Chemical Bonding
Infer bonding from electron behavior and observable properties.
Chemical Bonding
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Bond type explains what electrons do—and why materials behave differently
Ionic: electrons are transferred, producing positive and negative ions that attract. Covalent: atoms share electron pairs. Metallic: metal atoms contribute valence electrons that can move throughout the solid.
Need more background? Open this quick foundation
Why atoms bond: Valence electrons are the outer electrons involved in bonding. Atoms can reach a lower-energy, more stable arrangement by losing, gaining, or sharing these electrons.
How NaCl forms: Sodium has one valence electron that it can lose, becoming Na+. Chlorine can gain that electron, becoming Cl−. The opposite charges attract and repeat in a three-dimensional ionic lattice. NaCl is therefore described as a formula unit in a lattice—not as one isolated NaCl molecule.
How to distinguish the three major types:
- Ionic: commonly metal + nonmetal; strong attraction between ions; often brittle with high melting points; conducts only when ions can move.
- Covalent: commonly nonmetal + nonmetal; electrons are shared; often forms separate molecules, though network covalent solids are an important exception.
- Metallic: metal atoms with mobile electrons; usually conducts as a solid and can be bent or hammered without shattering.
Use composition
Metal + nonmetal often suggests ionic; nonmetal + nonmetal often suggests covalent. This predicts the likely bond type but is not the only evidence.
Use properties
Ask what particles carry charge, whether they can move, and how strongly the particles are held together.
Read every property as evidence about particles
Problem: A brittle high-melting solid conducts electricity when molten but not when solid.
Recognize each clue:
- High melting point: strong attractions hold charged particles in a rigid lattice, so much energy is needed to separate them.
- Brittle: when lattice layers shift, ions with the same charge can line up, repel, and split the crystal.
- No conduction as a solid: ions are charged, but they are locked in fixed positions.
- Conduction when molten: melting frees the ions to move and carry electric charge.
Do it fast: All four clues fit an ionic compound. Do not rely on “high melting point” alone; use the entire pattern.
Why it works
A formula gives an initial prediction, while physical properties reveal whether the material actually contains fixed ions, mobile electrons, or separate molecules.
Five forms you should recognize
Sodium tends to lose one valence electron, forming Na+. Chlorine gains that electron, forming Cl−. Their opposite charges attract throughout a crystal lattice. That electron transfer and electrostatic attraction make NaCl ionic.
Carbon and oxygen are both nonmetals. Instead of forming a metal cation and a nonmetal anion, they achieve more stable outer-electron arrangements by sharing electron pairs. The shared pairs form covalent bonds within each CO₂ molecule.
In metallic bonding, some valence electrons are delocalized: they are not confined to one bond between two atoms. Because these electrons can move through the metal lattice, they can carry electric charge even while the metal remains solid.
Electronegativity measures how strongly an atom attracts shared electrons. If one bonded atom attracts more strongly, the shared electron density shifts toward it, producing partial negative and positive ends. A larger difference generally means a more polar bond.
Lewis structures track valence electrons. One line between two atoms represents two shared electrons, or one bonding pair. Dots not used in a bond represent lone pairs. Count electrons before deciding whether the structure is complete.
Check before you commit
- Calling every polar bond ionic
- Saying electrons are shared in ionic bonding
- Expecting solid salts to conduct
- Confusing bonds with intermolecular forces
- Counting all electrons as valence electrons
- Using one property as absolute proof
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Chemical Bonding FAQ
Why does solid NaCl not conduct if it contains charged ions?
Its ions are locked in the crystal lattice. Charge can flow only when the ions become mobile, such as after melting or dissolving in water.
Why are many ionic solids brittle?
A force can shift lattice layers so that like charges face one another. Their repulsion can split the crystal.
Are all metal–nonmetal compounds perfectly ionic?
Bonding exists on a continuum, but introductory classification uses dominant character.
Why do metals bend without shattering?
Metallic bonding is nondirectional, allowing layers to shift while attraction through delocalized electrons remains.
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