FIRST LESSON

Question 1

FIVE SYMMETRY ELEMENTS

Answer 1

1. IDENTITY
2. PROPER AXIS OR ROTATIONAL AXIS OF SYMMETRY
3. PLANE OF SYMMETRY/ MIRROR PLANE
4. CENTER OF SYMMETRY/INVERSION CENTER
5. ROTOINVERSION

Question 2

• Corresponds to the operation of doing nothing to the object

Answer 2

identity

Question 2

Every object has ____

Answer 2

identity

Question 3

An object that requires rotation of a full 360 in order to restore it to its original appearance has no rotational
symmetry

Answer 3

 1- FOLD ROTATION AXIS

Question 3

An imaginary line passing through the center of mass around which a rotation by 360°/n leaves an object in an orientation indistinguishable from the original.

Answer 3

PROPER AXIS OR ROTATIONAL AXIS OF SYMMETRY

Question 3

If an object appears identical after a rotation of 180” that is twice in a 360 rotation,

Answer 3

 2- FOLD ROTATION AXIS

Question 4

TWO PLANE OF SYMMETRY/ MIRROR PLANE

Answer 4

RECTANGULAR PLANE OF SYMMETRY
DIAGONAL PLANE OF SYMMETRY

Question 4

Objects that repeat themselves upon rotation of 120

Answer 4

 3- FOLD ROTATION AXIS

Question 4

If rotation of 60 deg about an axis causes the object to repeat itself

Answer 4

 6- FOLD ROTATION AXIS

Question 5

If an object repeats itself after 90 deg of rotation

Answer 5

 4- FOLD ROTATION AXIS

Question 6

An imaginary plane divides the crystal in two parts in such a way that one part is mirror of the other, the crystal is saidnto have a

Answer 6

PLANE OF SYMMETRY/ MIRROR PLANE

Question 6

axis is the same as a center of symmetry.

Answer 6

 1- FOLD ROTOINVERSION

Question 7

is such a point that any line drawn through it touches the surface of crystal at equal distance in both directions.

Answer 7

CENTER OF SYMMETRY/INVERSION CENTER

Question 8

A combination of rotation with a center of inversion.

Answer 8

ROTOINVERSION

Question 9

involves first rotating the object by 180°then inverting it through an inversion center.

Answer 9

 2- FOLD ROTOINVERSION

Question 10

This involves rotating the object by 120°(360/120), and inverting through a center.

Answer 10

 3-FOLD ROTOINVERSION

Question 11

This involves rotation of the object by 90°then inverting. through a center

Answer 11

 4- FOLD ROTOINVERSION

Question 11

_____ axis involves rotating the object by 60 and inverting through a center.

Answer 11

6-fold rotoinversion

Question 12

is a set of axes. In other words, the structure is an ordered array of atoms, ions or molecules

Answer 12

CRYSTAL SYSTEM

Question 13

Two of the three axes are equal in length and all three axes are perpendicular to one another.

Answer 13

2. TETRAGONAL

Question 13

is obtained by attaching atoms, groups of atoms or molecules. This structure occurs from the intrinsic nature of the constituent particles to produce symmetric patterns.

Answer 13

Crystal Structure

Question 14

All three axes are unequal in length and all are perpendicular to one another

Answer 14

3. ORTHORHOMBIC

Question 14

7 SEVEN PRIMITIVE CRYSTAL SYSTEM

Answer 14

1. ISOMETRIC (CUBIC)
2. TETRAGONAL
3. ORTHORHOMBIC
4. HEXAGONAL
5. TRICLINIC
6. MONOCLINIC
7. RHOMBOHEDRAL (TRIGONAL)

Question 15

All three axes are equal in length and all are perpendicular to one another

Answer 15

1. ISOMETRIC (CUBIC)

Question 15

Of four axes three are equal in length, are separated by equal angles and lie in the same plane. The fourth axis is perpendicular to the plane of the other three axes.________ cells have lattice points in each of the two six-sided faces.

Answer 15

4. HEXAGONAL

Question 15

All three axes are unequal in length and none is perpendicular to another.

Answer 15

5. TRICLINIC

Question 15

three axes are unequal in length and two axes are perpendicular to each other

Answer 15

6. MONOCLINIC

Question 15

All three axes are of equal length and none of the axes is perpendicular to another but the crystal faces all have the same size and shape.

Answer 15

7. RHOMBOHEDRAL (TRIGONAL)

Question 15

Importance of Crystallography in Engineering

Answer 15

* Crystallography is useful in phase identification. * When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition. structure and proportions will influence the material's properties.