9/6/2025
Brownian motion
Brownian motion is the random, jerky movement of tiny particles (like pollen or dust) when they are floating in a liquid or gas.
Why does this happen?
Because water is made of tiny molecules that are constantly moving and bumping into the speck from all directions. These hits are uneven, so the speck gets pushed around randomly.
Rate of diffusion of gases
Rate of diffusion of gases means how fast a gas spreads out and mixes with another gas (or just spreads in the air).
What affects the rate:-
Temperature – Higher temp = faster particles = faster diffusion
Lighter gas – Light gases (like hydrogen) diffuse faster than heavy ones (like oxygen)
Concentration difference – Bigger difference = faster spread at first
Pressure – Higher pressure can sometimes make gases diffuse faster
difference between covalent bonding and ionic bonding :-
Covalent Bonding (Sharing)
What happens?Two atoms share electrons.
Between who?Usually non-metals + non-metals.
Example:In a water molecule (H₂O), hydrogen and oxygen share electrons.
Result:Molecules with no overall charge.
Ionic Bonding (Stealing)
What happens?One atom gives away electrons, and another takes them. This makes ions (charged atoms) that stick together.
Between who?Usually metal + non-metal.
Example:In salt (NaCl), sodium gives 1 electron to chlorine. Sodium becomes +, chlorine becomes −, and they attract.
Result:Ionic compounds made of + and − ions.
Example of a ionic bonding :-
Properties of periodic table :-
Periods and Groups
Periods are horizontal rows (7 in total)
Groups are vertical columns (18 in total)
Elements in the same group have similar chemical properties
Elements in the same period have the same number of electron shells
Elements in the same group have the same number of valence electrons
Atomic Number
Increases from left to right and top to bottom
Represents the number of protons in an atom
Metallic to Non-metallic Character
Left side of the table has metals (shiny, good conductors, malleable)
Right side has non-metals (brittle, poor conductors)
Elements along the zigzag line are metalloids (have mixed properties)
Reactivity Trends
Group 1 (alkali metals) are very reactive, especially with water
Group 17 (halogens) are very reactive non-metals
Group 18 (noble gases) are very unreactive due to full outer shells
Atomic Size (Radius)
Increases down a group (more electron shells)
Decreases across a period (stronger attraction from more protons)
Ionization Energy
The energy needed to remove an electron from an atom
Increases across a period (atoms hold electrons more tightly)
Decreases down a group (outer electrons are farther from the nucleus)
Electronegativity
The ability of an atom to attract electrons in a bond
Increases across a period
Decreases down a group
Electron Configuration
The arrangement of electrons in an atom
Similar configurations lead to similar chemical behavior in groups
THE END
10/6/2025
Group names of the periodic table :-
Group 1 – Alkali MetalsVery reactive metals like lithium, sodium, potassium.
Group 2 – Alkaline Earth MetalsReactive metals, but less than Group 1. Includes magnesium, calcium.
Groups 3 to 12 – Transition MetalsTypical metals: strong, shiny, good conductors. Includes iron, copper, zinc.
Group 13 – Boron GroupStarts with boron; includes aluminium and other metals.
Group 14 – Carbon GroupIncludes carbon, silicon, tin. Elements important in life and materials.
Group 15 – Nitrogen Group (Pnictogens)Includes nitrogen, phosphorus. Important for DNA and fertilizers.
Group 16 – Oxygen Group (Chalcogens)Includes oxygen, sulfur. Essential for life and biological compounds.
Group 17 – HalogensVery reactive non-metals like fluorine and chlorine. Form salts.
Group 18 – Noble GasesUnreactive gases like helium, neon, argon. Full outer shells.
What is Metallic Bonding?
It's the type of bonding in metals.
In metals, atoms lose their outer electrons, and those electrons move around freely.
These free electrons are called a "sea of electrons."
The metal ions (positive) are held together by their attraction to this sea of free-moving electrons.
Key Points:
Occurs in metals (like iron, copper, aluminium)
Atoms lose outer electrons → become positive ions
Electrons don’t belong to any one atom → they move freely
The positive ions and negative electrons attract → strong bond
Properties Because of Metallic Bonding:
Conduct electricity (because electrons can move)
Malleable and ductile (layers of atoms can slide)
High melting and boiling points (strong attraction between ions and electrons)
What is Avogadro's Constant?
It is the number of particles (atoms, molecules, ions, etc.) in one mole of a substance.
Symbol: L or Nₐ
Value: 6.022 × 10²³ particles per mole
Why it's important:
It links the mass of a substance to the number of particles.
Used in mole calculations in chemistry.
Helps convert between:
Grams ↔ Number of atoms/molecules
Moles ↔ Number of particle
Structure of Metals:
Metals are made of closely packed positive metal ions.
These ions are arranged in a regular, repeating pattern called a giant lattice.
Around the ions is a "sea of delocalised electrons" — free-moving electrons that come from the outer shells of the metal atoms.
THE END
11/6/2025
Why do different metals have different flame colours?
Because of the way metal atoms' electrons behave when they are heated.
When you heat a metal salt in a flame, its atoms absorb energy
This energy makes the electrons jump to higher energy levels (excited state)
But electrons don’t stay excited — they fall back down to their original levels
When they fall back, they release energy as light
The color of that light depends on the metal — because each metal has its own unique set of energy levels
Sodium → Yellow flame
Potassium → Lilac/purple flame
Copper → Green-blue flame
Calcium → Brick red flame
Lithium → Crimson red flame
Each metal = unique electron jump = unique light = unique colour
Why does sodium give a yellow flame?
When sodium is heated, its electrons absorb heat energy and jump from their normal place (called the ground state) to a higher energy level — this is called the excited state.
What exactly happens?
Sodium has one outer electron (in the 3s orbital).
When heated, this electron absorbs energy and jumps to a higher orbital — like 3p, 4s, or even higher, depending on the energy.
But it doesn’t stay there long — it’s unstable!
The electron falls back down to its original lower level.
As it falls, it releases energy as light.
For sodium, this light has a wavelength around 589 nanometers, which appears bright yellow to our eyes.
THE END
16/6/25
TEST FOR GASES :-
Oxygen (O₂)
Test: Insert a glowing splint into the test tube.
Result: The glowing splint relights.
Reason: Oxygen supports combustion.
Hydrogen (H₂)
Test: Insert a lit splint into the test tube.
Result: A ‘pop’ sound is heard.
Reason: Hydrogen is flammable and reacts explosively with oxygen.
Carbon Dioxide (CO₂)
Test: Bubble the gas through limewater (calcium hydroxide).
Result: Limewater turns milky or cloudy.
Reason: Forms insoluble calcium carbonate.
Chlorine (Cl₂)
Test: Hold damp blue litmus paper in the gas.
Result: The paper turns red, then gets bleached white.
Reason: Chlorine is acidic and a strong bleaching agent.
THE END
18/06/25
: How does the structure of a substance affect its chemical reactions?
The structure of a substance affects how easily it reacts, with what it reacts, and what it forms — because it changes the bond strength, reactive sites, and electron movement.
1. Bond Strength
Strong bonds (like in nitrogen gas, N≡N) are harder to break, so reactions are slower or need more energy
Weak bonds break easily — faster reactions
Is bond strength based on the structure of electrons?
YES.
Bond strength depends heavily on how electrons are arranged — their structure, sharing, and attraction between atoms.
Difference between Aqueous and Liquid:
Aqueous:
Means a substance is dissolved in water
Represented with the symbol (aq)
Always involves water as the solvent
Example: NaCl (aq) is salt dissolved in water
Liquid:
Refers to the physical state of a substance
Represented with the symbol (l)
Can be a pure substance or a mixture
Example: Pure water (H₂O), ethanol (C₂H₅OH), or mercury (Hg) in liquid state
In short:
Aqueous = substance in water
Liquid = substance in liquid form, not necessarily water-based
Polarity
Definition:Polarity refers to the distribution of electrical charge around atoms, chemical groups, or molecules.
Cause:It occurs when atoms in a molecule have different electronegativities, causing electrons to be shared unequally in a bond.
Types of Polarity:
Bond polarity: Exists when two atoms in a bond share electrons unequally.
Molecular polarity: Depends on both the polarity of individual bonds and the overall shape of the molecule.
Polar Bond:
Formed when one atom attracts electrons more strongly.
Results in partial positive and negative ends.
Non-polar Bond:
Electrons are shared equally between atoms.
No charge separation occurs.
Polar Molecule:
Has an uneven distribution of charge.
Example: Water (H₂O)
Non-polar Molecule:
Even charge distribution.
Example: Carbon dioxide (CO₂)
Key Factor:Polarity influences solubility, boiling point, melting point, and interactions between molecules.
THE END
