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Química Geral · Exam review

Revisão para a prova: átomos, elétrons e tendências periódicas

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O que você vai aprender

  • Convert between wavelength, frequency and photon energy per photon or per mole, and use the Bohr energies Eₙ = −2.179 × 10⁻¹⁸ J × Z²/n² for one-electron atoms and ions.
  • Use quantum numbers and the aufbau, Pauli and Hund rules to write ground-state configurations of atoms, including the Cr and Cu exceptions.
  • Write configurations of transition-metal and main-group ions (4s electrons leave first), count unpaired electrons and predict magnetism.
  • Rank atoms and ions by radius, ionization energy and related properties, and explain the group 2/13 and 15/16 ionization-energy anomalies and the jumps in successive ionization energies.

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Ler a aula gratuita (6 partes)

Light: three equations and a unit check

Use c = λν (c = 2.998 × 10⁸ m/s) and E = hν = hc/λ (h = 6.626 × 10⁻³⁴ J s) with λ in metres. Per mole of photons multiply by NA = 6.022 × 10²³ mol⁻¹; the handy product is hcNA = 0.1196 J m/mol. Worked example: a 486 nm photon carries 1.9865 × 10⁻²⁵ J m ÷ 4.86 × 10⁻⁷ m = 4.09 × 10⁻¹⁹ J, or 0.1196 ÷ 4.86 × 10⁻⁷ = 246 kJ/mol. Mixed-unit traps: MHz means 10⁶ Hz, nm means 10⁻⁹ m, and a kJ/mol value must become J/mol before you divide. In the photoelectric effect KEmax = hν − Φ, and an ejected electron then has its own de Broglie wavelength λ = h/√(2m·KE). The same photon-minus-binding-energy idea is photoelectron spectroscopy: KE = Ephoton − IE.

The Bohr atom and one-electron ions

For a one-electron species (H, He⁺, Li²⁺) Eₙ = −2.179 × 10⁻¹⁸ J × Z²/n²; the zero of energy is the free electron. A transition from n_high to n_low emits ΔE = 2.179 × 10⁻¹⁸ J × Z² × (1/n_low² − 1/n_high²); absorbing the same energy reverses it. The Rydberg form is 1/λ = R_H Z² (1/n_low² − 1/n_high²), R_H = 1.097 × 10⁷ m⁻¹. Ionization from level n needs 2.179 × 10⁻¹⁸ J × Z²/n², so hydrogen's ionization energy is 1312 kJ/mol and He⁺'s is 4 × 1312 = 5248 kJ/mol. Light that ionizes hydrogen from n = 2 (λ ≤ 365 nm) need not ionize it from n = 1 (λ ≤ 91.2 nm). Lines ending on n = 1 are ultraviolet (Lyman), on n = 2 mostly visible (Balmer: 656, 486, 434, 410 nm, converging on 365 nm in the near ultraviolet), on n = 3 infrared (Paschen).

Quantum numbers and ground-state configurations

n = 1, 2, 3 …; l = 0 … n − 1 (s, p, d, f); mℓ = −l … +l; ms = ±½. Each orbital holds two electrons of opposite spin (Pauli). Fill 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p (aufbau), and spread electrons over degenerate orbitals with parallel spins before pairing (Hund). The n = 3 shell holds 18 electrons, but period 3 has only 8 elements because 3d lies above 4s and fills in period 4. Exceptions to learn: Cr [Ar] 3d⁵ 4s¹ and Cu [Ar] 3d¹⁰ 4s¹ (also Mo and Ag). Worked example: Y (Z = 39) is [Kr] 4d¹ 5s²; the krypton core already contains 3d¹⁰, so yttrium has 10 + 1 = 11 d electrons and 1 unpaired electron. A configuration that obeys Pauli but not aufbau or Hund is an excited state, not an impossible one.

Ions and magnetism

Main-group atoms usually form ions with the nearest noble-gas configuration (Na⁺, Al³⁺, O²⁻, Cl⁻), but any gas-phase ion is written the same way: add electrons to, or remove them from, the highest-energy occupied subshell (F⁺ is 1s² 2s² 2p⁴; Sn²⁺ loses its 5p electrons before 5s and is [Kr] 4d¹⁰ 5s²). Transition metals fill 4s before 3d but lose 4s first: once 3d holds electrons, 3d lies below 4s, and the larger n = 4 orbital is the outermost. Fe is [Ar] 3d⁶ 4s², Fe²⁺ is [Ar] 3d⁶ (4 unpaired) and Fe³⁺ (drawn) is [Ar] 3d⁵ (5 unpaired, the most for a 3d ion). Any species with at least one unpaired electron is paramagnetic (drawn into a magnetic field); all paired means diamagnetic (Ti⁴⁺ with d⁰, Ga³⁺ and Ag⁺ with d¹⁰). Same electron count does not mean same configuration: Co and Cu²⁺ both have 27 electrons, but Co is 3d⁷ 4s² (3 unpaired) and Cu²⁺ is 3d⁹ (1 unpaired). Half-filled d⁵ is especially stable, which is why Mn²⁺ → Mn³⁺ (third ionization energy 3248 kJ/mol) is harder than Fe²⁺ → Fe³⁺ (2957 kJ/mol).

Periodic trends and their exceptions

Across a period the core charge felt by valence electrons (Zeff ≈ Z − core electrons) rises while n stays the same, so radius falls and first ionization energy, electronegativity and nonmetallic character rise. Down a group n rises, so radius grows and ionization energy falls. Two exceptions in the first ionization energy: group 13 is lower than group 2 (Mg 738 > Al 578 kJ/mol) because the np electron is higher in energy than ns; group 16 is lower than group 15 (P 1012 > S 1000 kJ/mol) because the fourth p electron pairs in an occupied orbital, and losing it leaves a half-filled p³ ion. Electron affinity has a well-known exception too: Cl (−349 kJ/mol) releases more energy than F (−328 kJ/mol) on gaining an electron, because the added electron is crowded into fluorine's small 2p shell. Isoelectronic ions shrink as Z rises: O²⁻ > F⁻ > Na⁺ > Al³⁺ (all 10 electrons, drawn). Successive ionization energies jump when the next electron comes from the core: Mg 738, 1451, then 7733 kJ/mol, so magnesium has two valence electrons.

What to carry forward

Keep λ in metres and energies in J per photon or J/mol, and include Z² for one-electron ions. Fill by aufbau, Pauli and Hund, remember Cr and Cu, and take 4s electrons off first when forming transition-metal ions; one unpaired electron makes a species paramagnetic. Trends follow Zeff and n; the exceptions (group 2 > 13, group 15 > 16, big jumps at the core) come from which orbital the electron leaves.

Problemas de prática (40)

Praticar é grátis com uma conta.

Preveja o produto 4

Ions and magnetism

  • Configuration of Co³⁺Write the configuration of a transition-metal 3+ ion by removing 4s electrons before 3d.

Light and the Bohr atom

  • An electron falls from n = 5 to n = 2Predict whether a hydrogen transition emits or absorbs light and in which spectral region the line lies.

Periodic trends and ionization energy

  • Largest of four krypton-like ionsPredict the largest member of an isoelectronic series from nuclear charge.

Quantum numbers and configurations

  • Ground-state configuration of nickelWrite the noble-gas configuration of a period 4 transition metal by aufbau filling.

Classificar 4

Ions and magnetism

  • Which ion is diamagnetic?Classify transition-metal ions as paramagnetic or diamagnetic from their d-electron configurations.

Quantum numbers and configurations

  • Quantum numbers of gallium's 4p electronSelect a valid quantum-number set for the highest-energy electron of a p-block atom.
  • Spot the true ground stateDecide which configuration among atoms and transition-metal ions is the actual ground state.

Periodic trends and ionization energy

  • Where the period 3 trend dipsClassify neighbouring period 3 pairs by whether first ionization energy rises or falls from left to right.

Comparar 5

Light and the Bohr atom

  • Rank photons given in different unitsRank photons described by molar energy, frequency, wavelength and a Bohr transition after converting each to energy per photon.

Periodic trends and ionization energy

  • Rank five atoms by first ionization energyRank atoms from different groups and periods by first ionization energy, including the group 15/16 anomaly.
  • Rank five atoms by second ionization energyRank atoms by second ionization energy by asking which electron each +1 ion must lose.

Ions and magnetism

  • Rank atoms and ions by unpaired electronsRank a mixed set of main-group atoms and transition-metal ions by their numbers of unpaired electrons.
  • Same electron count, different arrangementIdentify the pair of species that are isoelectronic but have different ground-state configurations.

Calcular 12

Light and the Bohr atom

  • Absorb at 97.2 nm, then emitFind the level reached by a hydrogen absorption and then calculate the wavelength of a subsequent emission.
  • Blu-ray versus DVD photons, per moleCompare the molar photon energies of two lasers by converting each wavelength to kJ/mol before subtracting.
  • The n = 3 → 2 line of He⁺Calculate an emission wavelength for a one-electron ion using the Z² dependence of the Bohr energies.
  • De Broglie wavelength of a photoelectronCombine the photoelectric equation with the de Broglie relation to find the wavelength of the fastest ejected electrons.
  • Wavelength of an FM radio signalConvert a frequency given in MHz into a wavelength with c = λν.

Periodic trends and ionization energy

  • Photoelectrons from argonCalculate the kinetic energy of photoelectrons from a photon energy and a first ionization energy, per mole.
  • Longest wavelength that ionizes sodium atomsConvert a molar ionization energy into the longest photon wavelength that can ionize one atom.

Ions and magnetism

  • How many are paramagnetic?Count the paramagnetic species in a mixed list of atoms and ions from their ground-state configurations.
  • Unpaired electrons in O⁻Count the unpaired electrons of a gas-phase main-group anion formed by adding one electron to an atom.

Quantum numbers and configurations

  • Period 4 atoms with one unpaired electronCount the period 4 atoms whose ground states have exactly one unpaired electron, transition metals and exceptions included.
  • Electrons with l = 0 in Zn²⁺Count the electrons with a given angular-momentum quantum number in a transition-metal ion after removing its 4s electrons first.
  • Electrons in d orbitals of zirconiumCount every electron with l = 2 in a period 5 transition metal, core and valence included.

Encontre o erro 4

Periodic trends and ionization energy

  • Find the false statement on a review sheetFind the incorrect periodic-trend statement among several that test the common exceptions.

Light and the Bohr atom

  • Is He⁺ as easy to ionize as H?Find the error in an ionization-energy estimate for He⁺ that ignores the nuclear charge.

Ions and magnetism

  • Fewer electrons, fewer unpaired?Evaluate a claim about the unpaired electrons of Fe²⁺ and Fe³⁺ by writing both configurations.

Quantum numbers and configurations

  • Is the oxygen atom diamagnetic?Identify which filling rule a proposed orbital diagram breaks and correct the magnetic prediction.

Interprete as evidências 2

Light and the Bohr atom

  • Which transition gave this photon?Match an emitted photon energy to a hydrogen transition using a table of level energies.

Periodic trends and ionization energy

  • Identify an element and its oxide from ionization energiesUse the jump in successive ionization energies to find a period 3 element's valence electrons and the formula of its oxide.

Trabalhe de trás para frente 4

Ions and magnetism

  • A diamagnetic period 5 dicationIdentify a period 5 element from the magnetism and the occupied subshells of its 2+ ion.

Quantum numbers and configurations

  • Five electrons in the fifth shellIdentify an element from the number of electrons in one shell and its number of unpaired electrons.
  • Name the atom from its orbital diagramIdentify a neutral atom from a valence orbital diagram by counting its electrons.

Periodic trends and ionization energy

  • A period 4 element with a half-filled cationIdentify a period 4 main-group element from a dip in first ionization energy and the configuration of its gas-phase cation.

Planeje uma síntese 1

  • Ionize only the excited atomsChoose a wavelength that ionizes hydrogen atoms in n = 2 but not those in the ground state.

Explique por quê 4

Ions and magnetism

  • Filled first, lost firstExplain why transition metals lose 4s electrons before 3d electrons even though 4s fills first.
  • Why Mn²⁺ resists oxidation more than Fe²⁺Explain an ionization-energy reversal between Mn²⁺ and Fe²⁺ from their d-electron configurations.

Periodic trends and ionization energy

  • Why Mg²⁺ is smaller than Na⁺Explain the size difference between two isoelectronic cations from nuclear charge.

Quantum numbers and configurations

  • Eighteen places, eight elementsExplain why period 3 has eight elements even though the n = 3 shell can hold 18 electrons.

Travou em revisão para a prova: átomos, elétrons e tendências periódicas? Escaneie o problema.

Tire uma foto da reação da sua lista ou do livro e desenhe o mecanismo com cada seta corrigida. 1 scan grátis agora, sem cadastro; mais 1 com uma conta gratuita.

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