Characteristics of periods The first period starts with hydrogen (H) and ends with helium (He). It has just two elements H (Z=1) and He (Z = 2). H has one electron in the first-shell. He has 2 electrons in the first-shell. As we have seen in the chapter on the structure of atoms, the first-shell […]
THE NOBLE GASES – GROUP 0 In this group, we have Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn). The electronic configuration will show that these atoms all have a complete outer shell of electrons and are not interested in reacting with other elements. These elements are therefore chemically
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THE HALOGENS – GROUP 7 The halogens are all in group 7 on the right of the periodic table. This group consists of elements like Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At). The Halogens are typical non-metals and form the 7th Group in the Periodic Table ‘Halogens’ means ‘salt formers’ and the
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TREND IN ATOMIC RADIUS Going down Group 2: There are more filled energy levels between the nucleus and the outer electrons, therefore the outer electrons are more shielded from the attraction of the nucleus So the electrons in the outer energy levels are further from the nucleus and the atomic radius increases. As the
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As you go down the group from one element down to the next the atomic radius gets bigger due to an extra filled electron shell. The outer electron is further and further from the nucleus and is also shielded by the extra full shell of negative charge, therefore the outer electron is less and less
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THE PERIODIC TABLE Dmitri Mendeleev is credited as being the Father of the modern periodic table. In 1869 he arranged the 50 or so known elements in order of atomic number, Z, putting elements with similar properties in the same vertical group, and leaving gaps for unknown elements, yet to be discovered. When the elements
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ISOTOPES It is interesting to note that atoms of a given atomic number can have different number of neutrons. Atoms of elements having the same atomic number with different mass numbers are called isotopes Some examples are listed below: Isotopes of Hydrogen Hydrogen atom (Z=1) has no neutrons. Number of protons = 1 Number
USES OF HYDROGEN GAS Hydrogenation/Hardening of unsaturated vegetable oils to saturated fats/margarine. When Hydrogen is passed through unsaturated compounds in presence of Nickel catalyst and about 150oC, they become saturated. Most vegetable oil are unsaturated liquids at room temperature. They become saturated and hard through hydrogenation. In weather forecast balloons. Hydrogen is the lightest
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THE STRUCTURE OF THE ATOM AND THE PERIODIC TABLE 1.1 The structure of the atom When scientists started exploring matter, they realized that matter can be divided into smaller and still smaller particles. They called the smallest particle an ‘atom’. The name ‘atom’ was derived from the Greek word ‘atoms’, meaning ‘indivisible’. They discovered that
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(a) Physical properties Hydrogen is a neutral, colourless and odourless gas. When mixed with air it has a characteristic pungent choking smell It is insoluble in water thus can be collected over water. It is the lightest known gas. It can be transferred by inverting one gas jar over another. (b) Chemical properties. (i)
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Occurrence Hydrogen does not occur free in nature. It occurs as Water and in Petroleum. School laboratory Preparation Procedure Put Zinc granules in a round/flat/conical flask. Add dilute sulphuric(VI) /Hydrochloric acid. Add about 3cm3 of copper(II)sulphate(VI) solution. Collect the gas produced over water as in the set up below. Discard the first gas jar. Collect several
REACTION OF METALS WITH WATER The higher the metal in the reactivity series the more reactive the metal with water. The following experiments show the reaction of metals with cold water and water vapour/steam. (a) Reaction of sodium/ potassium with cold water: Procedure Put about 500cm3 of water in a beaker. Add three drops of
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WATER POLLUTION Water pollution take place when undesirable substances are added into the water. Sources of water pollution include: (i) Industrial chemicals being disposed into water bodies like rivers, lakes and oceans. (ii) Discharging untreated /raw sewage into water bodies. (iii) Leaching of insecticides/herbicides form agricultural activities into water bodies. (iv) Discharging non-biodegradable detergents after
WATER Pure water is a colourless, odourless, tasteless, neutral liquid. Pure water does not exist in nature but naturally in varying degree of purity. The main sources of water include rain, springs, borehole, lakes, seas and oceans: Water is generally used for the following purposes: (i) Drinking by animals and plants. (ii) Washing clothes. (iii)
REACTIVITY SERIES OF METALS/ELEMENTS Metals compete for combined Oxygen. A metal/element with higher affinity for oxygen removes Oxygen from a metal lower in the reactivity series/less affinity for Oxygen. When a metal/element gains/acquire Oxygen, the process is called Oxidation. When metal/element donate/lose Oxygen, the process is called Reduction. An element/metal/compound that undergoes Oxidation is
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The following experiments show the reaction of non-metals with Oxygen and air. Burning Carbon Procedure (a) Using a pair of tongs hold a dry piece of charcoal on a Bunsen flame. Observe. Place the products in a beaker containing about 2cm3of water. Test the solution/mixture using litmus papers (b) Using a pair of tongs hold
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Oxygen is put in cylinders for use where natural supply is not sufficiently enough. This is mainly in: (i) Mountain climbing/Mountaineering-at high altitudes, the concentration of air/oxygen is low. Mountain climbers must therefore carry their own supply of oxygen for breathing. (ii) Deep sea diving-Deep sea divers carry their own supply of Oxygen. (iii) Saving
The following experiments show the reaction of metals with Oxygen and air. Burning Magnesium Procedure (a) Cut a 2cm length piece of magnesium ribbon. Using a pair of tongs introduce it to a Bunsen flame. Remove it when it catches fire. Observe. Place the products in a beaker containing about 5cm3 of water. Test the solution/mixture
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OXYGEN a) Occurrence. Fifty 50% of the earth’s crust consist of Oxygen combined with other elements e.g. oxides of metals About 70% of the earth is water made up of Hydrogen and Oxygen. About 20% by volume of the atmospheric gases is Oxygen that form the active part of air. b) School laboratory preparation
THE ATMOSPHERE The atmosphere is made up of air. Air is a mixture of colourless, odourless gases which is felt as wind (air in motion). All living things breathe in air for respiration. Plants use air for respiration and photosynthesis. The main gases present in the atmosphere/air The following experiments below shows the presence and