The Structure and Properties of an Atom

What
is the definition of atomic structure?

Atoms form the foundation of chemistry and everything else that exists in the universe. Every matter is composed of densely packed atoms.

Properties Of An Atom

Who
discovered atoms? Who discovered electron, proton and neutrons?

John Dalton proposed the first modern
atomic model or can be said as discovered atoms. The physicist J.J.Thomson
discovered the electrons in the year 1897. English physicist James Chadwick
discovered neutron in the year 1932. Ernest Rutherford discovered protons in
the year 1909.

What
are the parts of atom?

Each atom consists of small particles:
protons, neutrons and electrons. Electrons are the smallest pieces among the
three particles that make up an atom.  Electrons have negative charges. Protons have
positive charges.

The protons and neutrons are present in the
nucleus of the atom and the elcetrons rotate around in different orbits. These
orbits are known by different alphabet names

The closest orbit to
nucleus– K Shell

The second closest orbit to nucleus—L Shell

For more information on orbital shells , one can refer to

https://van.physics.illinois.edu/qa/listing.php?id=1224&t=atoms-shells-and-orbitals
https://education.jlab.org/qa/historyele_02.html
https://chem.libretexts.org/Bookshelves/…Atoms/Quantum_Numbers

Today, we will learn the intricate
properties of these three subatomic particles electrons, protons and neutrons.
Here, we discuss
the atomic mass, relative atomic weight and several other aspects of atoms.

What is the Relative Mass?

Atomic weight and atomic mass are the
two most vital concepts you come across in Physics as well as in Chemistry.
Most students assume that both the terms are interchangeable but they are not. Atomic mass is the total number of protons
and neutrons in an atom or isotope
.

Atomic
weight is the mass of all the naturally occurring isotopes present in an
element
. Atomic
weight
is also known as the relative
mass of an atom
. Both of them are expressed in the unit called (amu) or
atomic mass unit.

A single atom mass (ma) is
the collection of the masses of all three subatomic particles present in it:
protons, neutrons and electrons.

The relative mass is expressed as a
multiple of one-twelfth of the mass of a carbon 12 atom. This means that the
relative atomic mass denotes how many times an average atom of an element is
heavier than one-twelfth of an atom of carbon 12.

What is the relative mass of a proton?

The relative mass of
Proton = 1.6726231*10-27 kg

What is the relative mass of a neutron?

Neutron = 1.6749286*10-27
kg

What is the relative mass of an electron?

Electron =
9.1093897*10-31 kg

The relative
mass of protons and neutrons are considered as “1’to
avoid complicacy while solving the mathematical problems.

Relative mass of an
electron is one of the fundamental constants of Physics. The relative mass of
an electron is also known as “rest mass” (the mass of a stationary electron
needs to be calculated to determine its value). For mathematical derivations,
the mass is considered to be zero in most cases. 

In absolute units, protons and neutrons
have the mass of 10-27 kilograms. Electrons have an even smaller
mass as compared to a proton which is 10-30.

The standard value of atomic weight or relative
atomic massis derived from the
value that is cited for that element in the periodic table

What are Protons, Neutrons and Electrons?

Protons,
neutrons and electrons are the fundamental subatomic particles of an element.

Dalton’s Atomic Theory discusses the
first building block of the concepts on matter and its compositions. However,
it was not totally accurate. Years of scientific investigation finally revealed
that atoms could be broken into even smaller subunits or subatomic particles.
When Rutherford proposed that electrons orbit a positive nucleus, scientific research
found a completely new dimension to the study.

In later experiments, Rutherford found
a smaller positively charged particle in the nucleus and named it proton. He
had also proposed the presence of a neutral particle, within the
nucleus.  This neutral particle was the
‘neutron’ (which was confirmed after a series of experiments, conducted by his
student James
Chadwick).

Protons and neutron are heavier
elements that reside at the centre of the atom within the nucleus. The
extremely lightweight particle electron, exist in a cloud orbiting the nucleus.

What Are Protons?

Protons are positively charged
particles that exist within the atomic nuclei.

Some
facts about protons

  • They
    are slightly smaller in mass than neutrons
  • Have a relative mass of 0.9986 or about
    1.673×10-27 kg.
  • They are present in the nuclei of all
    atoms.
  • Mass of a proton is always slightly less
    than that of a neutron.
  • Different elements have different number of protons.

 The number of protons in an atom is also the
same as the atomic number of that element.

The
atomic number can be thus defined as the
total number of protons present in an element.

What are Electrons?

The
electrons are negatively charged elements that are electrically attracted to
the positively charged protons. J.J. Thomson, a British physicist, discovered
electron and initially named it “corpuscles.”

Some
facts about electron

  • Electrons are negatively charged
  • Electrons surround the atomic nucleus in
    specific pathways called orbitals
  • Inner orbitals are spherical in shape
  • The outer orbitals are much more
    complicated

Electron
configuration of an atom help determine the stability, conductivity and boiling
points of atoms of elements.

What
are Neutrons?

These
particles constitute every atomic nucleus except for ordinary hydrogen. It was discovered by James Chadwick in 1932.
Neutrons are particles of an atom that has a neutral charge. Neutrons are
neither positively charged (like protons) nor negatively charged (like
electrons).

Some
facts about neutrons

  • Various elements undergo nuclear reaction when
    bombarded by neutrons
  • The nuclear reactions progress as chain reaction.
  • Neutrons undergo radioactive decay when it breaks into
    proton , electron and antineutrino.

Neutrons play a major role in mass and
radioactive properties of an atom. Within a few years of its discovery, it was
revealed that various elements undergo a type of nuclear reaction (fission)
when bombarded by neutrons. The nucleus of a heavy element split into two
nearly equal halves in case of each nuclear reaction that can continue as a
chain reaction.

In 1942, Enrico Fermi and a group of
American researchers demonstrated how the chain reaction of the fission process
works. In subsequent years, this development led to the foundation of the
atomic bomb.

Neutrons undergo radioactive decay
where it breaks down into a proton, an electron and an antineutrino. This is
also known as beta decay and the half-life for this decay is 614 seconds.  A neutron has a relative mass of 1 and has a
physical mass of 1.6749x10-27 kg.

What
are the 4 types of atoms?

Atoms which are almost
same but have different number of neutrons are called isotopes.

Atoms with too many
neutrons in their nucleus, renders them unstable. They’re called radioactive.

Atoms with extra electrons or missing electrons are referred as ions. They can have either a positive charge or a negative electric charge.

Every
atomic particle has a twin anti-particle, with an opposite electric charge. The oppositely charged twin atoms
are called antimatter.

Mass of Proton Vs Electron

According to Physics,
the proton-to-electron mass ratio (μ or β) is considered as the rest mass of
the proton divided by that of the electron. As this is a ratio of similar
dimensioned physical quantities, the resultant becomes dimensionless. The final
numerical values are independent of the system of units as well.

μ = mp/me=
1836.15267389(17)

The enclosed parenthesis is the “measurement uncertainty” where the value of μ is about 0.1 parts per billion.

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Suggested Reads:-

https://www.wikilectures.eu/w/Atomic_Models
https://sciencing.com › Science › Chemistry › Atomic & Molecular Structure
https://www.nature.com/articles/nature08879

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