CHAPTER 5- THE PERIODIC TABLE

by • 14/07/2011 • 9th class ChemistryComments (6)1170

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.
properties:
(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.

Vacant Spaces

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.

 

Atomic Radius

Definition

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.

Unit

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)

Definition

The minimum energy needed to remove an electron from an isolated, gaseous atom in its ground state is called Ionization Energy.

Unit

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.

Electro negativity

Definition

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.

Electron Affinity

Definition

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.

Unit

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:

 

Periodic Table

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.

Group

The vertical column of elements in the periodic table are called Groups.

Period

The horizontal rows of elements in the periodic table are called Periods.

Periodicity

The repetition of physical and chemical properties of elements periodically is called Periodicity of Properties.

Periodic Law

Physical and chemical properties of elements are periodic function of their atomic masses.

Metal

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.

Non-Metals

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

Metalloids are semi metals have the properties which are intermediate between a metal and non-metal like Boron, Silicon, Germanium, Arsenic, Antimony etc.

Pin It

6 Responses to CHAPTER 5- THE PERIODIC TABLE

  1. oglaševanje na internetu says:

    Hey There. I found your weblog the use of msn. That is a very smartly written article. I’ll be sure to bookmark it and come back to read more of your helpful info. Thanks for the post. I’ll definitely comeback.

  2. iqra ashraf says:

    short answers plzz give us long definition

  3. iqra ashraf says:

    short answers

  4. billal khan says:

    modren periodic law kha ha

  5. irfan says:

    Kindly send me all notes of 9th class chemistry on
    irfan_196@hotmail.com

  6. ABDULLAH MAZHAR says:

    i want all revision exercises of class 9th. thanks.

Leave a Reply