What is element ,what kind of element? give answer in 20-30 word.
Answers
Answer:
An element is a pure substance that is made from a single type of atom. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium. An important number in an element is the atomic number.
Explanation:
Hope it helpful ✌️✌️
Answer:
NCERT IN TEXT QUESTIONS SOLVED
Q1. Did DobereinerA's triads also exist in the colurrxrts of Ne lord's Octaves? Compare and find out.
Ans. Yes, it exists in the Iewland's octave. It is Li, Na and
Q2. What were the limitations of Dobereiner's classification?
(a) All the existing elements were not classified.
(b) D bereiner could identify only three triads from the elements.
Hence this system wa4s not useful.
Q3. What were the limitations of Newlands� Law of Octaves?
Ans. • Newlands’ law was applicable only till calcium, after Ca, every eighth element did not possess properties similar to first.
• New elements discovered did not fit into the law.
• Wrong order of arrangement of elements was done, e.g. Co and Ni do not resemble halogen were found together in same slot, Fe being similar to Co and Ni was separated and kept in different slot.
Q4. Use Mendeleev's Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, 1Si, Ba
Ans.
Q5. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Ans. Besides gallium, germanium and scandium have been discovered.
Q6. What were the criteria used by Mendeleev in creating his Periodic Table?
Ans. (i) Increasing order of atomic mass of the elements.
(ii) Al elements in a group with similar properties.
(iii) The formula of oxides and hydrides formed by an element.
Q7. Why do you think noble gases are placed in a separate group?
Ans. Noble gases are inactive, do not resemble other elements and all of them show same properties, hence they are grouped separately.
Q8. How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?
Ans. Modern Periodic Table is based on the atomic number of elements, therefore
(i) problem of isotopes was solved because isotopes have same atomic number
(ii) wrong order of r, K, Go, Ni was removed.
Q9. Name two elements you would erect to show chemical reactions similar to magnesium. What is the basis for your choice?
Ans. Calcium and barium.
Reason : (i) Both of them belong to same group as magnesium.
(ii) Ba and Ca has same valence electrons as Mg, and will show same properties as of magnesium.
Q10. Name:
(a) Three elements that have a single electron in their outermost shells.
(b) vo elements that have two electrons in their outermost shells.
(c) Three elements with filled outermost shells.
Q11. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What,. if anythin, do their atoms have in common?
Ans. (a) All these metals are highly reactive, they have same valence electrons i.e. 1 and can readily loose electrons to become positive ions.
(b) Helium and neon have completely filled outermost shell.