LEARNER’S GUIDE
SENIOR SECONDARY COURSE: CHEMISTRY (313)
2
ATOMIC STRUCTURE
Table 2.1 Fundamental particles of atom and their
characteristics
• Atom (Given by Dalton): Matter is
made up of extremely small particles
which are indivisible in nature. It consists
of subatomic particles electron, proton
and neutrons knows as fundamental
particles. Atomic Number, Mass Number,
1. Electron (Named by Stoney):
Isotopes and Isobars
Discovered by Cathode Ray experiment • Atomic number (Z): The no. of protons or
[In crook’s tubes]. A long glass tube electron in a neutral atom or No. of protons
with two metal electrodes. At every low in an atom (or ion).
pressure when high voltage is applied a
• At mass no. (A): Total no. of protons and
flow is produced due to flow of − ve
neutron in an atom
charge particle [known as electron],
cathode rays. Cathode rays have −ve
change, travel in straight lines has
• Isotopes: Atoms of same element with
electric and magnetic field have heating
effect more penetrating effect. Charge different mass no.
on e- was found by Oil drop experiment • Isobars: Atoms of different element with
[Millikan].
same mass no.
2. Proton (Discovered by Goldstein in
• Isotones: Atoms of different element with
anode ray experiment: In a perforated
cathode tube with gas at low pressure same no. of neutron.
high voltage was passed between • Isoelectronic: Atoms, molecules or ions
electrode rays from cathode produced with same no. of e-[Ne; O2-].
green fluorescence on ZnS all. These Earlier Models
were called as anode rays. They travel
in straight line, with + ve charge, get Thomson’s Model
defected in electric and magnetic field.
• J.J. Thomson: The sphere of +ve change
3. Neutron: Fundamental particle which nucleus model of atom is 14 Chemistry
carries no charge but has mass equal to balanced by coulombic force of attraction
N atom or Proton. Discovered by James of e-. Like a Raisin Pudding Model
Chadwick.
Fig. 2.1: A pictorial representation of Thomson’s plum-
pudding model
1|Page CHEMISTRY (313)
, LEARNER’S GUIDE
SENIOR SECONDARY COURSE: CHEMISTRY (313)
Rutherford’s Experiment d. Wave no.: No. of waves per unit length
denoted by
• Ruther Ford (Discovery of nucleus):
particles (+ve charge) bombarded on
gold foil. e. Velocity: Linear distance travelled by a
a. 99.9% passed without deflection: wave in one second.
Most space inside the atom is empty.
(b) Only few deflected therefore mass
of atom centrally placed called
nucleus.
b. Very few deflected back therefore mass Electromagnetic Spectrum
of atom contains +ve charge particles
[Protons].
• Energy wise order for EM radiation.
c. Atom is electrically neutral hence −ve
change particles placed outside the
nucleus and have very less mass.
• Limitations: No distribution and
energies of e-considered, could not
Line Spectrum
explain e- does not fall into the nucleus
or not; no details of line spectra of H • When the vapors of some volatile
atom. substance are allowed to fall on the flame
of a Bunsen burner and then analyzed
Electromagnetic Radiations with the help of a spectroscope. Some
• Energy emitted from any source (in specific-colored lines appear on the
forms of waves) in which electric and photographic plate which is different for
magnetic fields oscillated perpendicular different substances. For example, sodium
to each other and travelling with a or its salts emit yellow light while
velocity to light is known as EM potassium or its salts give out violet light.
radiation.
Line Spectrum of Hydrogen Atom
Characteristic Parameters of
Electromagnetic Radiations • Hydrogen spectrum: When e- in
hydrogen atom is provided energy it
a. Wavelength: the distance of one crest
gets excited to higher shell from ground
and one trough in a wave. Denoted by ‘’
state, it comes back to ground state by
emitting energy in definite values.
b. Frequency:no. of waves • “Quanta”: The emission of light energy
passing through a given point in one is known as emission spectra. It
second. corresponds to each atom depending
upon which energy shell e-is excited. It
is discontinuousspectra as ‘’ of light
c. Amplitude: The height of crest or depth
of a trough denoted by ‘a’
2|Page CHEMISTRY (313)
SENIOR SECONDARY COURSE: CHEMISTRY (313)
2
ATOMIC STRUCTURE
Table 2.1 Fundamental particles of atom and their
characteristics
• Atom (Given by Dalton): Matter is
made up of extremely small particles
which are indivisible in nature. It consists
of subatomic particles electron, proton
and neutrons knows as fundamental
particles. Atomic Number, Mass Number,
1. Electron (Named by Stoney):
Isotopes and Isobars
Discovered by Cathode Ray experiment • Atomic number (Z): The no. of protons or
[In crook’s tubes]. A long glass tube electron in a neutral atom or No. of protons
with two metal electrodes. At every low in an atom (or ion).
pressure when high voltage is applied a
• At mass no. (A): Total no. of protons and
flow is produced due to flow of − ve
neutron in an atom
charge particle [known as electron],
cathode rays. Cathode rays have −ve
change, travel in straight lines has
• Isotopes: Atoms of same element with
electric and magnetic field have heating
effect more penetrating effect. Charge different mass no.
on e- was found by Oil drop experiment • Isobars: Atoms of different element with
[Millikan].
same mass no.
2. Proton (Discovered by Goldstein in
• Isotones: Atoms of different element with
anode ray experiment: In a perforated
cathode tube with gas at low pressure same no. of neutron.
high voltage was passed between • Isoelectronic: Atoms, molecules or ions
electrode rays from cathode produced with same no. of e-[Ne; O2-].
green fluorescence on ZnS all. These Earlier Models
were called as anode rays. They travel
in straight line, with + ve charge, get Thomson’s Model
defected in electric and magnetic field.
• J.J. Thomson: The sphere of +ve change
3. Neutron: Fundamental particle which nucleus model of atom is 14 Chemistry
carries no charge but has mass equal to balanced by coulombic force of attraction
N atom or Proton. Discovered by James of e-. Like a Raisin Pudding Model
Chadwick.
Fig. 2.1: A pictorial representation of Thomson’s plum-
pudding model
1|Page CHEMISTRY (313)
, LEARNER’S GUIDE
SENIOR SECONDARY COURSE: CHEMISTRY (313)
Rutherford’s Experiment d. Wave no.: No. of waves per unit length
denoted by
• Ruther Ford (Discovery of nucleus):
particles (+ve charge) bombarded on
gold foil. e. Velocity: Linear distance travelled by a
a. 99.9% passed without deflection: wave in one second.
Most space inside the atom is empty.
(b) Only few deflected therefore mass
of atom centrally placed called
nucleus.
b. Very few deflected back therefore mass Electromagnetic Spectrum
of atom contains +ve charge particles
[Protons].
• Energy wise order for EM radiation.
c. Atom is electrically neutral hence −ve
change particles placed outside the
nucleus and have very less mass.
• Limitations: No distribution and
energies of e-considered, could not
Line Spectrum
explain e- does not fall into the nucleus
or not; no details of line spectra of H • When the vapors of some volatile
atom. substance are allowed to fall on the flame
of a Bunsen burner and then analyzed
Electromagnetic Radiations with the help of a spectroscope. Some
• Energy emitted from any source (in specific-colored lines appear on the
forms of waves) in which electric and photographic plate which is different for
magnetic fields oscillated perpendicular different substances. For example, sodium
to each other and travelling with a or its salts emit yellow light while
velocity to light is known as EM potassium or its salts give out violet light.
radiation.
Line Spectrum of Hydrogen Atom
Characteristic Parameters of
Electromagnetic Radiations • Hydrogen spectrum: When e- in
hydrogen atom is provided energy it
a. Wavelength: the distance of one crest
gets excited to higher shell from ground
and one trough in a wave. Denoted by ‘’
state, it comes back to ground state by
emitting energy in definite values.
b. Frequency:no. of waves • “Quanta”: The emission of light energy
passing through a given point in one is known as emission spectra. It
second. corresponds to each atom depending
upon which energy shell e-is excited. It
is discontinuousspectra as ‘’ of light
c. Amplitude: The height of crest or depth
of a trough denoted by ‘a’
2|Page CHEMISTRY (313)
