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प्रश्न
Elements in the same group show the same valency. Give scientific reason.
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उत्तर
(a) The number of valence electrons in the outermost shell of an atom of an element is equal to the valency of an element.
(b) The number of valence electrons for all the elements in a group is the same. Therefore, the elements in the same group have the same valency.
(c) For example, the elements of Group I such as sodium (Na) and potassium (K) contain only one valence electron, and so, the valency of elements of Group I is one. Similarly, for Group II, the valency is two.
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संबंधित प्रश्न
Two elements ‘P’ and ‘Q’ belong to the same period of the modern periodic table and are in Group 1 and Group 2, respectively. Compare their following characteristics in tabular form:-
(a) The number of electrons in their atoms
(b) The sizes of their atoms
(c) Their metallic character
(d) Their tendencies to lose electrons
(e) The formula of their oxides
(f) The formula of their chlorides
An element 'X' belong to 3rd period and group 13 of the Modern Periodic Table.
(a) Determine the valence electrons and the valency of 'X'.
(b) Molecular formula of the compound formed when 'X' reacts with an element 'Y' (atomic number = 8).
(c) Write the name and formula of the compound formed when 'X' combines with chlorine
The elements 4Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:
(a) In which group should they be?
(b) Which one of them is least reactive?
(c) Which one of them has the largest atomic size?
What is meant by 'group' in the modern periodic table? How do the following change on moving from top to bottom in a group?
(i) Number of valence electrons
(ii) Number of occupied shells
(iii) Size of atoms
(iv) Metallic character of element
(v) Effective nuclear charge experienced by valence electrons
Name the element that has two shells, both of which are completely filled with electrons.
Which element has a total of three shells, with four electrons in its valence shell?
Classify the following elements into metals, non-metals and metalliods
As, C, Hg, Mg, S, Si
How do electronic configurations of elements change in second period of periodic table with increase in atomic numbers?
Arrange the following elements in increasing order of their atomic radii:
Li, Be, F, N
Rewrite the following statement after correction, if necessary:
The metallic character of elements in a period increases gradually on moving from left to right.
Fill in the blank in the following statement:
In going across a period (right to left) in periodic table, the atomic size of the atom ...............
How does the electropositive character of elements change on going down in a group of the periodic table?
How does the size of atoms (atomic size) generally vary in going from left to right in a period of the periodic table? Why does it vary this way?
In terms of electronic configurations, explain the variation in the size of the atoms of the elements belonging to the same period and same group ?
On moving from left to right in a period of the periodic table, the atomic number of elements increases. What happens to the size of atoms of elements on moving from left to right in a period?
(a) increases
(b) decreases
(c) remain the same
(d) first increases then decreases
Why fluorine has higher E.N. than chorine?
An element X belong to 3rd periods and group II of the periodic table state:
the valency,
Complete the following sentences.
The properties of the elements are a periodic function of their …………… (atomic number, mass number, reative atomic mass).
Which element has:
twice as many electrons in its second shell as in its first shell?
Chorine in the periodic table is surrounded by the elements with atomic number 9, 16, 18 and 35.
Which is more electronegative than chlorine?
F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.
An element 'M' has atomic number 12.
(a) Write its electronic configuration.
(b) State the group to which 'M' belongs.
(c) Is 'M' a metal or a non-metal.
(d) Write the formula of its chloride.
Taking into consideration the period of the elements given below, answer the following questions:
| Elements | Atomic Radius (pm) |
| O | 66 |
| B | 88 |
| C | 77 |
| N | 74 |
| Be | 111 |
| Li | 152 |
- Arrange the above elements in decreasing order of their atomic radii.
- State the period to which the above elements belong.
- Why this arrangement of elements is similar to the above period of modern periodic table?
- Which of the above elements have the biggest and the smallest atom?
- What is the periodic trend observed in the variation of atomic radius while going from left to right within a period?
Study the extract of the Periodic Table given below and answer the questions that follow. Give the alphabet corresponding to the element in question. DO NOT repeat an element. 
The ion of which element will migrate towards the cathode during electrolysis?
Fill in the blank
Most electropositive elements belong to ______ group.
'In a group, the atomic radii increase with increasing period number', explain this statement and justify it with reference to group 17.
Name the elements in period 1.
What is the common feature of electronic configurations of the elements at the end of period 2 and period 3?
Choose the most appropriate answer from the following list of oxides which fit the description.
A basic oxide.
Arrange the following as per instruction given in the bracket
Na, K, Cl, S, Si (increasing ionisation potential)
Arrange the following as per instruction given in the bracket.
K, Pb, Ca, Zn (increasing reactivity)
Atomic numbers of elements A, B, C, D, E, F are 8, 7, 11, 12, 13 and 9 respectively. State the type of ions they form.
An element A has 2 electrons in its fourth shell. State:
is it a metal or non-metal
The electronic configuration of an element is 2, 8, 4. State it:
group and period in the Modern Periodic Table.
The electronic configuration of an element is 2, 8, 4. State it:
name and write its one physical property.
Write the electronic configuration of two elements A and B whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element A reacts with element B. State whether this compound is acidic, basic or neutral. Give a reason to justify your answer.
Name or state following with reference to the element of the first three periods of the periodic table.
A covalent compound formed between an element in period 1 and a halogen.
Fill in the blanks from the words A to F given below.
A: Decreases
B: Increases
C: Remains same
D: Increases by one
E: Electropositive
F: Electronegative
Down a group in the Modern Periodic Table.
No. of electron shells __________; No. of valence electrons ________; Electronegativity ________ Character of elements changes from _________ to ____________.
