History of the periodic table Mendeleev and Meyer arranged the elements according to increasing atomic mass Mendeleev insisted that the elements with similar characteristics be listed in the same families This left several blank spaces in the table Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. With such arrangement of the elements, Mendeleev was able to predict the properties of then unknown elements Property (of Germanium) Mendeleevs Prediction (1871) Actual Value (1886) Atomic mass Density, g/cm ColorDark grayGrayish white Melting PointHigh947 Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. The periodic table arranged according to increasing atomic mass had inconsistencies Ar, like the other noble gases, is unreactive K, like the other elements in the first column of the periodic table, is reactive Atomic mass of Ar (Z = 18) is greater than that of K (Z = 19) Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. In a modern periodic table, the elements are arranged according to increasing atomic number (Z) Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. The elements in a horizontal row of the periodic table belong to the same period Properties of the element vary periodically across the period Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. The elements in a column of the periodic table belong to the same group or family Elements in the same group have similar properties Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. LT 1 Part 2 Jan 16, 2012 Class time The periodic table and electron configuration The electrons can be divided into categories depending on the type of subshell being filled Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. ns1ns1 ns2ns2 ns2np1ns2np1 ns2np2ns2np2 ns2np3ns2np3 ns2np4ns2np4 ns2np5ns2np5 ns2np6ns2np6 d1d1 d5d5 d 10 Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. The outer electron configurations are similar for elements belonging to the same group Some atoms lose electrons so that the resulting positively-charged species (cation) will have a noble gas configuration Na [Ne]3s 1 Na + [Ne] Ca [Ar]4s 2 Ca 2+ [Ar] Al [Ne]3s 2 3p 1 Al 3+ [Ne] Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Electrons are always removed first from the orbitals with the highest occupied principal quantum number (n) Li [He]2s 1 Li + [He] Ga [Ar]4s 2 3d 10 4p 1 Ga 3+ [Ar]3d 10 Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Atoms belonging to the same group lose the same number of electrons, hence they have the same charge Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Some atoms gain electrons so that the resulting negatively-charged species (anion) will have a noble gas configuration F 1s 2 2s 2 2p 5 F - 1s 2 2s 2 2p 6 or [Ne] O 1s 2 2s 2 2p 4 O 2- 1s 2 2s 2 2p 6 or [Ne] N 1s 2 2s 2 2p 3 N 3- 1s 2 2s 2 2p 6 or [Ne] Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Electrons are added first to an empty or partially filled orbital with the highest available principal quantum number (n) F 1s 2 2s 2 2p 5 F - 1s 2 2s 2 2p 6 or [Ne] Atoms belonging to the same group gain the same number of electrons, hence they have the same charge Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. -2-3 Atoms belonging to the same group either gain or lose the same number of electrons, depending which mode is easier (note: their goal is to have the configuration of a noble gas) Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. -2-3 Ions having the same electron configuration and same number of electrons are said to be isoelectronic Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. IonElectron Configuration Number of Electrons Na + [Ne]10 F-F- [Ne]10 O 2- [Ne]10 N 3- [Ne]10 The periodic table and classification of elements The elements can either be a metal, a nonmetal, or metalloid Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. lithiumsodium lead Here are some examples of metals Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. Metals have the following properties Shiny luster Conduct heat and electricity Malleable (can be pounded into thin sheets) Ductile (can be drawn into wire) All are solids at room temperature except for mercury (which is a liquid) Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. Here are some examples of nonmetals carbon tellurium chlorine bromine iodine sulfur Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. Phils: Pearson Education Asia Pte. Ltd. Chang, R Chemistry 7 th ed. Singapore: McGraw-Hill. phosphorus Nonmetals have the following properties Not lustrous Poor conductors of heat and electricity Usually brittle; some are hard, and some are soft Some are gases (H 2, N 2, O 2, F 2, Cl 2 ), one is a liquid (Br 2 ), and one is a volatile solid (I 2 ) The rest are solids that can be hard like diamond or soft like sulfur Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. Metalloids have properties intermediate between those of metals and nonmetals i.e. silicon looks like a metal but is brittle rather than malleable Poorer conductor of heat and electricity than metals silicon Brown, T., E. LeMay, and B. Bursten Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd.