Chapter 22 Section 2 Pages 694-702 Chemical bonding Chapter 22 Section 2 Pages 694-702

Chemical Bonding Bonding – attractions between atoms or ions There are several types of chemical bonds, but we will discuss three of the strongest types 1. Covalent bonds 2. Metallic bonds 3. Ionic bonds

Covalent Bonds Covalent bonds – bonds formed from atoms sharing pairs of electrons  Molecules formed this way: sugar, water - NO charged particles / ions involved - Sharing electrons between atoms  Each atom “donates” one electron to the shared pair

Covalent Bonds - Two atoms can share up to 3 pairs of electrons  1 shared pair = single covalent bond  2 shared pairs = double covalent bond  3 shared pairs = triple covalent bond

Covalent Bonds - Each shared pair represented as a line in a structural formula  Example: H - H *this is a single covalent bond **Goal of bonding is to fill the outer energy level and become stable

Covalent Bonds – Electron dot diagrams Valence electrons – electrons in the outermost energy levels of an atom Electron dot diagrams show the valence electrons as dots surrounding the chemical symbol  The chemical symbol represents the nucleus and all inner level electrons Electron dot diagrams show only the electrons in the outer energy level of an atom.

Covalent Bonds – Electron dot diagrams Each hydrogen shares one pair of electrons with the oxygen atom

Metallic bonds 2. Metallic bond – Closely packed metal atoms - Outer energy levels of metal atoms overlap - Valence electrons can move and flow freely throughout the substance - Allows flexibility of material to bend - Allows easy flow of electricity through material

Ionic Bonds 3. Ionic bond – bond between oppositely charged ions, involving a total transfer of electrons between atoms - Ion – a charged particle - Cations (which lose electrons and become positively charged) bond to Anions (which gain electrons and become negatively charged)

Ionic Bonds - One atom gains an electron(s) and one atom loses an electron(s) - The now oppositely charged ions are attracted to each other due to magnetism  Opposite charges attract

Ionic Bonds Ionic bonds usually are formed by bonding between metals and nonmetals.

Ionic Bonds One cation can bond to multiple (more than one) anion

Ionic Bonds When atoms form an ionic compound, their electrons are shifted to the other atoms, but the overall number of protons and electrons of the combined atoms remains equal and unchanged. Therefore, the compound is neutral.

Ionic Bonds - Ionic compounds are networks but there is a basic ratio of cations to anions  Formula unit – the basic ratio of ions Example: NaCl  1 Na : 1 Cl