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WVU CHEM 115 - LECTURE 4

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Periodic Table (Mendeleev 1869) Arranged such that elements with similar properties fall within the same group (column). Rows = Periods Columns = Groups elements within the same group have similar properties Periodic Table Terminology and Trends • Groups: elements that lie within the same column (labeled IA, IIIB, etc.) • Periods: elements that lie within the same row (Period 1 7) • Metals: all elements to lower left of dividing line (not including H). » Have similar properties: conduct heat & electricity, have luster, are malleable & ductile, and most are solids at RT. • Non-metals: elements to upper right of dividing line (includes H). » Have similar properties: poor conductors of heat & electricity, not malleable or ductile (are brittle), and can be s, l, or g at RT. • Metalloids: elements bordering dividing line (B, Si, Ge, As, Sb, Te, Po, At) » Have intermediate properties: conduct electricity but not as well as metals. • Representative/Main Group Elements: elements in A-Groups • Transition Elements: elements in B-Groups • Inner Transition Elements: elements in lanthanide and actinide series (elements in rows below main body of periodic table)• Alkali Metals: metals in Group IA (Li, Na, K, Rb, Cs) » Have similar properties: form +1 cations in ionic cmpds. & oxides are strongly basic. • Alkaline Earth Metals: metals in Group IIA (Be, Mg, Ca, Sr, Ba) » Have similar properties: form +2 cations & oxides are strongly basic but less soluble. • Halogens: non-metals in Group VIIA (F, Cl, Br, I, At) » Have similar properties: form -1 anions, exist as diatomic molecules in elemental form at RT (F2, Cl2, Br2, I2), & chlorides have a “salty” taste. • Noble Gases: non-metals in Group VIIIA (He, Ne, Ar, Kr, Xe, Rn) » Have similar properties: not very reactive and do not readily form compounds, & exist as monatomic gases at RT (He(g), Ne(g), Ar(g), etc.) Periodic Table Terminology and Trends • Chemical formulas are collections of chemical symbols that are used to describe elements and compounds – Free elements are not combined with other elements in a compound • Examples: Fe (iron) Na (sodium) K (potassium) – Many nonmetals occur as diatomic molecules (2 atom molecules) • Memorize this list (note their position on the Periodic Table) • H2, N2, O2, and F2, Cl2, Br2, I2 (the halogens)• NaCl is composed of the elements sodium and chlorine in a one-to-one (atom) ratio • Fe2O3 is composed of the elements iron and oxygen in a two-to-three ratio • CO(NH2)2 expands to CON2H4, but there are good reasons to write some compounds with parentheses • Hydrates are crystals that contain water molecules, for example plaster: CaSO4 • 2H2O – When all the water is removed (by heating), the solid that remains is said to be anhydrous (without water) Chemical formulas specify the composition of a substance Chemical Compounds Composed of two or more elements which are present in definite proportions and are chemically bound. • Chemical Formula: shorthand way of specifying the number and type of each element in a compound. • Example: How many atoms of each type are present in the following compounds? Ca(OH)2 Mg3(PO4)2 C12H22O11Chemical Equations A chemical equation describe what happens in a chemical reaction  gives the chemical formulas of the reactants on the left of the arrow and the products on the right. Symbols used in chemical equations show  the states of the reactants  the states of the products  the reaction conditions Hydrogen and oxygen combine to form water • Hydrogen and oxygen are called reactants • Water is called the product Reactants are separated from products with “” 2 H2 + O2  2 H2O Note that the “” is like an equal sign because both sides of the equation have the same number of each type of atom • This can be represented as: Note: Mass is conserved because the number of atoms of each type remains the same on each side of the arrow. (Both sides of the arrow show 4 H and 2 O atoms.) This equation is said to be balanced. The “2” in front of formulas H2 and H2O are called coefficients. They indicate the number of molecules of each type and can change when balancing a chemical equation. The “2” in the formulas H2 and H2O indicate atom ratios for the compound and must not change.• For solids use s, liquids use l, gases use g, and for aqueous solutions use aq. • For example, the reaction between stomach acid (an aqueous solution of HCl) and sodium carbonate (an antacid) can be written It is sometimes useful to include the physical state of reactants and products 2 HCl(aq) + CaCO3(s)  CaCl2(aq) + H2O(l) +CO2(g) Note: You can verify this equation is balanced by checking for mass balance: each side shows 1 Ca, 1 C, 2 Cl, 2 H, and 3 O. • Kinetic and potential energy are both important in chemistry – Kinetic energy is the energy an object has when moving – Potential energy is the energy an object has due to its position • Potential energy is “stored energy” because it can be converted into kinetic energy Almost all chemical reactions either absorb or give off energy, often as heat or light• Energy must also be conserved – The Law of Conservation of Energy: • Energy cannot be created or destroyed; it can only be converted from one form to another • Heat and temperature are related to kinetic energy • The temperature of an object is proportional to its average kinetic energy (average speed of its atoms) • Heat or thermal energy is transferred between objects with different temperatures • Heat flow spontaneously from hot to cold objects Ions: Cations and Anions Ions are charged species and are formed by gain or loss of electrons. Cations: positively charged ions • formed by loss of electrons • # protons > # electrons • In ionic compounds, metals tend to form cations. Anions: negatively charged ions • formed by gain of electrons. • # electrons > # protons • In ionic compounds, non-metals tend to form anions. Example: How many of each type of subatomic particle (# e-, # p, and # n) are present in the following? 27Al+3 32S-2Ions: Polyatomic and Monatomic • Polyatomic Ions: ions consisting of two or more elements – atoms are held together by covalent bonds – ion charge shared over all atoms in ion – atoms stay together as a unit


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