Structure of Atom Flashcards
wha are features of dalton atomic theory
This theory is based on law of mass conservation and law of definite proportions.
The salient feature’s of this theory are :-
(1) Every element is composed of extremely small particles called atoms.
(2) Atoms of a particular element are like but differ from atoms of other element.
(3) Atom of each element is an ultimate particle and it has a characteristic mass but is structureless
(4) Atoms are indestructible i.e. they can neither be created nor be destroyed.
(5) Atoms of different elements take part in chemical reaction to form molecule.
what are negatrons
Particles carrying negative charge were called negatrons by Thomson.The name negatron was changed to
‘electron’ by Stoney.
what the order of the diameter of atom and nucleus
Nucleus has a diameter of the order of 10–12
to 10–13 cm and the atom has a diameter of the order of
10–8
cm.
The radius of a nucleus is proportional to the cube root of the number of nucleons within it. give formula
R = A1/3
Þ = = R0 A⅟³
R0= 1.33 x 10⁻¹³cm
A= no of protons+ no of neutrons ie mass nubmber
what is extra nuclear part
There is an empty space around the nucleus called extra nuclear part. In this part electrons are present.
The number of electrons in an atom is always equal to number of protons present in the nucleus. As the
nuclear part of atom is responsible for the mass of the atom, the extra nuclear part is responsible for its
volume.
The volume of the atom is about 1015
Volumeof theatom (10 )-8X3
Volumeof thenucleus (10)-13x3 =1015
times the volume of the nucleus.
what are em waves
the energy is transmitted from one body to another in the form of waves and these
waves travel in the space with the same speed as light ( 3 × 108
m/s) and these waves are known as Electro
magnetic waves or radiant energy. The radiant Energy do not need any medium for propogation. The radiant energy have electric and magnetic fields and travel
at right angle to these fields.
what is photoelectric effect
Hertz in 1887 observed that when a light of certain frequency strikes the surface of a metal, electrons are
ejected from the metal. This phenomenon is known as photoelectric effect and the ejected electrons are
called photoelectrons.
what is work function
hv0 is the threshold energy (or) the work function denoted by f = hv0 (minimum energy of the photon to
liberate electron). It is constant for particular metal.
whata re the radius of bohr orbits
i) 0.529 angs
ii) 2.116 angs
iii) 4. 761 angs
iv) 8. 464 angs
diff b/w absorption and emission spectra
(i) emission
-> the wavelengths of the light possessed by the sample element is given in the photographic plate
(ii) absorption
-> the wavelengths of light of the element is absorbed by the element and the remainig all colours are given in the photographic plat.
explain millikan’s oil drop method
In this method, oil droplets in the form of
mist, produced by the atomiser, were allowed
to enter through a tiny hole in the upper plate
of electrical condenser. The downward motion
of these droplets was viewed through the
telescope, equipped with a micrometer eye
piece. By measuring the rate of fall of these
droplets, Millikan was able to measure the
mass of oil droplets.The air inside the
chamber was ionized by passing a beam of
X-rays through it. The electrical charge on
these oil droplets was acquired by collisions
with gaseous ions. The fall of these charged
oil droplets can be retarded, accelerated or
made stationary depending upon the charge
on the droplets and the polarity and strength
of the voltage applied to the plate. By carefully
measuring the effects of electrical field
strength on the motion of oil droplets,
Millikan concluded that the magnitude of
electrical charge, q, on the droplets is always
an integral multiple of the electrical charge,
e, that is, q = n e, where n = 1, 2, 3… .
describe x-rays
Wilhalm
Röentgen (1845-1923) in 1895 showed
that when electrons strike a material in
the cathode ray tubes, produce rays
which can cause fluorescence in the
fluorescent materials placed outside the
cathode ray tubes. Since Röentgen did
not know the nature of the radiation, he
named them X-rays and the name is still
carried on. It was noticed that X-rays are
produced effectively when electrons
strike the dense metal anode, called
targets. These are not deflected by the
electric and magnetic fields and have a
very high penetrating power through the
matter and that is the reason that these
rays are used to study the interior of the
objects. These rays are of very short
wavelengths (∼0.1 nm) and possess
electro-magnetic character (Section
2.3.1)
what is radioactivity
3.1).
Henri Becqueral (1852-1908)
observed that there are certain elements
which emit radiation on their own and
named this phenomenon as
radioactivity and the elements known
as radioactive elements. This field was
developed by Marie Curie, Piere Curie,
Rutherford and Fredrick Soddy
three types of radioactivity rays
It was
observed that three kinds of rays i.e., α,
β- and γ-rays are emitted. Rutherford
found that α-rays consists of high energy
particles carrying two units of positive
charge and four unit of atomic mass. He concluded that α- particles are helium
nuclei as when α- particles combined
with two electrons yielded helium gas.
β-rays are negatively charged particles
similar to electrons. The γ-rays are high
energy radiations like X-rays, are neutral
in nature and do not consist of particles.
As regards penetrating power, α-particles
are the least, followed by β-rays (100
times that of α–particles) and γ-rays
(1000 times of that α-particles).
what were the developments leading to bohr atomic model
(i) Dual character of the electromagnetic
radiation which means that radiations
possess both wave like and particle like
properties, and
(ii) Experimental results regarding atomic
spectra which can be explained only by
assuming quantized (Section 2.4)
electronic energy levels in atoms.
