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

Hydrocarbons and Chemical Formulas

Alkanes: A homologous series of hydrocarbons (compounds containing only carbon and hydrogen) in which all carbons are joined by single covalent bonds.

Alkenes: A homologous series of hydrocarbons containing at least one carbon-carbon double bond.

Understanding Chemical Formulas

• Structural Isomers: Molecules with the same molecular formula but different structural arrangements.
• Isomers: Compounds sharing the same molecular formula but possessing different structural formulas.
• Empirical Formula: The simplest whole-number ratio of atoms in a compound.
• Molecular Formula: The total number of each type of atom present in a molecule.
• Structural Formula: A representation showing how atoms in a molecule are joined together.

Definition of Average Speed

The average speed of a body is the total distance traveled divided by the total time taken to cover this distance.

Electron Shells in Sodium Ion (Na+)

Na+ is a positively charged sodium ion. Normally, an atom of sodium has 11 electrons; according to the formula, it has 2 electrons in the K shell, 8 electrons in the L shell, and 1 electron in the M shell. However, Na+ has only 10 electrons; therefore, it has 2 electrons in the K shell and 8 in the L shell. Since 2 and 8 are the full capacities of the K and L shells respectively, Na+ has completely filled K and L shells.

Safety Measures in High Jump Events

In a high jump athletic event, athletes are made to fall on either a cushioned bed or a sand bed. If the athlete were...

Atomic Nucleus and the Nature of Radioactivity

The nucleus is the small central core of an atom, containing a positive electric charge and the majority of the atom's mass. It is made up of nucleons (protons and neutrons) bound together by the strong nuclear force. This force is stronger than the electromagnetic force between the nucleus and electrons, but it only works over very short distances. The nucleus does not intervene in chemical changes.

Radioactive Decay and Radioisotopes

Some atoms, whether naturally occurring or artificial elements, have particular combinations of protons and neutrons that make them unstable. These atoms decompose by emitting energetic radiation and changing the nucleus. This process is known as radioactive decay,...

Foundational Concepts of Atomic Structure

Discovery of Subatomic Particles

• Electron: Discovered by J. J. Thomson (1897). Relative mass: 1/1837. Mass: 9.1 x 10⁻³¹ kg. Charge: -1.
• Proton: Discovered by Ernest Rutherford (1920). Relative mass: 1 atomic mass unit (u). Mass: 1.7 x 10⁻²⁷ kg. Charge: +1.
• Neutron: Discovered by James Chadwick (1932). Relative mass: 1 atomic mass unit (u). Mass: 1.7 x 10⁻²⁷ kg. Charge: 0.

Rutherford's Planetary Model (1911)

Ernest Rutherford proposed the Planetary Model, which is accepted today as the basic structure of the atom.

The atom consists of a very small central region, the nucleus, containing protons and neutrons, surrounded by orbiting electrons. The number of electrons equals the number of protons...

Colloids and Solutions

Colloids resist filtering, although some particles are retained in the filter. These particles can be detected by the scattering of light when it passes through the mixture; this property is called the Tyndall effect. Common examples of colloids include milk and certain juices.

In contrast, actual solutions contain particles with sizes similar to atoms or molecules (less than 1 nm). These cannot be filtered or decanted and do not exhibit the Tyndall effect.

Concentration and Solubility

The composition of a solution refers to the relative amount of solute in the mixture. Solutions have variable compositions, and their properties depend directly on these proportions. To describe a solution accurately, one must identify its...

Tension is a type of stress that a structural element experiences when subjected to two equal and opposite forces pulling outwards along the same axis.

These forces:

• Act on either side of the element.
• Are equal in magnitude.
• Are aligned along the element's axis.
• Pull in opposite directions.

If these forces deform the element, it will stretch. If the element fails, it will break in the middle, perpendicular to the force direction.

Compression is a type of stress that a structural element experiences when subjected to two equal and opposite forces pushing inwards along the same axis.

These forces:

• Act on either side of the element.
• Are equal in magnitude.
• Are aligned along the element's axis.
• Push in opposite directions.

If these forces deform the element,...

Classification of Substances

Substances can be classified according to different criteria:

• Natural and Artificial Substances

  Natural substances are those that exist in nature. Artificial substances are those formed from natural substances by chemical processes (man-made).

• Homogeneous and Heterogeneous Mixtures

  If we observe a substance that consists of several components and perceive distinct parts, we call it heterogeneous. Conversely, if we do not perceive a mixture, it is a homogeneous substance.

• Pure Substances and Mixtures

  Matter that contains a single substance is called a pure substance. Conversely, if it is formed by more than one substance, we call it a mixture.

• Solid, Liquid, and Gas States

  This is the best-known classification, made according

Understanding Chemical Bonds

Ionic Bond: This bond occurs when metallic elements interact with non-metal atoms. In this case, the metal atoms donate electrons to the non-metal atoms, becoming positively and negatively charged ions, respectively. These oppositely charged ions are attracted by strong electrical forces, being tightly bound and giving rise to an ionic compound. These electrical forces are called ionic bonds.

Covalent Bond: Covalent bonds are the forces that hold non-metallic atoms together. These atoms have many electrons in their outermost level (valence electrons) and tend to gain electrons rather than transfer them to acquire the stability of the electronic structure of a noble gas. Therefore, electrons from non-metallic atoms...

Fundamental Atomic Concepts

Atomic Number and Mass Number

Two fundamental properties of an atom are its atomic number and mass number.

• The Atomic Number (Z): This is the number of protons in the nucleus of an atom. For example, a neutral Sodium atom (Na) with atomic number 11 has 11 protons and 11 electrons.
• The Mass Number (A): This is the total number of protons and neutrons in the nucleus of an atom. For example, Sodium-23 (²³Na) has a mass number of 23.

The number of neutrons can be calculated by subtracting the atomic number from the mass number (A - Z).

The Atom, Molecule, and Orbitals

The Atom

In physics and chemistry, an atom is the smallest unit of a chemical element that retains its identity and properties. It cannot be divided further by...

Metals and Non-Metals Comparison

History of the Periodic Table

Mendeleev published the periodic table based on the principle that chemical elements vary periodically with their atomic mass. Other historical contributions include Newlands' Law of Octaves and Döbereiner's Triads.

The Modern Periodic Table

The current periodic table contains 117 elements, including metals, non-metals, metalloids, and noble gases, grouped in rows and columns. These elements are characterized by their metallic character and reactivity, and they are abbreviated by symbols....