Quantum Theory and Electronic Structure of Atoms

Flashcards covering key concepts from the 'Quantum Theory and Electronic Structure of Atoms' lecture notes.

Who proposed that molecules emit energy only in discrete quantities called quanta?

Max Planck

According to the Heisenberg uncertainty principle, what cannot be known exactly at the same time?

Both position and momentum of a particle

What is a 'wave' defined as in the context of energy transmission?

A vibrating disturbance by which energy is transmitted (not matter)

What property of a wave is related to the intensity or brightness of radiation?

Amplitude

How is frequency (ν) defined for a wave?

The number of cycles per second (s-1 or Hertz)

What is wavelength (λ) in the context of a wave?

The distance a wave travels in one cycle

What is the speed of light (c)?

3.00 x 10^8 m/s

What is the relationship between the speed of light (c), wavelength (λ), and frequency (ν)?

c = λ × ν

What is the collective term for all forms of radiation, such as visible light, X-rays, and microwaves, which can be described in terms of wave-like electric and magnetic fields?

Electromagnetic (EM) radiation

What is the approximate range of wavelengths that the human eye can sense, known as the visible spectrum?

380 nm (purple) to 750 nm (red)

According to Planck's Quantum Theory, how is the energy of electromagnetic waves described?

As quantized, rather than continuous

What is a quantum of energy (photon)?

A discrete bundle or packet of energy

What is the equation for the energy of a photon (E)?

E = hν (where h is Planck's constant and ν is frequency)

What is the value of Planck's constant (h)?

6.626 x 10^-34 J·s

What is the difference between a continuous spectrum and a line spectrum?

A continuous spectrum shows a rainbow of colors (all wavelengths), while a line spectrum shows discrete lines of emitted radiation specific to an atom.

What happens when atoms absorb energy and then emit it as electromagnetic radiation?

They produce a line spectrum

What were the three postulates of Bohr's model for the hydrogen atom?

1. Only orbits of certain radii are permitted. 2. An electron in a permitted orbit has a specific energy. 3. Energy is emitted or absorbed only when an electron changes between allowed energy states.

What formula did Bohr use to calculate the energies corresponding to each allowed orbit for the electron?

En = -RH(1/n^2) (where RH is the Rydberg constant and n is the principal quantum number)

What is the value of the Rydberg constant (RH)?

2.18 x 10^-18 J

What does the principal quantum number (n) represent in Bohr's model?

The energy level or quantum number of the electron, or the main shell an electron occupies.

What is the 'ground state' for a hydrogen atom in Bohr's model?

The lowest energy level, where n = 1

In Bohr's model for hydrogen, what type of electromagnetic radiation corresponds to electron transitions to n=1?

Ultraviolet (UV) radiation

What were the limitations of the Bohr model?

It only worked for the hydrogen atom and other one-electron systems, it described electrons as particles in fixed orbits, and it could not explain the spectra of multi-electron atoms.

What did De Broglie suggest about moving particles of matter, such as electrons?

That they can also be thought of as waves

What is De Broglie's equation for the wavelength (λ) of matter?

λ = h/(mu) (where h is Planck's constant, m is mass, and u is velocity)

In quantum mechanics, how is an electron in an atom viewed?

As a wave of certain allowed energy

What does the Heisenberg Uncertainty Principle state in the context of electrons in atoms?

It is not possible to specify the exact position of an electron, but one can calculate the probability of the electron being in some region around the nucleus.

What are wave functions (ψ) in the Schrödinger Equation?

The solutions to the wave equation, which describe orbitals as standing waves or electron clouds

What does the principal quantum number (n) describe for an orbital?

The size and energy level of the orbital, and it defines the electron shell.

What does the azimuthal (or angular momentum) quantum number (l) describe for an orbital?

The shape of the orbital and it divides shells into subshells.

What does the magnetic quantum number (ml) describe for an orbital?

The orientation of the orbital in space.

What are the possible values for the azimuthal quantum number (l) when n = 3?

0, 1, or 2

Which letter designations correspond to azimuthal quantum numbers l = 0, 1, 2, and 3?

l=0 is s, l=1 is p, l=2 is d, l=3 is f

What does the electron spin quantum number (ms) indicate?

The direction an electron spins, either +1/2 (↑) or -1/2 (↓)

What does an orbital shape represent?

A picture of the highest probable electron location around the nucleus (represented by ψ^2)

What is a 'node' in the context of atomic orbitals?

A region of zero electron density

Describe the general shape of an s orbital.

Spherical

Describe the general shape of a p orbital.

Two-lobed or dumbbell-shaped, with a nodal plane

Describe the general shape of a d orbital.

Four-lobed or cloverleaf-shaped (with one exception), with two nodal planes

How does the energy of an electron in a hydrogen atom differ from that in a many-electron atom?

In a hydrogen atom, energy depends solely on the principal quantum number (n). In many-electron atoms, energy depends on both n and the azimuthal quantum number (l).

Why is a 2s orbital lower in energy than a 2p orbital in many-electron atoms?

The 2s orbital has greater penetration toward the nucleus, leading to lower energy.

What is an electron configuration?

The distribution of electrons in different shells and subshells within an atom.

What is the Pauli Exclusion Principle?

No two electrons in the same atom can have the same four quantum numbers. Therefore, each orbital can hold a maximum of two electrons with opposite spins.

What is Hund's Rule?

When degenerate orbitals are available, the electron configuration of lowest energy has the maximum number of unpaired electrons with the same spin.

What is the definition of a diamagnetic substance?

A substance where all electrons are paired, making it not attracted to a magnet.

What is the definition of a paramagnetic substance?

A substance that has one or more unpaired electrons, making it attracted to a magnet.

What is the maximum number of electrons that a principal energy level (n) can hold?

2n^2

What is the Building-Up Principle (Aufbau principle)?

Electrons are fed into the lowest energy available orbital first.

In a condensed electron configuration, what do the bracketed noble gas symbols represent?

The completely filled inner shells of core electrons.

What is the difference between core electrons and valence electrons?

Core electrons are the inner-shell electrons corresponding to a noble gas configuration, while valence electrons are the outer-shell electrons involved in chemical bonding.