The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.
Dobereiner observed in a few atoms that the mass of one atom is equal to the average of two atoms. He defined almost all properties based on atomic weight. Hence, such an arrangement of elements called as Dobereiner triad.
Example: Lithium has 7, sodium has 23 whereas potassium has 39 as atomic masses.
23=(7+39)/2=23
Here, we observe that the atomic mass of sodium is the average of atomic masses of potassium and lithium.
Related Articles
- The atomic masses of three elements X, Y and Z having similar chemical properties are 7, 23 and 39 respectively.(a) Calculate the 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 element Y? (c) Which law of classification of elements is illustrated by this example? (d) What could the elements X, Y and Z be? (e) Give another example of a set of elements which can be classified according to this law.
- The electronic configurations of three elements X, Y, and Z are X - 2,8; Y - 2, 8, 7 and Z - 2, 8, 2. Which of the following is correct?(a) X is a metal(b) Y is a metal(c) Z is a non-metal(d) Y is a non-metal and Z is a metal
- (a) Explain why:(i) All the elements of a group have similar chemical properties. (ii) All the elements of a period have different chemical properties. (b) 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.
- The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?
- The electronic configuration of three elements X, Y and Z are as follows:X 2,4 Y 2,7 Z 2,1 (a) Which two elements will combine to form an ionic compound? (b) Which two elements will react to form a covalent compound? Give reasons for your choice.
- A, B and C are the elements of a Dobereiner’s triad. If the atomic mass of A is 7 and that of C is 39, what should be the atomic mass of B?
- The atomic numbers of the three elements X, Y and Z are 2, 6 and 10 respectively.(i) Which two elements belong to the same group? (ii) Which two elements belong to the same period? Give reasons for your choice.
- Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.
- In \( \Delta X Y Z, X Y=X Z \). A straight line cuts \( X Z \) at \( P, Y Z \) at \( Q \) and \( X Y \) produced at \( R \). If \( Y Q=Y R \) and \( Q P=Q Z \), find the angles of \( \Delta X Y Z \).
- Give the formulae of the chlorides of the elements X and Y having atomic numbers of 3 and 6 respectively. Will the properties of the two chlorides be similar or different? Explain your answer.
- X and Y are the two elements having similar properties which obey Newlands’ law of octaves. How many elements are there in-between X and Y?
- Identify ‘x’, ‘y’ and ‘z’ in the following reaction : $2KClO_3 (x) \xrightarrow{(y)} 2 KCl (x) + O_2(z)$(a) x = gas ; y = reaction condition, z = gas (b) x = solid ; y = liquid; z = gas (c) x = number of moles of KClO3 ; y = reaction condition; z = no. of molecules of oxygen. (d) x = physical state of KClO3 and KCl; y = reaction condition; z = physical state of O2.
- Four elements W, X, Y and Z contain 8, 11, 9 and 17 protons per atom respectively. The element which cannot form an anion is most likely to be :(a) W (b) X (c) Y (d) Z
- If \( a^{x}=b^{y}=c^{z} \) and \( b^{2}=a c \), then show that \( y=\frac{2 z x}{z+x} \).
- The composition of two atomic particles is given below : X YProtons : 8 8Neutrons : 8 9Electrons : 8 8(i) What is the mass number of X ?(ii) What is the mass number of Y ?(iii) What is the relation between X and Y ?(iv) Which element/elements do they represent ?
Kickstart Your Career
Get certified by completing the course
Get Started