Introduction
Hydrogen bonding occurs when hydrogen is attracted to electronegative atoms like oxygen or nitrogen.

P-Nitrophenol

• Intermolecular Hydrogen Bonding: In para-nitrophenol, hydrogen bonds form between hydroxyl (-OH) groups of different molecules.

O-Nitrophenol

• Intramolecular Hydrogen Bonding: In ortho-nitrophenol, the hydrogen of the hydroxyl group can form a bond with the nitro group on the same molecule, creating an internal bond.

Illustration

• P-Nitrophenol: Hydrogen bonding happens between molecules, causing a stronger intermolecular force.
• O-Nitrophenol: Hydrogen bonding happens within the same molecule, making it more stable due to the intramolecular bond.

Identifying Lewis Acids

Lewis Acids
A Lewis acid is a substance that can accept a pair of electrons.

Lewis Acids in the List

• AlCl3: Acts as a Lewis acid because it can accept electron pairs due to its electron-deficient nature.
• SnCl4: Also a Lewis acid because it can accept electron pairs from other molecules.

Explanation

• NH3: A Lewis base (donates electrons).
• CT: Not specified in the context, but likely not a Lewis acid.

Illustration
Think of a Lewis acid like a “vacuum” that attracts and accepts electron pairs from other molecules.

Introduction
Some non-metals exhibit lustrous properties, meaning they can shine or reflect light like metals.

Examples

1. Diamond
   • Diamond, a non-metal, is known for its brilliant shine and is often used in jewelry.
2. Iodine
   • Iodine crystals also have a shiny, metallic appearance when in solid form.

Illustration
Just like metals, diamonds sparkle and shine due to their crystal structure, while iodine crystals can shine in their solid state under light.

Frequency

• No change: The frequency of light remains constant when it moves from one material to another. This is because frequency is determined by the source of light.

Wavelength

• Changes: The wavelength of light changes depending on the medium. It decreases in denser materials (like glass) and increases in less dense ones (like air).

Speed

• Changes: The speed of light changes when passing through different media. Light travels slower in denser materials and faster in less dense ones. For example, light travels slower in water than in air.

Illustration
When light moves from air to water, its speed and wavelength decrease, but its frequency stays the same.

Definition
Terminal velocity is the constant speed that a freely falling object eventually reaches when the force of gravity pulling it down is balanced by the air resistance pushing it up.

Key Points

• Happens when forces are balanced: gravity = air resistance.
• The object stops accelerating and falls at a constant speed.

Illustration
For example, a skydiver reaches terminal velocity after falling for a while. Initially, they accelerate, but air resistance increases as speed builds. Eventually, the upward force from air resistance matches the downward pull of gravity, and they stop accelerating, falling at a constant speed.