Chemistry 9: Chemical Bonding PDF

Maria Montessori Children’s School ADOLESCENT PROGRAM CHEMISTRY 9 CHEMICAL BONDING Underst...

Maria Montessori Children’s School ADOLESCENT PROGRAM CHEMISTRY 9 CHEMICAL BONDING Understanding the Different Properties of Compounds Ionic and covalent compounds have different physical properties that will help distinguish them. 1. At normal atmospheric pressure and temperature, covalent compounds may exist in solid, liquid, or a gas, while ionic compounds exist only as crystalline solids. In covalent compounds, electrons are shared, leading to no full ionic charges and weaker intermolecular attractions compared to ionic compounds. Covalent molecules, like alcohol, exist as liquids or gases at room temperature. Ionic compounds, such as sodium chloride, have ions arranged in a rigid crystal lattice structure, resulting in solid forms under normal conditions. Sodium chloride is commonly used for flavoring and preserving foods. 2. Ionic compounds generally have higher melting and boiling points while covalent compounds have lower melting and boiling points. Ionic compounds have high melting and boiling point because it takes a lot of thermal energy for ions (charged atoms) in the crystal to separate them apart from each other. On the other hand, covalent compounds have low melting and boiling point because of the weak force of attraction between molecules. As a result, a small amount of thermal energy can separate them. 3. Ionic compounds are hard and brittle, while covalent compounds are soft and flexible. Crystal lattices are among the factors that affect the hardness and brittleness of compounds. This refers to the symmetrical three- dimensional arrangement of atoms inside a crystal. The crystal lattices of ionic compounds are hard and not easily scratched, however, it is brittle, which can lead changes to its shape or size. In contrast, covalent compounds have molecules that are weakly attracted to each other and are easily displaced. 4. Ionic compounds have high polarity, while covalent compounds have low polarity. Polarity in a compound is determined by the distribution of electrical charge among atoms connected by a chemical bond, influenced by the elements' electronegativity. Electronegativity measures an atom's ability to attract electrons in a bond. The polarity of a compound is assessed by calculating the electronegativity difference (EN) between the elements in the compound. If the difference in EN values between the metallic element and non-metallic elements is greater than 1.9, the compound is considered as ionic in character. Covalent compound may result in polar or nonpolar bond. Polar covalent bond results when the EN difference of two non-metallic elements is equal to 0.5 and lower than 1.9. On the other hand, nonpolar covalent bond results when the EN difference of nonmetallic elements is lower than 0.5. Two identical non-metallic elements (diatomic molecules) always produce nonpolar covalent bond like nitrogen gas (𝑁2), oxygen gas (𝑂2), and hydrogen gas (𝐻2). 5. Ionic compounds are usually soluble in water, while covalent compounds tend to be less soluble in water. Solubility refers to the ability of a solute to dissolve in a solvent, with many ionic compounds being highly soluble in water due to the polar nature of water molecules attracting ions. Ionic compounds are less soluble in solvents containing a common ion. Some covalent compounds are insoluble in water. Compounds with similar properties, especially polarity, tend to dissolve in each other, following the principle of "Like dissolves like." Substances with different polarities, like water and oil, are insoluble in each other due to their contrasting properties. 6. Ionic compounds tend to be less flammable than covalent compounds. Flammability refers to a substance's ability to burn and cause fire. Combustion occurs when carbon and hydrogen-containing substances react with oxygen to produce carbon dioxide and water. Organic compounds, common in covalent compounds, are flammable due to their carbon and hydrogen content. Covalent compounds are generally more flammable than ionic compounds, but not all covalent compounds burn; for example, water is difficult to ignite due to its polar covalent bonds. Liquefied Petroleum Gas (LPG) is a covalent compound containing a flammable mix of hydrocarbon gases used as fuel. Safety standards, outlined in the Department of Energy's circular DC 2014-01-0001, regulate the transportation and distribution of LPG. 7. Ionic compounds conduct heat and electricity compared to covalent compounds. The conductivity of a substance relates to its ability to transmit heat and electricity. Ionic compounds are good conductors of electricity in solution due to mobile ions that can transfer charge, and they are also efficient conductors of heat. Covalent compounds, however, act as insulators for both electricity and heat because they lack mobile charged particles and have shared electrons. The molecules in covalent compounds are not tightly held together like ions in ionic compounds, leading to less efficient heat transfer. Take note, these are only general properties, and there are always exceptions to every rule. Checking Ionic and Covalent Polarity Directions: Find the electronegativity difference of the following pair of elements and identify whether the pair of elements are likely to form an ionic or covalent (polar/nonpolar) compounds. Write your answers on a separate answer sheet. Guide Questions: 1. Why do we use electronegativity to determine bond polarity? 2. What kind of elements usually form nonpolar covalent compounds? 3. What is the electronegativity difference of given pair of elements in a nonpolar covalent compound? 4. How can you determine if a pair of elements will result in an ionic compound based on type of elements and electronegativity difference? 5. How can you determine if a pair of elements will result in a polar covalent compound based on type of elements and electronegativity difference?