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

Unit 1: Matter and Mixtures

Mixtures are combinations of two or more substances that are not chemically combined. They keep their physical properties and can be separated by physical means.

Homogeneous and Heterogeneous Mixtures

• Homogeneous Mixtures: These are uniform throughout. Components cannot be seen, and they cannot be filtered.
  • Solutions: Evenly distributed liquids that do not filter; substances are dissolved (e.g., salt and water).
  • Alloys: Two or more elements where at least one is a metal; these can be separated but not by simple physical means.
  • Colloids: These can be separated (e.g., mayonnaise or gelatin).
• Heterogeneous Mixtures: These are non-uniform. Components can be seen.
  • Suspensions: These can be filtered as large particles are visible

Galvanic Reaction in the Mouth

Biting on aluminum foil can be painful and is usually noticed if you have metal in your mouth from dental work (e.g., fillings, crowns). Basically, when you bite on foil, you set up a battery in your mouth, and the electrical current stimulates nerve endings in your tooth. Here is what happens:

• Pressure from biting brings two dissimilar metals (aluminum foil, mercury in fillings, or gold in crowns) in contact in a moist, salty environment (saliva).
• The two metals have an **electrochemical potential difference** or voltage across them.
• Electrons flow from the foil into the tooth (i.e., **electrical current**).
• The current gets conducted into the tooth's root, usually by the filling or crown.
• The current sets off a nerve

Q#6.3: Define (i) Crystal lattice (ii) Unit Cell.

Ans.(i) Crystal Lattice.

A particular three-dimensional arrangement of particles (atoms, ions, molecules) in a crystal is called a crystal lattice.

In a crystal lattice, particles are located at definite positions in space. These positions are represented by points in a crystal and are called lattice points or lattice sites. This arrangement is called a crystal lattice or space lattice. A crystal lattice actually shows the shape of a crystal.

(ii) Unit Cell.

The smallest geometrical portion of the crystal which is used to build up the whole crystal. OR

If is the smallest portion of a crystal lattice which includes all the positions of each type of particle in the crystal. For example, a cubic crystal...

Properties of Metals:

Shiny, lustrous, can be polished, strong, and solid.

Nonmetals:

Dull, not lustrous, cannot be polished, weak, half are gases.

18 Families or Groups, 18 Periods:

Elements in the same group have common characteristics. Horizontal is period, vertical is family or group.

Periodic Law:

The PT is organized by atomic number Z. Elements with similar properties are in the same family.

Properties of Metalloids:

Have characteristics of metals and nonmetals. Located between metals and nonmetals.

Johann Dobereiner (1829):

Classified elements into groups of three, called triads.

John Newlands (1838-1898):

Law of Octaves (1863) suggested arranging elements in octaves.

Dmitri Mendeleev (1834-1907):

Published a table of elements organized by increasing...

Fossil Fuels: Formation and Combustion

How Fossil Fuels Are Formed

Fossil fuels, including natural gas, petrol (gasoline), and coal, are formed from the remains of ancient living organisms over millions of years. These vital energy sources are primarily compounds of carbon and hydrocarbons.

Combustion of Fossil Fuels

The combustion of fossil fuels always produces carbon oxides and water. However, due to impurities present in these fuels, the burning process can sometimes release dangerous gases into the atmosphere.

Respiration: A Biological Combustion

A slow combustion reaction also takes place within the human body, known as respiration. The energy required for life is released when glucose reacts with the oxygen we breathe. This fundamental biological...

Kinetic Energy and the Nature of Matter

• Kinetic Energy: The energy an object possesses due to its motion.
• Kinetic Theory: States that all matter is composed of tiny particles in constant motion.

Pressure and Its Measurement

• Gas Pressure: Results from the force exerted by a gas per unit surface area of an object.
• Vacuum: An empty space devoid of particles and pressure.
• Atmospheric Pressure: Arises from the collisions of atoms and molecules in the air with objects.
• Barometer: A device used to measure atmospheric pressure.
• Pascal (Pa): The SI unit of pressure.
• Standard Atmosphere (atm): The pressure required to support 760 mm of mercury in a mercury barometer at 25ºC.

Phase Transitions and States of Matter

• Vaporization: The conversion of a liquid to a gas

Main Group Elements: Characteristics and Applications

Group 3 Elements (Boron to Thallium)

The elements in Group 3 (Boron, Aluminum, Gallium, Indium, Thallium) share the electron configuration ns²p¹.

Properties of Boron and Aluminum

• Boron (B): A hard, brittle solid with poor electrical conductivity. It primarily forms covalent bonds, such as B-B.
• Aluminum (Al): A shiny, malleable, and ductile metal with good electrical conductivity. Its common oxidation number is +3.

Chemical Reactions and Characteristics

• Boron reacts with Chlorine at high temperatures to form boron trichloride.
• Aluminum burns vigorously when heated in oxygen:

  2Al + 3O2 → 2Al2O3

• Aluminum forms a self-protective layer of aluminum oxide (Al₂O₃) on its surface, which prevents further

Foundations of Atomic Theory

Early Atomic Ideas: Democritus to Dalton

The concept of the atom has evolved significantly over centuries. Ancient Greek philosopher Democritus speculated that matter was composed of elementary, indivisible particles he called atoms.

Centuries later, John Dalton proposed the first modern atomic theory, laying the groundwork for modern chemistry. His postulates included:

• All matter is made of atoms.
• Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties.
• Compounds are formed by a combination of two or more different kinds of atoms.
• A chemical reaction is a rearrangement of atoms.
• Atoms can be neither created nor destroyed.

Discovery of the Electron: J.J. Thomson

J.J. Thomson'

Neologism

A new word in our language.

Etymology

The study of the origin and history of a word. It has its origins in Greek.

Coinage

The invention of totally new terms. The most typical sources are invented trade names for commercial products that become general terms. Examples: Aspirin, Vaseline, nylon, etc.

Eponyms

A word based on the name of a person or a place. These are usually based on the names of those who first discovered or invented things.

Calque

A direct translation of the elements of a word into the borrowing language. Example: Hot dogs (perros calientes).

Compounding

The process of combining words. Examples: bookcase, textbook.

Blending

The combination of two separate forms to produce a single new term by taking the first part of one word and...

The Quantum Mechanical Atomic Model

The current atomic model (quantum mechanical) addresses the issues raised by Bohr. It was modified by Heisenberg, who stated that it is impossible to know simultaneously the position and velocity of a particle surrounding the nucleus of an atom. This is known as the Heisenberg Uncertainty Principle. Consequently, a new atomic model emerged, known as the quantum mechanical model, which states that the atom exists in confined areas known as orbitals. These are regions where there is a higher probability of finding electrons, and these orbitals are grouped into different energy levels. To describe the location of each electron, it is necessary to know the so-called quantum numbers, which are used to obtain the...