History of the periodic table

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. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. http://www.bpc.edu/mathscience/chemistry/history_of_the_periodic_table.html

Brown, T., E. LeMay, and B. Bursten. 2000. 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) Mendeleev s Prediction (1871) Actual Value (1886) Atomic mass 72 72.59 Density, g/cm 3 5.5 5.35 Color Dark gray Grayish white Melting Point High 947

Brown, T., E. LeMay, and B. Bursten. 2000. 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)

In a modern periodic table, the elements are arranged according to increasing atomic number (Z) Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd.

Brown, T., E. LeMay, and B. Bursten. 2000. 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

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. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd.

The periodic table and electron configuration

The electrons can be divided into categories depending on the type of subshell being filled Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

ns 1 The outer electron configurations are similar for elements belonging to the same group ns 2 d 1 ns 2 np 1 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6 d 5 d 10 Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

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 Al [Ne]3s 2 3p 1 Ca 2+ [Ar] Al 3+ [Ne] Chang, R. 2002. 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. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

+1 +2 Atoms belonging to the same group lose the same number of electrons, hence they have the same charge +3 Chang, R. 2002. 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 N 1s 2 2s 2 2p 3 O 2-1s 2 2s 2 2p 6 or [Ne] N 3-1s 2 2s 2 2p 6 or [Ne] Chang, R. 2002. 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 -3-2 -1 Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

+1 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) +2 +3-3 -2-1 Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

Ions having the same electron configuration and same number of electrons are said to be isoelectronic Ion Electron Configuration Number of Electrons Na + [Ne] 10 F - [Ne] 10 O 2- [Ne] 10 N 3- [Ne] 10 Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

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. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd.

Here are some examples of metals lithium sodium lead Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. 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)

Here are some examples of nonmetals carbon tellurium chlorine bromine iodine sulfur phosphorus Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. Phils: Pearson Education Asia Pte. Ltd. Chang, R. 2002. Chemistry 7 th ed. Singapore: McGraw-Hill.

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8 th ed. Phils: Pearson Education Asia Pte. Ltd. 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. 2000. 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