Structure of the atom

PREPARED BY (Group –9)
 DEEPAK SHUKLA
 ADITAYA TRIPATHI
 VASU RAO
 AKSHAT SHARMA
CLASS – IX - C

 The atom is a basic unit of matter that consists
of a dense central nucleus surrounded by
a cloud of negatively charged electrons.
The atomic structure contains a mix of
positively charged protons and electrically
neutral neutrons(except in the case
of hydrogen-1, which is the only
stable nuclide with no neutrons). The electrons
of an atom are bound to the nucleus by the
electromagnetic force

 Thomson atomic model, earliest theoretical
description of the inner structure of atoms,
proposed about 1900 by Lord Kelvin and
strongly supported by Joseph john thomson,
who had discovered (1897) the electron, a
negatively charged part of every atom. Though
several alternative models were advanced in
the 1900s by Lord Kelvin and others, Thomson
held that atoms are uniform spheres of
positively charged matter in which electrons
are embedded. Popularly known as the plum-
pudding model,

 The Rutherford model is a model of
the atom devised by Ernest Rutherford.
Rutherford directed the famous Geiger
Marsden experiment in 1909 which suggested,
upon Rutherford's 1911 analysis, that the so-
called "plum pudding model" of J. Thomson of
the atom was incorrect

 Rutherford overturned Thomson's model in 1911
with his well-known gold foil experiment in which
he demonstrated that the atom has a tiny, heavy
nucleus. Rutherford designed an experiment to use
the alpha particles emitted by a radioactive
element as probes to the unseen world of atomic
structure.
 Rutherford presented his own physical model for
subatomic structure, as an interpretation for the
unexpected experimental results. In it, the atom is
made up of a central charge (this is the
modern atomic , though Rutherford did not use
the term "nucleus" in his paper) surrounded by a
cloud of (presumably) orbiting electrons

From purely energetic considerations of how far
particles of known speed would be able to
penetrate toward a central charge of 100 e,
Rutherford was able to calculate that the radius
of his gold central charge would need to be less
(how much less could not be told) than 3.4 x
10−14 metres. This was in a gold atom known to
be 10−10 meters or so in radius—a very surprising
finding, as it implied a strong central charge less
than 1/3000th of the diameter of the atom

 Most of the fast moving alpha particles passed
straight through the gold foil
 Some of the alpha particles were deflected by
the foil by small angles
 Surprisingly one out of every 12000particles
appeared to rebound

 There is a positively charged nucleus centre in
atom called Nucleus all mass resides in
Nucleus
 The electrons revolve around the Nucleus in
circular paths
 The size of the Nucleus is very small as
compared to the size of the atom

 Any particle in a circular orbit would undergo
acceleration .During acceleration charged
Particles would radiate energy. Thus, the
revolving electron would lose energy and
finally fall into the nucleus. If this were so ,the
atom should be highly unstable and hence
matter would not exist in the form.

 In atomic physics, the Bohr model, introduced
by Niels Bohr in 1913, depicts the atom as a small,
positively charged nucleus surrounded by
electrons that travel in circular orbits around the
nucleus—similar in structure to the solar system,
but with attraction provided by electrostatic
forces rather than gravity. After the cubic
model (1902), the plum-pudding model (1904),
the Saturnian model (1904), and the Rutherford
model (1911) came the Rutherford–Bohr model or
just Bohr model for short (1913). The improvement
to the Rutherford model is mostly a quantum
physical interpretation of it. The Bohr model has
been superseded, but the quantum theory remains
sound

 The neutron is a subatomic hadron particle that has the
symbol n or n0. Neutrons have no net electric charge and
a mass slightly larger than that of a proton. With the
exception of hydrogen-1, the nucleus of every atom consists
of at least one or more of both protons and neutrons.
Protons and neutrons are collectively referred to as
"nucleons". Since interacting protons have a mutual
electromagnetic repulsion that is stronger than their
attractive nuclear interaction, neutrons are often a necessary
constituent within the atomic nucleus that allows a
collection of protons to stay atomically bound
(seediproton & neutron-proton ratio). Neutrons bind with
protons and one another in the nucleus via the nuclear force,
effectively stabilizing it. The number of neutrons in the
nucleus of an atom is referred to as its neutron number,
which reveals the specific isotope of that atom

 In chemistry and physics, the atomic
number (also known as the proton number) is
the number of protons found in the nucleus of
an atom and therefore identical to the charge
number of the nucleus. It is conventionally
represented by the symbol Z. The atomic
number uniquely identifies a chemical element.
In an atom of neutral charge, the atomic
number is also equal to the number of electrons

 The mass number (A), also called atomic mass
number or nucleon number, is the total number
of protons and neutrons (together known as nucleons)
in an atomic nucleus. Because protons and neutrons
both are baryons, the mass number A is identical with
the baryon number B as of the nucleus as of the
whole atom or ion. The mass number is different for
each different isotope of a chemical element. This is not
the same as the atomic number (Z) which denotes the
number of protons in a nucleus, and thus uniquely
identifies an element. Hence, the difference between
the mass number and the atomic number gives
the number of neutrons (N) in a given nucleus: N=A−Z

 Isotopes are variants of a particular chemical element such
that, while all isotopes of a given element have the same
number of protons in each atom, they differ in neutron
number. The term isotope is formed from the Greek roots
isos (ἴσος "equal") and topos (τόπος "place"), meaning "the
same place". Thus, different isotopes of a single element
occupy the same position on the periodic table. The number
of protons within the atom's nucleus is called atomic
number and is equal to the number of electrons in the
neutral (un-ionized) atom. Each atomic number identifies a
specific element, but not the isotope; an atom of a given
element may have a wide range in its number of neutrons.
The number of nucleons (both protons and neutrons) in the
nucleus is the atom's mass number, and each isotope of a
given element has a different mass number

 Isobars are atoms (nuclides) of different chemical
elements that have the same number of nucleons.
Correspondingly, isobars differ in atomic
number(or number of protons) but have the
same mass number. An example of a series of
isobars would be 40S, 40Cl, 40Ar, 40K, and 40Ca. The
nuclei of these nuclides all contain 40 nucleons;
however, they contain varying numbers of protons
and neutrons.
 The term "isobars" (originally "isobares") for
nuclides was suggested by Alfred Walte Stewart in
1918. It is derived from the Greek word isos,
meaning "equal" and baros, meaning "weigh

Structure of the atom

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