Monday, 22 December 2008

The periodic table and metals on Earth

*Note that the table about group I, II and VII will not appear here. Please check the doc. . It is avaiable now in the Chemistry, "introductino to metals..." one.* Thanks. ------------- 1) Atomic no.(Z) = no. of protons while Mass no.(A) = no. of protons+ neutrons. In some other ways of expression, Mass no. = no. of electrons+ neutrons, no. of neutrons = Mass no.- Atomic no. The notation: AZX. 2) Isotopes -- same elements with different no. of neutrons. In another way, they have the same atomic no. but different mass no. For example the 3 isotopes of hydrogen, 1H(Protium), 2h (Deuterium) and 3H (Tritium) have 0,1 and 2 neutron(s) and 1 proton. 3) Relative abundance of isotope = % of existence of isotope in nature. 4) Those isotopes have similar chemical properties(same elements) but different physical properties (different mass). 5) Relative mass of 12C (by definition), = 12 while relative mass (roughly) = mass no. It’s also called relative isotopic mass. 6) Relative atomic mass = SUM of (isotopic mass of isotopes*relative abundance) and it’s the weighted average of isotopic mass of its natural isotopes on 12C scale. 7) The electrons fill the shells from the innermost shell. Nth shell can mostly hold 2n2 electrons. Unless one shell has been full, the electrons will keep filling in except potassium and calcium has only 8 electrons on the 3rd shell. 8) Electronic configuration -- (x1,x2,x3,x4…) represent xn electrons on the nth shell. 9) In the periodic table, Group no. = no. of electrons of the outermost shell and period no. = no. of occupied electron shells. There are 8 group (I, II…. VII and group 0) while the other elements which don’t belong to any group is called the transition metals. 10) Group 0/8 -- noble(inert) gases, fully filled outermost shell(octet structure)-- unreactive. The Octet rule-- elements with 8 outermost electrons is stable. 11) Group VII reacts with most metals to form salt so it’s also called salt-formers. The metals in Earth’s crust and ore mining 1) 24% of Earth’s crust are metals(by mass). The most abundant metal is Al while the most abundant elements are O(48%) and Si(28%). 2) The metals found in natural are usually metal ores in form of compounds. There are 3 common types of compound -- Metal oxide (M+O), sulphide (M+S) and carbonate (M+C+O). They can be extracted with carbon reduction. 3) Carbon reduction -- Metal oxide+ C →(heat)→ Metal + CO2. This is useful for PbO and CuO but useless for FeO unless the heating is hot enough (>1300C) 4) Gold and silver can be found in elements because it’s unreactive. The other metal ores include Haemetite --iron oxides; Bauxite -- Aluminium oxides; Galena -- Lead sulphides, Chalcopyrite -- Copper sulphides and iron sulphides and calcite for calcium carbonate. 5) There was ore mining industry in Hong Kong in the past. For example, galena in Tai Mo Shan and Haemetite in Ma On Shan. However, the ores weren’t pure enough (and, Hong Kong aren’t suitable for ore mining industry, from past to now). Thus they were closed now. 6) China is one of the most important source of ore mining. Quarter of the iron is being output from China. 7) There are two method for extracting the metals. The first one is physical method -- crush the rocks (with pure metal mixed with other matter) to small pieces and wash away the rocks. Gold is one of the metal that can be extracted by this gold panning method. The chemical method is carbon reduction. 8) Chemical change means there’s new matter forms while physical change will not produce anything new. Note that change of state is physical change.

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