Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 2 The Periodic Table Periodic Pattern Classification of the Elements A. “Metals” vs.”Nonmetals” (Before 1800) 1. Metals - Solids, Lustrous, Malleable, Ductile, Conductors 2. Nonmetals - Solids, Liquids, Gases, Poor Conductors B. In early 1800’s, 50-60 Elements Known 1. 1829 - Doebereiner - A System of “Triads” Cl, Br, I Li, Na, K S, Se, Te Ca, Sr, Ba Fe, Co, Ni Classification of the Elements 2. 1865 - Newlands - “Law of Octaves” a. Arranged lightest of known elements by atomic weight b. Observed a periodicity of eight H Li Be F Na Cl K B C N O Mg Al Si P S Ca Ti Mn Fe Cr c. Note: He, Ne, Ar, and Kr were undiscovered d. Introduced the idea of periodicity Classification of the Elements 3. 1869 - Mendeleev and Meyer a. Arranged Elements by Atomic Weight b. Also Considered Chemical Properties of Elements c. The Result - A Table in Which the “Families” of Elements Got Larger d. Additional Triumph of Mendeleev - Spaces were Left for Undiscovered Elements “I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.” --Mendeleev, Principles of Chemistry, 1905, Vol. II Features of the Modern Periodic Table A. The Common Form of the Table is One of Many B. Periods = Rows Groups = Columns C. “A” Groups = “Representative” “B” Groups = “Transition” Lanthanides and Actinides = “Inner Transition” D. Periodic Law - Elements within a given group have similar chemical and physical properties. These properties change gradually with an increase in atomic number. E. The terms metals, nonmetals, and metalloids are still used. Features of the Modern Periodic Table A. The Common Form of the Table is One of Many B. Periods = Rows Groups = Columns C. “A” Groups = “Representative” “B” Groups = “Transition” Lanthanides and Actinides = “Inner Transition” D. Periodic Law - Elements within a given group have similar chemical and physical properties. These properties change gradually with an increase in atomic number. E. The terms metals, nonmetals, and metalloids are still used. Metals Solids at room temperature, except Hg Reflective surface - shiny Conduct heat Conduct electricity Malleable - can be shaped Ductile - can be drawn or pulled into wires Lose electrons and form cations in reactions About 75% of the elements are metals Lower left on the table Nonmetals Found in all three states Poor conductors of heat Poor conductors of electricity Solids are brittle Gain electrons in reactions to become anions Upper right on the table - except H Metalloids Show some properties of metals and some of nonmetals Also known as semiconductors = Alkali metals = Halogens = Alkali earth metals = Lanthanides = Noble gases = Actinides = Transition metals Important Groups Hydrogen Alkali Metals-Group IA Li, Na, K, Rb, Cs, Fr Alkali Earth Metals-Group IIA Mg, Ca, Sr, Ba, Ra Halogens-Group VIIA F, Cl, Br, I, At Noble Gases-Group VIIIA He, Ne, Ar, Kr, Xe, Rn IA IIA VIIA VIIIA X2 A periodic table showing only the representative elements. Chemical periodicity occurs every eight elements. Ion Charge and the Periodic Table The charge on an ion can often be determined from an element’s position on the Periodic Table. Ion Charge and the Periodic Table Atomic Mass We previously learned that not all atoms of an element have the same mass - isotopes Isotopes have identical chemical properties. In calculations, we generally use the average mass of all an element’s atoms found in a sample. We call the average mass the atomic mass Example : If copper is 69.17% Cu-63 with a mass of 62.9396 amu and the rest Cu-65 with a mass of 64.9278 amu, find copper’s atomic mass. isotope masses, isotope fractions avg. atomic mass Mass Spectrometry Ions with a particular velocity pass through and are deflected into circular paths by the magnetic field. Ions with different masses strike the detector in different regions. The more ions of a given type, the greater the response of the detector . A gaseous sample is ionized by bombardment with electrons. The positive ions thus formed are subjected to an electrical force by the electrically charged velocity selector plates and a magnetic force by a perpendicular magnetic field. 80 Hg 200.59 The response of an ion detector converted to a relative scale The percent natural abundances of the mercury isotopes are 196Hg, 0.146% 201Hg, 198Hg, 13.22% 10.02% 202Hg, 199Hg, 29.80% 16.84% 200Hg, 204Hg, 23.13% 6.85%. Mass Spectrum of Chlorine Moles and Calculations with Moles Moles What is an amu ? 1.66 x 10-24 g We need a conversion to the macroscopic world. 1. How many hydrogen atoms are in 1.00 g of hydrogen? 1.00 g H x 1 H atom 1.66 x 10-24 g H = 6.02 x 1023 H atoms Avogadro’s Number Moles 2. Consider carbon-12 (the most abundant isotope of C)! ! ! What is the mass of one carbon-12 atom ? 12 amu C atom x 1.66 x 10-24 g amu = 1.99 x 10-23 g C atom What is the mass of Avogadro’s number of C atoms? g 6.02 x 1023 C atoms x 1.99 x 10-23 = 12.00 g C atom ! Chemical Packages - Moles Mole = number of particles equal to the number of atoms in 12 g of C-12 The number of particles in 1 mole is called Avogadro’s Number = 6.0221421 x 1023 1 mole of C atoms weighs 12.01 g and has 6.022 x 1023 atoms. The average mass of a C atom is 12.01 amu. Example : Calculate the number of atoms in 2.45 mol of copper mol Cu atoms Cu 1 mol = 6.022 x 1023 atoms Relationship Between Moles and Mass The mass of one mole of atoms is called the molar mass. The molar mass of an element, in grams, is numerically equal to the element’s atomic mass, in amu. The lighter the atom, the less a mole weighs. The lighter the atom, the more atoms there are in 1 g. Example : Calculate the moles of carbon in 0.0265 g of pencil lead gC mol C 1 mol C = 12.01 g Example : How many copper atoms are in a 3.10 g of copper? g Cu mol Cu atoms Cu 1 mol Cu = 63.55 g, 1 mol = 6.022 x 1023