Which Element Has A Total of Two Shells, with Three Electrons in Its Valence Shell? - Science

Short Note

Which element has a total of two shells, with three electrons in its valence shell?


Solution 1


Solution 2

Boron is an element with a total of two shells, with three electrons in its valence shell. Its atomic number is 5 and electronic configuration is 2,3.
Electronic configuration:- Shells:                   K L
                                          Electrons arranged: 2 3

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Chapter 5: Periodic Classification Of Elements - Exercise 1 [Page 284]


Lakhmir Singh Class 10 Chemistry (Science)
Chapter 5 Periodic Classification Of Elements
Exercise 1 | Q 47.4 | Page 284
NCERT Science Class 10
Chapter 5 Periodic Classification of Elements
Exercises | Q 3.4 | Page 91

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Fill in the blank:

The formulae of chloride of metal M is MCl2. The metal M belongs to ……………. group.

Elements in the same group show the same valency. Give scientific reason.

Write the electronic configuration of K and Ne.

The atomic masses of three elements A, B and C having similar chemical properties are 7, 23 and 39, respectively.

  1. Calculate the average atomic mass of elements A and C.
  2. Compare the average atomic mass with atomic mass of B.
  3. What could the elements A, B and C be?

Given below are some elements of the modern periodic table. Atomic number of the element is given in parentheses.

A(4), B(9), C(14), D(19), E(20)

(a) Select the element that has one electron in the outermost shell. Also, write the electronic configuration of this element.

(b) Which two elements amongst these belong to the same group? Give reasons for your answer.

(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius?

An element 'X' has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of 'X'. Also write group number, period number and valency of 'X'.

Write the number of periods the Modern Periodic Table has. State the changes in valency and metallic character of elements as we move from left to right in a period. Also state the changes, if any, in the valency and atomic size of elements as we move down a group.

Consider two elements 'X' (Atomic number 17) and 'Y' (Atomic number 20)

(i) Write the positions of these elements in the modern periodic table giving justification.

(ii) Write the formula of the compound formed by the combination of 'X' and 'Y'.

(iii) Draw the electron-dot structure of the compound formed and state the nature of the bond formed between the two elements ?

Which element has twice as many electrons in its second shell as in its first shell?

Classify the following elements into metals, non-metals and metalliods

As, C, Hg, Mg, S, Si

The following table shows the electronic configuration of the elements W, X, Y, Z:

Element w x y z
2, 8, 1 2, 8, 7 2, 5 1

Answer the following questions based on the table above:

1) What type of Bond is formed between :

a) W and X

b) Y and Z

2) What is the formula of the compound formed between :

a) X and Z

b) W and X

Differentiate between Normal elements and Transition elements.

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?

The atomic radii of three elements X, Y and Z of a period of the periodic table are 186 pm; 104 pm and 143 pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period.


Why does the size of the atoms progressively become smaller when we move from sodium (Na) to chlorine (Cl) in the third period of the periodic table?

Which of the following element would lose an electron easily?

(a) Mg
(b) Na
(c) K
(d) Ca

Which one of the following does not increase while moving down the group of the periodic table?

Name two elements you would expect to show chemical reactions similar to calcium. What is the basis of your choice?

Name the type of elements .

Outermost shell incomplete – ………………

Name the type of elements .

one electron short of octet – ……………………

An element A has atomic number 14. To which period does this element belong and how many elements are there in this period.


The element of period 3 with valency 4

Atomic number of metal ‚A‛ is 11, while atomic number of metal ‚B‛ is 20. Which of them will be more reactive? Write the chemical reaction of dilute HCl  with metal ‚A‛.

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
  1. Arrange the above elements in decreasing order of their atomic radii.
  2. State the period to which the above elements belong.
  3. Why this arrangement of elements is similar to the above period of modern periodic table?
  4. Which of the above elements have the biggest and the smallest atom?
  5. What is the periodic trend observed in the variation of atomic radius while going from left to right within a period?

K, Pb, Ca, Zn (In the increasing order of the reactivity) 

Explain, the statement 'In each period, the atomic radii gradually decrease with increase in atomic number'. Give one example to justify your answer.

Give the number of the group and the period of elements having three shells with three electrons in valence shell.

Refering to changes in the properties of elements on moving from left to right across a period of the periodic table. Choose the correct answer. 

The electronegativity

Element P has atomic number 19. To which group and period, does P belong? Is it a metal or a non-metal? Why?

An element belongs to the third period and Group IIIA (13) of the periodic table. State: the number of valence electrons,

An element belongs to the third period and Group IIIA (13) of the periodic table. State: the valency,

State the nature of compounds formed when group 17 elements combine with (i) metals (ii) non-metals.

An element A has 2 electrons in its fourth shell. State:

is it a metal or non-metal

(a) Fill in the blanks and rewrite the completed statements: 

(i) ________ group in the periodic table contains elements that are all gases at room temperature. 

(ii) Very fine particles mainly scatter ______ light.

Fill in the blank and rewrite the completed statement:

________ group in the periodic table contains elements that are all gases at room temperature.

Give Scientific Reason:
Atomic size increase down the group.

Answer the following question:
State the four blocks of the modern periodic table based on the electronic configuration of elements.

The position of certain elements in the Modern Periodic Table is shown below:

Using the above table answer the following questions giving reasons in each case :
(i) Which element will form only covalent compounds?
(ii) Which element is a non-metal with valency 2?
(iii) Which element is a metal with valency 2?
(iv) Out of H, C, and F which has the largest atomic size?
(v) To which family does H, C, and F belong?

Name the elements in Period 1.

Supply the missing word from those in bracket:

If an element has one electron in its outermost energy level [shell] then it is likely to be _______.

Name the period which is the shortest period of the periodic table.

Select the correct answer from the options given below.

It is a metal in period 2 having electronic configuration 2, 1?

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

Across a period from left to right in the Modern Periodic Table.
No. of electron shells _________; No. of valence electrons __________: Electronegativity increases Character of elements changes from electropositive to ________.


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