The difference between metals, insulators, and semiconductors is the size of the band gap. Metals have no band gap. In other words, the conduction band and valence band overlap, so an atom is not bound to any particular atom. If it has enough energy to leave, it just leaves. Semiconductors have a small band gap. If there is enough energy to pass this barrier, the material conducts.
Insulators have a large band gap. These terms are practical—anything which is considered an insulator has a band gap that is too large to cross in a realistic scenario. Trying to pass too much current through many insulators will destroy the material before electrons have enough energy to jump across the band gap.
Conductivity measures the amount of electrical current a material can carry. This equation was generalized for any situation involving electrical conductivity including ion conduction , but in most cases the charge carrier is just electrons. So conductivity is basically just how many electrons can squeeze through the wire in a given amount of time. Usually, if engineers can change the conductivity of something, they are changing , the mobility of electrons.
For example, grain boundaries can scatter electrons, reducing the speed they travel through the wire. Precipitates and alloying elements reduce conductivity for the same reason. The opposite of conductivity is resistivity or resistance. Resistivity is the intrinsic version of resistance.
Aluminum forms an electrically resistant oxide surface in electrical connections, which can cause the connection to overheat. High-voltage transmission lines which are encased in steel for additional protection use aluminum. At room temperature, zinc is brittle, but it becomes malleable at C. Malleable means it can be bent and shaped without breaking. Brass is a tensile metal used for smaller machines because it is easy to bend and mold into different parts. Its benefits over steel are that it is slightly more conductive, cheaper to purchase, less corrosive than steel, and still retains value after use.
Brass is an alloy. Iron has metallic bonds which is where the electrons are free to move around more than one atom. This is called delocalization. Because of this, iron is a good conductor. Platinum is an element with high electrical conductivity and is more ductile than gold, silver, or copper. It is less malleable than gold. The metal has excellent resistance to corrosion, is stable at high temperatures, and has stable electrical properties.
Steel is a conductor and an alloy of iron. Steel is typically used to encase other conductors because it is an inflexible and highly corrosive metal when exposed to air. It sees use in electrical contacts because, being a relatively soft metal, it deforms easily when tightened and makes a solid connection.
For example, the connectors for car batteries are typically made of lead. If different properties provided by alloying are required for additional hardness or strength, for example it is important to choose the alloy additions that do not significantly affect conductivity if that is also important.
Metals conduct electricity by allowing free electrons to move between the atoms. These electrons are not associated with a single atom or covalent bond. Since like charges repel each other, the movement of one free electron within the lattice dislodges those in the next atom, and the process repeats — moving in the direction of the current, toward the positively charged end. Thermal conductivity is similar to electrical in that exciting atoms in one section works to excite and vibrate adjacent atoms.
That motion or kinetic energy — not unlike rubbing your hands together to get warm — allows heat to move through the metal. Alloys, which are a combination of different metallic elements, tend to offer a lower level of thermal conductivity than pure metals.
Atoms of different size or atomic weight will vibrate at a different rate, which changes the pattern of thermal conductivity. If there is less energy transfer between atoms, there is less conductivity.
Pure silver and copper provide the highest thermal conductivity, with aluminum less so. A covalent bond is a bond that is formed when two atoms share electrons. Examples of compounds with covalent bonds are water , sugar and carbon dioxide. Ionic bonding is the complete transfer of valence electron s between a metal and non-metal. This results in two oppositely charged ions which attract each other. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion.
An example of an Ionic bond would be salt NaCl. Metallic bonding is the result the electrostatic attractive force that occurs between conduction electrons in the form of an electron cloud of delocalized electrons and positively charged metal ions. It may be described as the sharing of free electrons among a lattice of positively charged ions cations.
Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical resistivity and conductivity, opacity, and luster.
Metals contain free moving delocalized electrons. When electric voltage is applied, an electric field within the metal triggers the movement of the electrons, making them shift from one end to another end of the conductor. Electrons will move toward the positive side. Metal is a good conduction of heat.
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