Chapter 3: Electronic Structure of the Atom

Flashcards covering the Quantum-Mechanical Model, electromagnetic radiation properties, challenges to classical mechanics, Bohr model, quantum numbers, electron configurations, and periodic trends in atomic properties.

What model of the atom did Rutherford's gold foil experiment lead to?

The nuclear model of the atom.

What branch of mechanics attempts to describe matter at the atomic level?

Quantum mechanics

What is wavelength (λ)?

The distance covered by a wave, determining its color.

What is amplitude in the context of waves?

The height of the wave, determining its intensity or brightness.

What characterizes white light?

It is a mixture of all the colors of visible light.

What determines the color we see?

The wavelengths of light that are reflected, not absorbed.

Define frequency (ν) and state its unit.

The number of waves passing a given point per unit of time, measured in hertz (Hz or s⁻¹).

What is the relationship between frequency (ν) and wavelength (λ)?

They are inversely proportional.

What two properties determine the total energy of a wave?

Amplitude and frequency.

What is the constant speed at which all electromagnetic waves move through space?

The speed of light (c), which is 3.00 × 10⁸ m/s.

What is diffraction in the context of waves?

When traveling waves encounter an opening in a barrier, they bend around it.

Which part of the electromagnetic spectrum has the lowest frequency, longest wavelength, and lowest energy?

Radio waves

Which part of the electromagnetic spectrum has the highest frequency, shortest wavelength, and highest energy?

Gamma rays

List some challenges to classical mechanics that emerged in the late 19th to early 20th century.

Atomic emission, blackbody radiation, photoelectric effect, Bohr model of the atom, wave-particle duality, and the uncertainty principle.

What phenomenon occurs when an element absorbs energy and emits a unique color of visible light?

Atomic emission

What is observed when emitted light is directed into a prism?

A line (photoemission) spectrum of the component wavelengths.

What is the Rydberg equation used to describe?

The spectrum of hydrogen, relating wavelength or frequency to positive integers (ni and nf).

What is a blackbody?

A system that can absorb and emit radiation of all frequencies.

What is the ultraviolet catastrophe?

The error at high frequencies in the Rayleigh-Jeans law, predicting infinite energy, which was resolved by Max Planck's theory of quantized energy.

What did Max Planck propose about energy emission in 1900?

Energy was emitted in small, discrete packets called quanta.

What equation relates energy (E) to frequency (ν) and wavelength (λ) according to Planck?

E = hν = hc/λ, where h is Planck's constant (6.626 × 10⁻³⁴ J·s).

What is the photoelectric effect, as observed by Heinrich Hertz?

When a metal absorbs sufficient energy, its electrons are ejected from the surface.

What is the 'threshold frequency' in the photoelectric effect?

A minimum frequency of light needed before electrons would be emitted from a metal, regardless of the light's intensity.

What did Albert Einstein propose about electromagnetic radiation in 1905?

It exists as small particles called photons.

What is the Bohr model of the atom?

A model proposing that electrons are only allowed to travel in fixed, quantized orbits around the nucleus.

What is the Bohr radius?

The closest an electron can be to the nucleus (when the principal quantum number n = 1).

What is the significance of the negative sign in Bohr's energy equation for orbits (En = -2.18 × 10⁻¹⁸J (1/n²))?

It reflects the attractive force between the electrons and protons, as explained by Coulomb's law.

What is photoemission in the Bohr model?

It occurs as an electron relaxes from a higher energy state to a lower energy state, emitting light.

Which series of hydrogen emission is visible?

The Balmer series, where the final principal quantum number (nf) is 2.

What did Louis de Broglie theorize about matter in 1924?

If light has material properties, matter should also exhibit wave properties, with wavelength inversely proportional to its momentum (λ = h/mv).

What did the double-slit experiment show about electrons?

Electrons exhibit wave behavior by producing an interference pattern, rather than just two bands as particles would.

What is Heisenberg's Uncertainty Principle?

It is impossible to know both the momentum (Δmv) and position (Δx) of a particle with absolute certainty simultaneously (Δx·Δmv ≥ h/4π).

How does classical physics differ from quantum mechanics regarding determinacy?

Classical physics suggests determinacy (definite, predictable future), while quantum mechanics suggests indeterminacy (indefinite future) due to complementary properties.

What did Erwin Schrödinger propose in 1926?

An equation (HΨ = EΨ) that incorporated both the wave-like and particle-like behavior of electrons, whose solution gives a set of wave functions (orbitals) and energies.

What does the square of the wave function (Ψ²) represent?

A probability density map, indicating where an electron has a statistical likelihood of being at any given instant in time.

What four quantum numbers describe an orbital?

The principal quantum number (n), angular momentum quantum number (l), magnetic quantum number (ml), and spin quantum number (ms).

What does the principal quantum number (n) describe?

The energy level or shell on which the orbital resides, with higher n values corresponding to electrons farther from the nucleus and less tightly bound.

What does the angular momentum quantum number (l) define?

The shape of the orbital or subshell, with allowed integer values from 0 to n-1 (0=s, 1=p, 2=d, 3=f).

What does the magnetic quantum number (ml) describe?

The 3D orientation of the orbital, with allowed integer values from -l to +l.

How many orbitals are in s, p, d, and f subshells, respectively?

1 s-orbital, 3 p-orbitals, 5 d-orbitals, and 7 f-orbitals.

What is the shape of an s orbital?

Spherical, with its radius increasing with the value of n.

What is a radial node?

A region within an orbital where there is zero probability of finding an electron, calculated by n - l - 1.

What is the shape of a p orbital?

It consists of two lobes with an angular node between them.

How is the total number of nodes in an orbital calculated?

n - 1.

What does the spin quantum number (ms) describe?

The magnetic field of an electron (spin), which can be either spin up (+½) or spin down (-½).

What is the Pauli Exclusion Principle?

No two electrons in the same atom can have the same set of four quantum numbers (n, l, ml, ms), meaning each orbital can hold a maximum of two electrons with opposite spins.

How does the energy of orbitals differ between a one-electron hydrogen atom and a many-electron atom?

In a hydrogen atom, orbitals on the same principal energy level (n) are degenerate (same energy), but in a many-electron atom, electron repulsion causes them to no longer be degenerate.

What is the effective nuclear charge (Zeff)?

The net positive charge attracting an electron to a nucleus, calculated as Z - S (atomic number minus the number of core electrons).

Why does Zeff increase across a row in the periodic table?

The number of core electrons (S) remains the same, but the nuclear charge (Z) increases, leading to a stronger attraction for the valence electrons.

What is the Aufbau principle?

Electrons occupy the lowest energy orbitals available in an atom in its ground state, filling orbitals in increasing order of energy.

What is Hund's rule?

For degenerate orbitals, the lowest energy configuration is attained when the number of electrons with the same spin is maximized (i.e., orbitals are filled singly with parallel spins before pairing electrons).

What is a condensed electron configuration (or noble gas configuration)?

A simplified electron configuration that uses the symbol of the nearest noble gas to represent the core electrons, followed by the configuration of the valence electrons.

When writing electron configurations for transition metal ions, which electrons are removed first?

Electrons are removed from the s subshell prior to removing them from the d subshell.

What are the three particularly stable subshell configurations that lead to anomalies in electron configurations for transition metals?

Filled, empty, and half-filled subshells.

Distinguish between a paramagnetic and a diamagnetic substance.

A paramagnetic substance is attracted to a magnetic field (has unpaired electrons), while a diamagnetic substance is repelled (all electrons are paired).

What is the trend in atomic radius down a group?

Atomic radius increases from top to bottom due to the increasing principal quantum number (n), meaning electrons are in higher energy levels farther from the nucleus.

What is the trend in atomic radius across a period?

Atomic radius decreases from left to right due to the increasing effective nuclear charge (Zeff) which pulls the electrons closer to the nucleus.

How do cations compare in size to their neutral atoms?

Cations are smaller than their neutral atoms because their outermost electrons are removed, reducing electron-electron repulsions.

How do anions compare in size to their neutral atoms?

Anions are larger than their neutral atoms because electrons are added, increasing electron-electron repulsions.

What is an isoelectronic series?

A group of ions (or atoms) that have the same number of electrons.

Regarding size, how do ions in an isoelectronic series generally relate to each other?

Anion³⁻ > anion²⁻ > anion⁻ > neutral atom > cation⁺ > cation²⁺ > cation³⁺, where size decreases with increasing nuclear charge for the same electron count.

What is the first ionization energy?

The amount of energy required to remove the first electron from an atom or ion in the gas phase (an endothermic process).

What is the trend in first ionization energy down a group?

First ionization energy decreases from top to bottom due to the outermost electrons being farther from the nucleus and easier to remove (larger n).

What is the trend in first ionization energy across a period?

First ionization energy generally increases from left to right due to the increasing effective nuclear charge (Zeff), making it harder to remove electrons.

Why is there an exception to the first ionization energy trend between Groups IIA and IIIA?

The electron removed in Group IIIA comes from a p orbital, which is less penetrating and slightly farther from the nucleus than the s orbital of Group IIA, making it easier to remove.

Why is there an exception to the first ionization energy trend between Groups VA and VIA?

The electron removed in Group VIA comes from a doubly occupied p orbital, where electron-electron repulsion aids in its removal, making it easier than removing an electron from a half-filled p subshell in Group VA.

What is electron affinity (EA)?

The energy change accompanying the addition of an electron to a gaseous atom.

What is the general trend for electron affinity across a period?

Electron affinity generally becomes more exothermic (more negative) from left to right across a row, indicating a greater attraction for an added electron.

Why is there an exception to the electron affinity trend between Groups IA and IIA?

An added electron to a Group IIA element must go into a higher energy p orbital (as its s subshell is filled), which is farther from the nucleus and less attracted, often resulting in a positive or less negative EA.

Why is there an exception to the electron affinity trend between Groups IVA and VA?

An added electron to a Group VA element must go into an already occupied orbital in its half-filled p subshell, experiencing repulsion, which makes its EA less negative than expected.