➤ The electron carries a negative charge, the proton carries a positive charge, and the neutron has no charge (neutral).
★ This basic distinction is fundamental in atomic structure.

➤ Phosphorus is a different element and not an allotrope of carbon. Diamond, graphite, and buckminsterfullerene are different structural forms (allotropes) of carbon.
★ Allotropes are different physical forms of the same element.

➤ Lemon contains citric acid, milk contains lactic acid, vinegar contains acetic acid, and tamarind contains tartaric acid.
★ Knowledge of natural acids is important for understanding organic chemistry and nutrition.

➤ Alkanes → Ethane, Alkenes → Propene, Alkynes → Butyne, Aldehyde → Methanal.
★ This classification is based on carbon bonding types and functional groups.

➤ In $\text{Al}_2(\text{SO}_4)_3$, there are 3 sulphate ions and each has 4 oxygen atoms, giving 3 × 4 = 12 oxygen atoms per formula unit. So, 1 mole contains 12 moles of oxygen atoms.
★ Stoichiometry is essential in chemical calculations.

➤ Always add acid to water slowly to avoid splashing and violent reactions. Never add water to acid as it may cause exothermic reactions.
★ This is a lab safety rule.

➤ The atomic number of beryllium is 4, which means it has 4 protons in its nucleus.
★ Atomic number = Number of protons.

➤ Alkalis are bases that dissolve in water to produce hydroxide ions (OH⁻).
★ All alkalis are bases, but not all bases are alkalis.

➤ Use the formula C = (F − 32) × 5/9, so (59 − 32) × 5/9 = 27 × 5/9 = 15°C.
★ Temperature conversion is often asked in reasoning or science sections.

➤ Dobereiner grouped elements into triads (groups of three elements with similar properties) based on atomic masses.
★ This was an early attempt at classifying elements.

➤ Halogens (Group 17 elements) have 7 electrons in their outermost shell, making them highly reactive.
★ This explains their tendency to form salts.

➤ Electronegativity is the ability of an atom to attract shared electrons in a bond.
★ Fluorine has the highest electronegativity.

➤ The compound has a straight chain of six carbon atoms, which is n-Hexane.
★ Straight-chain alkanes are named with the prefix n-.

➤ Acetaldehyde has a straight chain (open chain) structure, while others are cyclic or aromatic compounds.
★ Open chain compounds are also called acyclic.

➤ Solidification is the process of a liquid turning into a solid, while fusion (melting) is the opposite — a solid turning into a liquid.
★ Solid ↔ Liquid transition involves fusion and solidification.

➤ Alicyclic compounds are cyclic but behave like aliphatic compounds. Cyclopropane is a ring compound without aromatic properties.
★ Alicyclic = Aliphatic + Cyclic.

➤ In the double displacement reaction between $\text{Na}_2\text{SO}_4$ and $\text{BaCl}_2$, $\text{BaSO}_4$ forms as a white precipitate.
★ Common in qualitative salt analysis.

➤ Stalagmites grow upward from the floor of caves, formed by deposition of calcium carbonate ($\text{CaCO}_3$).
★ “Stalagmite” grows from the ground, “Stalactite” hangs from the ceiling.

➤ Aniline contains a benzene ring, making it a benzenoid compound.
★ Benzenoids have aromatic rings in their structure.

➤ In meta (m-) position, two substituents are on carbons 1 and 3 of the benzene ring.
★ IUPAC naming uses numerical positions for clarity.

➤ 2-Methylpropan-2-ol has a tertiary carbon attached to the –OH group, thus it’s called tert-butyl alcohol.
★ Common tertiary alcohol used in labs.

➤ In IUPAC nomenclature, the root word (like meth-, eth-, prop-, etc.) tells the number of carbon atoms in the longest chain.
★ Correct identification of the root is essential for naming organic compounds.

➤ Chloroform ($\text{CHCl}_3$) is used in the production of Freon R-22 ($\text{CHClF}_2$), a hydrofluorocarbon used in refrigeration.
★ Freon gases are polyhalogen compounds involved in cooling systems.

➤ In 1789, Antoine Lavoisier proposed the Law of Conservation of Mass, stating that mass is neither created nor destroyed in a chemical reaction.
★ This law laid the foundation of modern chemistry.

➤ A hydrogen atom has 1 electron, so a hydrogen molecule ($\text{H}_2$) has 2 electrons, with 1 in each atom’s K shell. But each individual hydrogen atom has 1 electron in the K shell.
★ It’s key in understanding molecular formation.

➤ Butane is a saturated hydrocarbon (alkane) with 4 carbon atoms and 10 hydrogen atoms, giving the formula $\text{C}_4\text{H}_{10}$.
★ It’s used as a fuel and propellant.

➤ Eugenol is the main component of clove oil, known for its analgesic and antiseptic properties.
★ It’s commonly used in dental care.

➤ Gallium was discovered later and matched well with Mendeleev’s predicted eka-aluminium.
★ Proof of predictive power of Mendeleev’s table.