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Dobereiner’s Triads (1817), |
When elements are arranged in increasing order of their
atomic masses with atomic of middle atom average of other two, they show
similarity in properties |
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Examples of Dobereiner’s Triads, 30 elements were Known |
(Lithium, Sodium, Pottasium), (Nitrogen, Phosphorus, Arsenic),
(Calcium, Strontium, Barium), (Chlorine , Bromine, Iodine) |
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Newlands Law of Octaves (1866), 56 elements were Known |
Arranged 56 elements in order of increasing atomic
masses from Hydrogen to Thorium. Found 8th element had similar properties
as the 1st |
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Drawback of Newlands law of Octaves |
It was applicable only up to Calcium, Worked well for
lighter elements |
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Mendeleev’s Periodic law, Gave in 1969 |
Properties of elements are periodic functions of atomic
masses |
|
Achievements of Mendeleevs Periodic table , 63 elements
were known |
Boldly predicted the discovery of new elements e,g
Scandium, gallium, germanium, When discovered, Nobel gases were placed in the
table without disturbing other elements |
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Limitations of Mendeleev’s PT |
Position of Hydrogen not certain, Isotopes could not be
explained |
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Modern Periodic Law by Henry Mosely, 1913 |
The properties of elements are periodic properties of
the atomic numbers |
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Modern PT |
Consists of 18 Groups and 7 Periods |
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Trends in Modern Periodic Table |
Atomic Size: Increases down the group and decreases
across the Period. Metallic Properties: Increases down the group and Increases
across the period. Valency: Remains same down the group, First increases
then decreases across the table. |
Ans: The Dobereiners classification were applicable to few elements only.
He could find three triads from the elements known at that time.
Ans: Newlands law of octaves were invalid after discovery of noble gases.
They were applicable up to calcium only and sometimes two different elements were placed in same slot.
Newlands also assumed there were only 56 elements in nature and no new elements will be discovered.
Ans: Mendeleev's periodic table was based on Mendeleevs periodic law.
It states that properties of elements are periodic functions of atomic masses.
Ans: Noble gases are very inert, they did not react to form oxides and hydrides.
Besides that they were discovered very late and could have disturbed the periodic table.
OR
What are the merits of modern periodic table?
Ans: Modern periodic table classified elements into various groups based on atomic number.
Isotopes of various elements were placed in same position.
The position of hydrogen was settled.
Ans: The elements which will show similar chemical reaction as magnesium are calcium & strontium.
This is because all of them have same valancy.
a. Three elements that have single electrons in outermost shell?
b. Two elements that have two electrons in outermost shell?
c. Three elements with filled outermost shell?
Ans:
A. Lithium , Sodium, Potassium are three of the elements that have single electron in their outermost shell.
B. Magnesium, Calcium, and Strontium are the three of the elements that have two electrons in their outermost shell.
C. Helium, Neon, and Argon are the three of the elements that have filled outermost shell.
Ans: Lithium, Sodium, Pottasium all belong to Group 1 in periodic table. They all have one electron in outermost shell.
When they react with water, they form hydroxides with liberation of hydrogen gas.
Ans: Helium and Neon are noble gases which also includes argon, krypton, xenon.
Their atoms have completely filled outermost shell. Hence, they are very unreactive.
Ans: In the modern periodic table, Lithium and Beryllium are the two elements among first ten which are metals.
Ga, Ge, As, Se, Be
Ans: The Metallic character decreases from left to right in period and increases down a group. Therefore, Beryllium and Gallium should be more metallic. However, Gallium is more metallic because of larger size.
Ans: By knowing the electronic configuation of an element, we can know the Period and group to which it belongs.
Sodium (Na), which has atomic number 11 and electronic configuration 2, 8, 1 belongs to Ist group and third period.
Ans: The electronic configuation of calcium is 2,8,8,2. It has valancy of 2.
The elements which have same valance will have similar physical and chemical properties. Therefore, among the atomic numbers given above, the element with atomic number 12 (Magnesium) and 38 (strontium) will have same properties as calcium.
Ans:
Ans: The mendeleevs periodic table has many limitations.
1. The position of hydrogen was doubtful
2. The existance of Isotopes could not be explained.
3. Cobalt was placed before Nickel.
Q. How
does the size of atom generally vary in going from left to right in a period of
the periodic table? Why does it vary this way?
Ans: As we
move from left to right across the period, atomic size decreases. Since the
number of protons and electrons increases and due to the large positive charges
in the nucleus, the electron is pulled closer the nucleus.
Objective Type Questions:
Q. The modern periodic table was prepared by:
A. Dobereiner B. Bohr C. Mendeleev D. Newlands
Ans: B. Bohr
Q. The newlands law of octaves for the classification of elements was found to be applicable only upto the element:
a. Potassium b. Calcium c. Cobalt d. Phosphorus
Ans: b. Calcium
Q. The noble gas having only two electrons in its valence shell is
a. Argon b. Neon c. Helium d. Krypton
Ans: c. Helium
Q. In Mendeleev’s periodic table, gap was not left for one of the following elements. This element is:
a. Gallium b. Beryllium c. Germanium d. Scandium
Ans: b. Beryllium
Q. The electrons present in the valance shell of a noble gas atom can be:
a. 8 only b. 2 only c. 8 or 4 d. 8 or 2
Ans: d. 8 or 2
Q. On moving from left to right in a period of periodic table, atomic number of elements increases. With the increase in atomic number along a period, the atomic size
A. Increases
B. Decreases
C. First increase then decrease
D. Remains same
Ans: B. Decreases
Q. On moving from left to right in a periodic table, the metallic character;
A. Increases
B. Decreases
C. First increase then decrease
D. Remains same
Ans: B. Decreases
Q. An element having electronic configuration 2, 8, 2 is a
A. Metal
B. Non metal
C. Metalloid
D. None
Ans: A. Metal
Q. On moving down the group, the atomic size:
A. Increases
B. Decreases
C. Remains same
D. None of these
Ans: A. Increases
Q. Which property among the following shows regular variation on moving down the group or along the period?
A. Atomic size
B. Valency
C. Metallic character
D All of the above
Ans: A. Atomic size
Q. Which element among the following has highest atomic radius
A. Sodium Na
B. Magnesium Mg
C. Pottasium K
D. Calcium Ca
Ans: D. Calcium Ca
Q. Which among the following gives correct increasing order of the atomic radii of O, F and N
A. O, F, N
B. N, F, O
C. O, N, F
D. F, O, N
Ans: D. F, O, N
Clarification: F is fluorine, O is oxygen, N is nitrogen.
Q. Write the arrangement of Alkali metals in decreasing order of metallic character.
Ans: Cesium is more metallic than Rubidium which is more metallic than Pottasium. Pottasium is more metallic than sodium which is more metallic than lithium.
Cs > Rb > K > Na > Li
Q. Which among the following is most electronegative element among following;
A. Fluorine B. Chlorine C. Bromine D. Iodine
Ans: A. Fluorine
Q. In moving down the group in a periodic table, the non metallic character of element,
A. Increases
B. Decreases
C. First increase then decrease
D. None of above
Ans: B. Decreases
Hint: Nonmetallic character decreases but metallic character increases.
Q. The repetition of properties of elements after certain regular intervals is called 'periodicity of properties'. According to modern periodic law, the periodicity in properties is due to periodicity in their:
A. Atomic masses
B. Atomic numbers
C. Electronic configuration of outer shell
D. Both A and B
Ans: B. Atomic numbers
Q. All the elements in particular group of modern periodic table show similar chemical properties. This similarity in properties in because :
A. They have similar number of shells
B. They have similar mass number
C. They have similar electronic configuration
D. They have similar atomic size
Ans: C. They have similar electronic configuration
Q. On moving from left to right of a periodic table, the atomic number increases and the number of shells
A. Also increase
B. Remains same
C. Decrease
D. First increase then decrease
Ans: B. Remains same
Q. When we go down the group in periodic table, there is gradual change in
A. Chemical properties only
B. Physical properties only
C. Both physical and chemical properties
D. None of these
Ans: B. Physical properties only
Clarification: Both Physical and chemical properties may change in certian groups.
Q. An element having the electronic configuration of 2, 8, 8, 18, 7 belongs to
A. Alkali metals
B. Chalcogens
C. Halogens
D. Noble gases
Ans: C. Halogens
Q. Which arrangement of metals among the following shows the increasing order of reactivity?
A. Gold < Pottasium < Copper < Aluminium
B. Pottasium < Aluminium < Copper < Gold
C. Copper < Gold < Aluminium < Pottasium
D. Gold < Copper < Aluminium < Pottasium
Ans: B. Pottasium < Aluminium < Copper < Gold
Q. Which of the following shows no corrosion?
a.) Iron b.) Copper
c.) Gold d.) None of these
Ans:- Gold
Q. During galvanisation, iron metal is given coating of the following metal. The metal is;
a.) Cr b.) Br c.) Zn d.) Cu
Ans:--- Zn
Q. Oxidation is a process in which a substance;
a.) Gains electrons
b.) Gains oxygen
c.) Loses electrons
d.) None of these.
Ans:- Loses electrons
Q. Cl2 + 2Kl ---------> 2KCl +l2 is;
a.) Combination reaction
b.) Decomposition reaction
c.) Double decomposition reaction
d.) Displacement reaction
Ans:---- Displacement reaction
Q. Name two elements you would expect to show same kind of chemical reactivity as magnesium.
Ans:--calcium and strontium.
Q. Name three elements that have only a single electron in their outermost shells.
Ans:-- Lithium, Sodium and Potassium.
Q. Name two elements that have two electrons in their outermost shells.
Ans:-- Magnesium and Calcium.
Q.. Name three elements with filled outermost shells.
Ans:-- Neon, Argon and Krypton.
Q. In the modern periodic table, of the first ten elements, which are metals?
Q. Element X forms a chloride with the formula XCl2, which is a solid. X would most likely be in the same group of the periodic table as;
a. Na b. Mg c. Al d. Si
Ans:--- Mg
Q. which element has 2 shells , both of which are completely filled with electrons?
Ans:--- Neon.
Q. which element has the electronic configuration 2,8,2?
Ans:---Magnesium.
Q. which element has a total of three shells, with four electrons in its valence shell?
Ans:-- Silicon
Q. which element has a total of two shells, with three electrons in its valence shell?
Ans:-- Boron.
Q. Which element has twice as many electrons in its second shell as in its first shell?
Ans:-- Carbon.
Q. What property do all elements in the same column of the periodic table like boron have in common?
Ans:--- All elements of this column have 3 electrons in their valence shell like Boron.
Q. An atom has electronic configuration 2,8,7.
a.) What is the atomic number of this element?
Ans:-- 17.
b.) To which of the following element would it be chemically similar?
N(7), F(9),P(15) , Ar(18)
Ans:-- F(9)(2,7)
Q. The inert gas among the following is;
a.) Ar b.) K c.) Ca d.) Cl
Ans:--- Ar.
Q. The law of Triads was given by;
a.) Newlands b.) Mendeleev
c.) Moseley d.) Dobereiner
Ans:--- Dobereiner.
Q. Modern periodic table has;
a.) 8 groups b.) 18 groups
c.) 7 groups d.) None of these.
Ans:--- 18 Groups.
Q. In Mendleeve's periodic table, the properties of elements are a periodic function of their;
a.) Atomic size b.) Atomic mass
c.) Ionisation energy d.) Atomic number
Ans:-- Atomic mass
Q. Number of periods in modern periodic table is;
a.) 5 b.) 6 c.) 7 d.) 8
Ans:--- 7
Q. Number of groups and periods present in modern periodic table are;
a.) 16, 7 b.) 6, 16 c.) 18,7 d.) 18,6
Ans:-- 18,7
Q. Which of the following is least reactive alkali metal?
a.) Li b.) K c.) Na d.) Rb
Ans:--- Li
Q. As we move down the group, the atomic size;
a.) Increases b.) decreases
c.) remains constant d.) None of these.
Ans:---- increases.
a.) 36 b.) 56 c.) 115 d.) 63
Ans:-- 63
Q. Modern periodic table was given by;
a.) Mendeleev b.) Moseley
c.) Newlands d.) None of these.
Ans:-- Moseley
Q. Mendeleev placed Iron in;
a.) Group 3 b.) Group 8
c.) Group 7 d.) Group 1
Ans:--- Group 8
Q. Halogens lie in the modern periodic table in;
a) Group 17 b.) Group 7
c.) Group 16 d.) Group 18
Ans:-- Group 17
Q. Modern periodic table is based upon;
a.)Modern periodic law
b.) Mendeleev's periodic law
c.) Atomic weight
d.) None
Ans:-- Modern Periodic law
Q. which among the following is the most reactive;
a.) potassium b.) sodium
c.) calcium d.) Magnesium
Ans:--- Sodium
Q. An atom of the element whose first shell is complete and has no other shell, the atom is;
a.)Sodium b.) Helium
c.) Chlorine d.) Hydrogen
Ans:-- Helium
Copper, Aluminium, Silver, Zinc, Iron
Ans:
1.Aluminium
2. Zinc
3. Iron
4. Copper
5. Silver
Q. Which of following metals will be displaced from the solution of its salts by other three?
A. Magnesium
B. Silver
C. Zinc
D. Copper
Ans: B. Silver
a. Increases b. Decreases
c. Same d. First increase then decreases
Ans: B. Decreases
Q. On moving down the group in a periodic table, metallic character of elements:
a. Increases b. Decreases
c. Same d. First increase then decreases
Ans: . A. Increases
Q. F, Cl, Br and I belong to halogen family. All of them are electronegative. Which among these has highest electronegativity?
A. Flourine B. Chlorine
C. Bromine D. Iodine
Ans: A. Flourine
Q. When we go down the group in a periodic table, a new shell of electrons is added at eaach succeeding element. So what happens to the valency of elements down the group?
A. Increases
B. Decreases
C. Increases then decreases
D. Remains same
Ans: D. Remains same
Q. When we go down the group in a periodic table,
A. Only physical properties show variation
B. Only chemical properties show variation
C. Both show variation
D. Properties remain same
Ans: C: Both show variation
Q. Which of the following classifications concentrated on the compounds formed by the elements with oxygen and hydrogen?
A. Dobereiner’s triads B. Newlands law of Octaves
C. Mendeleev’s PT D. Modern PT
Ans: Mendeleev’s PT
Q. Which among the following is considered as the limitation of Mendeleev’s periodic table?
A. Prediction of New Elements B. Correction of atomic masses
C. Position of isotopes D. Both A and B
Ans: C. Position of isotopes
Q. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the Modern Periodic table?
A. The elements become less metallic B. The number of valance electrons increases
C. The atoms loose electrons more easily D. The oxides become more acidic
Ans: C. The atoms loose electrons more easily
Q. Arrange the following elements in the order of their decreasing metallic character:
Sodium Na, Silicon Si, Chlorine Cl, Magnesium Mg, Aluminium Al.
Ans: Since Metallic character decreases from Left to Right, Therefore,
Sodium Na > Magnesium Mg > Aluminium Al > Silicon Si > Chlorine Cl.
