Quantum Chemistry Concepts
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Questions and Answers

What is the equation for the maximum number of electrons in a principal energy shell?

  • 2n + 2
  • 2n
  • n^2
  • 2n^2 (correct)

What is the formula to calculate the maximum number of electrons in a particular subshell?

  • 2l
  • 2l + 1
  • 2l + l + 1
  • 2 × (2l + l) (correct)

What values can the magnetic quantum number (m) take?

  • –l to +l including zero (correct)
  • only positive values
  • 0 to l
  • –l to l excluding zero

Which statement best describes the spin quantum number (s)?

<p>It can take values of +1/2 and –1/2. (C)</p> Signup and view all the answers

What is the reason for increased stability in completely filled and half-filled subshells?

<p>Decreased shielding and symmetrical distribution of electrons. (B)</p> Signup and view all the answers

What does the term 'ATOM' originate from?

<p>Greek meaning not to be cut (D)</p> Signup and view all the answers

Which aspect of Dalton's theory of atoms is considered a limitation?

<p>Atoms of the same element can differ in mass (A)</p> Signup and view all the answers

Who first suggested the existence of atoms?

<p>Democritus (B)</p> Signup and view all the answers

What was the main significance of R.S. Mullikan's oil drop experiment?

<p>It determined the charge of an electron. (B)</p> Signup and view all the answers

Which subatomic particles are classified as fundamental?

<p>Proton, neutron, electron. (C)</p> Signup and view all the answers

What is the main postulate of Dalton's atomic theory?

<p>All atoms of an element are identical (C)</p> Signup and view all the answers

What did William Crookes study in 1879?

<p>The behavior of electrical discharge in gas. (D)</p> Signup and view all the answers

Which discovery showed that not all atoms are indivisible?

<p>Discovery of protons (B)</p> Signup and view all the answers

What concept explains why different elements have distinct properties?

<p>Differences in kinds of atoms (B)</p> Signup and view all the answers

What produces the greenish glow in a discharge tube during the cathode ray experiment?

<p>Fluorescent coating on the glass wall. (D)</p> Signup and view all the answers

Which of the following statements is true regarding isobars?

<p>They have the same atomic mass (C)</p> Signup and view all the answers

Which statement about cathode rays is incorrect?

<p>They are positively charged particles. (D)</p> Signup and view all the answers

What role does Dalton's theory play in understanding chemical combinations?

<p>It provides a basis for chemical reactions (C)</p> Signup and view all the answers

Why do cathode rays travel at high speeds?

<p>Due to the high voltage applied in the discharge tube. (D)</p> Signup and view all the answers

Who is credited with the discovery of the electron?

<p>J.J. Thomson. (B)</p> Signup and view all the answers

What is NOT a characteristic of cathode rays?

<p>They can change the composition of gases. (B)</p> Signup and view all the answers

What happens to cathode rays when they strike a heavy metal?

<p>They produce X-rays. (A)</p> Signup and view all the answers

What is the significance of excitation energy in atomic structure?

<p>It is the energy required to excite an electron from its ground state. (D)</p> Signup and view all the answers

How are the circumference of the nth orbit and the wavelength of an electron related?

<p>The circumference is equal to n times the wavelength. (D)</p> Signup and view all the answers

What does the Heisenberg's Uncertainty Principle state?

<p>Position and velocity of a particle cannot be accurately measured at the same time. (A)</p> Signup and view all the answers

What equation defines the relationship between wavelength, mass, charge, and potential difference for a charged particle?

<p>$ rac{h}{2mQV}$ (A), $ rac{h}{2mQV}$ (C)</p> Signup and view all the answers

In the wave mechanical model, what does the Schrödinger equation illustrate?

<p>The behavior of electrons in an atom. (C)</p> Signup and view all the answers

What does the principal quantum number (n) represent in quantum mechanics?

<p>The number of orbitals present in the nth shell. (C)</p> Signup and view all the answers

What type of power do cathode rays possess as they travel through a gas?

<p>Ionizing power. (A)</p> Signup and view all the answers

Flashcards

Atom

The smallest particle of an element, considered indivisible.

Dalton's Atomic Theory

A theory proposing that atoms are indivisible, elements contain identical atoms, and atoms combine to form compounds.

Isotopes

Atoms of the same element with different atomic masses.

Isobars

Atoms of different elements with the same atomic mass.

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Subatomic Particles

Particles smaller than atoms, such as protons, electrons, and neutrons.

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Indestructible Atom

The idea that atoms can neither be created nor destroyed.

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Democritus

Ancient Greek philosopher who first proposed the concept of atoms.

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Atomic Mass

The mass of an atom, often expressed in atomic mass units (amu).

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Cathode Ray Experiment

An experiment that demonstrated the existence of negatively charged particles (electrons) using a partially evacuated tube with electrodes.

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Electron

A negatively charged subatomic particle discovered by J.J. Thomson in 1897.

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Subatomic particle

A particle smaller than an atom, like electrons, protons, and neutrons.

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Charge on an electron

-1.602 x 10^-19 Coulombs. A fundamental electrical quantity.

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Cathode Rays

Invisible rays originating from the cathode (negative electrode) in a discharge tube, producing a glow.

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Properties of Cathode Rays

Travel in straight lines, produce mechanical effects (like spinning a wheel), consist of negatively charged particles (electrons), and possess high speed.

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Atomic Structure

The arrangement of subatomic particles (like electrons, protons, and neutrons) within an atom.

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Fundamental Subatomic Particles

The basic building blocks of atoms: protons, neutrons, and electrons.

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Excitation Energy

Energy needed to move an electron from its lowest energy level (ground state) to a higher energy level (excited state).

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Wave Mechanical Model

Describes the behavior of electrons as both waves and particles, within an atom.

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De Broglie Equation

Relates the wavelength of a particle to its momentum.

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Cathode Rays

Streams of electrons emitted from a heated cathode in a vacuum tube.

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Heisenberg's Uncertainty Principle

It's impossible to simultaneously measure both the position and momentum of a particle with perfect accuracy.

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Quantum Numbers

Specify the properties of atomic orbitals and the electrons that occupy them.

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Principal Quantum Number

Indicates the main energy level an electron occupies.

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De-Broglie wavelength

Wavelength of a particle calculated using its momentum.

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Maximum electrons per shell

The highest number of electrons that can occupy a specific principal energy level (shell) in an atom. Calculated as 2n² where 'n' is the principle quantum number.

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Subshell orbitals

The specific shapes and orientations of electron arrangements within a particular subshell, determined by the azimuthal quantum number (l).

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Magnetic quantum number (m)

Describes the orientation of electron orbitals in space, with values ranging from -l to +l, including zero.

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Electron spin quantum number (s)

Indicates the intrinsic angular momentum or spin of an electron. Can be +1/2 or -1/2.

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Stability of filled/half-filled subshells

Completely filled or half-filled electron subshells are more stable due to symmetrical electron distributions and exchange energy.

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Study Notes

Atomic Structure

  • Atoms are the fundamental units of matter
  • Atoms cannot be created or destroyed
  • Atomic theory was first proposed by John Dalton
  • Electrons and protons are subatomic particles
  • The mass of an electron is negligible compared to protons or neutrons
  • The charge of an electron is -1.602 × 10⁻¹⁹ Coulombs and the charge of a proton is +1.602 × 10⁻¹⁹ Coulombs.
  • Thomson's model postulated that atoms consist of a uniform sphere of positive charge with electrons scattered within it.
  • Rutherford's gold foil experiment disproved Thomson's model and suggested a small, dense, positively charged nucleus.
  • The atom is mostly empty space
  • Electrons move around the nucleus in specific energy levels.
  • Electrons can only gain or lose energy by 'jumping' between these levels
  • Atoms with more than one electron have more elaborate spectral lines
  • Quantum numbers help locate electrons within an atom
  • The principal quantum number (n) describes the electron shell and energy levels
  • The azimuthal quantum number (l) describes the shape of the subshell
  • The magnetic quantum number (ml) describes the orientation of the orbital within space
  • The spin quantum number (ms) describes the electron spin (either +1/2 or -1/2)

History of Atomic Models

  • J.J. Thomson discovered the electron in 1897
  • Johann Balmer derived a formula to predict the hydrogen spectrum in 1885
  • Rutherford proposed the nuclear model of the atom in 1911
  • De Broglie introduced the concept of dual nature of electrons in 1923
  • Erwin Schrodinger developed the electron cloud model in 1925
  • This model does not precisely locate electrons but defines probability regions called orbitals
  • Bohr proposed that electrons orbit the nucleus in specific orbits

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Description

This quiz explores fundamental concepts in quantum chemistry, including equations for the maximum number of electrons in energy shells and subshells. You will also learn about quantum numbers such as magnetic and spin quantum numbers, and the stability of filled subshells.

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