Chemistry Chapter 2
Questions for Short Answers
Why is it said that almost all the mass of an atom is
UM
concentrated in its nucleus?
Because the nucleus contains protons and neutrons, which
are much heavier than electrons.
ER
Why are elements different from one another?
Elements differ because they have different numbers of
IM
protons in their atoms.
How many neutrons are present in ²⁰⁹Bi?
TI
Neutrons = 209 (mass number) - 83 (atomic number) = 126
neutrons
AZ
Why is tritium (³₁H) a radioactive element?
Tritium has extra neutrons which makes its nucleus unstable,
so it gives off radiation to become stable.
How can an atom absorb and evolve energy?
Atoms absorb energy when electrons jump to higher levels
and release energy when they fall back.
, SECTION NO.2
Constructed Response Questions
UM
Why does the energy of electron increase as we move from
first shell to second shell?
ER
Because the electron is farther from the nucleus in the
second shell and needs more energy to stay there.
Why is it needed to lower the pressure of the gas inside the
IM
discharge tube?
Lower pressure helps electrons move freely and strike gas
TI
atoms to produce light or other effects.
AZ
What is the classical concept of an electron? How has this
concept changed with time?
Earlier, electrons were thought to revolve in fixed paths like
planets. Now, we know they exist in areas called orbitals and
their exact position can't be known.
Questions for Short Answers
Why is it said that almost all the mass of an atom is
UM
concentrated in its nucleus?
Because the nucleus contains protons and neutrons, which
are much heavier than electrons.
ER
Why are elements different from one another?
Elements differ because they have different numbers of
IM
protons in their atoms.
How many neutrons are present in ²⁰⁹Bi?
TI
Neutrons = 209 (mass number) - 83 (atomic number) = 126
neutrons
AZ
Why is tritium (³₁H) a radioactive element?
Tritium has extra neutrons which makes its nucleus unstable,
so it gives off radiation to become stable.
How can an atom absorb and evolve energy?
Atoms absorb energy when electrons jump to higher levels
and release energy when they fall back.
, SECTION NO.2
Constructed Response Questions
UM
Why does the energy of electron increase as we move from
first shell to second shell?
ER
Because the electron is farther from the nucleus in the
second shell and needs more energy to stay there.
Why is it needed to lower the pressure of the gas inside the
IM
discharge tube?
Lower pressure helps electrons move freely and strike gas
TI
atoms to produce light or other effects.
AZ
What is the classical concept of an electron? How has this
concept changed with time?
Earlier, electrons were thought to revolve in fixed paths like
planets. Now, we know they exist in areas called orbitals and
their exact position can't be known.
