Chemistry
Modern periodic table is based on:
- Atomic weight
- Atomic number
- Mass number
- Molecular mass
Periodic Table
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Answer
Atomic number
Reason — The Modern Periodic Law is stated as, 'the physical and chemical properties of elements are the periodic functions of their atomic number.'
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Related Questions
Assertion (A): Cobalt (atomic mass 58.94) is placed before Nickel (atomic mass 58.68) in Mendeleev's periodic table.
Reason (R): Physical and chemical properties of the elements are a periodic function of their atomic masses.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): Group 17 elements are known as alkaline earth metals.
Reason (R): Group 17 elements are salt formers.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
The modern periodic table organizes elements based on their atomic number revealing recurring properties. Consider the elements of the third period — Sodium (Na), Magnesium (Mg), Aluminium (Al), Silicon (Si), Phosphorus (P), Sulphur (S), Chlorine (Cl) and Argon (Ar).
Elements in a period show gradual changes in their properties on moving from left to right, due to increasing nuclear charge and more electrons added in the same shell, affecting attraction and size.Answer the following questions :
(a) Why does the size of atoms generally decrease from sodium to chlorine ?
(b) Identify the most metallic element and the most non-metallic element in the third period of the modern periodic table.
(c) Which element in this period acts as a semi-metal (metalloid) showing properties of both metals and non-metals ?
(d) Elements in the same group have similar properties. Give an example of elements from same group and explain why they are similar?
(e) Which element of the third period is a noble gas? Explain why it is unreactive ?
(f) How does the valency change from sodium to chlorine ?
An element 3517X and 4020Y are to be placed in the periodic table.
(a) In which group and period will X and Y be placed?
(b) State whether they are :
- Metal or non-metal.
- Oxidising agent or reducing agent.
(c) Can these two atoms combine to form a compound ? If yes, can you predict 3 properties of this compound?
(d) Write the formula of their oxide.