Atomic Structure, Chemical Bonds, and States of Matter

Atomic Model Today

The atomic model today: Matter is discontinuous and composed of small particles in constant motion. This can be observed in two phenomena: diffusion and Brownian motion.

Brownian Motion

Brownian motion is a phenomenon that demonstrates that matter is discontinuous and consists of particles in constant motion.

Atoms

Atoms are the smallest particles that make up matter.

Structure of the Atom

The Nucleus

The atomic nucleus is the core of an atom. It consists of protons and neutrons.

Electrons

Electrons are elementary particles that orbit the nucleus.

Atomic Number and Mass Number

Atomic number is the total number of protons in the nucleus and is designated by the letter "Z".

Mass number is the sum of the protons and neutrons and is designated by the letter "A".

Historical Atomic Models

Dalton's Atomic Theory

Dalton's atomic theory considered the atom as the fundamental particle of all matter. He believed that the atom was indivisible because he did not know about the existence of protons and electrons.

Thompson Model

The Thompson model recognized the existence of electrons, which possess a negative charge, and protons, which possess a positive charge.

Rutherford Model

The Rutherford model discovered that the atom is not homogeneous and has empty spaces.

Bohr Model

The Bohr model considered that electrons are located in energy levels, similar to floors of a building. However, his model was unstable.

Electrical Nature of Matter

Electrification by Contact

Electrification by contact occurs when bodies are electrified by friction.

Conductors and Insulators

Conductors are materials that allow the passage of electric charges. Examples include metals, salts, and acid solutions.

Insulators are materials that do not allow the passage of electrical charges. Examples include glass and sulfur.

Electrification by Induction

Electrification by induction is the transfer of electrons without touching the object to be electrified. A clear example is the Leyden jar.

Chemical Bonds and Molecules

Chemical Bonds

A chemical bond is the force of attraction between two or more atoms.

• Ionic bond: The force of attraction between two or more atoms where electrons are transferred.
• Covalent bond: The force of attraction between two or more atoms that share electrons.

Molecules

Molecules are stable combinations of two or more atoms held together by chemical bonds.

Chemical Formulas

Formulas are a set of symbols representing a chemical composition.

Types of Formulas

• Molecular formula: Represents the number of atoms in a molecule of a compound.
• Empirical formula: Represents the simplest whole-number ratio of atoms in a compound.
• Structural formula: Shows how atoms are arranged within a molecule.

Mol

A mol is the unit that measures the amount of a substance.

Nuclear Reactions

Nuclear Fusion

Nuclear fusion is the process by which two atomic nuclei join together to form a nucleus with a higher atomic weight.

Reactivity

Reactivity is the measure of a substance's ability to react with other substances.

Nuclear Reactor

A nuclear reactor is a device that produces a controlled nuclear reaction.

Physical States of Matter

Solid State

• Solids have a fixed shape.
• Their volume does not change practically under compression.
• Their structure is orderly.

Examples: Ice, snow, hail, frost

Liquid State

• Liquids take the shape of their container.
• Their volume varies little under compression.

Examples: Rivers, seas, dew

Gaseous State

Examples: Water vapor, clouds, fog

Changes of State

Depending on the conditions to which it is subjected, a body can change from one state to another.

• Ice from a lake, due to the heat of the sun, can be converted into liquid water, and this can evaporate, thus passing into the gaseous state.
• These changes of state have the following names:
  • Melting: Solid to liquid
  • Vaporization: Liquid to gas
  • Sublimation: Solid to gas
  • Solidification: Liquid to solid
  • Liquefaction: Gas to liquid
  • Deposition (or reverse sublimation): Gas to solid