Periodic Classification Of Elements
Class: 10 | Chapter: 5
Intext Questions with Answer
1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves ? Compare and find out.Ans. Yes, Two Dobereiner's triads existed in the column of Newlands' Octaves are :
[ Li Na K ] and [ Be Mg Ca ].
2. What were the limitations of Dobereiner’s classification ?
Ans. Dobereiner's Classification could make only three triads and couldn't be applicaple to other elements.
3. What were the limitations of Newlands’ law of octaves ?
Ans. 1. It is applicable only upto calcium (atomic no. 20) .
2. After the discovery of noble gases, places given to the elements in this classification got changed.
4. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements : K, C, Al, Si, Ba.
Ans. For K formulae will be K2O, for C formulae will be CO2, for Al formulae will be Al2O3, for Si formulae will be SiO2 and for Ba formulae will be BaO.
5. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table ?
Ans. Germanium ( eka - silicon) and Scandium ( eka - boron) we're left by Mendeleev in his periodic table.
6. What were the criteria used by Mendeleev in creating his Periodic Table ?
Ans. Mendeleev created his periodic table by using atomic mass .
7. Why do you think the noble gases are placed in a separate group ?
Ans. 1. These elements have fully filled electronic shells.
2. They don't react with other elements.
8. How could the modern periodic table remove various anomalies of Mendeleev’s periodic Table ?
Ans. Modern periodic table removed various anomalies of Mendeleev's periodic table such as :
1. Position of isotopes : In Modern periodic table, all isotopes have same position becouse all have same atomic number.
2. Inversion in the periodic table : This anomaly also removed becouse these elements were arranged in the increasing order of atomic number.
9. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice ?
Ans. Calcium, Strontium show same chemical reactions as magnesium becouse they belong to same group.
10. Name :
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outer most shells.
Ans. (a) Lithium, Sodium and Potassium
(b) Berilium, Magnesium
(c) Helium, Neon and Argon
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 ?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common ?
Ans. (a) Lithium, sodium and potassium belong to group 1 elements, they have same outer electronic configuration and hence sane chemical properties like they loose one electron to get oxidise and form basic oxides.
(b) These are noble gases and have completely filled outermost shell.
12. In the modern periodic table, which are the metals among the first ten elements ?
Ans. Lithium and Berilium are the metals among first ten elements.
13. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics ? Ga, Ge, As, Se, Be
Ans. Metals are placed on the left side of the periodic table. So, by considering the position of these elements Be would have maximum metallic character.
Exercise Questions with Answer
1. Which of the following statements is not a correct statement about the trends wlien 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.
Answer.(c) The atoms lose their electrons more easily.
2. Element X forms a chloride with the formula XCl2, which is solid with a high melting point. X would most likely to be in the same group of the periodic table as
(a) Na
(b) Mg
(c) Al
(d) Si
Answer. (b) Mg
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 ?
Answer. (a) Neon
(b) Magnesium
(c) Silicon
(d) Boron
(e) Carbon
4. (a) What property do all elements in the same column of the Periodic Table as boron have in common ?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common ?
Answer. (a) Boron has electronic configuration 2,3 and have valency 3 . So, all elements in the same column will have same general electronic configuration, valency 3 and will be metallic.
(b) Fluorine has electronic configuration 2,7. It has valency 8 - 7 = 1 and is non - mettalic. Therefore, all elements in same column will have 7 electrons in last shell, valency 1 and will be non - metallic.
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)
Answer. (a) Atomic no. = No. Of Electrons
So, atomic no. = 2 + 8 + 7 => 17
(b) Chemical nature depends upon electronic configuration. So, it will be similar to F (9) having electronic configuration 2,7.
6. The positions of three elements A, B and C in the periodic table are shown below :
(a) State whether A is a metal or non-metal.
| Group 16 | Group 17 |
| - | - |
| - | A |
| - | - |
| B | C |
(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 ?
Answer. (a) A is placed in group 17 and it is on the right side of periodic table. It has more than 4 electrons in last shell . So, acc to these results, it is a non - metal.
(b) C is placed in group 17 , it's a non - metal and non - metallic character decreases down the group. Therefore, C is less reactive than A.
(c) C is smaller than B becouse on going left to right in a period atomic size decreases.
(d) A is a non - metal so, it has tendency to gain electron . It will form anion by gaining electrons.
7. Nitrogen (atomic number 7) and phosphorus (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 ?
Ans. N = 2,5
P = 2,8,5
N will be more electronegative becouse electronegativity decreases down the group.
8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table ?
Ans. In Modern periodic table, electrons are described by their period no. and group no. Here period no. gives the shell no. and group no. tells about the no. of valence electrons. So, location of any element is related to their electronic configuration.
9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic number 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium ?
Ans. Ca = 2,8,8,2
12 = 2,8,2
19 = 2,8,8,1
21 = 2,8,8,1,2
38 = 2,8,18,2
Elements with atomic no. 12 and 38 will resemble with calcium becouse these elements have same outermost shell configuration.
10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.
Ans. Mendeleev's Periodic Table : 1. It was based on atomic mass.
2. There are 8 groups and subgroups like A and B were there.
3. Only 63 elements were there at that time.
4. It contained some gaps for future elements.
5. Noble gases were not included.
Modern Periodic Table : 1. It is based on atomic number.
2. It has 18 groups and nobsubgroups are present.
3. It has 118 elements.
4. No gaps are there.
5. Noble gas have separate group.