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Ch.18 - Chemistry of the Environment
All textbooksBrown 15th EditionCh.18 - Chemistry of the EnvironmentProblem 49
Chapter 18, Problem 49

(a) What are trihalomethanes (THMs)? (b) Draw the Lewis structures of two example THMs.

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Step 1: Understand what THMs are. THMs, or Trihalomethanes, are a group of organic compounds that contain one carbon atom and three halogen atoms. The halogens can be any of the following: fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).
Step 2: Choose two THMs to draw. For this example, let's choose trichloromethane (CHCl3) and tribromomethane (CHBr3).
Step 3: Draw the Lewis structure for trichloromethane (CHCl3). Start by drawing the carbon atom in the center, as carbon is less electronegative. Then, draw a single bond to the hydrogen atom and three single bonds to the three chlorine atoms. Each chlorine atom should have three lone pairs of electrons, and the hydrogen atom does not have any lone pairs.
Step 4: Draw the Lewis structure for tribromomethane (CHBr3). The process is similar to step 3. Start by drawing the carbon atom in the center, then draw a single bond to the hydrogen atom and three single bonds to the three bromine atoms. Each bromine atom should have three lone pairs of electrons, and the hydrogen atom does not have any lone pairs.
Step 5: Review your Lewis structures. Make sure that each atom has a full octet (except for hydrogen, which only needs two electrons), and that the total number of electrons equals the sum of the valence electrons of each atom.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They use dots to represent electrons and lines to represent bonds between atoms. Understanding how to draw Lewis structures is essential for visualizing molecular geometry and predicting the reactivity of compounds.
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Trihalomethanes (THMs)

Trihalomethanes (THMs) are a group of chemical compounds that consist of a methane molecule (CH4) where three of the hydrogen atoms are replaced by halogen atoms (such as chlorine, bromine, or iodine). They are commonly formed as byproducts in water chlorination processes and are important in environmental chemistry due to their potential health effects.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how an atom bonds with others. The number of valence electrons influences the atom's reactivity and the types of bonds it can form. In drawing Lewis structures, accurately accounting for valence electrons is vital to depict the correct bonding and electron arrangement in molecules.
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Related Practice
Textbook Question

The organic anion

is found in most detergents. Assume that the anion under-goes aerobic decomposition in the following manner: C18H29SO3- + 51 O2 → 36 CO2(aq) + 28 H2O (l) + 2 H+(aq) + 2 SO42-(aq) What is the total mass of O2 required to biodegrade 10.0 g of this substance?

Textbook Question

Magnesium ions are removed in water treatment by the addition of slaked lime, Ca(OH)2. Write a balanced chemical equation to describe what occurs in this process

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Textbook Question

In the lime soda process once used in large scale munici-pal water softening, calcium hydroxide prepared from lime and sodium carbonate are added to precipitate Ca2+ as CaCO3(s) and Mg2+ as Mg(OH)2(s): Ca2+(aq) + CO32-(aq) → CaCO3(s) Mg2+(aq) + 2 OH-(aq) → MgOH2(aq) How many moles of Ca(OH)2 and Na2CO3 should be added to soften (remove the Ca2+ and Mg2+) 1200 L of water in which [Ca2+] = 5.0x10-4 M and [Mg2+] = 7.0x10-4 M?