FREE ELECTRON THEORY - BASICS

FREE ELECTRON THEORY - BASICS 

Concept: 1

Free electrons in metals 

Free electrons in metals are electrons that are not bound to any specific atom within the metal's crystal lattice structure. 

In a metallic bond, the outermost (valence) electrons of metal atoms can move freely throughout the crystal lattice, which creates a "sea" of electrons that are not associated with any particular atom. 

These free electrons are responsible for many of the properties of metals, such as their high electrical and thermal conductivity.

In a pure metal, the number of free electrons is equal to the number of valence electrons per atom. 

However, impurities or defects in the crystal lattice structure can create additional free electrons, which can affect the metal's properties. 

For example, adding impurities to a metal can increase its electrical conductivity by increasing the number of free electrons available to carry electrical current.

Concept 2:

Free electrons in non metals 

Non-metals generally do not have free electrons in the same way that metals do. 

In non-metals, electrons are typically more tightly bound to individual atoms or shared between atoms in covalent bonds. 

Non-metals typically do not have a "sea" of free electrons like metals do, which is why they do not have the same electrical conductivity or other metallic properties.

However, some non-metals can become charged and gain free electrons under certain conditions. For example, when a non-metal is exposed to an external energy source such as light or heat, it can become ionized and release free electrons. (This is the principle behind technologies such as solar cells, where light energy is used to liberate electrons from non-metals like silicon.)

Concept 3: Metalloids

Some non-metals can form covalent bonds with metals to create materials known as metalloids, which can exhibit some metallic properties such as electrical conductivity due to the presence of both covalent and metallic bonding. 

Examples of metalloids include silicon and germanium.

7 Elements of Metalloids

1. Boron (B)

Boron has atomic number 5. It finds uses in many different chemical compounds. 

Properties:

- Pure crystalline Boron has a black, lustrous color and is extremely hard. 

- Boric acid and borates are safe for animals and toxic to arthropods, but essential for plant growth.

Uses:

- Used as an additive to harden steels and glass.

- Boron-based compounds are used as insecticides and fertilizers.

2. Arsenic (As)

Arsenic has atomic number 33. It poses a serious risk to human health due to its interference with cellular respiration (the process by which cells produce the energy they need). 

Properties:

- Has the ability to form up to 3 covalent bonds, allowing it to easily bond with many metals.

- Highly toxic to animals and plants when formed into an arsine or other organic derivatives, but inert in its elemental form.

Uses:

- Can be used as an additive to harden lead and other metal alloys.

- Used in some herbicides and insecticides and as a wood preservative.

3. Silicon (Si)

Silicon has atomic number 14. It is a highly versatile metalloid used in a variety of applications - most frequently in semiconductors and construction. 

Properties:

- Pure silicon is highly reactive in nature and its derivatives are often found in sands, rocks, and soils. 

- Has poor electrical conductivity that becomes more efficient at higher temperatures.

Uses:

- Commonly used in semiconductors.

- Used in the manufacturing of alloys, glass, enamels, and other ceramics.

4. Antimony (Sb)

Antimony has an atomic number of 51. It is commonly used in alloys and paints. 

Properties:

- Has a silvery-white, metallic appearance.

- Hard and brittle .

- Highly purified antimony has a poor electrical conductivity that improves with increased temperatures.

Uses:

- Used in semiconductors as a dopant.

- Used in the manufacture of alloys, glass, enamels, and other ceramics.

5. Polonium (Po)

Polonium has atomic number 84, is exceptionally radioactive, and is highly rare in the Earth’s crust. 

Properties:

- Is highly radioactive and emits alpha-particles.

Uses:

- Used to remove static electricity in machinery or dust from the photographic film. 

- Used as a lightweight heat source for thermoelectric power in space satellites.

6. Tellurium (Te)

Tellurium has atomic number 52 and is commonly used as an alloying element. 

Properties:

- Is highly rare and can be found in mined ores.

- Is crystalline and brittle.

- Remains stable in water but dissolves in nitric acid.

Uses:

- Is often used as an additive to improve strength and corrosion resistance in certain alloys.

7. Germanium (Ge)

Germanium has atomic number 32 and is commonly used as a semiconductor in transistors. 

Properties:

- Is hard and brittle with a metallic appearance.

- Has poor electrical conductivity that becomes more efficient at higher temperatures.

Uses:

- Is used as an additive to improve corrosion resistance in certain alloys.

- Is often used in semiconductors and infrared detectors.

Where can we find these elements in the periodic table? (See figure attached)

The metalloid elements are found along the “zigzag,” or “staircase” of elements lying  between the metals and the nonmetals on the periodic table. 

They are concentrated in the upper-right portion of the table.

Concept 4:

Free electrons in semiconductor 

Semiconductors are a class of materials that have properties intermediate between those of metals and insulators. In semiconductors, the electrons are tightly bound to individual atoms like in non-metals, but they can still move around in the material, though not as freely as in metals. The movement of electrons in semiconductors is highly dependent on temperature and other environmental factors.

Semiconductors have a unique property of having a "band gap" between the valence band (where electrons are bound to atoms) and the conduction band (where electrons are free to move). The size of this band gap determines how easily electrons can be excited to the conduction band and become free electrons. At room temperature, only a small fraction of electrons have enough energy to overcome the band gap and move to the conduction band, leaving the rest of the electrons bound in the valence band.

However, by adding impurities to a semiconductor (a process called doping), the number of free electrons in the material can be increased. This is achieved by intentionally introducing impurity atoms that have extra or missing electrons relative to the semiconductor atoms, creating either an excess of free electrons (n-type doping) or a shortage of electrons called "holes" (p-type doping). These extra or missing electrons can create a conductive path through the material, allowing for the controlled movement of electrons and enabling the creation of electronic devices such as transistors and diodes.