Chemistry in Everyday Life

Core concepts anchored to NCERT

States and classification of matter (NCERT Class IX, "Matter in Our Surroundings", "Is Matter Around Us Pure")

• Matter exists as solid (fixed shape and volume, particles closely packed), liquid (fixed volume, takes the shape of its container) and gas (no fixed shape or volume, particles far apart). The fourth state is plasma (an ionised gas, found in the Sun, stars and lightning); a fifth, the Bose-Einstein condensate, exists near absolute zero.
• Changes of state: melting (solid to liquid), freezing, evaporation, boiling, condensation, and sublimation (solid directly to vapour, as in camphor, naphthalene balls, ammonium chloride and dry ice).
• Matter is classified into pure substances (elements and compounds) and mixtures (homogeneous, such as a salt solution, and heterogeneous, such as sand in water). An element cannot be broken into simpler substances; a compound has elements chemically combined in a fixed ratio; a mixture can be separated by physical means.

Atomic structure and subatomic particles (NCERT Class IX, "Atoms and Molecules", "Structure of the Atom")

• An atom has a tiny dense central nucleus of protons (positive charge) and neutrons (no charge), with electrons (negative charge) revolving in shells around it.
• Electron discovered by J. J. Thomson (1897); proton by Ernest Rutherford (whose gold-foil experiment revealed the nucleus); neutron by James Chadwick (1932).
• Atomic number (Z) is the number of protons; it defines the element. Mass number (A) is protons plus neutrons.
• Isotopes have the same atomic number but different mass numbers (carbon-12 and carbon-14; uranium-235 and uranium-238 matter for nuclear technology, see space and defence technology). Isobars have the same mass number but different atomic numbers.
• Valency is the combining capacity of an element, set by the electrons in its outermost shell. Atoms combine to attain a stable noble-gas configuration (the octet rule).

The periodic table (NCERT Class X, "Periodic Classification of Elements")

• Dmitri Mendeleev arranged the earlier periodic table by increasing atomic mass and left gaps for undiscovered elements. The modern periodic law (Henry Moseley) states that the properties of elements are a periodic function of their atomic number.
• The modern table has 18 groups (vertical columns) and 7 periods (horizontal rows).
• Across a period (left to right) metallic character decreases and the atom gets smaller; down a group metallic character increases and the atom gets larger.
• Group 1 are the alkali metals (sodium, potassium), highly reactive. Group 17 are the halogens (fluorine, chlorine). Group 18 are the noble or inert gases (helium, neon, argon, krypton, xenon, radon), almost non-reactive with full outer shells. Hydrogen is placed separately as it shows mixed behaviour.

Acids, bases, salts and pH (NCERT Class X, "Acids, Bases and Salts")

• An acid releases hydrogen ions (H+) in water and turns blue litmus red; it tastes sour. A base releases hydroxide ions (OH-) and turns red litmus blue; it tastes bitter and feels soapy. A base soluble in water is an alkali.
• A neutralisation reaction between an acid and a base gives a salt and water.
• The pH scale runs from 0 to 14: below 7 is acidic, exactly 7 is neutral (pure water), above 7 is basic or alkaline. The lower the pH, the stronger the acid. The pH concept was given by Sorensen.
• Common acids: hydrochloric acid (gastric acid in the stomach), sulphuric acid (the "king of chemicals"), nitric acid, acetic acid (vinegar), citric acid (citrus fruit), tartaric acid (tamarind), formic acid (ant and bee sting), lactic acid (curd), oxalic acid (spinach).
• Common bases: sodium hydroxide (caustic soda), potassium hydroxide, calcium hydroxide (slaked lime), magnesium hydroxide (milk of magnesia, an antacid), ammonium hydroxide.

Metals, non-metals and metalloids (NCERT Class X, "Metals and Non-metals")

• Metals are generally lustrous, malleable, ductile, sonorous and good conductors of heat and electricity (iron, copper, aluminium, gold, silver). Mercury is the only metal liquid at room temperature.
• Non-metals are generally dull, brittle and poor conductors (sulphur, carbon, oxygen, nitrogen). A key exception is graphite, a non-metal that conducts electricity; diamond and graphite are both pure carbon (allotropes).
• Metalloids (silicon, germanium, arsenic) have intermediate properties and are vital semiconductors for electronics, see information technology and computing.
• The reactivity series ranks metals from most reactive (potassium, sodium) to least reactive (gold, platinum). A more reactive metal displaces a less reactive one from its salt.
• Corrosion: rusting of iron needs both air (oxygen) and moisture (water); rust is hydrated iron oxide. It is prevented by galvanisation (zinc coating), painting, greasing, oiling or making alloys such as stainless steel.
• Alloys are mixtures of metals (or a metal with a non-metal) with improved properties: brass (copper and zinc), bronze (copper and tin), steel (iron and carbon), stainless steel (iron, chromium, nickel), solder (lead and tin).

Carbon, fuels and polymers (NCERT Class X, "Carbon and Its Compounds")

• Carbon forms millions of compounds through catenation (chains and rings) and forms four covalent bonds. Allotropes of carbon include diamond (hardest natural substance), graphite (conductor, used as a lubricant and in pencil leads) and fullerene.
• Hydrocarbons are compounds of carbon and hydrogen; petroleum and natural gas are their main sources.
• Fuels: LPG (liquefied petroleum gas, mainly butane and propane) is the common cooking gas; CNG (compressed natural gas, mainly methane) is a cleaner vehicle fuel; an odorant (ethyl mercaptan) is added to detect gas leaks. The calorific value measures heat released per unit mass.
• Polymers are large molecules made of repeating units: natural (cellulose, rubber, proteins) and synthetic (polythene, PVC, nylon, polyester, bakelite). Plastics are durable but cause pollution, see environment and ecology.