covalent molecules. Determine the ΔEN value for each of the bonds within the molecule. - **Polar Covalent Bonds** - If the bond is polar, continue to the next question. - **Non-Polar Covalent Bonds** - If the bonding pair is shared equally, the molecule is non-polar. - Does the molecule have one bond or more than one? - **One bond** - This is a Diatomic molecule. - **More than one bond** - This is a polyatomic molecule. - Is the shape of the molecule symmetrical or asymmetrical? - **Symmetrical** - The molecule is non-polar. - **Asymmetrical** - The molecule is polar. ## Table 3: Some Rules for Determining Polarity of Polyatomic Molecules | **General Chemical Formula** | **Polarity** | **Examples** | |---|---|---| | Diatomic; 2 Different Atoms | Polar | HCI, CO | | Nitrogen and three other atoms of the same element | Polar | NH3, NF3 | | Oxygen and two other atoms of the same element | Polar | H2O, OCl2 | | Carbon and other atoms of two or more elements | Polar | CHCl3, C2H5OH | | Diatomic; 2 Identical Atoms | Non-Polar | N2, O2 | | Carbon and two atoms of the same element | Non-Polar | CH4, CO2 | ## Non-Polar Carbon Dioxide Molecule - The carbon-oxygen bond is considered polar due to a ΔEN of 1.0. - However, the linear shape of the molecule with the two oxygen atoms opposite one another, causes the opposing dipoles to cancel out, making the molecule non-polar. ## Non-Polar Molecules - In order for a molecule to be polar, it must have at least one polar covalent bond. - For example, oxygen is a non-polar molecule due to its symmetrical linear shape, and equal sharing of electrons in its double bond.. - Although carbon dioxide contains two polar bonds, the molecule is non-polar.