Notes P.1-2 January 22, 2014 Objectives • You will be able to: – Define metallic, ionic, and covalent bonds and explain their characteristics – State if two atoms will form a covalent or ionic bond – Write ionic formula units Overview of bonding • Chemical bond: mutual electrical attraction between the nuclei and valence electrons of different atoms that binds those atoms together. • Why do atoms bond? – Most atoms are more stable when they are bonded than they were as individual atoms Types of chemical bonds: • Metallic – sea of electrons – Occur between: between metals • Ionic – steal electrons – Occur between: metal—nonmetal • Covalent – share electrons – Occur between: nonmetal—nonmetal • Covalent or Ionic? – Determined by electronegativity difference Remember: Metallic Character NONMETALS (IN GREEN) METALS (IN YELLOW) Practice • Label as ionic, covalent, or metallic: NaF CaBr2 H2S Al2O3 Cu NO3 • • • • • • Ionic Ionic Covalent Ionic Metallic Covalent METALLIC BONDING – Results from the attraction of nuclei to a “sea of electrons” Sea of Electrons METALLIC BONDING – Why an “electron sea”? • Vacant p and d orbitals in metal's outer energy levels overlap, and allow outer electrons to move freely throughout the metal – Valence electrons do not belong to any one atom METALLIC BONDING – Common properties of metals: • High melting/boiling points • Conduct heat and electricity • Have luster (shiny) • Ductile/malleable – All thanks to the electron sea! IONIC BONDING • Results from the electrical attraction between cations and anions • Cation: + • Anion: - The resulting ions come together due to electrical attraction (opposites attract) IONIC BONDING Common Properties: • Solid crystals at room temperature • Very high melting/boiling points • (Most) Can dissolve in water • Conduct electricity when melted or dissolved Ionic Formula Units • The net (total) charge on the compound must equal zero • Positive and negative cancel out Hint: Use the criss-cross method Ionic Formula Units EXAMPLES: • Na and Cl • Na and O • Ca and O • Ca and Cl • Al and O Ionic Formula Units EXAMPLES: • Na and Cl Na+ + Cl- NaCl • Na and O Na+ + O2- Na2O • Ca and O • Ca and Cl • Al and O Na and O Na2O means that: Two sodium cations are needed to balance one oxygen anion. Positive and negative charges must cancel each other out EXAMPLES: • Na+ and Cl• Na+ and O2• Ca2+ and O2• Ca2+ and Cl• Al3+ and O2- NaCl Na2O CaO CaCl2 Al2O3 Total + Total - Net 1 2 2 2 6 1 2 2 2 6 0 0 0 0 0 Crystal Lattice • A network of alternating cations and anions Ionic compounds • The formula for ionic compounds does not show the exact number of atoms that are bonded together. • The formula tells the smallest whole number ratio of atoms that bond. COVALENT BONDING • Results from the sharing of electron pairs between two atoms (each has a full valence shell) • A covalent compound is called a molecule Each has a full octet COVALENT BONDING • Common properties of covalent compounds: • Low melting/boiling points • Many are liquids or gases at room temp • Non-conductors of heat and electricity Can you…? – Define metallic, ionic, and covalent bonds and explain their characteristics? – State if two atoms will form a covalent or ionic bond? – Write ionic formula units? – Homework 6A, Due Friday – Lab on Friday