Engr 54 Atomic Bonding, Metallic Crystal Structures, And Crystallographic Direction

Front 1

What are valence electrons?

Back 1

These electron occupy the outermost filled shell and determine chemical, electrical, thermal and optical properties of solids.

Front 2

electron configuration

Back 2

How are elements classified?

Front 3

column

Back 3

Elements in the same _______ have similar properties.

Front 4

What are electropositive elements?

Back 4

These elements give up an electron to complete an outer shell, are usually metallic and form positive ions (cations.)

Front 5

What are electronegative elements?

Back 5

These elements accept an electron to complete an outer shell, are usually non-metallic and form negative ions (anions.)

Front 6

What are effects of chemical bonding?

Back 6

These effects are a decrease in energy state and more stability.

Front 7

What is an ionic bond?

Back 7

This bond occurs by electron transfer between electronegative and electropostive elements (NaCl, CsCl, MgO.) Its energy is high, and it is nondirectionl (ceramics.)

Front 8

What is a covalent bond?

Back 8

This bond occurs when electrons are shared between close elements on the periodic table (SiC, C.) Its energy is variable , and it is direction (semiconductors, ceramics, polymer chains.)

Front 9

What is a metallic bond?

Back 9

In this bond valence electrons drift throughout the material (Cu, Al, Fe.) Its bond energy is variable, and it is nondirectional.

Front 10

What is a van der Waal bond?

Back 10

This bond occurs from coulombic attraction of dipoles (dipole = separation of opposite charge) and is much weaker than other bonds (noble gases, bonds between polymeric chains.) It is directional.

Front 11

What are properties related to bonding?

Back 11

These properties are melting temperature, coefficient of thermal expansion and elastic modulus.

Front 12

What are ceramics?

Back 12

These materials are covalently or ionically bonded with large energies and have large metling temperatures, large elastic molduli and small coefficients of thermal expansion.

Front 13

What are metals?

Back 13

These materials have variable bond energies and moderate melting temperatures, eleastic moduli and coefficents of expansion.

Front 14

What are polymers?

Back 14

These materials have covalent and secondary bonds. They have directions properties. Their secondary bonding dominates. They have small melting temperatures, small elastic moduli and large coefficients of thermal expansion.

Front 15

What is a crystal structure?

Back 15

This structure is a 3D periodic arrangement of atoms of its smallest repeating unit.

Front 16

What are the most common crystal structures?

Back 16

These structures are cubic and hexagonal.

Front 17

What is a simple cubic structure?

Back 17

This structure has one atom per unit cell, a lattice perimeter of length 2r and a coordination number of six and an APF of .52.

Front 18

What is a coordination number?

Back 18

This number used as a crystal structure characteristic is the number of nearest neighbors of an atom.

Front 19

What is the atomic packing factor (APF?)

Back 19

This number is the volume of atoms in a unit cell divided by the total volume of the unit cell

Front 20

What is a body centered cubic structure?

Back 20

This structure has two atom per unit cell, a coordination number of 8, and a lattice parameter of 4r/root3 and an APF of .68.

Front 21

What is a face centered cubic structure?

Back 21

This structure has four atoms per unit cell, a coordination number of 12, a lattice parameter of 4r/root2 and an APF of .74 (highest.)

Front 22

What is a hexagonal close packed structure?

Back 22

This structure six atoms per unit cell, a coordination number of 12, two lattice parameters a and c with a=2r, and an APF of .74.

Front 23

What is polymorphism (allotropy?)

Back 23

This characteristic is having two or possible more crystal for the same material. (Ti, C)

Front 24

What is true density (ro?)

Back 24

This number is the total atomic weight per unit cell volume.

Front 25

What is a crystallographic direction?

Back 25

This direction is a vector within a unit cell reduced to its smallest integers. [u v w]

Front 26

What is an anisotropic behavior?

Back 26

Single crystals of some materials exhibit this behavior that makes their physical properties dependent on direction.

Front 27

What isotropic behavior?

Back 27

This behavior is independent of direction.

Front 28

What is a family of directions?

Back 28

These directions are equivalent.