CHEMISTRY

Phosphorus is a non-metallic element belonging to Group 15 and Period 3 of the periodic table. It is highly reactive and is never found in the free uncombined state in nature. Atomic Properties Chemical symbol: P Atomic number: 15 Relative atomic mass: 31 Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p³ Oxidation states: −3, +3 and +5 Occurrence Phosphorus occurs naturally as phosphate rocks or phosphorite, primarily as calcium trioxophosphate(V), [Ca₃(PO₄)₂], and apatite, [Ca₅(PO₄)₃F]. It is also an essential component of living things, found mainly in bones and teeth as Ca₃(PO₄)₂. DNA, RNA and ATP contain phosphorus. Allotropes of Phosphorus Phosphorus exhibits allotropy, i.e. the existence of an element in two or more different physical forms in the same physical state. The three major allotropes of phosphorus are: 1. White phosphorus 2. Red phosphorus 3. Black phosphorus White Phosphorus 1. White phosphorus is a tetra-atomic molecule (P₄). 2. Each phosphorus atom undergoes...

SILICON Silicon is a metalloid which belongs to the same group in the Periodic Table as carbon. It does not occur free in nature but is found mainly in the combined form as: I. Silicon(IV) oxide, SiO₂, and  II. Trioxosilicates(IV). Silicon is the second most abundant element in the Earth's crust after oxygen. Naturally occurring silicon compounds exist mainly as: I. Silicon(IV) oxide, SiO₂ II. Metallic trioxosilicates(IV) Silicon(IV) oxide is commonly called silica . It occurs in crystalline forms such as: I. Quartz II. Flint III. Opal IV. Horn-stone V. Jasper It is also the main constituent of: I. Sand II. Kieselguhr Metallic trioxosilicates(IV) occur in rocks such as: I. Granite II. Basalt Clay and kaolin consist mainly of hydrated aluminium trioxosilicate(IV).   PREPARATION OF SILICON A. Amorphous silicon Amorphous silicon can be prepared by heating a mixture of pure dry sand and magnesium powder in a fire-clay crucible. Dilute hydrochloric acid is then added ...

OXIDES OF CARBON Carbon forms two important oxides, namely: 1. Carbon(IV) oxide, CO₂ 2. Carbon(II) oxide, CO   Carbon (IV) oxide, CO₂ The atmosphere contains about 0.03% by volume of CO₂. A small percentage of CO₂ is also found dissolved in water. In the combined form, carbon is found mainly as metallic trioxocarbonates(IV) and hydrogen trioxocarbonates(IV) in the Earth's crust, especially in limestone regions and coral reefs. Preparation of CO₂ A. Laboratory Preparation CO₂ is prepared in the laboratory by: (i) Action of dilute acids on trioxocarbonates(IV) or hydrogen trioxocarbonates(IV) For example: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) Another example is: NaHCO₃(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g) (ii) Heating metallic trioxocarbonates(IV) Except those of sodium and potassium, many metallic trioxocarbonates(IV) decompose on heating. CuCO₃(s) → CuO(s) + CO₂(g) However, sodium and potassium hydrogen trioxocarbonates(IV) decompose on heating: 2KHCO₃...

Carbon is a non-metal and occurs naturally in both free and combined states. In the free state, carbon occurs in different allotropic forms, including: 1. Diamond 2. Graphite 3. Amorphous carbon Carbon also occurs in the combined state in many substances, including: 1. Carbon(IV) oxide (CO₂) in the atmosphere and dissolved in water. 2. Metallic trioxocarbonates(IV), such as: Calcium trioxocarbonate(IV) (limestone), CaCO₃, Magnesium trioxocarbonate(IV) (dolomite), MgCO₃ 3. Petroleum 4. Natural gas 5. Coal 6. Wood and other living matter Carbon is an essential constituent of all living organisms. It is present in carbohydrates, proteins, fats and many other organic substances. The branch of chemistry that deals mainly with carbon compounds is known as organic chemistry.                                                Allotropes of Carbon Allotrope of carbon is...

Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms. The general molecular formula of a hydrocarbon is CₓHᵧ , where x and y represent the number of carbon and hydrogen atoms, respectively. Examples of hydrocarbons include: Methane (CH₄), Ethene (C₂H₄), Ethyne (C₂H₂), Benzene (C₆H₆) etc  Hydrocarbons are classified into two main groups according to their structure: 1. Aliphatic hydrocarbons e.g. Alkane, alkene, alkyne and cycloalkane 2. Aromatic hydrocarbons e.g. Benzene                  Sources of hydrocarbons  The natural sources of hydrocarbons are: 1. Natural gas 2. Crude oil (Petroleum) 3. Coal They are known as fossil fuels. •Natural gas is a gaseous fuel •Petroleum is a dark viscous liquid fuel •Coal is a solid fuel                  Properties of Alkanes 1. They are saturated hydrocarbons containing only single covalent bonds (C–C) . 2....

Isotope can be defined as atoms of the same element with the same atomic number but different mass number. Isotope could also be defined as atoms of the same element with the same number of protons but different number of electrons.                                 Isotopy Isotopy is a phenomenon whereby atoms of the same element have the same atomic number but different mass number. Examples of elements that exhibit isotopy:     Class activities   1. An isotope is defined as atoms of the same element that have the same (a) mass number (b) atomic number (c) number of neutrons (d) number of shells. 2. Isotopes of an element differ in their (a) number of protons (b) number of electrons (c) number of neutrons (d) atomic number. 3. Which of the following is a pair of isotopes? (a) ¹²₆C and ¹⁴₆C (b) ¹²₆C and ¹⁴₇N (c) ²³₁₁Na and ²⁴₁₂Mg (d) ¹⁶₈O and ¹⁴₇N 4. The chemical p...

Steel is an alloy of iron and carbon, containing about 0.1% to 2.0% carbon. The composition of Steel are: 1. Iron (Fe) – the main metal 2. Carbon (C) – increases strength and hardness.                           Types of Steel 1. Mild Steel (Low Carbon Steel): It contains a small amount of carbon. it is soft, tough, and easy to shape. 2. Medium Carbon Steel:  Stronger and harder than mild steel. 3. High Carbon Steel:  Very hard and strong but less flexible. 4. Stainless Steel: It contains carbon, Iron, chromium and nickel. It resists rust and corrosion.                     Properties of Steel 1. It is strong and durable 2. It is hard and tough 3. It can withstand heavy loads 4. It can be shaped into different forms 5. It is resistant to wear 6. Stainless steel is resistant to rust and corrosion               ...

The General Gas Equation states that for a given mass of gas, the ratio of the product of pressure and volume to the absolute temperature remains constant, provided no gas is added or removed. Formula P₁ V₁ /T₁ = P₂ V₂ /T₂ Where: P₁ = Initial pressure V₁ = Initial volume T₁ = Initial absolute temperature (Kelvin) P₂ = Final pressure V₂ = Final volume T₂ = Final absolute temperature (Kelvin)  Note Temperature must be converted to Kelvin (K) before using the formula. K = °C + 273 Worked Example A gas occupies 4.0 dm³ at a pressure of 100 kPa and a temperature of 27°C. If the pressure is increased to 200 kPa and the temperature becomes 127°C, calculate the new volume. Solution P₁ = 100 kPa V₁ = 4.0 dm³ T₁ = 27 + 273 = 300 K P₂ = 200 kPa T₂ = 127 + 273 = 400 K P₁ V₁ /T₁ = P₂ V₂ /T₂ 100 × 4/300 = 200 ×  V₂/400 V₂= (100 × 4 ×400)/(300×200)  V₂= 2.67 dm³ Class activities  1. The General Gas Equation is obtained by combining: (a) Boyle's law and Charles's law (b)...

Charles's Law states that the volume of a given mass of gas is directly proportional to its absolute temperature, provided the pressure remains constant. V ∝ T (V is directly proportional to T) V/T = k where: V = Volume              T = Temperature               k = a constant value for a given                         sample of gas at a constant                     pressure  V₁/T₁ = k and V₂/T₂ = k, we can set them equal to each other. This gives us the most practical form of Charles's Law:                          V₁/T₁ = V₂/T₂ Where: V₁ = Initial volume T₁ = Initial temperature (in Kelvin) V₂ = Final volume T₂ = Final temperature (in Kelvin) Note : Temperatures must always be converted to Kelvin (K) because the law ...

Water is a colourless, odourless, tasteless and transparent liquid. A molecule of water is made up of 2 hydrogen ( H ) atoms and 1 oxygen ( O ) atom. The chemical formula of Water is  H₂O. Water is essential for the survival of all living things. It is the most abundant substance on the Earth's surface. Water is a compound formed when hydrogen combines chemically with oxygen.                 2H₂ + O₂→ 2H₂O                                       Sources of Water The sources of water include: Rain, Rivers, Streams, Lakes, Springs, Wells, Boreholes, Oceans and seas (salt water)               Types of water   The two types of water are: 1. Soft water  2. Hard water                       Soft water Soft water is a type of water that form lather ...

Oxygen is one of the most abundant and important elements on Earth. It is essential for respiration in humans, animals, and many other living organisms. Oxygen also supports combustion(burning). Chemical Symbol of oxygen: O Atomic Number of oxygen: 8 Mass number of oxygen: 16 Molecular Formula of oxygen: O₂                   Isotopes of oxygen  The isotopes of oxygen are: 1. Oxygen-16 (¹⁶₈O) 2. Oxygen-17 (¹⁷₈O) 3. Oxygen-18 (¹⁸₈O)                 Occurrence of Oxygen Oxygen occurs: 1. In the atmosphere as oxygen gas (about 21% of air). 2. In water (H₂O). 3. In rocks and minerals as oxides. 4. In living plants and animals.       Physical Properties of Oxygen 1. It is a colourless, odourless and tasteless gas 2. It is slightly soluble in water. 3. It is denser than air. 4. It exists as a diatomic molecule (O₂).       Chemical Properties of Oxygen 1. It suppor...

                        HYDROGEN   Hydrogen is a non-metallic element with the chemical symbol H and atomic number 1. It is the lightest and most abundant element in the universe.             Occurrence of Hydrogen Hydrogen occurs: I. In water (H₂O). II. In acids e.g. hydrochloric acid (HCl) and sulphuric acid (H₂SO₄). III. In hydrocarbons such as petroleum and natural gas. IV. In living organisms. V. In the Sun and other stars, where it is the main fuel for energy production. Physical Properties of Hydrogen 1. It is a colourless, odourless and tasteless gas 2. It is the lightest known gas. 3. It is less dense than air. 4. It is slightly soluble in water. 5. It is highly flammable. 6. It exists as diatomic molecules (H₂)                   Isotopes of hydrogen Isotopes are atoms of the same element that have the same atomic number but d...

                              pH pH  stands for the potential of hydrogen. It is a measure of the degree of acidity or alkalinity (basicity) of a solution. It is measured by an instrument called pH meter.                           pH SCALE  The pH scale ranges from 0 to 14; the lower and upper limits respectively. Note : 1. Substances with pH < 7 is  Acidic e.g.battery acid, vinegar, gastric juice etc 2. Substances with pH = 7 is Neutral e.g. Pure water, table salt etc 3. Substances with pH > 7 is Alkaline (Basic) e.g. Bile, sea water, soap solution, NaOH etc                 Importance of pH 1. pH helps to determine whether a substance is acidic or alkaline. 2. It is used in agriculture to test soil before planting crops. 3. Used in medicine to monitor body fluids. 4. H...

                                  ACIDS An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water.                         Types of acids The two types of acids are: I. Organic acids II. Inorganic acids Organic acids occur naturally in plants and animals. Inorganic acids are called mineral acids, since they are produced from mineral ores. They are man- made. Examples of inorganic acids are: 1. Hydrochloric acid (HCl) 2. Trioxonitrate(V) acid (HNO₃) 3. Sulphuric acid (H₂SO₄) etc                   Properties of Acids 1.  Acids have sour taste. 2.  Acids turn blue litmus paper red. 3. Acids react with metals to produce hydrogen gas. 4. They conduct electricity in solution. 5. They have pH values less than 7.           ...