Chemical Earth Notes 32244f

1. The living and non-living components of the Earth contain mixtures. - Element; pure substance which cannot be decomposed into simpler substances. HOMOGENOUS. - Compound; pure substance which can be decomposed into simpler substances (e.g. elements). HOMOGENOUS. - Mixture; can separate into two or more pure substances via physical means. HOMOGENOUS & HETEROGENOUS. Sphere Elements & Mixtures Biosphere  Living matter consists of mixtures of carbon-containing compounds; e.g. sugars, proteins, fats, vitamins. Lithosphere  Rocks – various silicates e.g. silicon, oxygen, various metals.  Sand – mainly silicon dioxide and variable amounts of finely ground shell or dirt.  Soils – sand, decomposing matter and various aluminosilicates e.g. clays, aluminium compounds, oxygen and metals.  Mineral ores – mainly oxides, sulphides, carbonates, sulphates and chlorides of metals.  Coal, oil, natural gas – mixtures of carbon compounds formed from decayed matter. Hydrosphere  Mainly water with dissolved oxygen, nitrogen, carbon dioxide and other compounds. Atmosphere  Mainly mix of elements, e.g. N, O, Ar.  Small amounts of gaseous compounds, e.g. H2O, CO2, CO, nitrogen dioxide, sulphur dioxide. -

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Five most abundant elements in each zone of the Earth. Rank Biosphere Atmosphere Hydrosphere 1 Oxygen Nitrogen Oxygen 2 Silicon Oxygen Hydrogen 3 Aluminium Argon Chlorine 4 Iron Hydrogen Sodium 5 Calcium Carbon Magnesium

Lithosphere Oxygen Silicon Aluminium Iron Calcium

Solids of different sizes can be separated by sieving. Solids and liquids can be separated by filtration or decantation. Dissolved solids in liquids can be separated by using evaporation or distillation. Liquids can be separated by using distillation or fractional distillation depending on difference of b.p Gases are usually separated using either differences in b.p. or solubilities in liquids like water. Separation Method Property used in the separation Sieving Particle size Vaporisation Liquid has a much lower b.p. than the solid Distillation Big difference in boiling points Fractional Distillation Significant but small difference in b.p. Filtration One substance a solid, the other a liquid/solution Add solvent then filter One substance is soluble in the chosen solvent, while the others are insoluble. Separating funnel Components are immiscible liquids. - Gravimetric analysis used for determining the quantities of substances presents in a sample by weight/mass.  Helps decide if mineral deposit has enough required compound to make extraction economically viable.  Helps determine composition of soil in particular locations to see if it’s suitable for growing crop.  Helps determine amounts of substance present in water/air to see how polluted samples are.

2. Although most elements are found in combinations on Earth, some elements are found uncombined. - The more reactive an element is, the less chance there is of finding it in the Earth as an uncombined element. Metals Semi-metals Non-metals Elements which All other elements  Solids at room temperature have both metal  Very low tensile strength  Shiny or lustrous and non-metal  Some are hard but brittle (diamond and  Good conductors of heat and electricity properties. boron) while others are soft (sulphur).  Malleable (rolled into sheets)  Ductile (drawn into wires)  Show wide range of properties e.g. m.p.,  Show VERY wide range of properties; such as conductivity, tensile strength and hardness. gas, liquid, solid states at room temperature.  Common ones are Fe, Cu, Zn, Cr, Ni; all have  Major use as compounds; fuels, fertilisers, relatively high m.p. except copper and are hard. plastics, fibres, drugs, detergents, cosmetics.  Used in building materials, transport vehicles,  Graphite used as lubricant and electrodes. machinery, electrical wires and appliances.  Oxygen for medical purposes. 3. -

Elements in Earth materials are present mostly as compounds because of interactions at atomic level. Particles in matter: solids – vibrating, liquids – vibrating translational motion, gases – rapid translational motion. Electrons exist in energy levels which can only accommodate a certain number of electrons (2n2). Atomic number is the number of protons in the nucleus. Mass number is the number of protons and neutrons in the nucleus. Metals generally form positive ions; non-metals form negative ions. Losing an electron forms a positive ion (cation) and gaining an electron forms negative ion (cation). Ionic bonding is chemical bonding which involves the transfer of electrons from one atom to another. Molecules – smallest particles of a substance capable of separate existence; moves independently of each other. Noble gases are the only monatomic molecules, existing as independent atoms. Covalent bonds are formed between pairs of atoms by the atoms sharing electrons. Metal Ionic Covalent Lattice Covalent Molecule

4. Energy is required to extract elements from their naturally occurring sources. - A physical change is when no new substance is formed, easily reversed, less energy needed. - A chemical change is when at least one new substance is formed, hard to reverse, more energy needed. Needs to overcome strong bonds holding the atoms together in compounds. - Electrolysis produces two new substances (H & O) while boiling does not (only converts liquid to gas). - Decomposition reactions are where compounds can be decomposed into two or more other pure substances and usually requires the input of energy in the form of heat, light or electricity.  Calcium carbonate is decomposed by heating to make lime, cement and glass.  Aluminium is extracted by electrolysing molten aluminium oxide. - Direct combination/synthesis reactions are where elements combine to form compounds, energy is released.  Burning of coke (carbon) which releases heat energy.  Rusting of iron and steel to form iron(III) oxide (synthesis of iron and oxygen). - The stronger the bonds of attraction, the higher the energy needed to separate atoms in a compound.

5. The properties of elements and compounds are determined by their bonding and structure. Mixture Element/Compound Can be separated using physical means. Cannot be separated by physical means. Homogenous or heterogeneous. Homogenous. Displays properties of pure substances making it up. Properties (e.g. appearance) that are constant. Variable composition Fixed composition - Metals exist as three-dimensional lattices in a sea of electrons. - Ionic compounds exist as repeating three-dimensional lattices of ions; empirical formula (absence of molecules). Covalent Molecular Covalent Lattice Ionic Metallic M.P/B.P Low High High Variable Electrical conductivity No No In molten state Yes Hardness Soft Hard Hard and brittle Variable hardness Forces Intermolecular Covalent bonding Electrostatic Delocalised electrons - Properties of ionic substances;  M.P/B.P: electrostatic forces between ions are strong, therefore much energy (high temperature) is needed to melt or boil a substance.  Electrical conductivity: solid ionic compounds don’t conduct electricity because ions are tightly bound, however when ionic substances are molten/dissolved in water, the orderly arrangement of ions is broken and ions can move about freely and migrate towards a charged electrode.  Hardness: strong electrostatic attraction between pairs of ions make it hard but if orderly array of ions is disturbed by a strong force, the ions of same charge come close together then repel each other shattering the crystal which makes it brittle. - Properties of covalent molecular;  M.P/B.P: intermolecular forces between molecules are weak, melting and boiling breaks apart these weak bonds resulting in low melting and boiling points.  Electrical conductivity: cannot conduct as covalent molecular structures are pure species.  Hardness: soft, due to weak intermolecular forces. - Properties of covalent lattice;  M.P/B.P: melting and boiling covalent lattices require a lot of energy (high temperature) due to the strong covalent bonds holding the structure together.  Electrical conductivity: does not conduct electricity as it contains no ions and all electrons are either being held by individual atoms or shared by pairs of atoms, none are free to roam around.  Hardness: it is hard due to the strong covalent forces holding the structure together.