Notes, summaries, assignments, exams, and exercises for Chemistry for Secondary education

Chemical Bonding and Molecular Structure

• • Ionic Compound: A chemical substance composed of positive and negative ions.
  • Crystal: A solid with flat faces that form sharp angles, whose atoms, ions, or molecules are arranged in a regular three-dimensional arrangement.
  • Double Bond: A covalent bond in which two pairs of electrons are shared between two atoms.
  • Electronegativity: The attraction an atom in a molecule exerts on the electrons of a covalent bond.
  • Electronegative Element: Elements, particularly fluorine, oxygen, and nitrogen, have a very strong attraction for the electrons involved in chemical bonding.
  • Covalent Bond: An electron pair shared between two atoms in a molecule.
  • Nonpolar Covalent Bond: A chemical bond in which one or more pairs of electrons

Formulation of Oxides

To formulate oxides, write the element symbol followed by the oxygen symbol, then exchange their valencies and simplify if possible.

• Traditional Naming: Uses specific suffixes based on valency: -ic for one valency; -ous (lower) and -ic (higher) for two; hypo-...-ous, -ous, and -ic for three; and per-...-ic for four.
• Systematic Nomenclature: Uses prefixes such as mono-, di-, tri-, tetra-, penta-, and hexa-.
• Stock Nomenclature: Uses the term "oxide" followed by the metal name and its valency in Roman numerals.

Examples:

• K₂O: Dipotassium monoxide / Potassium oxide
• N₂O₅: Dinitrogen pentoxide / Nitrogen oxide (V)

Hydrides

In hydrides, hydrogen acts with a valency of -1, and valencies are exchanged.

Examples:

• PbH₄: Lead(IV) tetrahydride

Ionic Bonding

Bonding between a non-metal and a metal where electrons are transferred from the metal to the non-metal. This results in the non-metal forming a negative ion and the metal forming a positive ion. The structure is a giant ionic lattice with strong electrostatic forces between ions. A lot of energy is needed to break these forces, resulting in high melting and boiling points. Ionic compounds conduct electricity when aqueous or molten, as the ions are free to move around. They can be represented using dot and cross diagrams.

Covalent Bonding

Bonding between two non-metals. Covalent compounds do not conduct electricity as there are no charged particles. Small molecules are liquids or gases at room temperature due to weak intermolecular...

Q#9.1: How order of reaction is experimentally determined.

Ans. Order of reaction is determined by the following two methods.

1. From Rate Law.

   In this method, the rate of reaction is measured using chemical and physical methods (volumetric, gravimetric, spectrophotometer, pH-meter, conductometric methods). The dependence of the rate of reaction on the concentration of reactants tells us about the order of reaction. For example, a reaction in which the rate of reaction doubles when the concentration of reactants is doubled will be of first order. If the rate increases four times by doubling the concentration, the reaction will be of second order.

2. Ostwald’s Isolation Or Large Excess Method.

   This method is used to determine the order of complicated

Electronegativity

Measure of the tendency of an atom to attract bonding pair of electrons.

Cation

Ion that has a positive charge.

Ionic Bond

Chemical bond formed between two ions with opposite charge.

Anion

Ion that has a negative charge.

Chemical Bond

Electrical attraction between nuclei and valence electrons that binds atoms together.

Covalent Bond

Bond formed when atoms share one or more pairs of electrons.

Non Polar Bond

Type of chemical bond where two atoms share a pair of electrons with each other.

Polar

Uneven distribution of charge.

Polar Bond

Type of chemical bond where a pair of electrons is unequally shared between two atoms.

Molecule

Neutral group of atoms that are held together by covalent bonds.

Molecular Compound

Chemical compound whose simplest...

Thermal Decomposition of Ferrous Sulfate

Observations

• Crystals: FeSO₄ crystals are light green.
• Initial Heating: Steamy fumes condense on the cooler parts of the boiling tube.
• Liquid Analysis:
  • Blue litmus paper: No change.
  • Red litmus paper: No change.
  • Cobalt chloride paper: Turns pink (indicates water).
• Strong Heating: FeSO₄ crystals crumble into a white powder, which eventually turns reddish-brown. A colorless gas is released that fumes strongly in air.
• Gas Analysis:
  • Acidified potassium dichromate paper: Turns from orange to green.
  • Moist blue litmus paper: Turns red.
  • Moist red litmus paper: No change.

Conclusions

1. FeSO₄ crystals are light green.
2. Steamy fumes represent the water of crystallization, which evaporates and condenses as water droplets.
3. The colorless

Mixture

A mixture is a physical blend of two or more components.

Heterogeneous mixture

A mixture in which the composition is not uniform throughout is a heterogeneous mixture.

Homogeneous mixture

A homogeneous mixture is a mixture in which the composition is uniform throughout. Another name of homogeneous mixture is a solution.

Phase

The term phase is used to describe any part of a sample with a uniform composition and properties.

Filtration

The process that separates a solid from the liquid in a heterogeneous mixture is called filtration.

Distillation

One way to separate water from the other components in tap water is through a process called distillation.

Properties of Matter

Mass

The matter of an object is a measure of the amount of matter the object...

Saturated Solution

Contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure.

Solubility

Is the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution.

Unsaturated Solution

A solution that contains less solute than a saturated solution at a given temperature and pressure.

Supersaturated Solution

Contains more solute than it can theoretically hold at a given temperature.

Miscible

Forming a homogeneous mixture when added together.

Immiscible

Liquids that are insoluble in one another.

Henry's Law

States that at a given temperature, the solubility of a gas in a liquid is directly proportional to the pressure of gas above the liquid....

Chromium: A Versatile and Essential Element

Chromium is a useful, very hard, crystalline, steel-gray metal, discovered by Louis Vauquelin in 1797 while working with a material known as Siberian red lead (crocoite). While you might think of highly polished chrome electroplating, purified chromium metal is grayish in color, but still very bright and lustrous. The attribute that makes electroplating perfect is that it's really corrosion resistant. It won't easily rust.

Chromium's symbol is: Cr. Its atomic number is 24. It is located in group 6, and period 4.

The name of the element is derived from the Greek word, chrōma, meaning color, because many chromium compounds are intensely colored.

Applications of Chromium

Chromium plating can be used to give...

C

Circumnavigate

To sail or travel all the way around.

Citadel

A fortress defending a city.

Clandestine

Concealed or secret for an evil purpose.

Classic

Of the highest quality.

Cleave

To cling.

Climatic

Having to do with the climate.

Cloister

Covered walk, with columns on one side.

Clone

An exact duplicate.

Clout

A blow.

Cloy

To cause to feel too full when eating; overly sweet.

Coddle

To baby.

Cogitate

To ponder.

Cohort

A group.

Commemorate

To honor the memory of.

Commiserate

To express sorrow or sympathy for.

Commodious

Spacious, roomy.

Compatible

Harmonious.

Competent

Capable.

Compile

To gather together.

Comply

To act or be in accordance with.

Composed

Calm.

Compromise

A settlement of differences in which each side gives up something.

Compunction

Remorse.

Concave

Curved inward.

Concede

To