Silicon (Si, atomic number Z = 14) has 2 unpaired electrons. Its electronic configuration is [Ne] 3s² 3p². The 3p subshell contains 2 electrons distributed across 3 p-orbitals. By Hund's rule of maximum multiplicity, each electron occupies a separate orbital (3px¹ 3py¹ 3pz⁰), leaving 2 singly occupied orbitals — hence 2 unpaired electrons.
Silicon (Z=14) has 2 unpaired electrons.
Electronic configuration of silicon: 1s² 2s² 2p⁶ 3s² 3p² or [Ne] 3s² 3p².
The 2 unpaired electrons are both in the 3p subshell: 3px¹ 3py¹ 3pz⁰.
Hund's rule: electrons occupy separate orbitals singly before pairing.
Silicon has 4 valence electrons (3s² 3p²), making it a tetravalent element.
Silicon is a semiconductor used in chips and solar cells due to its 4-electron valence.
Spin multiplicity of silicon in ground state = 2(1)+1 = 3 (triplet state).
Silicon: Atomic number (Z) = 14, Symbol = Si, Period 3, Group 14
Full electronic configuration: 1s² 2s² 2p⁶ 3s² 3p²
Condensed (noble gas) notation: [Ne] 3s² 3p² (where [Ne] = 1s² 2s² 2p⁶, the neon core, accounting for 10 electrons)
Breakdown by subshell: Subshell | Electrons 1s | 2 2s | 2 2p | 6 3s | 2 3p | 2 Total | 14 ✓
The valence shell is n=3, with 4 valence electrons (3s² 3p²).
Hund's Rule of Maximum Multiplicity states: Electrons occupy orbitals singly (one per orbital) before pairing up within the same subshell, with all unpaired electrons having parallel spins (same spin direction).
The 3p subshell of silicon: • 3p subshell has 3 orbitals: 3px, 3py, 3pz • Silicon has 2 electrons to place in the 3p subshell.
Filling by Hund's rule: Orbital | Electrons | Spin 3px | 1 | ↑ 3py | 1 | ↑ 3pz | 0 | —
(Both electrons enter different p-orbitals rather than pairing in one.)
Result: • 3px: 1 electron (unpaired) • 3py: 1 electron (unpaired) • 3pz: 0 electrons (empty)
Number of unpaired electrons in silicon = 2
Orbital box notation for silicon (1s² 2s² 2p⁶ 3s² 3p²):
1s: [↑↓] 2s: [↑↓] 2p: [↑↓][↑↓][↑↓] 3s: [↑↓] 3p: [↑ ][↑ ][ ]
Reading the 3p orbitals: • First 3p box: one electron (↑) — UNPAIRED • Second 3p box: one electron (↑) — UNPAIRED • Third 3p box: empty — no electrons
Unpaired electrons = 2 (the two 3p electrons)
Spin multiplicity = 2S + 1 = 2(1) + 1 = 3 (triplet state) (Since two electrons have parallel spins, total spin S = ½ + ½ = 1)
Hund's rule is obeyed because:
Electron repulsion: • Electrons are negatively charged and repel each other. • Placing electrons in separate orbitals (rather than the same orbital) keeps them farther apart, reducing repulsion and lowering energy.
Exchange energy: • Electrons with parallel spins (in different orbitals) gain stabilisation from a quantum-mechanical exchange interaction. • This lowers the energy of the configuration where electrons are unpaired.
Pauli exclusion principle: • Two electrons in the same orbital must have opposite spins (↑↓). • This pairing requires energy (pairing energy). • When separate orbitals are available, electrons avoid this energy cost by remaining unpaired.
For silicon, the two 3p electrons find it energetically favourable to occupy separate 3px and 3py orbitals with parallel spins, rather than pair up in one 3p orbital.
Silicon's 2 unpaired electrons and 4 valence electrons have important chemical consequences:
Valency and bonding: • Silicon has 4 valence electrons (3s² 3p²) → typically forms 4 covalent bonds. • In sp³ hybridisation, silicon can pair all 4 valence electrons with 4 bond partners (e.g., SiO₂, SiCl₄, SiH₄). • In the ground state, 2 electrons are unpaired (the 3p pair); the 3s² pair can also contribute to bonding via promotion/hybridisation.
Semiconductor nature: • Silicon is a semiconductor due to its 4 valence electrons in a tetrahedrally bonded crystal lattice. • Its band gap (~1.1 eV) allows controlled electrical conductivity.
Comparison with neighbouring elements: | Element | Z | Config. | Unpaired e⁻ | |---------|----|-------------- |-------------| | Mg | 12 | [Ne] 3s² | 0 | | Al | 13 | [Ne] 3s² 3p¹ | 1 | | Si | 14 | [Ne] 3s² 3p² | 2 | | P | 15 | [Ne] 3s² 3p³ | 3 | | S | 16 | [Ne] 3s² 3p⁴ | 2 | | Cl | 17 | [Ne] 3s² 3p⁵ | 1 | | Ar | 18 | [Ne] 3s² 3p⁶ | 0 |
Silicon has 2 unpaired electrons. Its electronic configuration is [Ne] 3s² 3p². By Hund's rule, the 2 electrons in the 3p subshell occupy separate p-orbitals (3px¹ 3py¹ 3pz⁰), so both are unpaired.
Silicon (Z=14) has the electronic configuration 1s² 2s² 2p⁶ 3s² 3p², often written as [Ne] 3s² 3p² where [Ne] represents the neon core of 10 electrons.
Silicon's two 3p electrons occupy separate orbitals (3px and 3py) rather than pairing in one orbital because of Hund's rule: electrons in separate orbitals experience less mutual repulsion and gain exchange energy stabilisation. This makes the unpaired arrangement energetically lower.
Silicon has 4 valence electrons — 2 in the 3s subshell and 2 in the 3p subshell (3s² 3p²). This is why silicon forms 4 covalent bonds and belongs to Group 14 of the periodic table.
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