The atomic structure was first described by scientists John Joseph Thomson and Ernest in 1900. This model of atom is still used as basis of modern atomic theory.
Atoms are nothing but basic building blocks of matter, which has mass and takes up space. All the matter is made up of atoms. The word atom is obtained from Greek and is indivisible.
In the late twentieth century there has been a great renewal in the history of medieval atomism. It has long been thought that ancient atomists such as Epicurus or Lucretius were re-discovered during the Renaissance. Later on atomism was devised by Leucippus and his student Democritus and gave an overview of the concept.
- Each atom is considered as a parmenidean unit, and each is indivisible. There is no differentiation between from one part of an atom from another.
- There is no empty space within an atom.
- Comparison between Anaxagoras and Empedocles was made and the atomists offered quantitative pluralism.
An atom is a small particle and is obtained from broken particles of matter, but the atoms cannot be broken down further. An atom looks like a tiny solar system. Nucleus is the center of the atom which has positive electric charges and is the cluster of protons and neutrons.
The electrons are smaller and have negative charges. The first atomic theory was proposed by Dalton, an English Scientist in 1808. It is based on the observations of atomic and molecular weight of an atom.
The Properties of an Atom has Described Below:-
Democritus had meant the following in his postulates.
- The atomists declared that each atom is uniform, and that they are homogeneous, colorless, tasteless, and indivisible.
- According to Democritus atomist universe each atom moves about the void space, collide and attach to each other to form compounds.
- Atoms have secondary qualities but these could be reduced to primary qualities of their component atoms.
- In other words the secondary qualities of a compound are completely determined by and reducible to the primary qualities of its component atoms.
- The movement of an entire system of atoms is just the sum of the movements of all its individual component atoms.
Structure of an Atom has given Below:-
- It is physically impossible to divide an atom
- It is conceptually impossible to divide an atom
- Atoms are particles of elements or substances. These cannot be broken further without changing the chemical nature of the substance.
- Atomic structure of an atom mainly consists of three particles such as electrons, protons, and neutrons.
- These sub atomic particles have different properties. The center of the atom has nucleus which consist of protons and neutrons.
- Protons have positive electric charge and it should be much larger and heavier than electrons.
- Neutrons have no electrical charges and it is much heavier and larger like protons.
- Electrons are very small, tiny, and lighter particles and it has negative electric charge.
- Electrons are present at considerable distance from the nucleus in a series of levels called energy levels.
- Each energy level can hold certain number of electrons only. The first energy level which is very close to the nucleus can hold only 2 electrons, the second and third level can hold only 8 electrons.
Electrons can arrange from inner level to outer level.
For example see the structure of hydrogen and carbon atom. Hydrogen has only one proton so it has only one electron. Carbon has 6 protons, so the first energy level can hold 2 electrons and remaining 4 electrons can hold by the second energy level. The group number of the atom depends upon the number of electron present in the outer most orbital or energy level.
For example barium is in the group 2, since it has 2 electrons in the outer most orbital and iodine is group 7 since the iodine has 7 electrons in the outer most orbital.
The general structure of atoms is described with the help of quantum mechanics. Of these, Bohr’s theory of hydrogen based on Rutherford’s nuclear atom and making use of those ideas of Planck to triggered the discussion of atomic structure.
- Bohr’s semi classical theory was not general enough to describe more than the gross features of the simplest one-electron atom, but it provided a model of an atom which is viable and accepted as well.
- The general atomic structure consists of three fundamental particles, protons and neutrons, which are basically contained within the atomic nuclei and electrons which surround the nuclei.
- Protons and neutrons are nothing but considered to be the composite particles with each having three quarks and are therefore not fundamental particles in true sense.
- They might be considered as fundamental particles for all kinds of chemical purposes.
- General structure of an atom mainly consist sub atomic atoms like protons, electrons, and neutrons.
- Below figure shows the general structure of an atom. The most of the atoms are empty space, but some of the atoms consist of positively charged nucleus which is consist of positively charged protons and no electrical charges (neutral) of neutrons that are surrounded by negatively charged electrons which are form a complex cloud around the nucleus.
- So, the nucleus is the center of the atom surrounded by a cloud of electrons.
- Protons are resided in the center of the nucleus of an atom that contains large mass with positive charged particle.
- Many type of elements defined by the number of protons in the nucleus which is referred to as its atomic number. For example the atomic number hydrogen atom is one, since it has only one proton in nucleus and the atomic number of carbon atom is six, since it has six protons in that nucleus.
- Neutrons are resided in the center of nucleus of an atom along with protons. Neutron mass is almost identical to the proton mass.
- Electrons are move around the nucleus and placed in the atomic orbital, which are called as energy level.
- The principle quantum number (n), and secondary quantum number (I) are used to define the energy level of an atom.
- Usually, the number of electrons are equal to number of protons, so the net charges in the atom is zero, such type of type of atoms are called as electrically neutral atom. Some times atoms can loose or gain electrons resulting in negative or positive charge atoms, such type of atoms are called as ions.
- The atomic number of any element can used to indicate how many number of protons and electrons are their in that element.
- A proton atom has 1836 times that of electrons mass, since electron atom has very little mass and neutron mass is almost identical to proton mass. Electrons are having very little mass compared with proton, so they are not taken in the consideration for the calculation of atomic mass.
The atomic mass of any element can used to indicate only how many numbers of protons and neutrons are their in that element not number of electrons.
- The structure of an atom is mainly composed of three sub atomic particles like protons, neutrons and electrons.
- The most of the atomic mass of the elements depends upon the protons and neutrons of the atom.
- Both protons and neutrons are present inside of the nucleus and the electrons are present in the orbitals or different energy level around the nucleus.
- Protons have positive charge; electrons have negative charge but neutrons do not have any charge, since they are neutral.
- The number of protons present in the atom determines the atomic number of atom.
- For example atomic number of hydrogen is H =1, since it has only one proton. In some cases, for example the hydrogen and uranium has the same proton number (atomic number) but varying mass number because both the elements have different neutron number.
Atomic number = Number of protons present in nucleus
Atomic mass = Number of protons + Number of neutrons
The above figure shows the atomic and mass number of fluorine. It has 9 protons and 9 electrons and 10 neutrons. The elements which are having same number of atomic number and varying mass number are called as Isotopes
, for example three kinds of carbon atoms 12C, 13C, 14C. All the carbon atoms have same number of protons but different numbers of neutrons. 12C, 13C, 14C have 6 protons, and varying neutrons like 6, 7, 8 respectively, so it has different mass number. So these different carbons atoms are called as isotopes
. Heavy elements have large number of protons and neutrons, for example uranium has 92 protons and 146 neutrons. Light elements have less number of protons and neutrons, for example hydrogen has only one proton and no neutron. Bohr model and the Wave model are mainly used to describe the structure of an atom.
Bohr model shows how the electrons are circulating around the nucleus at different energy levels or orbitals and this model can only explain the structure of simple atoms like hydrogen. The wave model and quantum theory can gives the probability of locating electrons in a particular location.
- The structure of an atom consists of a nucleus which is comprised of proton (+), neutron, and electron (-).
- The nucleus is positively charged, which is determined by the number of protons present in the nucleus.
- The negatively charged electrons are present in the orbit of definite energy level which is surrounded by nucleus.
- Most of the chemical properties of the element and molecules depend upon the electrons of the atoms involved.
- The atom can either gain or lose electrons to become negatively or positively charged.
- The atoms which have 1, 2, or 3 electrons present in outer most orbital can loss the electrons while interaction with atoms which have 5, 6, or 7 electrons present in the outer most orbital.
- The atom which have 5, 6, or 7 electrons in the outer most orbital can gain the electrons while interaction with atoms which have 1, 2, or 3 electrons in the outer most orbital.
- The atoms which have 4 electrons in the outer most orbital will tend neither to totally lose not totally gain electrons during interactions.
- Atoms can form stable electrons by either losing electrons, sharing electrons, or gaining electrons.
- Atoms are basically neutral, since the positive protons are neutralized by negative electrons. So the number of protons is equal to the number of electrons.
The modern atomism dealt with mainly Dalton and his postulates where he states that
- Every atom is composed of indivisible particles called atoms
- Atoms of one element are all alike and have the same atoms
- Atoms are indestructible and can combine together to form compounds in definite ratio of whole number
The concept of indestructibility of atom has been discarded by the discovery of various fundamental particles like electrons, protons and neutrons. Faraday made an extensive study of the decomposition of solutions of salts, acids, and bases by the passage of electric current.
Faraday stated his law of electrolysis from these findings. It was soon realized that in solution current is carried by the charged particles of matter called ions.