Chemistry · Rung 4 of 24

Bonds

Atoms stick together because it lowers their energy, and they almost always aim for eight electrons in the outer shell. There are three ways. Ionic: a metal gives electrons away and a nonmetal takes them, leaving two oppositely charged ions that attract; the result is a hard, high-melting solid that conducts only when dissolved or molten, like salt. Covalent: two nonmetals share a pair; the result is separate molecules, soft and volatile, that do not conduct. And metallic: the cations sit in a lattice with loose electrons over them, which explains why a metal conducts, shines and can be drawn into wire. The rule of thumb is the electronegativity difference: over 1.7 tends to ionic, under 0.4 to pure covalent, and in between lies polar covalent, which is where water lives.

Where this sits

Comes after
The periodic table, Inside the atom
Opens up
Formulas and names, The shape of molecules, Water, the solvent

Exercises from this rung

Generated by the app, from easiest to hardest

  1. What kind of bond does table salt, NaCl, have?

    • Ionic
    • Hydrogen bonding
    • Metallic
    • Covalent

    Why Sodium is a metal with one electron too many and chlorine a nonmetal one short: sodium hands it over, leaving Na⁺ and Cl⁻ attracting by pure electricity. That is an ionic bond, and it does not form separate molecules but a lattice: a salt crystal holds no “molecule of NaCl”, it holds millions of alternating ions.

    easier

  2. Why does a metal conduct electricity?

    • Because its electrons move freely
    • Because it has no bonds
    • Because its atoms are very small
    • Because it has loose ions

    Why In a metal the atoms hand their valence electrons to a common pool: what remains is cations in an orderly lattice and a sea of electrons moving over them. That sea explains at a stroke the three things a metal does: it conducts current and heat, it shines because the free electrons throw light back, and it can be drawn out without breaking because the layers of cations slide without losing the bond.

    in between

  3. What is a polar covalent bond?

    • One shared unevenly between the two atoms
    • One that only exists in solution
    • One where an atom hands over the whole electron
    • One between two identical atoms

    Why They share, but not equally: the more electronegative atom pulls harder and the pair drifts towards it, leaving a partial negative charge on it and a positive one on the other. It neither gives outright (that would be ionic) nor shares evenly (that would be pure). It is the commonest and most useful case: water's O—H bond is polar, and nearly everything odd that water does follows from it.

    harder