Metallic bonding explains why metals conduct electricity, bend without breaking, shine, and form useful mixtures called alloys. This cheat sheet helps students connect particle-level structure to the physical properties they observe in metals. It is useful for reviewing bonding models, comparing pure metals and alloys, and predicting how structure affects strength and conductivity.
The core idea is that metal atoms form a lattice of positive metal ions surrounded by mobile delocalized electrons. These electrons explain electrical conductivity, thermal conductivity, and metallic luster. Alloy properties depend on how added atoms change the metal lattice, often increasing hardness while reducing ductility or conductivity.
Key Facts
- Metallic bonding is the electrostatic attraction between positive metal ions and a sea of delocalized electrons.
- Metals conduct electricity because delocalized electrons can move through the lattice when a potential difference is applied.
- Metals conduct heat well because mobile electrons and closely packed ions transfer kinetic energy through the lattice.
- Metals are malleable and ductile because layers of metal ions can slide while delocalized electrons keep the bonding attraction intact.
- Metallic bond strength generally increases when metal ions have greater charge and smaller radius, because attraction to delocalized electrons is stronger.
- An alloy is a mixture containing at least one metal, and its composition can be written using percent by mass as .
- Substitutional alloys form when atoms of similar size replace metal atoms in the lattice, while interstitial alloys form when small atoms fit into spaces between metal atoms.
- Alloys are often harder than pure metals because different-sized atoms distort the lattice and make it harder for layers to slide.
Vocabulary
- Metallic bond
- A bond formed by attraction between positive metal ions and mobile delocalized electrons.
- Delocalized electrons
- Electrons that are not attached to one atom and can move throughout a metal lattice.
- Metal lattice
- A regular arrangement of positive metal ions held together by delocalized electrons.
- Alloy
- A mixture of elements that contains at least one metal and has metallic properties.
- Substitutional alloy
- An alloy in which atoms of one element replace some metal atoms in the crystal lattice.
- Interstitial alloy
- An alloy in which small atoms fit into gaps between larger metal atoms in the lattice.
Common Mistakes to Avoid
- Saying metals conduct because ions move, which is wrong because the metal ions mostly vibrate in fixed lattice positions while electrons move.
- Describing metallic bonding as electron sharing between two atoms, which is wrong because metallic bonding involves many atoms and delocalized electrons spread through the lattice.
- Assuming all alloys are more conductive than pure metals, which is wrong because alloy atoms usually disrupt electron flow and can lower conductivity.
- Confusing malleability with brittleness, which is wrong because malleable metals can be hammered into sheets while brittle substances crack when layers shift.
- Forgetting that alloy properties depend on composition, which is wrong because changing percent by mass can change hardness, melting point, corrosion resistance, and conductivity.
Practice Questions
- 1 An alloy contains of chromium and of iron. What is the percent by mass of chromium?
- 2 A sample of brass has a total mass of and is zinc by mass. What mass of zinc does it contain?
- 3 Rank magnesium, sodium, and aluminum by expected metallic bond strength using ion charge and atomic size as evidence.
- 4 Steel is harder than pure iron but often less ductile. Explain this difference using the particle model of an alloy lattice.