Q1: Write down the general characteristic group of IA, VIIA and VIIIA?
Ans:Group IA(ALKALI METAL): The alkali metals lithium, sodium, potassium, rubidium, cesium and francium are light metal. They are very reactive and chemically are strongly electropositively.As the group is descending there is a gradual decrease in ionization potential with an increase in the size of the atom. They contain one electron in their outer most shell and form ionic bonds by loss of valence electron. Compound of these metal were obtained from wood ashes.
Group VIIA(HALOGEN FAMILY):-Fluorine, chlorine, bromine and iodine constitute a group or family of element called the halogen, a term which means “salt forms”. The halogen are very active non-metal and are very much a like in their chemical properties. Each of the halogen has seven valence electron. Halogen are highly electronegative element and their electro negatively decrease down the group.Flourine and chlorine are gases at ordinary temperature bromine is a liquid and iodine is a solid. all the halogen exit as diatomic molecule.
Group VIIIA(NOBLE GASES):-The element of group VIIIA are called “noble gases” or “inert gases” or “zero gases” element. They are monatomic and low boiling gases. Since the outermost shell of these element are complete therefore these element are mostly chemically unreactive.All the noble gases except radon are normally present in the atmosphere. They are mostly obtained from air by liquefaction process.
Q2) What are transition element write four properties of them?
Ans: Transition element: Element of group IB, IIB, through VIIB are known as transition element. They include the element scandium, yttrium, thanum and actinium and the two rare-earth series of element the lanthanide and actinide series.
(1) These element have incomplete inner electron shell.
(2) All transition element are metal.
(3) The bond between the atom are very strong and they have melting points.
(4) These compound are formed by coordinate covalent bond.
Q3)Define and explain Mendeleyv’s Period Table and Periodic Law also discuss the Defects in Mendeleyv’s Periodic Table
Ans: Mendeleyv’s Period Table and Periodic Law
Russian Chemist, Mendeleyv’s (186) who was working separately from Lother Mayer published a table of elements.
According to Mendeleyv’s when the element were arranged in order of their increasing atomic masses, the elements with similar properties were repeated after regular interval and were placed one above the other. A table obtained in this manner is called Periodic Table. Mendeleyv’s stated this periodicity in the form of Periodic Law.
Important Features of Mendeleyv’s Periodic Table
The important features of Mendeleyv’s Periodic table are:
Periods and Groups
The horizontal rows which run from left to right in Periodic Table are called Periods and they are twelve in number.
The vertical rows which run from top to bottom in periodic table are called groups and they are eight in number.
Mendeleyv’s left many vacant spaces for the still unknown elements. For example, next to Calcium (40) should be Titanium (48) but it resembled silicon (28) instead of Aluminum (27). He left vacant space for element with atomic mass 44.
Discovery of New Element
Mendeleyv’s discovered new elements and also guessed their atomic mass and properties.
Atomic Mass Correction
Mendeleyv’s corrected the atomic masses of certain elements on basis of their properties and provided proper place to them in the periodic table.
Defects in Mendeleyv’s Periodic Table
The Mendeleyv’s Period Table has following defects:
Irregular Position of Some Elements
According to Mendeleyv’s Periodic Law Potassium (39) should be placed before Argon (40) but he placed Argon (40) before Potassium (39) which goes against his law.
Position of Isotopes
Mendeleyv’s periodic table gives no indication about the position of isotopes.
Structure of Atom
Mendeleyv’s Periodic table gives no idea about structure of atoms.
Position of Lanthanides and Actinides
Lanthanides and Actinides have not been given proper place in Periodic Table.
Coinage and Alkali Metals
Alkali metals and coinage metals with different properties are placed in the same group. This defect has been replaced by placing them into two sub groups.
Q4)Define the following with its unit,factors,tends or variation in groups and periods.
One half of the distance between the nucleus of two identical atoms when these are in close contact with each other is called Atomic Radius.
It is measured in angstrom unit A.
Trend in Period
The atomic radii decreases from left to right within a period in the periodic table. This is because nuclear charge increases with the increase of atomic number. But the number of shells remains same within a period.
Trend in Group
Atomic radius increases from top to bottom in a group. This is because, although nuclear charge increases from top to bottom but at the same time on new shell is also added for each successive element down the group.
Ionization Energy (I.E) or Ionization Potential (I.P)
The minimum energy needed to remove an electron from an isolated, gaseous atom in its ground state is called Ionization Energy.
It is expressed in electron volts or kilo-joules per mole.
1 ev = 96.49kj
Factors Affecting Ionization Energy
The ionization energy of elements depends upon the following factors:
1. Effect of Nuclear Charge on I.E
The greater the nuclear charge the higher is the ionization energy.
2. Effect of Atomic Size
The larger the size of atom the lower is the ionization energy.
Trend of I.E in Period
Ionization energy increases from left to right in a period due to increase in nuclear change and decrease in atomic size.
Trend of I.E in Group
I.E decreases from top to bottom in a group due to increase in atomic size.
The tendency of each atom in a covalent molecule to attract a shared pair of electrons towards itself is known as its electro negativity.
Factors Affecting Electro negativity
Electro negativity depends upon the following factors:
- Atomic size
- Atomic Number
- Electron Affinity
- Ionization Energy
Trend or Variation in the Period
Electro negativity increases from left to right within a period due to increase in nuclear charge and decrease in atomic size.
Trend or Variation in the Group
Electro negativity values decreases from top to bottom within a group due to increase in atomic size.
The energy change that occurs when an electron is gained by an atom in the gaseous state is known as Electron Affinity.
Electron Affinity for the addition of first electron is negative i.e. energy is released but for further addition of electrons it is positive because energy has to be added to over come repulsion between negative ion and electron.
It is measured in KJ/mol or in e.v per atom.
Factors Affecting Electron Affinity
- Atomic Size
- Nuclear Charge
Tend or Variation of Electron Affinity in Group
Down the group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.
Trend or Variation of Electron Affinity in Period
In a period, the electron affinity increases from left to right because the incoming successive atoms have higher nuclear charge and attract electron more towards itself.
Q5)Define the following:
A table of elements obtained by arranging them in order of their increasing atomic number in which elements having similar properties are placed in the same group is called Periodic Table.
The vertical column of elements in the periodic table are called Groups.
The horizontal rows of elements in the periodic table are called Periods.
The repetition of physical and chemical properties of elements periodically is called Periodicity of Properties.
Physical and chemical properties of elements are periodic function of their atomic masses.
Elements which are good conductors of heat and electricity are malleable and ductile and have a metallic luster are called Metals like Sodium, Potassium, Gold, Copper etc.
Elements which are non or bad conductor of heat and electricity are neither malleable or ductile and have no metallic luster are called Non-Metals like Carbon, Nitrogen, Chlorine etc.
Metalloids are semi metals have the properties which are intermediate between a metal and non-metal like Boron, Silicon, Germanium, Arsenic, Antimony etc.