Introduction of Atomic strcture:-
- Atomic structure is a fundamental concept in chemistry that forms the basis for understanding the behavior of matter at the molecular and atomic levels.
- Knowledge of atomic structure is crucial for various competitive exams, including chemistry, physics, and engineering.
Key Concepts :
Atom:
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- An atom is the smallest unit of an element that retains its chemical properties.
- Atoms are composed of three subatomic particles: electron, proton, and neutron.
Proton(p) :-
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- Positively charged subatomic particles found in the nucleus of an atom.
- Protons determine the element’s identity and contribute to its atomic mass.
- Each element has a unique number of protons, known as the atomic number.
Neutron(n) :-
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- Neutrally charged subatomic particles also located in the nucleus.
- The number of neutrons can vary within the same element, leading to isotopes with different atomic masses.
Electron(e-) :-
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- Negatively charged subatomic particles found in electron shells or energy levels surrounding the nucleus.
- Electrons are involved in chemical reactions and determine an atom’s chemical behavior.
- The distribution of electrons in different energy levels follows specific rules and patterns.
Atomic Number (Z):
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- The number of protons in an atom, which is unique to each element.
- Elements are arranged in the periodic table based on their atomic numbers.
Mass Number (A):
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- The sum of protons and neutrons in the nucleus of an atom.
- Isotopes of the same element have different mass numbers due to varying numbers of neutrons.
Electron Configuration:
Describes the arrangement of electrons in an atom’s energy levels.
Follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule.
Atomic Mass:
The weighted average mass of all naturally occurring isotopes of an element.
Expressed in atomic mass units (amu) or unified atomic mass units (u).
Bohr Model:
A simplified atomic model that represents electrons in specific energy levels or orbits around the nucleus.
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- Useful for understanding atomic emission spectra.
Quantum Mechanical Model:
A more modern and accurate model that describes electrons as wave-like entities occupying orbitals in three-dimensional space.
Explains the probability of finding an electron in a specific region around the nucleus.
Periodic Table:
Organizes elements based on their atomic number and chemical properties.
Elements in the same group have similar electron configurations and exhibit similar chemical behavior.
Most important SSC atomic structure questions:
Understanding atomic structure is crucial for explaining the behavior of matter, chemical reactions, and the properties of elements.
Protons and Neutrons
just like helium nuclei
Explain- Alpha (α) particles are mainly helium
(2He4) nuclei. They are formed by two protons and
two neutrons.
James Chadwick
James Chadwick
J J Thomson
Solutions
Explanation: The solution of two or more components is
called homogeneous mixture. There are three types of
solution, 1- Gaseous solution 2- Liquid solution, 3-
Solid solution.
Lithium (Li) is a s-block element. Its atomic
number is 3. It has 3 protons in its nucleus.
mass of electron = 1/1837 times of proton
Cathode rays are the stream of electrons
which move from cathode electrode to anode electrode
in the discharging tube, hence cathode rays are the
group of highly moving negative particles and these
negative particles are electrons.
The electrons in the atom revolve in different
orbits around the nucleus. Niels Bohr Bury devised
some rules to find the number of electrons in different
orbits, called as Bohr-Bury Rule. According to the Bury
rule, the number of given by electrons in an orbit is the
maximum 2n2
, where n is the number of orbitals,
For, n = 1,
⇒ 2 × (1)2
= 2
for n=2; 2n2=8
Hence, the number of electron for first shell is 2.
The size of the nucleus of an atom is 10–15
meter (approximately)
The atomic number of oxygen is 8 having
atomic mass of 16 u or amu.
The atomic number of oxygen is 7 having
atomic mass of 14 u or amu.
Nitrogen (N2)
Atoms having same atomic number but different mass number are known as isotopes.
Isotopes of hydrogen are protium (1H1) ,Deuterium (1H2) and Tritium (1H3) .
Scandium (Sc) is the element of the p-block of the periodic table, its atomic number is 21 and its
atomic weight is 44.95u It has 13 isotopes whose atomic weight varies from 40 to 52.
Frederick Soddy
Atoms of the same element whose atomic
number is similar but mass number is different, is
called as isotopes.
Elements having same mass number but
different atomic number are known as isobars.
e.g. 19K40 and 20Ca40.
Same mass numbers but different atomic
numbers
Elements which have different atomic number but same mass number are called isobars. Since
the mass number of Argon and Calcium are same they are isomeric pairs. Both of these mass number is 40 u.
Radioactivity
The atom make bonds to reduce potential
energy and gain stability.
Polar Covalent Bond–When covalent bond
is formed between two different atoms, e.g. HF, HCl
and the shared pair of electrons between them get
displaced more towards higher electronegativity atom.
The resultant bond is known polar covalent bond.
The shared pair of electron gets displaced move
towards chlorine since electronegativity of Cl is greater
than H.
The production of iron from its ore involves the process of reduction.
Sulphur and Chlorine has polar covalent bond. Since electronegativity of Cl is greater than S,
the shared paired of electrons get displaced, move towards Cl.
Ans. (d) Among the following forming covalent compounds in an appropriate property of Beryllium.
Calcium fluoride is an inorganic element, its
chemical formula is CaF2. Its charge is 0. but individually ca and cl has +2 and -1 charge respectively.
Oxidation is the process of removal of electron,
hydrogen and electro positive element or group and
additon of oxygen and electro negative element or
group.
(a) If it has more electrons than protons
(d) : Corrosion of iron is called rusting. Corrosion
occures when metal formed metal oxide. Thus oxygen
gas must need for rusting. Corrosion accelerated due to
the presence of moisture in atmosphere, Hydrated iron
oxide is known as rust.
Ans(a) aluminium
Cation:- The ions have positive charge is
called as “cation”.
Eg- NH4+, Ca++, Al3+, H3O+
Anion:– The ions have negative charge is called as
“anions”. Eg- Br–, I–, Cl–, OH–