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Unformatted text preview: Periodic Table: Anomalies of first member of group Number 68 1 C hem F actsheet www.curriculum-press.co.uk Before working through this Factsheet you should: Be familiar with the general trends across periods and down groups in the periodic table; Be familiar with general properties of Groups 1, 2 and 7. After working through this Factsheet you will: Understand why period 2 elements generally display noticeably different properties to the other elements in the same group; Be familiar with examples of the atypical properties of lithium, beryllium and fluorine; Understand what is meant by the "diagonal relationship" in the Periodic Table. Anomalies of lithium Thermal decomposition of carbonates, nitrates and hydroxides to give the oxide. This is due to the high charge density of the lithium ion - combination with the high charge density oxide ion is favoured. Does not form peroxides and superoxides readily due to small size of the ion. Some compounds show a degree of covalent character due to polarising power of the small Li + ion. Relatively low solubility of carbonate, fluoride, hydroxide and phosphate due to the high lattice enthalpy. Anomalies of beryllium Compounds show appreciable covalent character - eg dissolving in organic solvents, low melting points, hydrolysed by water. This is due to its much larger ionisation energy and the much smaller size of its ions. Amphoteric hydroxide. Does not form oxide in air at room temperature. Will not react with water and dilute acids. Anomalies of fluorine Hydrofluoric acid is a weak acid (due to the high H-F bond strength). Hydrogen fluoride has a high boiling point (hydrogen bonding). The F-F bond strength is very low, because the small size of the atom brings the lone pairs close together. Forms compounds with all elements except helium, neon and argon. Does not form oxy-acids as it is more electronegative than oxygen. Only exhibits oxidation state of -1, as it is the most electronegative element. Is such a strong oxidising agent that it must be prepared by electrolysis, rather than chemically. Because of its small size, more fluorine atoms can be packed around a central atom - eg AlF 6 3 is formed, but only AlCl 4 . Why are period 2 elements different? The atoms are very small in size; The elements are very electronegative; They have no d-orbitals....
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This note was uploaded on 03/08/2011 for the course CHEM 101 taught by Professor Hard during the Spring '11 term at UT Arlington.
- Spring '11
- Periodic Table