Structure of an Atom | Part 1/1 | English | Class 9
Summary
TLDRThis video explains the structure of an atom, exploring the discovery of subatomic particles like electrons, protons, and neutrons. It covers key atomic models, including Thomson's 'watermelon' model, Rutherford's nuclear model, and Bohr's theory of discrete electron orbits. The video also highlights experiments like Rutherford’s gold foil experiment, which led to the conclusion that atoms have a small, dense nucleus. The video ends by introducing neutrons and their role in the atomic nucleus, setting the stage for a deeper discussion on electron distribution in the next video.
Takeaways
- 🌐 The structure of an atom is crucial for understanding the differences between elements.
- 🔬 Atoms are not indivisible; they consist of smaller, charged particles.
- 📚 The electron was the first subatomic particle discovered, with a negative charge.
- 🔵 In 1886, protons were discovered, which have a positive charge and are much heavier than electrons.
- 🍉 J.J. Thomson proposed a 'plum pudding' model of the atom with electrons embedded in a positively charged sphere.
- 🔬 Ernest Rutherford's gold foil experiment led to the discovery that atoms have a small, dense nucleus.
- 💥 Rutherford found that most alpha particles passed through the gold foil with little deflection, indicating a mostly empty interior.
- 📉 A very small number of alpha particles were deflected at large angles, suggesting a concentrated positive charge and mass in a tiny volume.
- 🌕 Rutherford's nuclear model placed a positively charged nucleus at the atom's center, with electrons orbiting it.
- 🌀 Niels Bohr introduced the concept of discrete orbits to explain the stability of atoms, where electrons do not radiate energy.
- 🇳 In 1932, James Chadwick discovered neutrons, neutral particles that also reside in the nucleus.
Q & A
What is the significance of the alpha particle scattering experiment conducted by Rutherford?
-Rutherford's alpha particle scattering experiment revealed that most of the space inside an atom is empty, with a small, dense, positively charged nucleus at its center. This experiment led to the discovery of the nuclear model of the atom.
What were the key postulates of Niels Bohr's atomic model?
-Bohr's atomic model postulated that: 1) Electrons revolve in certain discrete orbits without radiating energy. 2) These orbits or shells are represented by the letters K, L, M, N or the numbers n=1, 2, 3, 4, etc. These stable orbits prevent the collapse of the atom.
How did J.J. Thomson's atomic model describe the structure of an atom?
-Thomson's atomic model described the atom as a positively charged sphere with negatively charged electrons embedded in it, similar to seeds in a watermelon. The positive and negative charges were equal, making the atom electrically neutral.
What did Goldstein discover, and how did it contribute to our understanding of the atom?
-In 1886, Goldstein discovered the proton, a positively charged subatomic particle. This discovery helped establish that atoms consist of charged particles and that protons, with a mass approximately 2000 times that of an electron, are found within the nucleus.
Why was Rutherford's atomic model considered incomplete or flawed?
-Rutherford's model was flawed because it suggested that electrons, revolving around the nucleus, would radiate energy and eventually spiral into the nucleus, causing the atom to collapse. This instability contradicts the observed stability of matter.
What new particle did James Chadwick discover, and what role does it play in the atom?
-James Chadwick discovered the neutron in 1932. Neutrons are neutral particles with a mass nearly equal to that of a proton. They are found in the nucleus and contribute to the atomic mass, but do not affect the atom's charge.
Why did Rutherford choose gold foil for his experiment, and what was the outcome?
-Rutherford chose a thin gold foil, only 1000 atoms thick, because he needed a material with as thin a layer as possible. The experiment showed that most alpha particles passed through the foil, with only a few being deflected, indicating that atoms are mostly empty space.
How did Rutherford conclude that the positive charge is concentrated in a small nucleus?
-Rutherford concluded that the positive charge is concentrated in a small nucleus because very few alpha particles were deflected by large angles. This indicated that the positively charged mass of the atom is confined to a very small central region.
What is the significance of Bohr's model in explaining atomic stability?
-Bohr's model explained that electrons move in specific, stable orbits where they do not radiate energy. This stability of orbits prevents electrons from spiraling into the nucleus, explaining why atoms do not collapse and remain stable.
How is the mass of an atom determined according to the discoveries of protons and neutrons?
-The mass of an atom is primarily determined by the sum of the masses of protons and neutrons in the nucleus, as electrons have a negligible mass. The discovery of neutrons helped complete the understanding of atomic mass composition.
Outlines
🔬 Introduction to Atomic Structure and Early Discoveries
The video opens with a discussion on the structure of the atom, exploring the existence of different substances due to the atoms they are composed of. It raises key questions: why atoms of different elements differ and whether atoms are truly indivisible. An experiment with a comb and small pieces of paper demonstrates that rubbing objects can charge them. This introduces the concept that atoms are divisible and contain charged particles. The 19th-century discovery of the electron and proton is discussed, highlighting the proton's larger mass and opposite charge to the electron. Early atomic models, such as Thomson's 'watermelon' model, are introduced, explaining that atoms consist of a positively charged sphere with embedded electrons, making them electrically neutral.
⚛️ Rutherford's Alpha Particle Scattering Experiment
The second section details Rutherford's groundbreaking experiment, designed to study the arrangement of electrons in an atom. In the experiment, fast-moving alpha particles were directed at a thin gold foil. Contrary to expectations, most alpha particles passed straight through, while some were deflected at small angles, and a few even rebounded. From these results, Rutherford concluded that most of the atom is empty space, the positive charge is concentrated in a small nucleus, and the mass of the atom resides in this nucleus. He calculated that the nucleus is much smaller than the overall size of the atom and presented the nuclear model of the atom, where electrons orbit around a central nucleus. However, he also noted the instability of electrons in circular orbits, raising concerns about the stability of matter.
💡 Bohr’s Model and Discovery of Neutrons
The final section of the video discusses the limitations of Rutherford’s model and how Niels Bohr addressed these concerns by proposing that electrons revolve in discrete orbits where they do not radiate energy. These orbits are represented by letters (K, L, M, N) or numbers (n = 1, 2, 3, 4). The video also highlights the discovery of the neutron by James Chadwick in 1932, a particle with no charge and a mass similar to that of a proton, which resides in the nucleus of all atoms except hydrogen. The mass of an atom is determined by the sum of its protons and neutrons. The video concludes by previewing the next lesson on electron distribution in orbits.
Mindmap
Keywords
💡Atom
💡Subatomic Particles
💡Electron
💡Proton
💡Neutron
💡Thompson’s Atomic Model
💡Rutherford's Atomic Model
💡Alpha Particle Scattering Experiment
💡Bohr's Model
💡Nucleus
Highlights
Introduction to the structure of atoms and how atoms of different elements vary.
Activity demonstrating how rubbing objects generates an electric charge.
Discovery of subatomic particles, starting with the electron, and the divisibility of atoms.
Goldstein's discovery of the proton in 1886 and its properties.
Introduction to Thompson's atomic model, comparing it to a watermelon.
Thompson's model explained that the atom is electrically neutral due to balanced positive and negative charges.
Introduction to Rutherford’s alpha particle scattering experiment and its unexpected results.
Rutherford's findings that most of the space in an atom is empty.
Conclusion from Rutherford’s experiment that the positive charge and mass of an atom are concentrated in a small nucleus.
Rutherford's nuclear model of the atom introduced the idea of electrons revolving around a small nucleus.
Limitation of Rutherford's model: The instability of revolving electrons due to energy loss.
Bohr’s postulates resolving Rutherford's model limitations with the idea of discrete electron orbits.
Bohr’s model proposed that electrons do not radiate energy while in these discrete orbits.
Chadwick's discovery of the neutron in 1932, adding a third subatomic particle to the atomic model.
Explanation that the mass of an atom is the sum of the mass of protons and neutrons in the nucleus.
Transcripts
[Music]
[Applause]
[Music]
hello friends
welcome to this video session
topic we are going to study in this
session is
structure of atom we have seen
that the existence of different
substances
is due to the atoms from which they are
made
but why does the atom of
one element differ from the atoms of
another element and are
atoms really undivided
we will find the answers of these
questions
in some upcoming videos
let us do an activity to know the nature
of particles
in matter dry hair
now move this comb close to the small
pieces of paper
what do you see yes the comb
attracts small pieces of paper we
conclude
that on rubbing two objects together
they become electrically charged
where does this charge come from
this question can be answered by knowing
that an atom
is divisible and consists of
charged particles
by the 19th century scientists
had discovered that an atom is
not an ordinary and indivisible particle
but it contains at least one
subatomic particle that is
electron in 1886
e goldstein discovered another subatomic
particle
whose charge was equal to but
opposite to the charge of the electron
and the mass was
approximately 2 000 times
more than the electron these particles
were named proton
now the biggest question was
how these particles structure the atom
to understand this many scientists
presented different types of models
let us first study thompson's atomic
model
thompson presented a model related to
the structure of an atom
that was like a watermelon
according to this the positive charge in
the atom
is spread all over like the red edible
part of the watermelon
while the electrons are studded
in the positively charged sphere
like the seeds in the watermelon
thompson proposed that one
an atom consists of a positively charged
sphere and the electrons are embedded
in it 2. the negative
and positive charges are equal in
magnitude
so the atom as a whole is
electrically neutral
although thompson's model explained that
atoms are electrically neutral
the results of experiments carried out
by other scientists could not be
explained by this model
ernest rutherford was interested in
knowing
how the electrons are arranged within an
atom
brother ford designed an experiment for
this
in this experiment fast moving alpha
particles
were made to fall on a thin gold foil
one he selected a gold foil
because he wanted as thin a layer as
possible
this gold foil was about 1000 atoms
thick
2. alpha particles
are doubly charged helium ions
and they are positively charged and
since they have a mass of 4u
the fast-moving alpha particles have a
considerable amount of energy
three it was expected
that alpha particles would be deflected
by the subatomic particles in the gold
atoms
since the alpha particles were much
heavier
than the protons he did not expect to
see
large deflections
was the result of alpha particle
scattering experiment
as expected by rutherford
no rather the alpha particle scattering
experiment
gave totally unexpected results
one most of the fast moving alpha
particles
passed straight through the gold foil
two some of the alpha particles
were deflected by the foil by small
angles
three surprisingly
one out of every twelve thousand
particles
appeared to rebound
rutherford derived the following results
based on an alpha particle scattering
experiment
one most of the space
inside the atom is empty because
most of the alpha particles passed
through the gold foil without getting
deflected
two very few particles were deflected
from their path
indicating that the positive charge of
the atom
occupies very little space
three a very small fraction
of alpha particles were deflected by
180 degrees indicating that
all the positive charge and mass of the
gold atom
were concentrated in a very small volume
within the atom
four from the data he also calculated
that
the radius of the nucleus is about
10 raised to 5 times less than the
radius
of the atom based on his experiments
rutherford presented the nuclear model
of the atom
one there is a positively charged
center in an atom called the nucleus
nearly all the mass of an atom resides
in the nucleus two
the electrons revolve around the nucleus
in circular parts
three the size of the nucleus is
very small as compared to the size of
the atom
were there any drawbacks in rutherford's
model
yes the orbital revolution of the
electron
is not expected to be stable
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
and if this were so the atom should be
highly unstable and hence
matter would not exist in the form that
we know
we know that atoms are quite stable
in order to overcome the objections
raised against
rutherford's model of the atom
niels bohr put forward the following
postulates
about the model of an atom one
only certain special orbits known as
discrete orbits of electrons are
allowed inside the atom
two while revolving in discrete orbits
the electrons do not radiate energy
these orbits or shells are represented
by the letters k l m
n or the numbers n
is equal to 1 2 3
4 and so on do
only protons and electrons exist in an
atom
in 1932 j chadwick
discovered another subatomic particle
which had no charge and a mass
nearly equal to that of a proton
it was eventually named as
neutron neutrons are present in the
nucleus of all atoms except
hydrogen in general a neutron is
represented
as n the mass of an atom
is therefore given by the sum of the
mass of protons
and the mass of neutrons present in the
nucleus
in this video we studied the structure
of
atom in the next video we will learn
about the distribution of electrons
in orbits
[Music]
Ver Más Videos Relacionados
Modelos atómicos (Goldstein, Becquerel, Curie, Rutherford) - Química Desde Cero
11AS01 - History of the atom - WACE Chemistry Year 11
Rutherford's Atomic Model, Chemistry
Development of Atomic Theory: An Introduction
Atomic Structure & Coulomb's Law - AP Chem Unit 1, Topic 5a
GCSE Chemistry - History of the Model of the Atom #7
5.0 / 5 (0 votes)