Chemistry: Atoms First 2e · Representative Metals, Metalloids, and Nonmetals

Structure and General Properties of the Metalloids

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In 30 seconds
Why this matters
The college version
Eli explains
Key takeaway
Check yourself
Study tools
Sources & references

In 30 seconds

Between the metals on the left of the periodic table and the nonmetals on the right runs a diagonal "staircase" of elements with intermediate properties: boron, silicon, germanium, arsenic, antimony, and tellurium (polonium and astatine are sometimes included, but their chemistry is poorly studied). These are the metalloids. They look somewhat metallic — shiny, brittle solids — yet they bond covalently like nonmetals, and their oxides are (able to act as acid or base depending on the partner).

Their signature property is behavior. Silicon and germanium conduct electricity far better than insulators but far worse than metals — and their conductivity increases when heated, the exact opposite of a metal. That one property, plus the ability to fine-tune it by adding trace impurities (), is the physical foundation of every computer chip, solar cell, and LED on Earth.

Why this matters

Silicon is the element of the information age. Transistors, microprocessors, and solar panels are built from doped silicon; germanium was the original transistor material and still matters in fiber-optic and infrared optics.
The dual personality teaches periodicity: metallic character increases down a group and decreases across a period — exactly what the staircase shows.
Health and history: arsenic and antimony compounds have a long, dark history in medicine and poison; their oxides are toxic, a reminder that "elemental" does not mean "harmless."
Exam value: expect questions locating metalloids on the staircase, explaining why silicon is a semiconductor while aluminum conducts and sulfur insulates, and assigning oxidation states in oxides.

The college version

Core Concepts

Where the metalloids sit

The metalloids form the diagonal band from boron (group 13) down to tellurium (group 16), with valence configurations ns²np¹ through ns²np⁴: B 2s² 2p¹, Si 3s² 3p², Ge 4s² 4p², As 4s² 4p³, Sb 5s² 5p³, Te 5s² 5p⁴. Half-filled or nearly half-filled p subshells and high ionization energies keep these elements from shedding electrons the way metals do. The staircase marks the transition: below and to the left are metals; above and to the right are nonmetals. Moving down a group, metallic character increases — boron is essentially a nonmetal; tellurium behaves almost like a metal.

Structure: covalent networks, not metal lattices

Metals pack atoms with freely moving valence electrons, which is why they are malleable and conductive. Metalloids do the opposite: each atom shares electrons in covalent bonds with its neighbors, building extended networks. Silicon and germanium adopt the diamond structure — every atom bonded to four neighbors in a tetrahedral network — giving hard, brittle solids with high melting points (Si melts near 1414 °C) and no free electrons at low temperature. Boron is built from B₁₂ icosahedra and is extraordinarily hard; arsenic and antimony form layered structures; tellurium forms helical chains. Because the electrons are tied up in bonds, pure metalloids conduct poorly at room temperature — that is what makes them semiconductors rather than metals.

Semiconductors and the band gap

Band theory explains the difference. In a solid, atomic orbitals blend into energy bands: the filled and the empty are separated by a gap.

Metals: bands overlap or the conduction band is partially filled → electrons move freely → high conductivity.
Insulators: a large gap (several eV) that thermal energy cannot bridge → essentially no conductivity.
Semiconductors: a small gap (0.67 eV for Ge, 1.1 eV for Si) → a few electrons jump the gap at ordinary temperatures → modest conductivity that rises with temperature.

Heating a metal slows its conductivity (vibrating atoms scatter electrons); heating a semiconductor increases conductivity by promoting electrons into the conduction band — the memorable "opposite" behavior.

Doping — replacing a few silicon atoms with impurities — makes semiconductors useful. Phosphorus (group 15) contributes an extra valence electron that becomes a mobile carrier (n-type); boron (group 13) leaves a "hole" that acts like a positive charge carrier (p-type). Junctions between n- and p-type regions are the basis of diodes, transistors, and solar cells. Only parts-per-million levels of dopant are needed — trace composition controlling bulk behavior.

Chemical behavior: the dual personality

Metalloids react as metals or nonmetals depending on the partner:

Amphoteric oxides: GeO₂, As₂O₃, Sb₂O₃, and TeO₂ react with both strong acids and strong bases, whereas metal oxides are basic and nonmetal oxides are acidic. SiO₂ (sand, quartz) is acidic — it reacts with molten base to form silicates, which is why glass slowly dissolves in strong alkali.
Positive oxidation states from covalent sharing: B is +3; Si and Ge are +4 (Ge also +2); As and Sb are +3 and +5; Te is +2, +4, and +6.
Covalent hydrides are volatile and often toxic: silane (extSiH₄), arsine (extAsH₃), and stibine (extSbH₃) are gases; arsine and stibine are extremely poisonous and are handled only with industrial-grade containment — never generated casually in teaching labs.
Covalent halides such as SiCl₄ and BCl₃ are liquids or low-melting solids, unlike the ionic halides of metals.

Examples: metalloids by the numbers

Example 1 — How many silicon atoms are in a wafer?

A modern silicon wafer is a thin disk, 300 mm in diameter and 0.775 mm thick, with density ρ= 2.33 g/cm³. How many silicon atoms does it contain? Volume is the disk area times thickness; convert to centimeters first (r = 15.0 cm, h = 0.0775 cm):

$V = π r 2 h = π (15.0 cm) 2 (0.0775 cm) = 54.8 cm 3$

Now chain volume → mass → moles → atoms, canceling units:

$m = 54.8 cm 3 \times 2.33 g 1 cm 3 = 128 g$

$N(Si) = 128 g 28.09 g/mol \times 6.022 \times 1023 atoms 1 mol = 2.74 \times 1024 atoms$

Roughly 2.7 × 10²⁴ silicon atoms — about 4600 moles' worth — in one thin disk.

Example 2 — How little dopant is "parts per million"?

An n-type chip contains 1.00 × 10⁻⁶ g of phosphorus (one part per million by mass) in 1.00 g of silicon. How many P atoms per Si atom? Moles of each:

$n(P) = 1.00 \times 10 -6 g 30.97 g/mol = 3.23 \times 10 -8 mol$

$n(Si) = 1.00 g 28.09 g/mol = 3.56 \times 10 -2 mol$

$N(P) N(Si) = 3.23 \times 10 -8 3.56 \times 10 -2 = 9.1 \times 10 -7$

Only about 1 phosphorus atom per 1.1 million silicon atoms — yet that trace level makes the crystal a working electronic device.

Example 3 — Oxidation states in metalloid oxides

Oxygen is −2 and the sum of oxidation states in a neutral compound is zero. For GeO₂:

$x + 2(-2) = 0 \Rightarrow x = +4$

For As₂O₃:

$2x + 3(-2) = 0 \Rightarrow x = +3$

Germanium is +4 in GeO₂; arsenic is +3 in its common oxide (and +5 in As₂O₅). The positive states confirm that metalloids share electrons with oxygen — covalent, not ionic, behavior.

Common Confusions

Do Not Confuse	With	Difference
Metalloid	Metal or nonmetal	Metalloids are intermediate: covalent bonding like nonmetals, but shiny solids with some conductivity like metals.
Silicon (Si)	Silica (SiO₂)	Si is the element, a semiconductor; SiO₂ is its oxide — sand, quartz, and the main ingredient of glass.
Semiconductor heating	Metal heating	Heating a semiconductor increases conductivity; heating a metal decreases it.
n-type	p-type	n-type has extra electrons (group 15 dopants); p-type has electron holes (group 13 dopants).
Pure silicon	Doped silicon	Pure silicon conducts poorly; parts-per-million doping boosts conductivity enormously.
Being an element	Being harmless	Arsenic is an element, yet its compounds are potent poisons. Elemental ≠ safe.

Eli explains

The same idea, in plain words

Explain it like I’m 10

Metalloids are the "in-between" elements on the periodic table's staircase. They look like shiny rocks and can act like metals sometimes and nonmetals other times. Their superpower is being just okay at conducting electricity — and getting better when warmed up. That is why the silicon inside your phone works as a switch for the tiny electric signals that make it think.

Key takeaways

Six main metalloids: B, Si, Ge, As, Sb, Te — the diagonal staircase between metals and nonmetals.
Covalent network structures (diamond-like for Si and Ge) → hard, brittle, high-melting solids.
Small band gap = semiconductor: conductivity increases with temperature — opposite of metals.
Doping: group 15 dopants (P, As) → n-type; group 13 dopants (B, Al) → p-type; parts-per-million levels suffice.
Amphoteric oxides (extGeO₂, extAs₂ extO₃, extSb₂ extO₃, extTeO₂); extSiO₂ is acidic.
Metallic character increases down the staircase: B nearly a nonmetal, Te nearly a metal.
AsH₃ and SbH₃ are deadly toxic — industrial containment only.

Check yourself

6 review questions from the chapter. Try each one, then open the answer.

Name the six main metalloids and explain why they sit where they do on the periodic table.
Show answer
B, Si, Ge, As, Sb, Te. They form the diagonal band between metals (left/below) and nonmetals (right/above), with intermediate electronegativity and ionization energy.
Why does the conductivity of silicon increase when heated, while copper's decreases?
Show answer
In silicon, heating gives electrons enough energy to jump the small band gap into the conduction band, raising conductivity. In copper, heating makes atoms vibrate more, scattering electrons and lowering conductivity.
A silicon wafer has volume 100 cm³ and density 2.33 g/cm³. How many moles of silicon does it contain? (M: Si = 28.09 g/mol.)
Show answer
m = 100 cm³ × 2.33 g/cm³ = 233 g; n = 233 g ÷ 28.09 g/mol = 8.29 mol.
What are the oxidation states of Sb in Sb₂O₃ and Te in TeO₂?
Show answer
Sb₂O₃: 2x + 3(−2) = 0 → x = +3. TeO₂: x + 2(−2) = 0 → x = +4.
Would doping silicon with gallium (group 13) make it n-type or p-type? Why?
Show answer
p-type: gallium has three valence electrons (one fewer than silicon), creating electron holes.
Germanium has a of 0.67 eV and diamond about 5.5 eV. Which is a semiconductor and which an insulator, and why?
Show answer
Germanium (0.67 eV) is a semiconductor — thermal energy bridges the gap. Diamond (5.5 eV) is an insulator — the gap is far too large for ordinary thermal excitation.

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Study tools & related lessonsKey vocabulary · Related

Key vocabulary

Metalloid: An element with properties between metals and nonmetals (B, Si, Ge, As, Sb, Te).
Semiconductor: A solid with a small band gap whose conductivity rises with temperature.
Band gap: The energy difference between the valence and conduction bands.
Valence band: The filled band of bonding electrons in a solid.
Conduction band: The empty band electrons enter to become mobile charge carriers.
Doping: Adding trace impurity atoms to control a semiconductor's conductivity.
n-type / p-type: n-type: extra electrons from group 15 dopants; p-type: holes from group 13 dopants.
Amphoteric: Able to react as an acid or a base.

Sources & references

openstax.org — Chemistry Atoms First 2e

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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