# KSEEB Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

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## Karnataka State Syllabus Class 10 Science Chapter 5 Periodic Classification of Elements

### KSEEB Class 10 Science Periodic Classification of Elements Intext Questions and Answers

Question 1.
Did Dobereiner’s triads also exist in the columns of New lands octaves? Compare and find out?
Dobereiner’s triads were also found in Newland’s octaves.
Ex: Li, Na, K.

Question 2.
What were the limitations of Dobereiner’s classification?
Dobereiner’s could form only three triads from the elements known at that time.

Question 3.
What were the limitations of New lands law of octaves?

• The law of octaves was applicable only up to calcium as after calcium every eighth element did not passes properties similar to that of the first.
• New lands assumed that only 56 elements existed is nature and no more elements were discovered in the future. After some time, several new elements were discovered, properties did not fit into the law of octaves.
• New lands adjusted two elements in the same slot – But also put some unlike elements undue the same slot – But also put some unlike elements under the same slot.

Question 4.
Use mendeleevs periodic table to predict the formulae for the oxides of the following
elements K,C,H Si, Ba.
K2O, CO2>Al2O, SiO2, BaO

Question 5.
Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table?
Scandium and Germanium.

Question 6.
What were the criteria used by Mendeleev in creating his periodic table?
Mendeleev used the relationship between the atomic masses of the elements and their physical and chemical properties. Among chemical properties, he examined the compound formed by elements with oxygen and hydrogen. He found that if the 63 elements known at that time were arranged in the increasing order of their atomic masses, the properties of elements and also formulae of their oxides and hydrides gradually changed from element to element and at a certain interval they suddenly started almost repealing relationship was expressed by Mendeleev’s periodic law. i,e the properties of examinants are the periodic functions of their atomic masses.

Question 7.
Why do you think the noble gases are placed in a separate group?
Noble gases like helium (He), neon (Ne) and argon (Ar) etc are chemically inert and are present in atmosphere in extremely low concentration. Thus owing to their similar inert behaviour and similar electronic configuration, they are justified to be placed in a separate group.

Question 8.
How could the modern periodic table remove various anomalities of Mendeleevs periodic table?
Because of placement of elements in increasing atomic masses in Mendeleev’s periodic table, certain chemically similar elements were separated and, chemically dissimilar elements were to be grouped together.

As the modem law is based on atomic no. or no. of electors, elements with similar valence electrons fall in the same group. Since the chemical properties of elements depend on their valence electrons, anomalies in the Mendeleevs table are automatically removed. Further placement of hydrogen with alkali metals is now justified on the basis of its electric configuration.

Question 9.
Name two elements you would expect to show chemical reactions similar to magnesium? What is the basic of your choice?
Beryllium (Be) and calcium (Ca) Basis of choice: Both Be and Ca have electronic configuration similar to magnesium.

Question 10.
Name

i. Three elements that have a single electron is their outermost shells?
Lithium, sodium, potassium

ii. Two elements that have two electrons in their outer most shells?
Beryllium, magnesium

iii. Three elements with filled outermost shells
Helium, neon, Argon.

Question 11.
a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas is there any similarity in the atoms of these elements?
All these metals have one electron in their respective outermost shells.

b) Helium is an uncreative gas and neon is a gas of extremely low reactivity. What if anything do their atoms have in common?
The outermost shells of the atoms of helium and neon are completely filled with electrons.

Question 12.
In the modern periodic table, which metals are first ten elements?
The first ten elements are – H, He, Li, Be, B, C, N, 0, F, Ne. Among these only . two elements Li and Be are metals.

Question 13.
By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
Ga, Ge, As, Se, Be
Maximum metallic characteristic is found in elements on the extreme left side of the periodic table, out of the above given elements beryllium ( Be) will have the maximum metallic characteristic because it is on the extreme left side is the periodic table (Group 2).

### KSEEB Class 10 science Periodic Classification of Elements Textbook Exercise Questions and Answers

Question 1.
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
(c) The atoms lose their electrons more easily.

Question 2.
Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na
(b) Mg
(c) Al
(d) Si
(b) Mg

Question 3.
Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2,8,2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?
(a) Ne (2, 8)
(b) Mg (2, 8, 2)
(c) Si (2, 8, 4)
(d) B (2, 3)
(e) C (2,4)

Question 4.
(a) What property do all elements in the same column of the Periodic Table as boron have in colmmon?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in, common
(a) Elements in the same column or, group as boron have valence of three and are metalloids or semi metals
(b) Elements in the same column or group as flourine form acidic oxides and have seven electrons in their outer most shells.

Question 5.
An atom has electronic configuration 2,8,7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar?
(Atomic numbers are given in parentheses.)
N(7)       F(9)       P(15) Ar(18)
(a) 17
(b) F (9)

Question 6.
The position of three elements A, B and C in the Periodic Table are shown below

(a) State whether A is a metal or non­metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
(a) A is a non-metal.
(b) C is less reactive than A.
(c) C is smaller in size than B.
(d) A will form anion.

Question 7.
Nitrogen (atomic number 7) and phosphorous (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
N = 2, 5
P = 2,8,5
Nitrogen will be more electro negative because outer most shell is nearer to nucleus and thus nucleus will attract electrons more strongly.

Question 8.
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
The position of the element in the periodic table is related to the number of electrons in the outer most shell. In a given column or group all elements have the same number of electrons in their outer most shells.

Question 9.
In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?Answer:
Atomic number 12 = 2, 8, 2
Atomic number 20 = 2, 8, 8, 2
Atomic Number 19 = 2,8, 8, 1
Atomic number 21 = 2, 8, 9, 2
Atomic number 38 = 2, 8, 18, 8, 2
Calcium will have similar physical and chemical properties as element with atomic numbers 12 and 38.

Question 10.
Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table

 Mendeleev’s periodic table Modern periodic table 1) Elements are arranged in the order of increasing atomic masses. 1) Elements are arranged in the order of increasing atomic numbers. 2) There are nine vertical columns called groups. 2) There are 18  vertical columns called groups. 3) Transition elements are arbitrarily placed together in group VIII. 3) Transition elements fit in the middle of long periods.

Fill in the blanks:

Question 1.
The atomic radius of nitrogen is ………………. that of phosphorus.
Less

Question 2.
The atomic radius of Cl is ……………  than that of Ar
Less

Question 3.
Metallic character ………………… as one moves down a group.
Increases

Question 4.
Elements in the same group have ………… chemical properties.
Similar

Question 5.
The horizontal rows in the periodic table are called ……………
Periods

Question 6.
On moving from right to left is the same period, the no of valency electrons ……………….
Decreases

Question 7.
In a group electropositive character from top to bottom.
Increases

Question 8.
Hydrogen resembles with ………………. as well as ……………………  because it can gain ………………… electron like ………………  and lose ……………… electron like ………………
Alkali metals, halogems, one, alkali metals, one, halogens,

Question 9.
The amount of energy released when a neutral gaseous atom gains one electron is called   ………………..
Electron affinity

Question 10.
The measure of the tendency to attract shared pair of electron towards itself is called …………………
Electronegativity.

Question 11.
If an element is present in 3rd group of periodic table, the formula of its oxide is
A2O3

Multiple Choice Questions

Question 1.
According to new lands law of octaves, there are X elements between two similar elements choose the right value of X.
a) X = 6
b) X = 7
c) X = 8
d) none
a) X = 6

Question 2.
The formula of oxide of X is XO. Then which of the following compounds is not formed by (X)?
a) X(NO3)2
b) X2(SO4)
c) XCl2
d) X3N2
b) X2(SO4)

Question 3.
Elements A, B, C, and D have atomic numbers as 9,17,19,35 respectively. Choose the odd element.
(a) A
b) B
c) C
d) D
c) C

Question 4.
Which of the following species does not have electrons equal to 18?
a) K+
b) Cl
c) Ca2+
d) K
d) K

Question 5.
Choose the metalloid from amongst the following elements?
a) Boron
b) Sodium
c) Chlorine
d) Aluminium
a) Boron

Question 6.
Choose the ion with the largest ion size
a) F
b) O2
c) Na+
d) Mg2+
b) O2

### KSEEB Class 10 Science Periodic Classification of Elements Additional Questions and Answers

Question 1.
What is elector negativity? How does it compare with electron affinity?
Though both elector negativity and electron affinity refer to the attraction of electron but are used in different contexts: Elector negativity refers to the attraction of bonding electron or shared pair of electron whereas electron affinity refers to the attraction of electron by an isolated gaseous atom.

Question 2.
Give reasons for the following
a) Metals have tendency to form cations
As the effective nuclear charge on the valence electrons in metals is comparatively less, they have tendency to form cations.

b) Fluorine atom is smaller than chlorine atom.
Fluorine atom smaller than chlorine atom as it has less number (Z) of shells compared to that in chlorine (shells 3)

c) Non metals have tendency to gain electrons.
Non metals have high nuclear attraction on the outermost shells and thus these have tendency to attract / gain electrons.

Question 3.
Draw a part of the long form of periodic table showing a non- metal surrounded by non-metals from all four sides.

Question 4.
Pick up the trail from the following elements and calculate the atomic mass of the element not given in bracket but is the last element of the trial.
Mg (24), Ca ( ), Br (80), Cl(35.5), B (), F ( ), I ( )
Let atomic mass of I = x
By data Cl = 85.5 and Br = 80
$$\frac { x+35.5 }{ 2 } =80$$
⇒ x = 160 -35.5 = 124.5

Question 5.
What are metalloids? How many electrons can be present in the valency shell of their atoms? In what part of the periodic table these are located? What type of oxides are formed by these elements?
Metalloids are elements which resemble both metals and non-metals. The valency shell of metalloids contains 3, 4, 5, 6 electrons starting from periods 2 to 5 respectively. These are found on the right side of the table in the zig­zag column. These form amphoteric oxides.
Ex: Boron, silicon, germanium.

Question 6.
Which period is the longest period in the modern periodic table.
6th period (32 elements)

Question 7.
Why are the elements of group 18 called zero-valent?
Group 18 elements have their outermost shells completely filled and the atoms of these elements have no tendency to gain or lose electrons. Thus, the elements of this group are zero-valent and almost unreactive.

Question 8.
Explain why sodium is more reactive than lithium?
Sodium is more reactive than lithium because sodium is larger in size. Outer most electrons are less tightly held in sodium than in lithium. As a result, sodium loses its outermost electron more easily than lithium. Hence it is more reactive than lithium.

Question 9.
Is it possible to have an element with atomic number 2.5?
No. because the atomic numbers of elements are always in whole numbers.

Question 10.
A part of the early classification of elements is given below:

 H Li Be B C N 0 F Na Mg A1 Si P S

a) Which law of classification of elements illustrated by the above arrangement of elements.
b) Name the scientist who proposed such a classification of elements.
c) Why is such a classification of elements compared with a characteristic of a musical scale.
d) State one limitation of this classification of elements.
a) New land law of octanes
b) New lands
c) In this classification the repetition in the properties 8 NOTE in octane music.
d) It could be applied only up to the calcium.

Question 11.
Mendelev predicted the existence of certain elements not known at that time and named two of them are Eka-Al and Eka-silicon

(a) Name the element that has taken the place of

• eka-aluminium
• eka- silicon

(b) Mention the period
(c) Write the group
(d) Classify these elements as Metals, non-metals or metalloids.
a) (I) Gallium (IT) Germanium
b) 4th period
c) Gallium 13th group and Ge .14th group
d) Gallium-metal, Germanium – metalloid

Question 12.
The atomic masses of 3 elements X,Y and Z having similar chemical properties are 7,23,39 respectively.
a. Calculate average atomic mass of elements X and Z.
b. How does the average atomic mass of elements X and Z compare with the atomic mass of elements Y.
c. What could the elements X, Y and Z.
d. Give another example of a set of elements which can be classified according to this law.
e. Which law of classifications of elements.
$$\text { a) } \frac{39+7}{2}=\frac{46}{2}=23$$
b) The average atomic mass of elements X and Z is equal to the atomic mass of element Y.
c) X is Lithium, Y is Sodium, Z is Potasium
d) Cl, Br, I
e) Dobereiner’s law of Triads.

Question 13.
a) Did Mendeleev have gaps in his periodic table
b) Write any 3 limitations of Mendeleev periodic table.
a) Gaps were left for undiscovered elements.
b)

• Position of Hydrogen was not justified.
• Increasing order of atomic mass could not be maintained.
• Isotopes have similar chemical properties but different atomic masses. This can not be given a separate plane.

Question 14.
Explain
a) Atomic size
b) Ionization energy
c) Metallic property
d) Electro positivity
(e) Electro negativity
a) Along the period left to right decreases down the group increases.
b) Along the period left to right increases down the group decreases.
c) Alongtheperiodlefttorightdecreases down the group increases.
d) Along the period left to right decreases down the group increases.
e) Along period left to right increases down the group decreases.

Question 15.
Name
a) Three elements that have a single electron in their outer most shells.
b) Two elements that have two electrons in their outer most shell.
c) Three elements with filled outer most shells.
a) Li, Na, K
b) Be, Mg
c)He, Ne, Ar

Question 16.
Write the electronic configuration group, period, block of the 1 to 50. Elements in the periodic table.
Remember easy to find out the group Sn, pn+12, dn+2

Note:
Order of filling electron

Question 17.
Explain types of groups in the periodic Table
Alkali Metals

• Alkali Metals belong to the group 1.
• The exceptions in this group is Hydrogen which is non metal.
• Alkali metals have only 1 valence electron.
• They can lose their 1 valence electron very easily to form positive ion with +1 charge, [ex. Sodium chloride]
• The chemical reactivity of alkali metals increases as the atomic number increases, [ex. Sodium potassium]

Alkaline Earth Metal

• Alkaline Earth Metals belongs to the group 2.
• They earth metals have 2 valence electrons.
• They lose electrons to form positive ions with +2 charge.
• They are less reactive than Alkali metals.
Ex: Magnesium
Calcium

Transitions Earth Metals

• The Transitions earth metals belong to the group 3 to 12.
• Transition elements are both ductile and malleable and conduct electricity and heat
ex: Copper, Silver, aluminium, Iron, Chromium
• The transitions metals have density greater than the group 1 or group 2

Metalloids

Metalliods have properties of both metals and non metals ex: Silicon and hermanium. In these elements p orbitals are being filled.

Halogens

• The elements belong to group 17.
• They are highly reactive.
• Halogens do not occur alone in nature. They are always found combined with other elements.
• Fluorine is the most reactive and Iodine is the least reactive.
• In these elements p orbitals are being filed.
Ex: Chlorine
flurine

Noble Gases or Rare Gases

• The elements belong to group 18.
• They all conduct electricity.
• The outer most shell is complete. Hence they do not loses electron +0 form Ions.
• They are stable.
• They are also called zero group as their valency is zero.
Ex: Helium, Neon, Krypton, Xenon, radon etc.

Inner Transition Metals

• The inner Transition Metals are found below the Transitions metals group it comprises of two rows with the columns each.
• The f block elements number 58 to 71 and 90 to 103 are called the inner Ticnsitions elements.
Ex: Lanthanides
Actinides