5. Inside the Atom
1.
Answer the following.
a. What
is the difference in the atomic models of Thomson and Rutherford?
Ans:
|
Thomson
Theory |
Rutherford
Theory |
|
1. According to Thomson’s
atomic model, the negatively charged electrons are embedded in a gel of
positive charge. |
1. According to
Rutherford’s atomic model the negatively charged electrons revolve around the
nucleus. |
|
2. Atom is homogenous
sphere of positive charge. |
2. The positive charge is
in the nucleus of the atom. |
|
Does not give any idea about constituents of
nucleus |
States that nucleus is composed of protons
and neutrons |
b. What is meant by valency of an element?
What is the relationship between the number of valence electron and valency?
Ans: Valency: The capacity of an ; element to combine
with another element is known as valency.
Valency of an atom is determined
by its electronic configuration.
It gives idea about the number of electrons loss
or gain in order to achieve the nearest noble gas configuration.
For example: Na(11) = 2,8,1 So, its valency is 1
Cl(17) = 2,8,7 So, its valency is also 1
Number
of valence electron : It is defined as the number of electrons present in
the outermost shell of an atom.
It is not necessary that all the valence electrons
take part in bonding.
For example: Na(11) = 2,8,1 So, its number of
valence electron is 1
Cl(17) = 2,8,7 So its number of valence electron is 7
It can be seen that valency of an element is
related to number of valence electrons in that atom.
c. What is meant by atomic mass number ? Explain how the atomic number and
mass number of carbon are 6 and 12 respectively
Ans: The total number of protons and neutrons in the nucleus of the atom is
called the atomic mass number.
Atomic mass number = number of
protons + number of neutrons.
Atomic number = number of protons = number of electrons. It
is denoted by Z.
Mass number = number of protons + number of neutrons. It is
denoted by A.
For example : Carbon atom its, Number of proton = 6
Number of neutrons = 6
Number of electron = 6
Atomic number(Z) = number of protons = number of electrons = 6.
Mass number(A) = number of proton + number of neutrons = 6 + 6 =12.
d. What
is meant by subatomic particle ? Give
brief information of three subatomic particles with reference to electrical
charge, mass and location.
Ans: A
particle which is a constituent of an atom hence smaller than the atom is
called subatomic particle.
An atom is formed from the nucleus and the
extranuclear part. These contain three types of subatomic particles.
The nucleus contains two types of subatomic
particles together called nucleons. Protons and neutrons are the two types of nucleons or
subatomic particles and electrons are subatomic particles in the extra nuclear
part.
Difference between subatomic
particles are as follows :
Electron
1. Electrons are present outside the nucleus of an
atom.
2. Electrons are negatively charged that is (coulomb).
3. The mass of an electron is considered to
negligible. It is 1800 times less than that of a hydrogen
4.Relative mass = 1/ 1840 times hydrogen
5. It revolves around the nucleus in the discrete
orbit.
Proton
1. Protons are present in the nucleus of an atom.
2. Protons are positively charged that is (coulomb).
3. The mass of a proton is approximately
1u(1Dalton) that is ().
4. They are closely bound in the nucleus.
Neutron
1. Neutrons are present in the nucleus of an atom.
2. Neutrons are neutral.There is no charge.
3. The mass of a neutron is nearly equal to the
mass of a proton that is 1u(1Dalton) that is ().
4. They are closely bound in the nucleus.
2. Give
scientific reasons.
a. All the mass of an atom is concentrated in
the nucleus.
Ans: All the mass of
an atom is concentrated in the nucleus because atom contains three subatomic
particles like electron, proton and neutron.Out of which, nucleus present at
the centre of an atom contains two subatomic particles that's protons and
neutrons and the mass of nucleus is the sum of mass of protons and neutrons
located at the centre of an atom.
b. Atom
is electrically neutral.
.Ans: Atom is electrically neutral
because in an atom electrons and protons carry charges and each atom has equal numbers of protons (positively charged)
and electrons (negatively charged).
c.
Atomic mass number is a whole number.
Ans: The total number of protons and neutrons in
the nucleus of the atom is called the atomic mass number (A). As protons and
neutrons are whole numbers, the atomic mass number is also a whole number.
d.
Atoms are stable though negatively charged electron are revolving within it.
Ans: The entire mass of the atom is
concentrated in the nucleus and the positively charged nucleus at centre of an
atom. The negatively charged electrons revolve around the nucleus. The total
negative charge on all the electron is equal to positive charge on the nucleus.
As the opposite charges are balanced, the atom is stable.
3.
Define the following terms
a. Atom
Ans : An atom is the smallest particle of an element which retains its
chemical identity in all physical and chemical changes.
b. Isotope
Ans : Atoms of the same element having the same atomic number, but different
atomic mass numbers are called isotopes.
c. Atomic number
Ans: The number of electrons or protons in an
atom is called the atomic number. It is denoted by Z.
d. Atomic mass number
Ans: The total number of protons and neutrons in the nucleus of the atom is
called the atomic mass number. It is denoted by A.
e. Moderator in nuclear reactor
Ans: The substance which reduces the speed of fast-moving neutrons produced
in a fission is called a moderator.
Graphite or heavy water is used as moderator
for reducing the speed of neutrons.
4.
Draw a neat labelled diagram.
a. Ruthrford's scattering experiment
b. Thomson's atomic model
c. Diagramatic sketch of electronic
configuration of Magnesium (Atomic number 12)
d. Diagramatic sketch of electronic
configuration of Argon (Atomic number
18)
5. Fill in the blanks.
a. Electron, proton, neutron are the types
of subatomic particles in an atom.
b. An
electron carries negative charge.
c. The
electron shell K is nearest
to the nucleus.
d. The
electronic configuration of magnesium is
2, 8, 2. From this it is understood that the valence shell of Magnesium
is M shell.
e. The valency of hydrogen is 'one' as per the
molecular formula H2O. Therefore valency of 'Fe' turns out to be three as per the
formula Fe2O3.
6. Match the pairs.
Group ‘A’ Group ‘B’
a.
Proton i.
Negatively charged
b. Electron
ii.
Neutral
c. Neutron
iii.
Positively Charged
|
Group
‘A’ |
Group
‘B’ |
|
a.
Proton |
iii.
Positively Charged |
|
b.
Electron |
i.
Negatively charged |
|
c.
Neutron |
ii.
Neutral |
7. Deduce from the datum provided.
|
Datum |
To deduce |
|
Na112 |
Neutron |
|
C614 |
Mass
number |
|
Cl1737 |
Proton
number |
Datum | To deduce |
Na1123 | Neutron number = Mass number - Number of protons |
C614 | |
Cl1737 | |
|
|