CHEM 101 1st Edition Lecture 4 Outline of Last Lecture I. IsotopesII. The Periodic Table of ElementsOutline of Current Lecture I. Continuation of Periodic Table of Elements Groups II. Molecules, Ions and their CompoundsCurrent Lecture- Group 3Ao Elements of the 3rd main group (Al, Ga, In, and Ti) are metals, whereas boron (B) is a metalloid (semimetal) Gallium is 1 of the few metals that can be liquid close to room temperature (by holding it in your hands)o Al s the most abundant metal in the Earth’s crust at 8.2% by mass. It’s exceeded in abundance only by the nonmetal oxygen (O) and the semimetal silicon (Si) Ex: of the main sources of Al:Sapphire: AL2O3 with Fe3+ or Ti3+ impurity gives a blue color whereas U3+give a violet colorRuby: Al2O3 with Cr3+ impurity gives off a red/ruby color*Note: AlO3 is not colored! It’s the addition of other elements that adds the colors!- Group 4Ao Elements of the 4th main group (C, Si, Ge, Sn, Pb) is represented by nonmetals, metalloids and metals.o Because of the change from nonmetallic to metallic behavior, more variation occurs in the properties of the elements of this group than in most otherso This is reflected, for example, by the oxides CO2, SiO2, GeO2 and PbO2o A nonmetal such as C can exist in different so-called allotropes (same element, different forms) Ex: Carbon can make graphite, diamond, and buckminsterfullereness (C-60)- Group 5AThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o The first elements in the 5th main group (N, P, As, Sb, Bi), Nitrogen, exists as a diatomic molecule (molecules composed of only 2 atoms) in natureo The atmosphere consists of 78% (by volume of dry air). Nitrogen compounds are important in many applications (as fertilizer, explosives) and are of fundamental biochemical importanceo Phosphorous exists in different allotropes. It’s also essential to life. It’s an important constituent in bones, teeth and DNA. White Phosphorous glows in the dark if it’s in the air. o In addition the Nitrogen there are several elements that exist in nature as diatomic or polyatomic molecules. - Group 6Ao The first element in the 6th main group (O, S, Se, Te, Po), Oxygen, is the most abundant element in earth’s crust. It constitutes 21% of the volume of air. The most common allotrope of Sulfur is S8o Group 6A is also called chalcogens (from the Greek word khalkos, for copper) because most copper ores contain these elements*Note: the book may say oxygen is not apart of the chalcogens, but it is. The whole group is!- Group 7Ao Elements of the 7th main group (F, Cl, Br, I, At) are known as halogens (from the Greek words “hals” meaning salt and “genes” meaning formingo These elements are considered as nonmetals (although this isn’t clear for the highly radioactive At)o All exist as diatomic molecules- Group 8Ao Elements of the 8th main group (He, Ne, Ar, Kr, Xe, Rn) are collectively known as the Noble or Inert Gaseso They are the lease reactive elements of the period and exist as single atomso Amounts of the noble gases in the atmosphere He 5.2 x 10^(-4) Vol-% Ne 1.8 x 10^(-3) Vol-% Ar 0.93 Vol-% Kr 1.1 x 10^(-4) Vol-% Xe 8.7 x 10^(-6) Vol-% Rn 6 x 10^(-18) Vol-%o Imagine that the lecture class has a length of 20m, a width of 25m, and height of 10m (5000m^3) then we would have about 23L of He, 80L of Ne, 47,000L of Ar, 5L of Kr and some ten parts of a billion L of Rn.o It was first thought that the Noble gases wouldn’t combine chemically to form stable compounds. However in 1962, xenon and fluorine compounds were 1stprepared (XeF4 and XeF4) opening the way to the preparation of a number of other such compounds- Clicker Question: Which of the following elements is a metalloid?o Germanium (correct)o Sulfuro Berylliumo Aluminum- Clicker Question: What is the most abundant element in Earth’s crust? o Calciumo Oxygen (correct) o Carbono Magnesium- Molecules, Ions and their Compoundso Compounds- a combination of two or more elements in definite ratios by mass The character of each element is lost when they form a compoundo Molecules- the smallest unit of a compound that retains the characteristics of the compound (usually a nonmetal combined with another nonmetal) They can be described by the chemical name, the molecular formula, the condensed formula, the structural formula or a molecular model. Ex: Molecular Condensed Structured MolecularName Formula Formula Formula Model s H 3D imageMethane CH4 Ch4 H-C-H pyramid H shape H HEthanal C2H6O CH3CH2OH H-C-C-O-H H Ho Different molecular model representations for methane molecule Dashed line means behind the paper plane Solid line means in front of the paper
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