The strength of metals suggests that these atoms are held together by strong bonds. These bonds must also allow atoms to move; otherwise how could metals be hammered into sheets or drawn into wires? A reasonable model would be one in which atoms are held together by strong, but delocalized, bonds.
Bonding Such bonds could be formed between metal atoms that have low electronegativities and do not attract their valence electrons strongly. This would allow the outermost electrons to be shared by all the surrounding atoms, resulting in positive ions cations surrounded by a sea of electrons sometimes referred to as an electron cloud. Figure 1: Metallic Bonding. Because these valence electrons are shared by all the atoms, they are not considered to be associated with any one atom.
This is very different from ionic or covalent bonds, where electrons are held by one or two atoms. The metallic bond is therefore strong and uniform. Since electrons are attracted to many atoms, they have considerable mobility that allows for the good heat and electrical conductivity seen in metals. Above their melting point, metals are liquids, and their atoms are randomly arranged and relatively free to move. However, when cooled below their melting point, metals rearrange to form ordered, crystalline structures.
Figure 2: Arrangement of atoms in a liquid and a solid. Crystals To form the strongest metallic bonds, metals are packed together as closely as possible. Standard Search Advanced Search. Limit to results with full text. Select All Expand All. Collapse All. Citation Export Print. Javascript must be enabled for narrowing. Results 1 - 1 of 1. Search took: 0. Similarity and difference between fcc, bcc and hcp metals from the view point of point defect cluster formation.
The coordination number of this structure is 2, while the number of atoms per unit cell is 6. Here, HCP layers cycle among two layers. That means; the third layer of the structure is similar to the first layer.
FCC is a face-centred cubic close packing structure of lattices while HCP is hexagonal close packing structure of lattices. Aluminium, copper, gold, lead, silver, platinum, etc. In summary, FCC is a face-centred cubic close packing structure of lattices and HCP is hexagonal close packing structure of lattices.
The unit cell of the FCC has spheres in each corner of a cube and also in the centre of each cubic face. Then the unit cell of FCC has 12 spheres. Overview and Key Difference 2. What is BCC 3. What is FCC 4. The term BCC stands for the body-centred cubic arrangement of spheres atoms, molecule or ions from which the lattice is made of. In this arrangement, the spheres are located in each corner of a cube and one sphere in the middle of the cube. A unit cell of a lattice is the smallest unit that resembles the whole structure of the lattice.
Since a cube has 8 corners, there is a total of 9 spheres in a BCC structure eight in the corners plus on in the middle. However, each sphere in the corner of the unit cell of BCC is a member of the neighbouring unit cell. That is because the lattice is made of many unit cells packed together. Since there are 8 spheres in a unit cell which are the corners of other unit cells, the coordination number of the BCC structure is known to be 8.
The eight corners together form one sphere, and there is one sphere in the middle, together with results in two spheres.
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