Chemistry free essay sample

# 8211 ; Bonding Essay, Research Paper Electron Pair Repulsion Theory: The negatron brace repulsive force theory provinces that the negatron brace in the valency energy degree of an atom repel each other, and hence are arranged as far apart as possible. For illustration, H2O: Due to this theory, different molecules with different sums of braces of negatrons have different forms. Shapes of Molecules: Some common forms of molecules include additive, rhombohedral planar, tetrahedral, rhombohedral pyramidal and v-shaped ( set ) molecules. Examples are drawn below- a ) linear ( CO2 ) B ) tetrahedral ( CH4 ) degree Celsiuss ) v-shaped/bent ( H2O ) vitamin D ) rhombohedral planar ( BF3 ) vitamin E ) trigonal pyramidal ( NH3 ) The negatron point diagrams must be drawn foremost in order to work out the form of the molecule. Molecular Mutual opposition: The mutual opposition can be determined from the form of the molecule. In kernel, a molecule is polar if there is an overall electronegativity difference in the molecule. | Across a Period| Down a Group| Ionization energy| Increases| Decreases| Atomic radius| Decreases| Increases| Melting point/boiling point| Increase in metals, and then decrease in gases| Increase| Valency| Increases| Stays the same according to group number| Electronegativity| Increases| Decreases| Reactivity | Decreases| Increases| Extraction of Metals * The ease of extraction depends on the reactivity of the element. The less reactive, the easier. * A mineral is any pure crystalline compound that occurs in the Earth’s crust, and is considered an ore if it is economically viable to extract a substance from the mineral. * The cost of metals is also important when choosing appropriate metals. * Less abundant ores are generally more expensive Some metals are expensive to extract from their ores (aluminium requires electrolysis, and is therefore more expensive then iron or copper) * Cost of transportation – ores found in remote areas require extensive, and sometimes specialized transport * The yield is the amount of a product as a percentage of what is scientifically expected, and is important because it is critical when determining whether a mining or industrial venture is economically viable. * Eg. With a reaction of copper (I) sulfide with oxygen, the expected amount of copper is 2. 33 tonnes, but it is only 1. 97 tonnes. Therefore the yield is: 1. 972. 3 x 100 = 85% * The extraction of copper from sulfide ores (chalcopyrite CuFeS2): * Concentration through froth flotation, where air is blown through tiny jets into a detergent solution, forming froth. The detergent means the sulfide particles are un-wettable and therefore will not be drawn into the bubbles. (2-25% Cu) * Heat the ore with sand, leaving Cu2S, producing the immiscible liquids of copper (I) sulfide, and the unwanted iron. This is known as smelting, where the substances are heated to high temperatures to form a molten material to extract a metal. 2CuFS2(s) + 5O2(g) 2Cu(l) + 2FeO(s) + 4SO2(g)