Learn Unit I: Chemical Substances - Nature and Behaviour with Free Lessons & Tips

To observe what happens when quicklime (calcium oxide) is added to water in a beaker, follow these steps:

1. Take a small amount of quicklime (calcium oxide) and place it in a clean, dry beaker.
2. Add a small amount of water to the quicklime in the beaker, using a dropper or a stirring rod to mix them together.
3. Observe the reaction carefully and note down any changes that occur.

Some elements exist in molecular form because their atoms prefer to share electrons to achieve a stable electron configuration through covalent bonding. Other elements exist in atomic form because they tend to form metallic bonds or ionic bonds, or because they are noble gases with stable electron configurations.

• Identification of Non-metal A and Its Oxides B and C:

  • Non-metal A is carbon (C).
  • Oxide B is carbon monoxide (CO), which is toxic.
  • Oxide C is carbon dioxide (CO2), which contributes to global warming.

• Element A Burning with Golden Flame in Air and Reacting with Element B:

  • Element A is sodium (Na).
  • Element B with atomic number 17 is chlorine (Cl).
  • Product C is sodium chloride (NaCl).
  • Aqueous solution of C on electrolysis gives compound D, which is sodium hydroxide (NaOH), and liberates hydrogen gas (H2).
  • Reactions:
    • 2Na(s) + Cl2(g) → 2NaCl(s)
    • 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)

• Sour substances contain acidic compounds that can react with copper and brass to form toxic compounds such as copper acetate or copper sulfate. These compounds can leach into the food or drink stored in the vessels, posing health risks. Therefore, it is not advisable to keep sour substances in brass and copper vessels.

• Characteristics of a period include:

  • Elements in the same period have the same number of electron shells.
  • The number of valence electrons increases across a period from left to right.
  • Chemical properties of elements within a period gradually change as one moves across the periodic table.