Atom and molecules: What is the atom?
The smallest particle of an element that may or may not have an independent existence but still takes place in a chemical reaction is called an atom. An atom is defined as the smallest unit that holds the properties of an element.
Atom and molecules: Theories about it
The atom was considered indivisible till the 19th century, but at the beginning of the 20th century, it was proved by scientific discoveries and research that although the atom is a very small particle, it also has a complex structure and the atom itself is composed of various types of very fine particles.
Is made up of electrons comprised of protons and neutrons, thus according to the modern concept of nuclear positively charged protons, electrons, and neutral neutrons, the charges on protons and neutrons are exactly opposite to each other and equal.
The atom is electrically neutral.
Atom and molecules: Nucleus of the molecules
The center part of the atom is called the nucleus.
The nucleus contains neutrons and protons, which give the atom its weight and positive charge.
Neutron is completely neutral it has no positive charge or negative.
A proton carries a single positive charge and also has a mass of one unit.
The atomic number of an element is equal to the number of protons, or positive charges, in the nucleus.
The atomic mass of an element is equal to the sum of its protons and neutrons in the nucleus.
An electron carries a single negative charge.
For an atom of an element to have no charge, it must have the same number of electrons as protons.
These electrons revolve around the atomic nucleus like the layers of an onion.
Atom size
The size of an atom is very small we cannot CN an atom with our necked eyes.
The size of an item is so small that it can accommodate millions and billions of atoms in a paper seat.
However, the size of an atom can be estimated by assuming that the distance between adjacent atoms is half the radius of an atom.
Atomic radius is usually measured in nanometers.
It’s measured with a manometer uni which represents 10 -⁹nm = 1 m
It’s measured with a manometer uni which represents 10 -⁹nm = 1 m
People who discovered
Electron. -J J Thompson
Proton - Rutherford
Neutron -Chadwick
Atomic number
The total number of protons present in the nucleus of an atom of an element is called the atomic number of that element, it is represented with Z.
The atom of any element is electrically neutral and the number of protons in it is equal to the number of electrons.
Atomic number Z = number of rotors = number of electrons.
Mass number
The sum of the number of protons and neutrons present in a nucleus of a mass is called the mass number of an atom.
Mass number A =no of protons= number of neutrons
Atomic weight
The atomic mass of an element is the number that shows how many times an atom of the element is heavier than one-third of the mass of the carbon atom, that is, we estimate the mass of an atom as 12 parts to the carbon atom.
An atomic number equal to
The atomic mass of an element ÷ 12th of the mass of a carbon atom
Molecular weight
The molecular mass of a substance is a number that shows how many times one molecule of that substance is heavier than one-twelfth of an atom of the carbon-12 isotope.
Molecular weight=
The molecular weight of the substance ÷ 1/12× mass of carbon 12 atom
For the example-molecular weight of NaCl
The molecular weight of the Ca + 2× molecular weight of the Cl = 40.08+2×35.45=110.98
Atomic Masses of Some Elements
Elements Atomic Mass (u)
Hydrogen. 1
Carbon 12
Nitrogen 14
Oxygen 16
Sodium 23
Magnesium. 24
Sulfur 32
Atomic orbit
According to modern ideas based on the wave progression of electrons, there are no clear circular orbits around the atomic nucleus.
These regions are called atomic orbitals.
In words, the area outside the center in which the electron is most likely to be found is called four types, it is represented by s,p,d, and f.
These names mean sharp, principal, diffuse, and fundamental, respectively, based on the spectrum. It should be known that two electrons can reside in the outermost orbit of an electron.
Orbit base K. L. M. N
N of orbit base. 1, 4, 8. 16
Type of orbit. 1 1…. 1,3,5…. 1,3,5,7….
Max no of electron 2 8 18 32
Forces between atoms and molecules
The simplest forces between atoms are those due to the transfer of electrons.
A simple example is sodium fluoride.
The sodium atom has a nuclear charge of +11, with 2 electrons in the K-shell, 8 in the L-shell, and 1 in the M-shell.
The fluorine atom has a core charge of 9 with 2 electrons in K and 7 in it.
L lag.
The outermost electron of the sodium atom can be easily transferred to the fluorine atom; both atoms now have full shells, but sodium now has a net charge of +1 and fluorine a net charge of -1.
These ions, therefore, attract each other by direct Coulomb interaction.
The force between them is strong, it varies as x-2, where x is the distance between the ions, and it acts in the direction of the line connecting the ions.
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Q1- what is the atom?
Answer-the atom is the smallest particle of element which participate in a chemical reaction.
Q2-Can a molecule have one atom?
Answer-an electrically neutral group of two or more atoms held together by chemical bonds is the most basic definition of molecule. In that sense, no, by nature, a molecule can not be formed from a single atom.
Q3-What is the difference between atoms and molecules?
Answer-What is the difference between atoms and molecules?
A tiny particle of a chemical element is called an atom, which may or may not exist independently. Molecules refer to the group of atoms that the bond binds together, representing the smallest unit in a compound. Two or more identical or distinct atoms are chemically bonded.
Q4-Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Answer-the postulate of Dalton’s atomic theory that is the result of the law of conservation of mass is—the relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor destroyed in a chemical reaction
Q5-Define the atomic mass unit.?
Answer-one atomic mass unit is equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12. The relative atomic masses of all elements have been found with respect to an atom of carbon-12.
Q5-Why is it not possible to see an atom with naked eyes?
Answer-Atom is too small to be seen with naked eyes. It is measured in nanometres.
1 m = 109 nm
Q6-Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Answer-The relative number and kinds of atoms are constant in a given compound..
