Metal atoms form metallic bonds through free electrons. All characteristic properties of metals can be explained by this bonding.
Basic Knowledge
Because metal atoms have low ionization energies, they readily release outer-shell electrons and become cations. When metals gather, electrons released from each atom are shared throughout the metal and move as free electrons among the metal ions (cations). This bonding form is a metallic bond.
Common properties of metals (the three main properties of metals plus others):
① Electrical conductivity: They conduct electricity well because free electrons move.
② Thermal conductivity: Free electrons also carry thermal energy.
③ Metallic luster: Free electrons reflect light well.
④ Malleability (can be spread into thin sheets) and ductility (can be drawn into thin, long wires): Free electrons maintain the bond even when atom positions shift.
Aggregates of metal atoms are called metallic crystals and have regular arrangements such as face-centered cubic (Cu, Al, Ag, Au), body-centered cubic (Fe at room temperature, Na, K), and hexagonal close-packed structures (Mg, Zn).
Metallic bond（A bond formed by metal ions and free electrons）
Free electron（An electron that moves freely within a metal. It is responsible for various types of conductivity）
Malleability and ductility（The properties of being spread into thin sheets or drawn into thin wires）
Metallic luster（The shine caused by free electrons reflecting light）
Alloy（A mixture of several metals or a metal with elements such as C. It improves properties）
Metallic crystal（A regular arrangement such as face-centered cubic, body-centered cubic, or hexagonal close-packed）
Further Study (Background and Significance)
The physical properties of metals are directly connected to familiar technologies.
・Electrical wiring: Copper Cu (high conductivity and relatively inexpensive); gold Au is also used in submarine cables and precision equipment.
・Pots and cookware: Aluminum Al (high thermal conductivity and lightweight); stainless steel (a corrosion-resistant alloy).
・Construction materials: Iron Fe (high strength); stainless steel (corrosion resistance).
・Decoration: Gold Au, silver Ag, and platinum Pt (beautiful luster and corrosion resistance).
Alloys are made to compensate for weaknesses of pure metals.
・Steel: Iron + a small amount of carbon. Hard and strong. Used in construction and automobiles.
・Stainless steel: Fe+Cr(+Ni). Resistant to rust.
・Brass: Cu+Zn. Brass instruments and the 5-yen coin.
・Bronze: Cu+Sn. Statues and the 10-yen coin.
・Duralumin: Al+Cu+Mg+Mn. Lightweight and strong. Aircraft.
・Nichrome: Ni+Cr. Has high electrical resistance. Heating wires.
・Amalgam: An alloy of mercury Hg and another metal. Dental treatment (now declining).
Mercury Hg is the only metal that is liquid at room temperature, while tungsten W has the highest melting point (used in light-bulb filaments; its use is declining as LEDs spread).
- Metallic bond = metal ions + free electrons
- Metal properties: electrical conductivity, thermal conductivity, metallic luster, malleability, and ductility
- Free electrons maintain bonds when positions shift → malleability and ductility
- Metallic crystals: face-centered cubic (Cu,Al), body-centered cubic (Fe,Na), hexagonal close-packed (Mg,Zn)
- Alloys improve properties (steel, stainless steel, brass, bronze)
- Conductivity: Ag > Cu > Au > Al > Fe
- Mercury Hg is liquid at room temperature; tungsten W has the highest melting point
Points to Note (Common Confusions)
① Do not confuse ionic bonds (metal ions + anions) with metallic bonds (metal ions + free electrons). ② The melting points of pure metals vary widely (mercury -39℃ to tungsten 3422℃). Metals do not necessarily have high melting points. ③ Distinguish malleability (spreading into sheets, as with gold foil) from ductility (drawing into wires, as with copper wire). ④ Alloys are mixtures, not compounds. Their composition ratios can vary continuously.
Practice
- Using free electrons, explain why metals conduct electricity well.
- What is the difference between malleability and ductility?
- What components make up the alloy steel?