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Who proposed that atoms are indivisible?
Dalton
In what year did Dalton propose his atomic theory?
1808
What experiment did J.J. Thomson conduct?
Cathode Ray Experiment
What did the cathode ray experiment prove?
The existence of negatively charged particles (electrons) within the atom.
What are the conditions required for the Cathode Ray Experiment?
Low pressure and high voltage in a vacuum tube.
What is the charge of an electron?
-1.6 x 10^-19 Coulombs.
What is the mass of an electron?
Negligible.
Who discovered the proton?
E. Goldstein.
What experiment led to the discovery of the proton?
Anode ray or canal ray experiment.
What is the charge of a proton?
+1.6 x 10^-19 Coulombs.
How does the mass of a proton compare to the mass of an electron?
The mass of a proton is about 2000 times greater than the mass of an electron.
Who discovered the neutron?
James Chadwick.
In what year was the neutron discovered?
In th year 1932
What is the charge of a neutron?
Zero (neutral).
How does the mass of a neutron compare to the mass of a proton?
They are almost equal.
What model did J.J. Thomson propose for the structure of the atom?
The plum pudding or watermelon model.
According to Thomson's model, how are positive and negative charges distributed in an atom?
Positive charge is uniformly distributed, and negative charges (electrons) are embedded within it.
What did Thomson's model state about the overall charge of an atom?
The overall charge is neutral.
What was the name of the experiment conducted by Rutherford?
Gold Foil Experiment.
What type of particles were used in Rutherford's experiment?
Alpha particles.
What is an alpha particle?
A positively charged particle, which is a double charged helium ion.
Why was gold foil used in Rutherford's experiment?
Gold is highly malleable and can be made into very thin sheets.
What were the key observations of Rutherford’s gold foil experiment?
Most alpha particles passed straight through; some alpha particles were deflected at an angle; a very small number of alpha particles were reflected back.
What were the main conclusions drawn from the Rutherford experiment?
Most of the space in an atom is empty; the atom has a dense, positively charged nucleus; the nucleus is very small compared to the atom; most of the atom's mass is concentrated in the nucleus.
According to Rutherford, how do electrons move in an atom?
Electrons revolve around the nucleus in well-defined orbits.
What was the major drawback of Rutherford’s model?
It could not explain the stability of atoms.
What did Bohr propose regarding electron orbits?
Electrons revolve in discrete (special) orbits without radiating energy.
What are the different names given to these discrete orbits by Bohr?
Energy shells or energy levels.
What are the names of the energy levels/shells?
K, L, M, N.
What is the ground state of an electron?
The lowest energy level which is the K shell.
When do electrons emit or absorb energy according to Bohr's model?
When they jump from one orbit to another.
How is energy emitted or absorbed when electrons jump?
Electrons emit energy when jumping from a higher energy level to lower energy level; electrons absorb energy when jumping from a lower to higher energy level.
What is atomic number?
The number of protons in an atom.
How is atomic number represented?
By the letter Z.
In a neutral atom, how do the number of protons and electrons compare?
They are equal.
Why is the number of protons used to define atomic number rather than electrons or neutrons?
Because the number of protons is constant for a given element, while electrons can be gained or lost, and the number of neutrons can vary.
What is mass number?
The sum of protons and neutrons in an atom's nucleus.
How is mass number represented?
By the letter A.
What is another name for mass number?
Nucleon number.
How do you calculate the number of neutrons in an atom, given its mass number and atomic number?
Mass number - Atomic number.
If an atom has an atomic number of 10 and a mass number of 22 how many protons, neutrons and electrons does it have?
Protons - 10, Neutrons - 12, Electrons - 10 (if neutral).
What formula determines the maximum number of electrons a shell can hold?
2n² where 'n' is the shell number.
What is the maximum number of electrons the K shell can hold?
What is the maximum number of electrons the L shell can hold?
What is the maximum number of electrons the M shell can hold?
What is the maximum number of electrons the N shell can hold?
What is the maximum number of electrons in the outermost shell of an atom?
8
Which shell must be filled first, according to the distribution rule?
The smallest shell or the inner shell.
What is electronic configuration?
The distribution of electrons in different shells of an atom.
What is the electronic configuration of aluminum?
2, 8, 3.
What is the electronic configuration of calcium?
2, 8, 8, 2.
What is the electronic configuration of chlorine?
2, 8, 7.
What is the electronic configuration of a sodium ion (Na+)?
2, 8 (it loses one electron).
What is the electronic configuration of calcium ion (Ca+2)?
2, 8, 8 (it loses two electrons).
Why do atoms combine with each other?
To achieve stability, by attaining a noble gas electronic configuration, with 8 electrons in their outermost shell (octet rule) or 2 in the case of the first shell (duplet).
What are valence electrons?
The electrons present in the outermost shell of an atom.
What is valency?
The combining capacity of an atom, or the number of electrons an atom will lose, gain, or share to achieve stability.
What is the valency of chlorine?
1 (it needs to gain 1 electron).
What is the valency of oxygen?
2 (it needs to gain 2 electrons).
What is the valency of lithium?
1 (it loses 1 electron).
If an atom has 1, 2, 3, or 4 electrons in its outermost shell, what is its valency?
The same as the number of valence electrons, respectively.
If an atom has 5, 6, 7, or 8 electrons in its outermost shell, how do you determine its valency?
Subtract the number of valence electrons from 8.
What is the exception to the rules for determining valency?
Helium whose valency is zero even with two electrons in its outer shell.
What is the valency of boron?
What is the valency of carbon?
What is the valency of nitrogen?
What is the valency of oxygen?
What is the valency of fluorine?
What are isotopes?
Atoms of the same element with the same atomic number but different mass numbers.
What is the key difference between isotopes?
They have a different number of neutrons.
How many isotopes of hydrogen are there?
Three.
What are the names of the isotopes of hydrogen?
Protium, Deuterium, and Tritium.
What is the atomic number and mass number of Protium?
Atomic Number - 1, Mass number - 1.
What is the atomic number and mass number of Deuterium?
Atomic Number - 1, Mass number - 2.
What is the atomic number and mass number of Tritium?
Atomic Number - 1, Mass number - 3.
How do the chemical properties of isotopes compare?
They have identical chemical properties.
Why do isotopes of an element have similar chemical properties?
Because they have the same number of protons and electrons.
How do the physical properties of isotopes compare?
They have different physical properties.
What is a use of Uranium isotopes?
As fuel in nuclear reactors.
What is a use of Cobalt isotopes?
In the treatment of cancer.
What is a use of Iodine isotopes?
In the treatment of goiter.
Why do some elements have fractional atomic masses?
Because they are a mixture of different isotopes, and the atomic mass is an average of these different isotopes.
What are isobars?
Atoms of different elements with the same mass number but different atomic numbers.
What is the key difference between isobars?
They have a different number of protons and neutrons.
Give an example of isobars.
Argon, Potassium and Calcium.
What is a common mass number of the isobars Argon, Potassium and Calcium?
40
How do the chemical properties of isobars compare?
They have different chemical properties.
Why do isobars of an element have different chemical properties?
Because they have a different number of protons and electrons.
How do the physical properties of isobars compare?
They have similar physical properties.
What is the key difference between isotopes and isobars with respect to atomic and mass numbers?
Isotopes have same atomic numbers and different mass numbers. Isobars have different atomic numbers and the same mass number.
How do isotopes and isobars compare with respect to chemical properties?
Isotopes have similar chemical properties, while isobars have different chemical properties.
How do isotopes and isobars compare with respect to physical properties?
Isotopes have different physical properties while isobars have similar physical properties.
What is the key idea behind the 'PG' in the mnemonic for remembering the scientists?
P stands for Proton discovered by Goldstein.
What does 'T' represent in the scientist mnemonic?
T stands for Thomson, discoverer of the electron.
What does 'RG' represent in the scientist mnemonic?
Rutherford and his Gold foil experiment.
What was the key contribution of Bohr according to the mnemonic?
He was like a father to Rutherford, correcting his mistakes.
What does the 'no cheating' represent in the scientist mnemonic?
Neutron discovery by Chadwick.
Why are the outermost shells of atoms important?
They determine the atom's chemical behaviour and valency.
In an atom, what is the role of the nucleus?
It contains the protons and neutrons and holds the mass of the atom.
Why is the concept of stability important for understanding the structure of the atom?
Atoms want to be stable, and this is why they lose, gain, or share electrons and combine.
