Arrow Lab

Química Geral · Atoms, electrons and the periodic table

Configurações eletrônicas

Uma lição resolvida gratuita e 40 problemas de prática em que você mesmo desenha cada seta curva.

Travou em configurações eletrônicas? 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.

Escaneie sua lição de graça

O que você vai aprender

  • Write full and noble-gas ground-state configurations of atoms with the Aufbau principle and the Pauli exclusion principle, and work back from a configuration to the element.
  • Draw orbital diagrams with Hund's rule and count unpaired electrons to decide whether an atom or ion is paramagnetic or diamagnetic.
  • Recognise the chromium- and copper-type exceptions and write configurations of transition-metal ions by removing ns electrons before (n − 1)d electrons.
  • Identify isoelectronic species and count valence electrons from a configuration.

Lição gratuita

O texto da lição resolvida. No Arrow Lab, cada etapa vem com as estruturas e as setas desenhadas.

Ler a aula gratuita (7 partes)

Filling orbitals: Aufbau and Pauli

In the ground state electrons occupy the lowest-energy orbitals available (the Aufbau principle). For neutral atoms the filling order follows the n + l rule: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p. The Pauli exclusion principle allows at most two electrons per orbital, with opposite spins, so an s subshell holds 2 electrons, p 6, d 10 and f 14. Sulfur (Z = 16) is 1s² 2s² 2p⁶ 3s² 3p⁴. A noble-gas configuration replaces the core with the symbol of the preceding noble gas: vanadium (Z = 23) is [Ar] 3d³ 4s², and tin (Z = 50) is [Kr] 4d¹⁰ 5s² 5p²; the filled 4d¹⁰ must not be forgotten (36 + 10 + 2 + 2 = 50). A configuration that obeys Pauli but does not put every electron in the lowest orbitals, such as sodium 1s² 2s² 2p⁶ 3p¹, is an excited state; one that puts more than two electrons in an orbital, such as 2p⁷, is impossible.

Reading the periodic table as a configuration map

The blocks of the table show which subshell fills last: s block (groups 1–2), p block (groups 13–18), d block (groups 3–12) and f block (lanthanides and actinides). The period gives n of the outer s and p subshells; a d subshell has n one less than the period, and an f subshell two less. So working back from [Kr] 4d¹⁰ 5s² 5p³ gives 36 + 10 + 2 + 3 = 51 electrons: antimony, p block, group 15. For main-group elements the valence electrons are those of the outermost ns and np subshells; filled (n − 1)d¹⁰ and (n − 2)f¹⁴ subshells are core electrons. Selenium, [Ar] 3d¹⁰ 4s² 4p⁴, has 6 valence electrons, the same as oxygen and sulfur, which is why elements of one group share their chemistry.

Orbital diagrams, Hund's rule and magnetism

Within a set of degenerate orbitals, electrons occupy separate orbitals with parallel spins before any orbital receives a second electron (Hund's rule). Electrons in different orbitals repel each other less, and electrons with parallel spins gain exchange stabilization. Nitrogen's 2p³ is therefore ↑ ↑ ↑ (three unpaired electrons), oxygen's 2p⁴ is ↑↓ ↑ ↑ (two), and iron's 3d⁶ is ↑↓ ↑ ↑ ↑ ↑ (four). An atom or ion with at least one unpaired electron is paramagnetic and is drawn into a magnetic field; one with every electron paired, such as zinc ([Ar] 3d¹⁰ 4s²), is diamagnetic. The spin-only magnetic moment, μ = √(n(n + 2)) µB for n unpaired electrons, links a measurement to n: 1.73 µB for one, 2.83 for two, 3.87 for three, 4.90 for four and 5.92 for five.

Half-filled and filled d subshells: chromium and copper

In the first transition series 4s and 3d are close in energy. Two atoms break the simple filling order because a half-filled or filled 3d subshell is especially stable: chromium (drawn) is [Ar] 3d⁵ 4s¹, not [Ar] 3d⁴ 4s², and copper is [Ar] 3d¹⁰ 4s¹, not [Ar] 3d⁹ 4s². The same pattern appears below them: molybdenum is [Kr] 4d⁵ 5s¹ and silver [Kr] 4d¹⁰ 5s¹. Chromium has six unpaired electrons, five in 3d and one in 4s. A few heavier elements have other irregular configurations; gadolinium, [Xe] 4f⁷ 5d¹ 6s², keeps a half-filled 4f subshell. Exceptions like these are learned from data rather than predicted from the filling order.

Configurations of ions

For a main-group ion, add electrons for a negative charge or remove them for a positive charge, starting from the highest-energy subshell: Cl⁻ is [Ne] 3s² 3p⁶ = [Ar], and Al³⁺ is [Ne]. Transition metals lose their ns electrons before any (n − 1)d electrons, because once the atom is ionized the d orbitals drop below the s orbital. Iron, [Ar] 3d⁶ 4s², gives Fe²⁺ [Ar] 3d⁶ (drawn) and Fe³⁺ [Ar] 3d⁵, with four and five unpaired electrons. Copper gives Cu⁺ [Ar] 3d¹⁰ (diamagnetic) and Cu²⁺ [Ar] 3d⁹ (one unpaired electron). Write the neutral atom first, exceptions included, then remove the electrons: Mn²⁺ is [Ar] 3d⁵, never [Ar] 3d³ 4s².

Isoelectronic species

Species with the same number of electrons are isoelectronic. Count electrons as Z minus the charge: S²⁻ (16 + 2), Cl⁻ (17 + 1), Ar (18), K⁺ (19 − 1) and Ca²⁺ (20 − 2) all have 18 and the configuration [Ne] 3s² 3p⁶; Ti⁴⁺ (22 − 4) belongs to the same series. Molecules can be isoelectronic with atoms too: H₂O has 8 + 2 = 10 electrons, like Ne. Isoelectronic species are not identical: their nuclear charges differ, so their sizes and ionization energies differ. Equal electron counts do not even guarantee the same configuration across the d block: Cr and Fe²⁺ both have 24 electrons, but Cr is [Ar] 3d⁵ 4s¹ and Fe²⁺ is [Ar] 3d⁶.

What to carry forward

Fill subshells in the n + l order, two electrons of opposite spin per orbital, and spread electrons over degenerate orbitals with parallel spins before pairing. Use the preceding noble gas for the core, remember the chromium and copper exceptions, and for transition-metal cations remove the ns electrons first. Count unpaired electrons from the orbital diagram to judge magnetism, and count electrons as Z minus charge to find isoelectronic species.

Problemas de prática (40)

Praticar é grátis com uma conta.

Preveja o produto 7

Exceptions and transition-metal ions

  • Ground-state configuration of chromiumRecall the chromium exception to the Aufbau filling order.
  • Configuration of Fe²⁺Write the configuration of a first-row transition-metal dication by removing the 4s electrons first.
  • Configuration of the silver ionCombine a copper-type exception with the s-electrons-first rule to write the configuration of a second-row transition-metal cation.

Aufbau and full configurations

  • Full configuration of sulfurWrite the full ground-state electron configuration of a third-period main-group atom.
  • Noble-gas configuration of tinWrite the noble-gas configuration of a fifth-period p-block element, including its filled d subshell.
  • Noble-gas configuration of vanadiumWrite the noble-gas configuration of a first-row transition metal using the 4s-before-3d filling order.

Isoelectronic species and valence electrons

  • Ti⁴⁺ and the noble gasesPredict which noble gas a highly charged transition-metal cation is isoelectronic with, and what its configuration implies.

Classificar 7

Aufbau and full configurations

  • Block and group from a configurationAssign a main-group element to its block and group from its noble-gas configuration.
  • An excited sodium atomClassify configurations of a given electron count as ground state, excited state, impossible or belonging to an ion.

Exceptions and transition-metal ions

  • Magnetism of the copper ionsClassify the two common copper ions as paramagnetic or diamagnetic from their configurations.

Orbital diagrams and magnetism

  • Which atom is diamagnetic?Classify ground-state atoms as paramagnetic or diamagnetic from their configurations.
  • Nitrogen's 2p orbital diagramChoose the orbital diagram that obeys Hund's rule for a half-filled p subshell.

Isoelectronic species and valence electrons

  • Find the isoelectronic seriesDistinguish an isoelectronic series from a group of ions that share a charge or a configuration pattern.
  • Isoelectronic with argonIdentify a monatomic ion isoelectronic with a given noble gas by counting electrons as Z minus charge.

Comparar 4

Isoelectronic species and valence electrons

  • Cr and Fe²⁺: same count, same configuration?Compare an atom and an ion with the same electron count and show that their configurations and unpaired-electron counts differ.

Orbital diagrams and magnetism

  • Rank atoms by unpaired electronsRank main-group and transition-metal atoms by the number of unpaired electrons in their ground states.
  • Same number of unpaired electronsCompare unpaired-electron counts of second-period atoms whose p subshells are less than and more than half full.

Exceptions and transition-metal ions

  • Rank ions by unpaired electronsRank first-row transition-metal ions by unpaired electrons after writing their d-electron configurations.

Calcular 10

Exceptions and transition-metal ions

  • Unpaired electrons in a chromium atomCount the unpaired electrons of an atom whose ground state is an exception to the filling order.
  • Unpaired electrons in Fe³⁺Count the unpaired electrons of a transition-metal cation after removing the 4s electrons first.

Orbital diagrams and magnetism

  • Unpaired electrons in a cobalt atomCount the unpaired electrons of a transition-metal atom by filling its d orbitals with Hund's rule.
  • Unpaired electrons in gadoliniumCount unpaired electrons when an atom has two partly filled subshells, one of them an f subshell.
  • Unpaired electrons in an oxygen atomCount the unpaired electrons of a second-period atom from its orbital diagram.
  • Completely filled orbitals in phosphorusUse an orbital diagram to count completely filled orbitals as distinct from half-filled ones.

Isoelectronic species and valence electrons

  • How many are isoelectronic with neon?Count the atoms, ions and molecules in a list that have the same total number of electrons as a noble gas.
  • Valence electrons of seleniumCount the valence electrons of a p-block atom whose configuration includes a filled d subshell.

Aufbau and full configurations

  • Electrons in iodine's fourth shellCount the electrons in one shell of a heavy atom by writing its full configuration.
  • Period 4 atoms with 3d electronsUse the filling order across a whole period to decide which atoms contain electrons in a given subshell.

Encontre o erro 4

Orbital diagrams and magnetism

  • Does a carbon atom have four unpaired electrons?Diagnose the confusion between an atom's ground-state configuration and the bonding model of its compounds.

Isoelectronic species and valence electrons

  • Are Na⁺ and Ne the same?Diagnose the error of treating isoelectronic species as having identical properties.

Exceptions and transition-metal ions

  • Find the error: the Mn²⁺ configurationFind the error in a transition-metal ion configuration that removes d electrons before s electrons.

Aufbau and full configurations

  • Find the impossible configurationRecognise an electron configuration that breaks the Pauli exclusion principle by overfilling a subshell.

Interprete as evidências 1

  • Which ion has this magnetic moment?Interpret a spin-only magnetic moment as a number of unpaired electrons and match it to a transition-metal ion.

Trabalhe de trás para frente 4

Isoelectronic species and valence electrons

  • Anion isoelectronic with kryptonFind the atomic number of an element from an isoelectronic relationship between its anion and a noble gas.
  • Which metal forms this 2+ ion?Work back from the configuration of a transition-metal dication to the element.

Aufbau and full configurations

  • Atomic number from a configurationWork back from a noble-gas configuration that contains a filled d subshell to the atomic number of a neutral atom.
  • Identify the element from its configurationIdentify a sixth-period element from a noble-gas configuration that includes filled f and d subshells.

Explique por quê 3

Isoelectronic species and valence electrons

  • Why the alkali metals behave alikeExplain the similar chemistry of a group in terms of a shared valence configuration.

Exceptions and transition-metal ions

  • Why copper is [Ar] 3d¹⁰ 4s¹Explain the copper exception in terms of 3d–4s energy closeness and filled-subshell stability.

Orbital diagrams and magnetism

  • Why Hund's rule holdsExplain the energetic reason for Hund's rule in a set of degenerate orbitals.

Travou em configurações eletrônicas? 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.

Escaneie sua lição de graça