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

States of Matter

Properties of Gases: A gas tends to occupy the entire volume of the container; the mass of the gas remains the same even if you modify the size of the container. Gases are very sensitive to temperature changes.

Properties of Fluids and Liquids

Liquids have a constant volume. The liquid adapts to the shape of the container. They swell much less than gases.

Properties of Solids

Solids have a fixed volume and a constant shape. They swell even less than liquids.

Phase Changes and Transitions

• Evaporation: The change from liquid to gas occurs at the surface of the liquid.
• Boiling: In appropriate circumstances, a change of state can occur within the liquid; then, the formed gas bubbles rise to the surface and escape.

Common State Transitions

• Solid

Plum Pudding Model

• The first model to explain the structure of the atom.
• Development was based on the fact that electron mass is significantly smaller than proton mass.
• The nucleus, containing protons, occupies a central space, while electrons are embedded within it.
• This model explains the formation of ions:
  • Anion: An atom that gains electrons, becoming negatively charged.
  • Cation: An atom that loses electrons, becoming positively charged.

Rutherford Model

• Rutherford experimentally proved the Thomson model was not possible.
• He suggested the atom is essentially empty space, with mass concentrated in a small, positive nucleus and electrons revolving around it.
• Discrepancies between electron and proton mass led to the discovery of neutral particles: neutrons.

Fuel Properties and Combustion

Oil is formed by the decomposition of organic matter, primarily plankton, in marine environments. It contains the remains of animals and is a mineral found in sedimentary rock formations.

Soluble compounds begin to form, undergoing thermal decomposition into hydrocarbons (HC).

Gaseous Fuels

Gaseous fuels, also called hydrocarbons (HC), are designed for use in combustion. They are divided into natural gas fuels and manufactured gaseous fuels.

Advantages and Properties of Gaseous Fuels

The calorific value varies greatly depending on the type of gas and the presence of non-combustible components. Non-combustible components lower the heat efficiency of combustion.

Calorific value is the heat released during combustion.

Specific

Chemical Bonding

Chemical bonding is the attractive force that holds atoms together in atomic groupings. Atoms that achieve stability by sharing electrons with other atoms are linked by a covalent bond.

Water

Water remains liquid at room temperature, whereas other similar substances are immediately converted into gases.

• The density of water increases to abnormally high temperatures from 0 to 4°C, reaching a maximum value of 1000 kg/m³. Above or below these temperatures, water expands, and its density decreases.
• In its solid state, water floats on liquid water, contrary to what occurs with other substances.
• Water is an excellent heat storage medium. Its resistance to increasing or decreasing its temperature is higher than that of other liquids or

Early Atomic Theories and Discoveries

Early Theories

• Greek philosophers believed everything was made by combining a few simple, undecomposable substances: the four elements: water, air, fire, and earth.

Dalton's Atomic Theory

• Matter is made up of extremely small, indivisible, and indestructible atoms.
• All atoms of a specific chemical element are identical but differ from atoms of other elements.
• Chemical compounds are formed by the union of atoms of different elements in the same, fixed proportions.

Fundamental Definitions

• Chemical Element: A substance that cannot be decomposed into simpler substances.
• Compound: A substance that can be decomposed into simpler substances.
• Electrolysis: A process used to decompose a pure substance using an electrical current.

Atomic Structure and Composition

All atoms contain one or more negatively charged particles called electrons. Every atom belongs to a specific chemical element. To represent them, we use the symbol _Z^AX, where Z indicates the atomic number (number of protons) and A is the mass number (the sum of protons and neutrons).

Isotopes and Ions

• Isotopes: Atoms that have the same number of protons but a different number of neutrons.
• Ions: Atoms often gain or lose electrons when combining with other elements.
  • When an atom loses electrons, it acquires a positive charge and becomes a cation.
  • When an atom gains electrons, it acquires a negative charge and becomes an anion.

Radioactivity and Nuclear Processes

Radioactivity involves the loss of particles from an unstable...

Pure Substances and Mixtures

Pure substance: Each type has a defined composition and specific properties and invariant features.

Examples: Distilled water, pure gold, oxygen, table salt.

Mixture: Consists of two or more substances in varying proportions.

Examples: Milk, tap water, air.

Types of Mixtures

Heterogeneous mixtures: Components can be distinguished with the naked eye or with optical instruments.

Examples: Granite, water and oil.

Homogeneous mixtures (Blended): The components cannot be distinguished because the particles are completely mixed.

Examples: Sea water, bronze.

Colloidal Dispersions: To distinguish the components, you need to use microscopes. The set of all colloids consists of a dispersed phase and a substance called the dispersing...

Amino Acids and Amphoteric Properties

Amino acids are amphoteric, resulting in three forms: cationic (positive), anionic (negative), and the dipolar ion or zwitterion.

Amino acids behave differently depending on the pH of their environment. They all have a characteristic pH value, known as the isoelectric point (pI), at which the amino acid exists 100% as a dipolar ion.

• Acidic pH: At a pH lower than the pI, the amino acid exists in a high percentage (though not 100%) in the cationic form.
• Basic pH: At a pH higher than the pI, the anionic form predominates.

Peptide Bonds

A peptide bond is formed through the loss of a water molecule (H₂O) from the carboxyl group (-OH) of one amino acid and the amino group (-NH₂) of another.

Protein Denaturation

Denaturation...

Fundamental Chemistry Definitions

• Solute: Substance dissolved in a dispersing phase.
• Saturated Solution: Contains the maximum quantity of solute that can be dissolved.
• Solution: A homogeneous mixture.
• Solvent: The medium in which the solute is dispersed.
• Homogeneous Mixture: Maintains constant concentration throughout.
• Heterogeneous Mixture: Varies in the amount of components throughout.

Concentration and Measurement Units

• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kilogram of solvent.
• Density: Mass per unit of volume.
• Molar Mass: The sum of atomic masses of a substance (grams per mole).
• Moles: The ratio between mass and molar mass.
• % w/w (Mass/Mass): Grams of solute in 100 grams of solution.
• % m/v (Mass/Volume)

Fundamental Atomic Definitions

• Atom: The smallest unit of a chemical element that retains its identity and properties, which cannot be split by chemical processes.
• Element: A substance composed of identical atoms.
• Compound: A substance made up of different atoms combined in a specific numerical relationship.

The Bohr Model of the Atom

Taking the Rutherford model as a starting point, Niels Bohr sought to incorporate the phenomena of gas absorption and emission, alongside the new theory of energy quantization developed by Max Planck. The atom is described as a miniature solar system with a nucleus at the center and electrons moving in well-defined orbits.

• Each orbit has an associated energy level; the further the orbit is from the nucleus, the higher