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Chapters 7 & 8 Ionic Bonding and Ionic Compounds Covalent Bonding Valence Electrons • Valence Electrons are the electrons of an atom which are in the highest energy level.(outermost levels) • They largely determine the chemical properties of an element. • The # of Valence electrons in an atom is directly related to the elements grouping on the periodic table (1a,2a,etc…) • Valence electrons are usually the only electrons used in chemical bonds and for the most part only the valence electrons are used in atomic dot structures. Electron Dot Structures • Electron dot structures are diagrams that show valance electrons as dots • The inner electrons and the atomic nuclei are included in the letter symbol for the element being represented. Example of Oxygen Electron Dot Structure Electron Dot Structure • Electron Dot Structure-a notation that depicts valence electrons as dots around the atomic symbol of the element; represents inner electrons of the nucleus Xe has 8 valence electrons Pb has 4 valence electrons Cations and Anions • A cation is a positively charged ion. It is caused by an atoms loss of a valance electron. • The most common cations are caused by the loss of an electron from metal atoms which, having 1-3 valance electrons, can easily lose one or two. • An anion is an atom with a negative charge, they are created by the gain of an electron to a neutral atom. Cations/Anions • Cation-positive charged ion produced from loss of valance electron from an atom • Example: NaNa+ + e• Anion-atom or group of atoms with negative charge • Example: Cl + e-Cl• Octet Rule-electrons try to gain the configuration of a noble gas, which has 8 valence electrons Cation and Anion Formulas • Cation Example Formula • Na 1s22s22p63s1Na+ 1s22s22p6 Octet: 2s22p6 • Anion Example Formula • Cl 1s22s22p63s23p5Cl- 1s22s22p63s23p6 Octet: 3s23p6 • Halide Ions-the ions produced when halogens gain electrons Ionic Bonds • Because Anions and Cations have opposite charges, naturally, they would attract each other. They do so by using electrostatic forces. Forming Ionic Bonds • At room temperature most ionic compounds are crystalline solids, these structures are very stable. Argonite (CaCo3) Ionic Compounds Ionic Bonds Ionic Compounds • Ionic Compounds-a compound composed of positive and negative ions • Properties of Ionic Compounds: » crystalline solid @ room temperature » Ions arranged in repeating 3D patterns » Very stable » High melting temperature Metallic Bonds • Metals are made up of closely packed cations rather than neutral atoms • These cations are surrounded by mobile valence electrons which can drift freely from one metal to another • Metallic bonds consist of the attraction of free floating valence electrons for the positively charged metal ions Metals and Free Electrons Metal Properties • Metals are good conductors of electricity because these 'free' electrons carry the charge of an electric current when a potential difference (voltage!) is applied across a piece of metal. Metals are also good conductors of heat. This is also due to the free moving electrons. Non-metallic solids conduct heat energy by hotter more strongly vibrating atoms, knocking against cooler less strongly vibrating atoms to pass the particle kinetic energy on. In metals, as well as this effect, the 'hot' high kinetic energy electrons move around freely to transfer the particle kinetic energy more efficiently to 'cooler' atoms. • Unlike ionic solids, metals are very malleable, they can be readily bent, pressed or hammered into shape. The layers of atoms can slide over each other without fracturing the structure (see below). The reason for this is the mobility of the electrons. When planes of metal atoms are 'bent' or slide the electrons can run in between the atoms and maintain a strong bonding situation. This can't happen in ionic solids. Properties of Metals • Metals are good conductors of electrical currents because electrons can flow freely • They are ductile and malleable because electrons can move freely. • An alloy is a mixture composed of two or more elements, at least one of which is metal Alloys • Alloys-mixtures composed of two or more elements at least one of which is a metal • Alloys are prepared by melting the mixture of the ingredients and then cooling the mixture • Brass is an alloy of copper and zinc • Bronze is an alloy of 7 parts copper and one part tin • Steel is an alloy of iron and carbon. It is corrosion resistant ductile, hard and tough. Alloy Properties • Shows an alloy mixture. It is NOT a compound but a physical mixing of a metal plus at least one other material (shown by red circle, it can be another metal eg Ni, a non-metal eg C or a compound of carbon or manganese, and it can be bigger or smaller than iron atoms). Many alloys are produced to give a stronger metal. The presence of the other atoms (smaller or bigger) disrupts the symmetry of the layers and reduces the 'slip ability' of one layer next to another. The result is a stronger harder less malleable metal. Alloy Properties Covalent Bonds and Polarity • Covalent bonds involve electron sharing between atoms • Groups forming covalent bonds: non-metals ( and Hydrogen)…all want to gain, “tug-ofwar” on electrons • These bonds share electrons, causing each side to possibly have a different charge • Non- polar covalent is when the bonding electrons are shared equally(no charge) • polar covalent bond is when the electrons Electrostatic Charge Applications • Car shocks http://www.stopshox.com/ • Getting “shocked” http://www.staticsol.com/articles/static_shocks.htm • air purifiers • http://www.oreck.com/airpurifiers/air8.cfm?keycode=CK690#five_st age Double Bonds Bond Types • Non-Polar- no charges, both sides have equal pulls; diatomic, ex. O2 • Polar-partial charges, one side has a greater pull than the other; ex. H2O • Ionic- full charges; transfer of electrons Crystalline shape, ex. NaCl Non-Polar: Equal Sharing Polar Compounds Polar Compound Hydrogen Bonding