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प्रश्न
The atomic masses of three elements A, B and C having similar chemical properties are 7, 23 and 39, respectively.
- Calculate the average atomic mass of elements A and C.
- Compare the average atomic mass with atomic mass of B.
- What could the elements A, B and C be?
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उत्तर
(a) The average atomic mass of elements A and C = `(7+39)/2=46/2=23`
(b) The average atomic mass of elements A and C is equal to the atomic mass of element B.
(c) A is lithium, B is sodium and C is potassium.
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संबंधित प्रश्न
Taking the example of an element of atomic number 16, explain how the electronic configuration of the atom of an element relates to its position in the modern periodic table and how valency of an element is calculated on the basis of its atomic number.
Na, Mg and Al are the elements of the same period of Modern Periodic Table having, one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating reason for each case.
Write the atomic numbers of two elements 'X' and 'Y' having electronic configuration 2, 8, 2 and 2, 8, 6 respectively.
Consider two elements 'A' (Atomic number 17) and 'B' (Atomic number 19) :
(i) Write the positions of these elements in the modern periodic table giving justification.
(ii) Write the formula of the compound formed when 'A' combines with 'B.'
(iii) Draw the electron dot structure of the compound and state the nature of the bond formed between the two elements.
Calculate the mass of Calcium that will contain the same number of the atom as are present in 3.2 gm of Sulphur.
[Atomic masses: S=32, Ca=40]
The metal of Group 2 from top to bottom arc Be, Mg, Ca, Sr, and Ba.
1) Which one of these elements will form ions most readily and why?
2) State the common feature in the electronic configuration of all these elements.
How does the number of valence electrons vary on moving from left or right in the first period of the periodic table?
How does the number of valence electrons vary on moving from left or right in the second period of the periodic table?
How does the valency of elements change of moving from left to right in the third period of the periodic table?
For each of the following triads, name the element with the characteristics specified below:
| Elements | Least atomic radius | Chemically least reactive |
| (i) F, Cl, Br (ii) Li, Na, K |
.................... .................... |
.................... .................... |
Given alongside is a part of the periodic table. As we move vertically downward from Li to fr?
| Li | Be |
| Na | |
| K | |
| Rb | |
| Cs | |
| Fr | |
| rA | Ra |
What happens to the size of atoms?
An element which is an essential constituent of all organic compounds belongs to following group of modern periodic table:
(a) group 4
(b) group 14
(c) group 15
(d) group 16
The element which has the maximum number of valence electrons is:
(a) Na
(b) P
(c) Si
(d) A
In each of the following pair, choose the atom having the bigger size:
Na (At. No. 11) or K (At. No. 19)
An element has 2 electrons in its N shell.
State the name assigned to this group.
Why fluorine has higher E.N. than chorine?
How does the number of:
valence electrons and
An element X belong to 3rd periods and group II of the periodic table state:
the number of valence electrons,
Complete the following sentences.
The properties of the elements are a periodic function of their …………… (atomic number, mass number, reative atomic mass).
Chorine in the periodic table is surrounded by the elements with atomic number 9, 16, 18 and 35.
Which of these have physical and chemical properties resembling chlorine.
K, Pb, Ca, Zn (In the increasing order of the reactivity)
'In a group, the atomic radii increase with increasing period number', explain this statement and justify it with reference to group 17.
Copy and complete the following sentence choosing the correct word or words from those given below, at the end of the sentence:
The similarities in the properties of elements belonging to a group are because they have the same ______
The following table represents the first period of the modern periodic table. Study the table and answer the questions that follow:
- Write the formula of the sulphate of the element with atomic number 13.
- What type of bonding will be present in the oxide of the element with atomic number 1?
- Which feature of the atomic structure accounts for the similarities in the chemical properties of the elements in group VIIA of the periodic table?
- Name the element which has the highest ionization potential.
- How many electrons are present in the valence shell of the element with atomic number 18?
- What is the name given to the energy released, when an atom in its isolated gaseous state accepts an electron to form an anion?
- What is the electronic configuration of the element in the third period which gains one electron to become an anion?
- Fill in the blanks:
The atomic size ______ as we move from left to right across the period, because the ______ increases, but the ______ remains the same.
Use the letters only written in the Periodic Table given below to answer the questions that follow:
(a) State the number of valence electrons in the atom J.(b) Which element shown forms ions with a single negative charge?
(c) Which Metallic element is more reactive than R?
(d) Which element has its electrons arranged in four shells?
Arrange the following as per instruction given in the bracket.
Cs, Na, Li, K, Rb (increasing metallic character)
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)
Choose the word or phrase from the bracket which correctly complete each of the following statement:
Metals are good ................. (oxidising agents/reducing agents) because they are electron ............. (acceptors/donors).
With reference to the variation of properties in the Periodic table, which of the following is generally true?
The position of elements A, B, C, D and E in the periodic table are shown below:
|
Group 1 |
Group 2 |
Group 17 |
Group 18 |
|
|
|
|
D |
|
|
B |
C |
|
|
A |
|
|
E |
Which is larger in size (i) D or E (ii) B or C
An element belongs to the third period and Group IIIA (13) of the periodic table. State: if it is a metal or non-metal?
Name and state the following with reference to the elements of the first three periods of the periodic table.
Metalloid in Period 3.
Based on the group valency of element write the molecular formula of the following compound giving justification:
Compound formed when an element A of group 2 combines with an element B of group seventeen.
What is the common feature of the electronic configuration of the elements at the end of Period 2 and Period 3?
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 elements in the correct order of their increasing atomic numbers present in the first, second, and third short periods of the periodic table.
State which of the elements are –
- metallic
- non-metallic
- noble gases
in each of the periods 2 and 3.
State the property trends in general of elements on moving down in a group of the periodic table.
Name or state following with reference to the elements of the first three periods of the periodic table.
A metalloid in period 2 and in period 3.
