List one limitation each of them both the following: Newlands law of octaves Dobereiner's triads

The two limitations of Newland's law of Octaves are as follows- Newland’s law of octaves held only for elements up to calcium. Elements with greater atomic masses could not be accommodated into octaves. It was assumed by Newland that only 56 elements existed in nature and no more elements would be discovered in future. But, later on several new elements were discovered, whose properties did not fit into the Law of Octaves. Limitations of Dobereiner’s Triads: The key shortcomings of Dobereiner’s method of classifying elements are listed below. The identification of new elements made this model obsolete. Newly discovered elements did not fit into the triads. Only a total of 5 Dobereiner’s triads were identified. Even several known elements did not fit into any of the triads.

A part of modern periodic table is given below. On its basis, answer the following question: Group No. → 1 2 13 14 15 16 17 18 Period ↓ 2 A B 3 E D F C Write the molecular formula of the compound formed by the combination of A and F .

The element in both group and period 2 is Beryllium (Be) and the element of group 17 and period 3 is chlorine (Cl). The valency of beryllium is 2 and that of halogen i.e. chlorine is 1 . Hence, the formula of the compound formed will be BeCl 2 .

A part of modern periodic table is given below. On its basis, answer the following question: Group No. → 1 2 13 14 15 16 17 18 Period ↓ 2 A B 3 E D F C Write the molecular formula of the compound formed by the combination of E and B .

Element E belongs to a group 1 of the periodic table, hence it shows a valency of 1 . Element B belongs to group 16 of the periodic table, hence it shows a valency of 2 . So, the formula of the compound will be E 2 B . Since, period is also given 3 period group 1 element is Sodium and element of 2 period and group 16 is oxygen. Hence, the chemical formula between them is Na 2 O .

A part of modern periodic table is given below. On its basis, answer the following question: Group No. → 1 2 13 14 15 16 17 18 Period ↓ 2 A B 3 E D F C Which of the elements is a noble gas?

Noble gases have an octet electronic configuration and it is a more stable electronic configuration. The electronic configuration of elements are: C ( 18 ) = 2 , 8 , 8 Argon is the third noble gas whose atomic number is equal to 18 . This element is denoted by the symbol Ar.

A part of modern periodic table is given below. On its basis, answer the following question: Group No. → 1 2 13 14 15 16 17 18 Period ↓ 2 A B 3 E D F C Which of the element is a metalloid?

Element ' D '' is metalloid because it belongs to the group 14 . On the left side, all the metal are present as we move from left to right the metallic character decrease and the condition where element are neither metal nor non-metal they are metalloid. Silicon is a member of group 14 and period 3 which is classified as a metalloid, since some of its properties are similar to those of metals and some of its properties are similar to those of nonmetals. For example, silicon is known to have a bluish-grey metallic lustre, but is not an amazing conductor of electricity.

State Newlands law of Octaves.

The Newlands law of octaves states that every eighth element has similar properties with the first one when the elements are arranged in the increasing order of their atomic masses. Newlands law founds similarity with the octaves of music, there also every eighth note is comparable to the first note. But, this law of octaves was true only for elements up to calcium.

Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period, and why is it so?

Atomic size is the distance between the outermost shell of an isolated atom and the centre of the nucleus. Its unit of measurement is picometer pm or angstrom. Moving down in the groups in the Periodic Table the atomic size increases because of the increased number of shells in the atoms. Moving across the periods the atomic size of an atom decreases because of the increased number of electrons in the outermost shells which are under the influence of nuclear attraction.

The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1 , 3 , 5 and 7 , electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. Write the electronic configuration of the atoms of B and D, and the molecular formula of the compound formed when B and D combine.

These A, B, C, D elements are distributed in three shells having 1 , 3 , 5 , 7 respectively electrons in their outermost shell. The group numbers of these elements placed in the Modern Periodic Table are: A – 1 st group. B – 13 th group. C – 15 th group. D – 17 th group. The electronic configuration of the atoms of B and D is: B= atomic number= 13 = 2 , 8 , 3 D= atomic number= 17 = 2 , 8 , 7 The molecular formula of the compound when B and D combine is BD 3 .

How does the metallic character of elements vary on moving from left to right in a period? Give a reason for your answer.

Metallic character decreases as you move across a period in the periodic table from left to right. The metallic character of elements decreases because the electropositive character decreases. On moving from left to right, the size of the atoms decreases, and the nuclear charge increases. Hence, the tendency to release electrons decreases. So the electropositive character decreases.

List any three observations which posed a challenge to Mendeleev’s Periodic law.

The observations that posed a challenge to Mendeleev’s Periodic law are as follows: (i) Mendeleev periodic table doesn't fix the position of Hydrogen. (ii) The position of isotopes could not be explained. (iii) Wrong order of atomic masses of some elements could not be explained.

Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.

Henry Moseley showed that atomic number of an element is a more fundamental property than its atomic mass. He showed that the prediction of properties of elements could be done with more precision by considering the atomic number of the elements. Elements are placed in periods and groups.

The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts.

1. Dobereiner: Advantage: Dobereiner give the concept of Dobereiner triads. He placed three elements having similar properties in the same group. These elements were arranged in increasing order of atomic mass and the mass of middle element was the average of the other two. Limitation: Only 4 triads were identified by him. He also failed to group nitrogen, phosphorus and arsenic because atomic mass of phosphorus is not the average of other two. 2. Newland: Advantages: Newland arranged the elements in horizontal rows in order of increasing atomic mass such that the property of every 8th element was similar to that of 1st element. Limitation: His arrangement was only applicable to lighter elements having atomic masses upto 40. 3. Mendeleev: Advantage: He states that the properties of elements are the periodic functions of their atomic masses. He left some spaces in the periodic table for the discovery of new elements. Limitation: Position of hydrogen and isotopes were not justified in his periodic table.

State modern periodic law.

The modern periodic law states that, the physical and chemical properties of the elements are the periodic function of their atomic numbers. That is, various elements with similar properties repeat after certain regular intervals or in other words it can be said as, the elements having similar electronic configuration show similar properties.