Question:
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Answer:
The theory that 'all matter is made up of very tiny indivisible particles (atoms)' is called atomic theory of matter. Dalton put forward his atomic theory of matter in 1808.
1.All the matter is made up of very small particles called 'atoms'.
2.Atoms cannot be divided.
3.Atoms can neither be created nor destroyed.
4.Atoms are of various kinds. There are as many kinds of atoms as are elements.
5.All the atoms of a given element are identical in every respect, having the same mass, size and chemical properties.
6.Atoms of different elements differ in mass, size and chemical properties.
7.Chemical combination between two (or more) elements consists in the joining together of atoms of these elements to form molecules of compounds.
Atoms and Molecules
Q 1.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 2.
What is gram-atomic mass of an element?
Q 3.
Define 'formula mass' of a compound.
Q 4.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 5.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 6.
What is the chemical symbol for iron?
Q 7.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 8.
Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.
Q 9.
Give four examples of diatomic molecules.
Q 10.
Who established the two important laws of chemical combinations?
Q 11.
Define molecule. What are its important properties?
Q 12.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 13.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 14.
How many atoms are there in 0.25 mole of hydrogen ?
Q 15.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 16.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 17.
What is the significance of a chemical symbol?
Q 18.
Write the formulae of the following compounds. Also name the elements present in them.
(a) Water
(b) Ammonia
(c) Methane
(d) Sulphur dioxide
(f) Ethanol
Q 19.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Q 20.
When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?
Q 21.
Name the international organization who approves names of elements.
Q 22.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 24.
Name one element each which forms diatomic and tetra atomic molecule.
Q 25.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 26.
What is the numerical value of Avogadro number ?
Q 27.
What are the postulates of Dalton's atomic theory?
Q 28.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 29.
What are ionic compounds?
Q 30.
Give one major drawback of Dalton's atomic theory of matter.
Q 31.
State Law of constant proportions. Explain with an example.
Q 32.
A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
Q 33.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 34.
Fill in the blanks:
Atomic radius is measured in __________.
Q 35.
Which element has the smallest atom in size?
Q 36.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 37.
How many atoms are present in a
(i) H
2S molecule and
(ii) PO
43- ion?
Q 38.
An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?
Q 39.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 40.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 41.
What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na
2SO
3)?
Q 42.
Give an example to show Law of conservation of mass applies to physical change also.
Q 43.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 44.
Calculate the molecular mass of chloroform (CHC1
Q 45.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 46.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 47.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 48.
Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Q 49.
Give examples of triatomic molecules.
Q 50.
What is Formula Unit Mass? How it is different from molecular mass?
