Transcript Chapter 7:
The Elements In the universe, there are 92 naturally occurring elements. The other elements are synthetic, or created in a laboratory. Remember, that elements in Groups 1A-8A are also called the representative elements. Remember that the number that comes in front of the A, tells how many valence electrons the elements in the group have. The electrons of all representative elements are in the s and p blocks of the periodic table. Remember that the elements in the same group have the same number of valence electrons. The properties of the elements in a group are not the same, but the properties are the similar. This is because the numbers of nonvalence electrons is not the same. When metals react they lose electrons. As the atomic number increases, the reactivity of the metals increases. On the other hand, nonmetals, when they react tend to gain electrons. As their atomic number increases, their reactivity decreases. Some metals have more properties in common with a neighboring group than with the other elements in their group. This kind of relationship is called a diagonal relationship. Although hydrogen is placed in group 1A, it is not a member of any group because it has properties of both metals and nonmetals. It behaves as a metal when it loses its electron. It behaves as a nonmetal when it gains an electron. The universe contains more than 90% hydrogen by mass. Hydrogen reacts violently with oxygen in the production of water. The main use of hydrogen is in the production of ammonia. These metals are soft metals that are highly reactive. They easily lose their single valence electron to form 1+ ion. Lithium is the least reactive. Sodium and potassium are the most abundant alkali metals. The most common sodium compound, is sodium chloride or, table salt. Potassium compounds are included in fertilizers. http://video.google.com/videoplay?docid=2134266654801392897 These metals are hard, shiny solids. They are less reactive than 1A elements. They form 2+ ions. Beryllium is used in nuclear reactions and in alloys for non-sparking tools. Calcium is needed for human bone strength and teeth. Calcium carbonate is found in rocks, antacids, and in abrasives. It can also be used to make soil less acidic, remove pollutants from smoke stacks, and to make mortar. Magnesium is used in alloys b/c it is lightweight and heat-resistant. 1. Compare each of the following in terms of group #, # of valence e-, typical ion formed, ionization energy and reactivity. a. Calcium and strontium b. Lithium and francium c. Cesium and barium 2. Identify the following group 2A elements based on their properties. a. An element that forms an oxide used to line furnaces b. An element with two valence e- that is used to moderate neutrons in nuclear reactors P block elements include metals, nonmetals and metalloids. Many of the elements can form more than one ion. These elements have three valence electrons. This group includes a metalloid and all of the others are metals. Boron and aluminum can form 3+ ions. Gallium and indium form 3+ and 1+ ions. Thallium forms only 1+ ions. Boron is found in borax, which is used as a cleaning agent and as fireproof insulation. Aluminum is the most abundant metal. Gallium is used in some thermometers. Allotropes are forms of an elements in the same physical state with different structures and properties. Alloys mixtures of metals. These elements have 4 valence electrons. Carbon is the most important. Branch of chemistry called organic to study compound compounds in cells. Carbon takes various forms like graphite and diamond. Silicon is the 2nd most abundant element in Earth’s crust, and in silica, sand, quartz and glass. This group has 5 valence electrons. Nitrogen gas makes up most of the Earth’s atmosphere. Bacteria converts the nitrogen into usable form for plants and animals. Nitrogen is used to make ammonia, nitric acid, fertilizer, dyes and explosives. Phosphorous can be found in baking powder, cleaning products and fertilizer. 3. Find the following pairs on the periodic table. State the name of each. Then compare in terms of group # and # of valence e-. Identify each as a metal, nonmetal or metalloid. State a use for each element. a. C and Pb b. Si and P c. Ga and N These elements have 6 valence e-. Oxygen is the most abundant element in Earth’s crust. Oxygen has 2 allotropes: O2 and O3 (ozone). Sulfur has 10 allotropes and is used to make sulfuric acid. Selenium is used in solar panels and photocopiers. These elements have 7 valence e-. They are highly reactive. Fluorine is the most electronegative element, and is used in toothpaste. Chlorine is used as a disinfectant, bleach and to make some plastics. Silver bromide and iodide are used in photography. Iodine is important for maintaining thyroid health. These elements have filled outer energy levels and are extremely unreactive. Helium is used for balloons. Neon is used in light displays. Argon is used to stop reactions from taking place. Argon and Krypton are used to extend the life of filaments in incandescent lightbulbs. 4. 5. An elements is a gas at room temperature. It does not form any compounds. It has 8 valence electrons and is higher in atomic mass than the element phosphorous but lower in mass than arsenic. Identify the element’s group name and number, and name the element. An element is metallic and radioactive. It has 6 valence electrons. Identify the element’s group number and name the element. The transition metals make up the B groups of the periodic table. They can be divided in the d-block, transition metals, and the f-block, inner transition metals. The final electrons of transition metals enter a d sublevel. They have typical metallic properties such as malleability and electrical conductivity. Most are hard and have high melting and boiling points. Transition metals generally lose their two s electrons to form 2+ ions. However, some can also lose d electrons and take on higher charges. In the d-block, positive ions that have unpaired electrons are generally colored. Because these electrons can move easily, these elements can be magnetic. If all electrons are paired the metal is diamagnetic, that is not attracted to a magnetic field. If there is an unpaired electron, the metal is paramagnetic, or slightly magnetic. Some metals (e.g., iron, cobalt) are ferromagnetic, or have a strong attraction to a magnetic field. The final e- in these metals enters the f sublevel. They are placed below the main body of the periodic table. They include the lanthanide and actinide series. The lanthanides have very similar properties, are silvery metals with high melting points. They are used in welder’s glasses, TV screens and lasers. The actinide series are all radioactive and most are synthetic. They include the transuranium elements, elements that have an atomic number greater than 92.