<–2/”>a >Atomic Structure
In 1897 J.J. Thomson discovered electron as a constituent of atom. He determined that an electron had a negative charge and had very little mass as compared to that of the atom. Since an atom was found to be electrically neutral it was inferred that some source of positive charge must be present in the atom. This soon led to the experimental discovery of the proton, which is a positively charged subatomic particle. Proton was found approximately 1840 times heavier than an electron. Further‘ experiments revealed that the atomic masses were more than that expected from the presence of just protons and electrons in the atom.Sir James Chadwick discovered neutraly charged neutron in 1932.
Various theories put forwarded regarding the structure are as follows:-
Dalton’s atomic theory
John Dalton used the Greek concept of an atom and the laws of definite proportions, conservation of mass and multiple proportions to give the atomic theory on scientific basis. Dalton’s atomic theory states that all matter is made of atoms. Atoms are indivisible and indestructible, all atoms of a given element are identical in mass and properties,compounds are formed by a combination of two or more different kinds of atoms and a Chemical Reaction is a rearrangement of atoms.
J . J. Thompson Plum pudding model
The discovery that atoms contained electrons caused Thompson to predict an atomic structure, according to which the whole atom was considered to be a positive sphere,
with negatively charged electrons embedded in it like a plum in a pudding. Thompson’s model did not have any nucleus in it.
But, with the discovery of the nucleus and positively charged proton and neutrally charged neutrons, two more important models of atomic structure were put forward:
Rutherford atomic model
Rutherford atomic model, though a major breakthrough with a central nucleus and surrounding electrons, did not explain how an electron keeps revolving around the nucleus without losing energy.
Bohr’s atomic structure
Niels Bohr expanded Rutherford’s theory further and gave a clear concept of balancing the attractive force and the centrifugal force of the revolving electrons.
The atomic theory put forward by Niel’s Bohr, was completely successful, except for certain corrections, like replacement of the orbits of Bohr by orbitals, etc.,
An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics is impossible. Instead, quantum mechanics must be used to correctly describe and predict their behavior.
The center of an atom, called the nucleus, contains protons and neutrons. The protons have a positive electric charge, the neutrons have no electric charge, and the electrons have a negative electric charge. The number of protons in the nucleus is called the atomic number, and it determines the chemical element of the atom. For example, all carbon atoms have 6 protons in their nucleus. The number of neutrons in the nucleus is called the neutron number, and it can vary for atoms of the same element. Atoms with the same number of protons but different numbers of neutrons are called isotopes. For example, carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.
The electrons in an atom are arranged in shells around the nucleus. The shells are numbered from 1 to 7, with the innermost shell being shell 1 and the outermost shell being shell 7. The number of electrons that can fit in each shell is limited by the Pauli exclusion principle, which states that no two electrons can have the same set of quantum numbers. The quantum numbers of an electron are its principal quantum number, its angular momentum quantum number, and its magnetic quantum number. The principal quantum number determines the shell that the electron is in, while the angular momentum quantum number and the magnetic quantum number determine the subshell that the electron is in.
The electron configuration of an atom is the arrangement of its electrons in its shells and subshells. The electron configuration can be written in a tabular form, with the shells and subshells listed down the left-hand side and the number of electrons in each subshell listed in the right-hand column. For example, the electron configuration of carbon is 1s2 2s2 2p2. This means that carbon has two electrons in its 1s shell, two electrons in its 2s shell, and two electrons in its 2p shell.
The atomic radius of an atom is the distance from the nucleus to the outermost electron. The atomic radius is typically measured in picometers (pm). The atomic radius of an atom increases as the number of shells increases. This is because the electrons in the outermost shell are further away from the nucleus than the electrons in the inner shells.
The electronegativity of an atom is a measure of its ability to attract electrons. The electronegativity is typically measured on a scale of 0 to 4, with fluorine having the highest electronegativity (4.0) and cesium having the lowest electronegativity (0.7). The electronegativity of an atom increases as the number of protons in the nucleus increases. This is because the protons in the nucleus have a positive charge, which attracts the electrons in the atom.
An isotope is an atom of an element that has a different number of neutrons than the most common isotope of that element. Isotopes of an element have the same number of protons but different numbers of neutrons. The different isotopes of an element have the same chemical properties, but they may have different physical properties. For example, carbon-12 is the most common isotope of carbon, while carbon-14 is a radioactive isotope of carbon.
The mass number of an atom is the total number of protons and neutrons in the nucleus of the atom. The mass number is typically written as a superscript to the left of the chemical symbol of the element. For example, the mass number of carbon-12 is 12, while the mass number of carbon-14 is 14.
A proton is a subatomic particle that has a positive electric charge. Protons are found in the nucleus of an atom. The number of protons in the nucleus of an atom is called the atomic number.
A neutron is a subatomic particle that has no electric charge. Neutrons are found in the nucleus of an atom. The number of neutrons in the nucleus of an atom is called the neutron number.
A valence electron is an electron in an atom that is located in the outermost shell. Valence electrons are the electrons that are involved in chemical bonding.
The Aufbau principle states that electrons fill atomic orbitals of the lowest energy first. The Hund’s rule states that electrons will occupy degenerate orbitals with the same spin before pairing up. The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers.
What is the difference between a proton and a neutron?
Protons and neutrons are both subatomic particles that make up the nucleus of an atom. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. The number of protons in the nucleus determines the chemical element of the atom. For example, all atoms with one proton in the nucleus are hydrogen atoms, all atoms with two protons are helium atoms, and so on. The number of neutrons in the nucleus can vary, and atoms with the same number of protons but different numbers of neutrons are called isotopes.
What is the difference between an electron and a proton?
Electrons and protons are both subatomic particles, but they have different properties. Electrons have a negative charge, while protons have a positive charge. Electrons are much lighter than protons, and they are found outside the nucleus of the atom. Protons are found in the nucleus of the atom, along with neutrons.
What is the difference between an electron and a neutron?
Electrons and neutrons are both subatomic particles, but they have different properties. Electrons have a negative charge, while neutrons have no charge. Electrons are much lighter than neutrons, and they are found outside the nucleus of the atom. Neutrons are found in the nucleus of the atom, along with protons.
What is the difference between an atom and a molecule?
An atom is the smallest unit of matter that retains all of the chemical properties of an element. A molecule is a group of two or more atoms that are held together by chemical Bonds. Atoms can combine to form Molecules in a variety of ways, and the properties of a molecule depend on the types of atoms that are present and the way in which they are bonded together.
What is the difference between a compound and a mixture?
A compound is a substance that is made up of two or more Elements that are chemically combined. A mixture is a substance that is made up of two or more elements or compounds that are not chemically combined. The properties of a compound are different from the properties of its constituent elements, while the properties of a mixture are the same as the properties of its components.
What is the difference between a physical change and a chemical change?
A physical change is a change in the state or properties of a substance without a change in its chemical composition. A chemical change is a change in the composition of a substance that results in the formation of new substances. Physical changes can be reversed, while chemical changes cannot.
What is the difference between a solid, a liquid, and a gas?
A solid is a state of matter that has a definite shape and volume. A liquid is a state of matter that has a definite volume but no definite shape. A gas is a state of matter that has neither a definite shape nor a definite volume. The properties of a substance depend on its state of matter. For example, solids are typically hard and rigid, while liquids are typically soft and flowable. Gases are typically invisible and expand to fill any container.
What is the difference between a solution, a suspension, and a colloid?
A solution is a homogeneous mixture of two or more substances. A suspension is a heterogeneous mixture of two or more substances in which the particles of the dispersed phase are large enough to be visible to the naked eye. A colloid is a heterogeneous mixture of two or more substances in which the particles of the dispersed phase are too small to be visible to the naked eye but too large to be dissolved. The properties of a mixture depend on the type of mixture. For example, solutions are typically clear and transparent, while suspensions are typically cloudy or opaque. Colloids are typically translucent or opaque.
What is the difference between a pure substance and a mixture?
A pure substance is a substance that has a definite composition and is made up of only one type of atom or molecule. A mixture is a substance that is made up of two or more substances that are not chemically combined. The properties of a pure substance are different from the properties of its components, while the properties of a mixture are the same as the properties of its components.
What is the difference between a physical property and a chemical property?
A physical property is a property of a substance that can be observed or measured without changing the composition of the substance. A chemical property is a property of a substance that describes its ability to undergo a chemical change. Physical properties can be used to identify a substance, while chemical properties can be used to predict how a substance will react with other substances.
What is the difference between a physical change and a chemical change?
A physical change is a change in the state or properties of a substance without a change in its chemical composition. A chemical change is a change in the composition
Sure, here are some MCQs without mentioning the topic Atomic structure:
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Which of the following is not a subatomic particle?
(A) Proton
(B) Neutron
(C) Electron
(D) Photon -
The number of protons in the nucleus of an atom is called the
(A) atomic number
(B) mass number
(C) charge number
(D) electron number -
The number of neutrons in the nucleus of an atom is called the
(A) atomic number
(B) mass number
(C) charge number
(D) electron number -
The total number of protons and neutrons in the nucleus of an atom is called the
(A) atomic number
(B) mass number
(C) charge number
(D) electron number -
Atoms of the same element with different numbers of neutrons are called
(A) isotopes
(B) ions
(C) molecules
(D) compounds -
The number of electrons in a neutral atom is equal to the
(A) atomic number
(B) mass number
(C) charge number
(D) electron number -
The electrons in an atom are arranged in shells, which are further divided into subshells. The maximum number of electrons that can be in a subshell is
(A) 2
(B) 8
(C) 18
(D) 32 -
The electrons in the outermost shell of an atom are called valence electrons. The number of valence electrons in an atom determines its chemical properties.
(A) True
(B) False -
When atoms combine to form molecules, they do so by sharing electrons. This is called covalent bonding.
(A) True
(B) False -
Ions are atoms or molecules that have a positive or negative charge. They are formed when atoms or molecules gain or lose electrons.
(A) True
(B) False
I hope these questions were helpful!