Bonding

Chemical Bond Electrical attraction between nuclei and valence electrons of different atoms that bind the atoms together Compounds form by gaining, losing, or sharing electrons, to lower their potential energy (PE). Bond type based on differences in electronegativity values between atoms. (Sliding scale between purely covalent to purely ionic (we will discuss this further later in the chapter))

Molecular (Covalent) Compounds Composed of nonmetals only Neutral Covalent bond: bond created by SHARING electrons between two or more nonmetals A chemical formula of covalent compound: molecule Weak intermolecular forces BETWEEN molecules Can exist as solid, liquid, gas Relatively low MP and BP Exist as individual molecules

Bond energy: energy required to BREAK chemical bond Bonds form to lower potential energy (PE) Electron from one atom attracts proton of another Nuclei and electrons repel Forces cancel and bond formed with lower PE than each originally had Bond formation RELEASES ENERGY

Ionic Bond Formed when electrons are TRANSFERRED from one atom to the other Ionic compound: Cation + anion Electrically Neutral (numbers of + charges = numbers of – charges) Hard, brittle solids High MP and BP Conduct electricity when molten (melted) or dissolved in water Chemical formula of ionic compound: formula unit Crystal lattice (a 3-D network of cations and anions strongly electrostatically attracted to each other). Non conductive in solid state bc ions are not free to move, they’re bound together in the lattice structure Ions minimize potential energy by combining in a crystal lattice. Attractive forces exist between oppositely charged ions. Repulsive forces exist between like-charged ions Attractive and repulsive forces determine: distances between ions pattern of the ions’ arrangement in the crystal

Ions minimize potential energy by combining in a crystal lattice. Attractive forces exist between oppositely charged ions. Repulsive forces exist between like-charged ions Attractive and repulsive forces determine: distances between ions pattern of the ions’ arrangement in the crystal

Ionic Vs. Covalent Bonding

Melting and Boiling Points of Compounds

The Metallic-Bond Model Metallic bonding: results from attraction between metal atoms and the surrounding sea of electrons How metallic bonding works: Vacant orbitals overlap. Allows outer e- to roam freely Electrons are delocalized Forms sea of electrons around the metal ions, which are packed together in a crystal lattice. The unique characteristics of metallic bonding gives metals characteristic properties: electrical and thermal conductivity malleability ductility shiny appearance (they do not belong to any one atom but move freely through the empty atomic orbitals)

Properties of Substances with Metallic, Ionic, and Covalent Bonds