Understanding Materials, Atoms, and Chemical Processes
Material Classification
Materials are classified according to their source (natural materials, manufactured materials, or newly created) or according to their properties (metals and metal alloys, polymers, ceramics).
Manufacturing Processes
Manufacturing involves materials that have undergone a change or were obtained from a chemical process. Some materials are transformed without altering their chemical composition, while others are newly created.
Natural Materials
Natural materials are obtained from raw sources: animal, vegetal, or mineral.
Metals
Metals are obtained from minerals. They are usually dense, though lighter ones exist. Their melting points vary. Metals are **malleable** and **ductile**, possessing good electrical and thermal conductivity.
Polymers
Polymers are giant structures obtained by the union of smaller units called **monomers**. They may be natural or synthetic. Two types exist:
- Thermosets: Do not melt.
- Thermoplastics: Melt when heated.
Ceramics
Ceramics possess properties contrasting with metals. They are **fragile**, very hard, and excellent thermal and electrical insulators. **Glass** is an inorganic material formed by suddenly melting silica, soda, and lime in a kiln. **Clay** is the result of the decomposition of minerals.
Atomic Structure
An **atom** is the smallest, indivisible unit of matter.
Subatomic Particles
- Proton: Located in the nucleus of the atom, carries a positive (+) charge.
- Neutron: Located in the nucleus of the atom, carries no charge.
- Electron: Located in the electron shell (or ‘bark’) of the atom, carries a negative (-) charge.
Isotopes
Isotopes are atoms that differ in the number of neutrons but have the same number of protons.
Ions
Ions are atoms that can lose or gain electrons; these new atoms are called ions.
- Anion: An ion that gains electrons and becomes negatively charged.
- Cation: An ion that loses electrons and becomes positively charged.
Atomic Number
The atomic number is the number of protons in the nucleus.
Mass Number
The mass number represents the total number of particles (protons + neutrons) in the nucleus.
Radioactivity
Approximately 87% of natural radioactivity comes from cosmic rays, 13% from industries (human activity), and 0.1% from nuclear power.
The phenomenon of radioactivity was discovered in 1896 by the scientist **Henri Becquerel**. Radioactivity is a phenomenon in which atoms of one element transform into atoms of another element.
Radioactive Decay Law
Atoms of radioactive elements do not disintegrate all at once, but rather gradually. Elements are characterized by their **radioactive decay half-life**, which is the time required for a certain quantity of a radioactive element to halve.
Artificial Radioactivity
Artificial radioactivity is radiation that occurs, for example, in nuclear power. It is a phenomenon with the same characteristics as natural radioactivity, with the only difference being that radioactive nuclei are produced artificially in a laboratory.
Applications of Radioactivity: Dating Methods
These methods are based on the half-life of radioactive isotopes.
Applications of Radioactivity: Radiotherapy
Radiotherapy is an efficient way to combat cancer.
Nuclear Energy
Nuclear energy is energy that holds immense power. It can be released using two processes: **fission** or **fusion**.
Nuclear Fission
In nuclear fission, a nucleus of **Uranium-235** absorbs neutrons, causing it to break into two smaller nuclei, generating new elements and releasing more neutrons (typically 2-3) that can impact other uranium nuclei. This is a **chain reaction** that generates a large amount of energy.
Nuclear Fusion
In nuclear fusion, two lighter nuclei can **fuse**, generating a heavier nucleus and releasing a great quantity of energy.
Pure Substances
A pure substance is a material constituted by a single, homogeneous class of substances.
- Simple Substances: Consisting of one type of atom.
- Compound Substances: Formed by different types of atoms.
Electrolysis
Electrolysis is a process that relies on an electric current passing through a continuous solution of a salt or a molten salt, resulting in the appearance of new substances.
Mixtures (Impure Substances)
A mixture is a combination of pure substances. In **homogeneous mixtures**, components cannot be distinguished with the naked eye, whereas in **heterogeneous mixtures**, they can.
Chemical and Physical Changes
Physical Change
A physical change does not modify the chemical nature of the substance involved.
Chemical Change
A chemical change is one in which new substances are produced that did not exist before the change.
Reactants
Reactants are the initial substances that undergo changes or chemical reactions.