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Thursday 18 October 2012

SHORT QUESTIONS CHEMISTRY 9TH


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Periodic table & periodicity of properties
Short Questions:

1.                 Dobereiner’s law of traids:
Dobereiner arranged elements in groups of three.
2.                 Newlands Law of octaves:
Newlands arranged elements in groups of eight.
3.                 Mendleeve’s periodic table:
Mendleeve was the first who arranged elements into groups and periods.The arrangements of elements in order of their increasing atomic masses in such a way that properties of elements are periodic functions of their atomic masses.
4.                 Limitations Mendleeve’s periodic table:
  1. position of isotopes
  2. wrong order of atomic masses of some elements.
5.                 Modern periodic table:
The arrangements of elements in order of their increasing atomic numbers
 in such a way that properties of elements are periodic functions of their atomic numbers.
6.                 Modern periodic law:
Properties of elements are periodic functions of their atomic numbers
7.                 Periods:
The 7 horizental rows of elements in periodic table are called periods.
8.                 short period:
 First period has 2 elements is called short period.
9.                 normal periods:
Second and third periods have 8 elements are called normal periods.
10.            long periods:
Fourth and fifth periods have 18 elements are called long periods.
11.            Very long periods:
Sixth period has 32 elements and Seven period is incomplete are called very long periods.
12.            Lanthanides
Elements with atomic numbers 57 to 71 follow Lanthanum in 6th period  are called Lanthanides
13.            Actinides.
Elements with atomic numbers 89 to 103 follow Actinium in 7th period  are called Actinides.
14.              Groups.
The 8 vertical  columns of elements in periodic table are called Groups.
And on the basis of similar electronic configurations, elements are classified into 4 Blocks;
15.             “s” block elements:
Elements of group 1 and 2 have valence electron in s sub shell are called s block elements.
16.            “P” block elements:
Elements of group 13 and 18 have valence electron in p sub shell are called p block elements.
17.            “D” block elements:
Elements lies between s and p blocks have valence electron in d sub shell are called d block elements.
18.            “F” block elements:
Elements lies at the bottom of periodic table have valence electron in f sub shell are called f block elements.
19.            Transition elements:
The d block elements and f block elements are also called transition elements.
20.            Atomic Size or radius:
The distance between centre of nucleus to valence electrons is called Atomic Size or radius.
21.            Shielding Effect:
The decrease in attractive force between nucleus and valence electrons due to increasing number of shells or shell electrons is called Shielding Effect.
22.            ionization energy:
The amount of energy required when an electron is removed from outermost shell of an isolated gaseous atom is called ionization energy. Its unit is KJ per mole
23.            electron affinity:
The amount of energy released when an electron is added to outermost shell of an isolated gaseous atom is called electron affinity.Its unit is KJ per mole.
24.            Eletronegativity:
The relative tendency of an atom to attract shared paired of electrons to itself is called eletronegativity.
   MCQS ANSWERS:   s  1.b,2.d,3.b,4.b,5.c,6.d,7.a,8.b,9.c,10.c

                STRUCTURE OF MOLECULES
Short questions;

1.    Duplet rule
Attaining 2 electronic configuration of outermost shell either by sharing,by losing or giving electrons.
2.    Octate rule
Attaining 8 electronic configuration of outermost shell either by sharing,by losing or giving electrons.
3.    Chemical Bond
" the force of attraction between two atoms or ions that hold them together in a unit is called Chemical Bond".sThere are three types of chemical bonds:
    Ionic bond or Electrovalent bond
    Covalent bond
    Coordinate Covalent bond
4.    IONIC BOND OR ELECTROVALENT BOND    
   Chemical bond formed due to transfer of electrons from one atom to the other is called "Ionic bond" or "electrovalent bond".

5.    COVALENT BOND         
Chemical bond formed by the mutual sharing of electrons between two atoms is called Covalent bond.  It is represented by a short line (- ).
TYPES OF COVALENT BOND 
6.    SINGLE COVALENT BOND   
  A covalent bond formed by the mutual sharing of one electron pair is called a "Single   Covalent bond."It is represented by single short line(_ )
  Examples:
7.    DOUBLE COVALENT BOND 
  A covalent bond formed by the mutual sharing of two electron pairs is called a "double covalent bond". It is represented by double short line (= )
 
  Examples:


8.    TRIPLE COVALENT BOND    
  A covalent bond formed by the mutual sharing of three electron pairs is called a "Triple covalent bond". It is represented by triple short line (  ).
  Examples:



9.    POLAR COVALENT BOND    
  A covalent bond formed between two different atoms is known as Polar covalent bond.
  Examples:

 when a Covalent bond is formed between H and Cl , it is polar in nature because Cl is more   electronegative than H atom and attracts electron pair towards itself with greater force.

10.           NON-POLAR COVALENT BOND
  A covalent bond formed between two like atoms is called Non-polar bond.
 Examples:
H - H
Cl - Cl
F – F
The difference of  electro negativity is zero therefore both atoms attract electron pair equally  and the whole molecule becomes neutral.

11.           COORDINATE COVALENT BOND      
".
The type of chemical bond in which one atom provides shared pair of electron for bond formation is called "Coordinate Covalent Bond".
The atom that provides electron pair is called "Donor".The other which takes it is called "Acceptor".
It is represented by an arrow (è ), pointing from donor atom to the acceptor.
Examples:
Ammonium ion , Hydronium ion



12.           lone pair
A pair of electrons that is not involved in a chemical bond
13.           Bond pair
A shared pair of electrons

Ionic Compound

  1. Crystalline solids (made of ions)
  2. High melting and boiling points
  3. Conduct electricity when melted
  4. Many soluble in water but not in nonpolar liquid

Covalent Compounds

  1. Gases, liquids, or solids (made of molecules)
  2. Low melting and boiling points
  3. Poor electrical conductors in all phases
  4. Many soluble in nonpolar liquids but not in water

14.           Metallic bond
   Chemical bond formed between metals due to free electrons.
15.           Intermolecular forces
The forces of attraction present between the molecules are called intermolecular forces.

These are of following types: -
      16.  Dipole-Dipole Forces The forces of attraction, which appears due to the difference in electro negativities of
the bonded atoms in polar molecules.
    17.  Hydrogen bonding
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine.


Physical state of matter
Short Questions
1.    Properties of Gas
1. It has no definite shape.
2. It has no definite volume, so it can be compressed or expanded.
3. The molecules of one gas can diffuse easily into the molecules of other gas.
4. The molecules of a gas are in continuous motion.
2.    Properties of Liquids
1. A liquid has no definite shape.
2. It has a fixed volume.
3. The diffusion of a liquid into the other liquid is possible if both of the liquids are polar or non-polar.
4. It can be compressed to a negligible.
3.    Properties of Solids
1. A solid has a definite shape.
2. It has a fixed volume.
3. The rate of diffusion of solid with is very slow.
4. It cannot be compressed easily.

4.      Diffusion.
The movement of molecules from a higher concentration to a lower concentration is called Diffusion. The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread throughout the room.
5.    Effusion
Movement of gas molecules through a small opening.
6.    PRESSURE
Force per unit area is called PRESSURE.
P = F/A
1 atmosphere = 760 torr or mm of Hg
The pressure exerted by gas is due to the collision of its molecules with one another and  the walls of the container.
7.    Melting point
The temperature at which the solid is converted to liquid on heating is called melting point.

8.    Boiling Point
The temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure is called boiling point.

9.    Freezing Points
The temperature at which the liquid changes state from a liquid to a solid. 

10. Evaporation
Conversion of liquid into its vapours at any temperature is called evaporation.
11.                 Vapour Pressre
The pressure exerted by the vapours of a liquid in its equilibrium state with the pure liquid at a given temperature is called vapour pressure.
12.                 Boyle’s Law
The volume of the gas is inversely proportional to its pressure at constant temperature.
Mathematically it may be written as
V ∞ 1 / P
V = K / P
PV = K
Boyle’s law can also be stated as
The product of the pressure and volume of a given mass of a gas is always constant at constant temperature.
P1V1 = P2V2
13.                 Charle’s Law
 The volume of the gas is directly proportional to its absolute temperature at constant pressure.
 Mathematically it may be written as
V ∞ T
V = K T
V / T = K
14.                 Absolute zero
The temperature at which the volume of an ideal gas becomes zero equal to -273.15°C.
TYPES OF SOLIDS
15.                  CRYSTALLINE SOLIDS
1. They have geometrical shape.
2. They have highly ordered three-dimensional arrangements of particles.
3. They have sharp melting and boiling points.
Examples:
Diamond, Graphite, NaCl, Sugar etc
16. AMORPHOUS SOLIDS
2. They do not have highly ordered three-dimensional arrangements of particles.
3. They don’t have sharp melting points.                                                                                                                     
 Examples:
Coal, Coke, Glass, Plastic, rubber etc
 17.       Allotropy or allotropism is the property of some solids to exist in two or more different forms.
Allotropes of carbon: a) Diamond, b) Graphite,c) buckyball
Transition temperature is the temperature at which a allotrope changes into another allotrope.  For example, when rhombic sulfur is heated above 96°C it changes into monoclinic sulfur. When cooled below 96°C it changes into rhombic sulfur.
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