Chemistry
What are isotopes? How does the existence of isotopes contradict Dalton's atomic theory?
Answer
Isotopes are the atoms of the same element with the same atomic number but a different mass number due to the difference in the number of neutrons in their nucleus.
According to Dalton's theory, atoms of an element are identical in all respects like size, mass, density, chemical properties. But isotopes of an element have atoms that have same atomic number i.e. same number of protons and electrons but different mass number i.e. number of neutrons are different. So isotopes differ from each other in their physical properties like density, melting point, boiling point, etc. This is a contradiction to Dalton's atomic theory.
Related Questions
(a) According to the modern atomic model, what are the two main parts of which an atom is made of ?
(b) Where is the nucleus of an atom situated ?
(c) What are energy levels or shells of an atom ?
(a) State the rule according to which electrons are filled in various energy levels.
(b) Give the number of electrons that can be present in the first four shells of an atom using this rule.
(c) What is the maximum number of electrons present in the outermost (valence) shell ?
What is valency ? Name two elements having variable valency and state their valencies.
State the mass number, the atomic number, number of neutrons and electronic configuration of the following atoms.
(a) 12C6
(b) 16O8
(c) 19F9
(d) 20Ne10
(e) 27Al13
(f) 35Cl17
Also, draw atomic diagrams for each of them.