When the crystalline structure of a material changes from body centered cubic to
ID: 479037 • Letter: W
Question
When the crystalline structure of a material changes from body centered cubic to hexagonal close-packed (and temperature remains about the same) one expects the density to increase ____In the metallic bond electrons are shared only with nearby atoms. ____Say a bacterium has a length of about 1µm. This length is equivalent to that of about 3,000 atoms in a row. ____Stone can handle tensile stresses very well, but it fails easily under compression. ____Atomic arrangement is important for the materials properties of small objects (e.g. a microchip) but not for the properties of km-long steel components. ____In an ionic bond the atoms are held together mainly by electrostatic attraction. ____Steel conducts electricity because ions move easily through the material. ____Tungsten (W) melts at a higher temperature than Aluminum (Al). ____A stronger interatomic bond usually leads to a higher melting temperature. ____The strength-to-weight ratio measures the ability of a material to support a weight hanging from a 1 in^2 bar made out of that material. ____At the equilibrium distance, the net force between atoms is highest. ____At the equilibrium distance, the bond interaction energy is at a minimum. ____Bond energy may be determined by measuring how much heat it takes to evaporate a known amount of the solid made up of atoms held together by that bond. ____The larger the unit cell of a crystal, the larger the density of the crystallized material. ____Ceramic materials are those made by any combination of two or more different metalsExplanation / Answer
1) true : density = mass / volume when crystals changes from BCC to FCC number of atoms increases from 5 to6 per unit cell so mass increases but volume of unit cell remains same hence density increases.
2) False : in matallic bond electrons are free to move over the entire crysstal.
3) True : atoms have size of nanometer.
4) true : stone can handle tensile strength very well but because of brittle natuer it fails under compression
5) False : The arrangement of atoms in crystal decides its proprties like density, melting point etc The property of small object or long steel is affecterd by arraangement of atoms in it.
6) False : Ionic bond is formed by positive and negative ions held together by strong electrostaatic force of attraction and not atoms.
7) False: steel conducts electricity due to freee movement of electrons and not ions.
8) True : tungsten forms sstrong metallic bond when compare to alluminum because of more number of valence electron in outer shell which contribute to metallic bonding.
9) True : For a compound to melt the interatomic bond must break and molecules must become free to move, a stronger interatomic bond means more energy required to break the bond and hence higher melting point.
10) True : strength to weight ratio is the ability of matrial to support the weight.
11) True : at equillibrium distance the net force is more, as attractive force balances the repulsive force betweeen the atoms.
12) False : Evaporation involves the breaking of vander-walls force of attraction of between the molecules and not bond.
13) True : evaporation of atoms involves breaking of bond between atoms.
14) False : density = mass / volume, larger unit cell has larger volume hence density dcrease.
15) false : ceramic is made up of clay and not metal.
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