Overview
This lecture covers chemical bonding, focusing on the differences between ionic and covalent compounds, how they form, and their properties.
Metals, Non-metals, and Metalloids
- Metals, metalloids, and non-metals can be identified on the periodic table by color coding.
- Metals are shown in red, metalloids in yellow, and non-metals in blue.
- Metals include elements like iron and silver, while hydrogen and neon are non-metals; boron is a metalloid.
Introduction to Compounds and Chemical Bonding
- Compounds are substances made of two or more elements chemically combined.
- Chemical bonding is the lasting attraction between atoms, ions, or molecules to form compounds.
Ionic Bonding
- Ionic bonds form via complete transfer of electrons from one atom to another, usually between metals and non-metals.
- Atoms bond to achieve stability, often following the octet rule.
- An ion is an atom or molecule with a positive (cation) or negative (anion) charge.
- A cation forms when a metal loses electrons; an anion forms when a non-metal gains electrons.
- Example: Sodium chloride (NaCl) forms when sodium (metal) transfers an electron to chlorine (non-metal).
Covalent Bonding
- Covalent (molecular) bonds involve sharing electron pairs between atoms, usually between non-metals.
- Non-metals have high electronegativity and tend to share electrons to stabilize.
- Example: In water (H₂O), oxygen shares electrons with two hydrogens.
- Two types of covalent bonds:
- Non-polar covalent (equal sharing, e.g., H₂)
- Polar covalent (unequal sharing, e.g., H–F, with electrons pulled toward fluorine)
Properties of Ionic and Covalent Compounds
- Ionic compounds: solid at room temperature, high hardness, high melting/boiling points, low water solubility in organic solvents, high solubility in water, brittle, not malleable or ductile, low conductivity.
- Covalent compounds: can be solid, liquid, or gas, more flexible, lower melting/boiling points, high volatility, soluble in organic solvents but not in water, not malleable or ductile, very low conductivity.
Key Terms & Definitions
- Metal — Element typically solid, shiny, conducts electricity, loses electrons in bonding.
- Non-metal — Element that is usually gas or brittle solid, poor conductor, gains or shares electrons.
- Metalloid — Element with properties intermediate between metals and non-metals.
- Compound — Substance made from two or more elements chemically bonded.
- Ion — Atom or molecule with a net electric charge.
- Cation — Positively charged ion (lost electrons).
- Anion — Negatively charged ion (gained electrons).
- Valence Electron — Electron in the outermost shell of an atom.
- Ionic Bond — Chemical bond via electron transfer between metal and non-metal.
- Covalent Bond — Chemical bond via sharing of electrons between non-metals.
- Electronegativity — Measure of an atom’s ability to attract electrons in a bond.
Action Items / Next Steps
- Review the periodic table to practice identifying metals, non-metals, and metalloids.
- Remember the properties and differences between ionic and covalent compounds.