A matter is any substance which has mass and occupies space. All the objects around you, this book, your pen or pencil and natural things, such as rocks, water, and plants are the subject of the universe.A matter is made up of atoms. The smallest indivisible particle of matter is an atom.The various scientist gave the theory about the complex structure of an atom.
A structure of an atom consists of several small particles.Three important particles are
- Proton and
These particles are main constituents of the atom we call as fundamental particles. The electrons present around the atom are attracted to the protons.These protons are present in an atomic nucleus.The force with which these electrons are attracted is an electromagnetic force. The protons and neutrons also attract each other in the nucleus.But this force is called as the nuclear force.
Except for hydrogen, all elements made up of atoms are having three subatomic particles electron proton and neutrons. Hydrogen is made up of one electron and one proton. It does not contain any neutron.The atoms of different elements are different in number of protons electrons and neutrons when these subatomic particles put together they give a structure of an atom
Atomic Structure Definition
An atom is the smallest part of the matter. An atom participates with its chemical properties. It is made up of electron proton and neutron. Atoms are very small. There size typical around a ten-billionth of a meter.
Properties of an Atom
- Dalton, in 1808, proposed that atoms are very very small, inseparable particles.
- Atoms are tasteless and colorless.
- An atom is electrically neutral.
- The number of protons and neutrons together decide mass of an atom.
- The number of atoms before and after the reaction remain same.
- Atom is the smallest particle of an element that participates in the chemical reaction.
- When the group of atoms gets together may be same or different types we call as a molecule.
- The size of an atom varies between .3 Å(1angstrom=10−10 m) to 3 Å.
- Atom is the smallest particle of an element that retains all its properties and enters into a chemical reaction.
General Structure of an Atom
The concept of Structure of an atom was given by the three scientists.Out of which Neil Bohr successfully explained the structure of an atom. A comparison between the different models proposed by the three scientist JJ Thomson, Rutherford and Neil Bohr is given below:
J J Thomson Atomic Theory
Ernest Rutherford Atomic Theory
Neils Bohr Atomic Theory
|An atom consists of a ball. positive charge(+) and electrons(-) are embedded like a seed.The number to the total positive charge equals to the negative charge due to which an atom has no charge.It means atoms are electrically neutral||An atom consists of the positively charged nucleus at the centre. Electrons revolve around the circular path with a very high speed.There exists an electrostatic force between the proton and the negative charge electron which keep the atom hold together. The number of protons is equalled to the number of negative electrons.Due to which atom is electrically neutral.Almost entire mass of an atom in the nucleus.Most of the atom is empty space.||Bohr model of atom states that an atom is made up of three particles electron proton neutron.An electron has a negative charge, proton having a positive charge while the neutron has no charge. Electrons revolve in a fixed energy level donated as 1,2,3,4,5,6 or by letter K, L, M, N, O, P counted from the centre to outward|
Explain the Structure of an Atom
The general structure of an Atom has explained below:
- The structure of an atom is made of smaller particles.These smaller particles are known as subatomic particles.
- The three subatomic particles are electron proton and neutron.
- An electron is having a negative charge, a proton has a charge of positive while neutron has no charge.
- The entire mass of an atom is in the nucleus as proton and neutrons are present in a small nucleus at the centre of an atom.
- The electrons revolve around the nucleus.They have a very small mass.
- The nucleus is having a positive charge because of the presence of protons at the centre.
- The electrons revolve around the nucleus at a very high speed in a fixed circular shell known as energy level or shell.
- An atom on a whole is electrically neutral it is because the number of electrons outside the nucleus is equal to the number of the proton inside the nucleus. Therefore, an atom on a whole has no positive or negative charge.So, Atom is electrically neutral.
Atomic Structure of an Atom
- It can now be evidence at the end that atom consists of two parts: Nucleus and Extra-nuclear part.
- A nucleus is a central part of an atom where all the proton and neutrons are present.
- The negatively charged electrons revolve in a fixed orbit around the nucleus.The path is thus term as extra-nuclear part.
- Scientist now believes that In chemistry, atomic structure protons and neutrons lose their identity. They merge together to form a tiny dense ball-nucleus.
- Protons and neutrons are considered as composite particles with having three quarks each. So, they are not fundamental particles in the true sense.
- The constituents of the nucleus, both proton, and neutron, are often termed as nucleons.
- After the discovery of electron, protons, neutrons, many other important particles were also invented.These are positron, mesons, antiprotons etc.
- These particles are present within the nucleus.
- The positron or anti-electron has a charge same as an electron and has the same mass as an electron.
- Antiprotons are stable and have a short life period.
- positron: It is the positive counterpart of an electron, discovered by Anderson. On combining with electrons, produce γ-rays.
- Neutrino and antineutrino: This discovery was by scientist Fermi in 1934. Their mass is negligible and has no charge.
- π- mesons and μ- mesons: This discovery was by scientist Yukawa. Their mass is in between that of electron and proton.
Describe the Structure of an Atom
- The number of protons distinguishes the atom of one element from atoms of another element
- The atoms of the same element are the Identical in all respects, size, size, and mass.
- Atoms of various elements combine with a certain ratio to form a compound which is term as molecules.
- The atomic number of an element does not change during a chemical reaction.
- Proton and the neutrons have unit mass each, the atomic mass of an atom is numerically equal to the sum of proton and neutron.
- The atomic number of an element is donated by the letter Z.
- The atomic number tells us the number of proton in an atom of an element.
- It also tells the number of electrons in a normal atom.
- An electron has negligible mass and they have almost no contribution towards the weight of an atom. However, the volume of an atom is mainly due to this part.
- The mass number of an atom is donated by the letter A.
- Hence the mass number of an atom is the number of its nucleons.Mass number = No. of protons + No. of neutrons.
Atomic Number and Mass Number
- In 92U238, atomic number, Z = 92 and mass number, A = 238.
- In 8O16, atomic number, Z = 8 and mass number, A =16.
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