Characteristics and Uses of the Main Group Elements

Chapter 21: All

• Reading Preparation
• WebLecture
• Study Activity
• Preparation work for chat
• Online Quiz
• Lab Instructions

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 21: 1-11.

Study Notes

• 21.1 Hydrogen and helium atoms formed in the early universe; all other elements form as a result of nuclear fusion inside stellar cores. Many of the heavier elements that form the Earth and other planets come from the dust and gas clouds out of which our own sun collapsed under gravitational forces. Because this cloud already contained these elements, it must have originated in the explosion of an earlier star. An exception to this is oxygen, which is not found in such profusion on any other planet, and appears to be the result of anaerobic lifeforms and metabolic processes unique to Earth within our solar system.
• 21.2 We can use the periodic table as a guide to element groups that share similar chemical properties as well as reactivity patterns. Each group combines with oxygen and hydrogen in specific identifying ratios. As we have seen, electron configurations determine confirmation patterns. Elements in the same group have the same valence electrons, and therefore formed the same kinds of bonds.
• 21.3 Hydrogen is produced commercially by exposing pure carbon to steam. Oxygen is attracted to the carbon, splitting the water molecule and releasing hydrogen as a diatomic gas. The poisonous carbon monoxide gas formed in this process is then re-exposed to steam to release more hydrogen gas and form carbon dioxide, which can be safely vented. Note that in manufacturing chemicals for commercial use, chemists must also identify and deal with dangerous byproducts. finding methods of production which are economically feasible, have low energy costs, are sustainable, and eliminate dangerous waste products is a logistic as well as technical challenge.
• 21.4 The Alkali Metals, Group 1A, include sodium and potassium, both of which have important commercial value. Both are extracted from liquid forms of their compounds using electrolysis. Pure sodium can then be recombined with other elements to form sodium hydroxide (lye), sodium carbonate, and sodium bicarbonate, all of which have important uses as cleaning or food components.
• 21.5 The Alkali Earth Elements, Group 2A, include calcium and magnesium. Most magnesium is extracted from seawater through precipitation reaction with calcium hydroxide. Calcium compounds are used as filtering mechanisms during the production of iron and aluminum, as fertilizers, and in mortar
• 21.6 Boron, Aluminum, and the Group 3A elements: Most people are familiar with aluminum, since it shows up in a more or less perform in our pots and pans, silverware, and as foil. Until relatively recently, extracting and purifying aluminum was an extremely expensive process. An aluminum tableware set was worth more than pure silver! In the late 19th century, chemists in both France and America simultaneously discovered a way to extract aluminum oxides from their silica cores and then purify the aluminum using electrolysis. Boron compounds may be less familiar, but they are no less important: boron is used to harden glass and make it more heat resistant.
• 21.7 Silicon and the Group 4A elements lie below carbon on the periodic table (we discussed carbon in a later chapter). Silicon shares with carbon the ability to form up to four individual bonds, and in the form of silicon dioxide (silica), is a major component of most rocks. The crystal form is essential for radiofrequency controls, so much so that quartz crystals are synthesized through controlled precipitation reactions from supersaturated solutions (similar to the way rock crystal candy is made from sugar). Silicon compounds have important functions in nature and industrial uses in cement, drugs based on purified clays, and zeolites. Silicon polymers are used in cosmetics, lubricants, and caulking materials.
• 21.8 Nitrogen, Phosphorus, and the Group 5A elements are essential for life on earth. If you have studied biology, you have certainly run into both the nitrogen and phosphorus "cycles". While nitrogen is the most abundant gas in our atmosphere, the triple bond in this diatomic molecule makes it difficult to break down so that nitrogen can be combined with other elements. Bacteria fix nitrogen in ammonia compounds, and so do human chemists! The production of ammonia compounds for fertilizer is one of the major industrial uses of nitrogen. Nitrates and nitrites (nitrogen-oxygen compounds) are used in other chemical processes and drugs. Amine groups (NH₂ groups) are attached to other elements to form the 20 amino acids that make up our proteins. Phosphates (PO₄ compounds) are likewise important biological components in DNA, and necessary nutrients for plants, but they can also be problematic when over-abundant in the water supply. Most industrial phosphorus is extracted from phosphate ores, and the phosphorus must be separated from calcium components.
• 21.9 Oxygen, Sulfur, and the Group 6A elements are reactive elements and have numerous industrial applications as well as being important for life processes. Perhaps surprisingly, pure oxygen is not extracted in industrial quantities by splitting water with electrolysis, but through fractional distillation of air. Sulfur is mined from sulfur deposits. Sulfuric acid is a major component of car batteries.
• 21.10 The Halogens, Group 7A, includes some of the most reactive elements. Fluorine and chlorine are both extracted from solid compounds but because of their reactivity, extraction is difficult and expensive. Fluorine is used as an additive in many city water supplies to reduce dental cavities among the population (this is a controversial issue in many locations). Chlorine is used in bleache, of course. Another Group 7A element, iodine, is extracted for similar medicinal properties and is often added to salt to prevent goiter, a thyroid deficiency disease.
• 21.11 The Noble Gases, Group 8A, contains elements which do not, under normal circumstances, form compounds, or even molecules with each other. you leave is used as a coolant for magnets in sensing equipment such as MRIs, and also as a component in birthday balloons, since it is lighter than air. The Earth's supply of helium is limited however. Our goal is far more abundant, being a noticeable component of the Earth's atmosphere. It is used as insulation between panes of glass in windows for many residential and commercial buildings. Xenon is the only one of the noble gases which forms compounds, although there is as yet no commercial application.

Read the following weblecture before chat: Main Group Elements and their Characteristics

Study Activity

Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

• Required: Complete the Mastery exercise with a passing score of 85% or better.
• Go to the Moodle and take the quiz for this chapter.

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(Aligns to) AP LAB #17 GUIDED INQUIRY — — Determine water impurities using gravimetric analysis — Phases IIU

Use the method of gravimetric analysis to determine the impurity levels in your five selected sources. Estimate your error and organize your data. If necessary, repeat tests and perform all necessary calculations to determine the level of impurities in your samples. File your formal report. Resources:

• AP2009 16 Analytical Gravimetric Determination
• APGIE Investigation 3: What Makes Hard Water Hard?
• IGHCE Lab 20.3 Quantitative Analysis of SeaWater

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