Introduction to Bonding Ionic, Metallic & Covalent

Valence electrons are the electrons in the highest occupied energy level (outer-most energy level) of an element’s atoms. Crack out the Periodic Table

Electron Dot Diagrams are diagrams that show valence electrons as dots referred to as “Lewis Structures” named after the scientist that first used them Show only Valence Electrons

Lewis Dot Examples

Octet Rule Gilbert Lewis (1916) explained why atoms form certain kinds of ions and molecules. In forming compounds, atoms tend to achieve the electron configuration of a noble gas(i.e. 8 valence electrons) Atoms of the metallic elements tend to lose their valence electrons, leaving a complete octet in the next lowest energy level. Atoms of some nonmetallic elements tend to gain electrons or to share electrons with another nonmetallic element to achieve a complete octet.

Formation of Ions When an atom gains or loses electrons it becomes either positively or negatively charged Cations are positively charged ions Anions are negatively charged ions

Cations Become POSTIVELY charged because they LOSE an electron Metals have fewer than 4 valence electrons so they lose them to become cations. 1+ means one electron was lost 2 + means 2 electrons were lost 3 + means 3 were lost

Transition Metal Cations For transition metals, the charges of cations may vary. An atom of Iron, for example, may lose two or three electrons. the Fe2+ ion is called Iron (II) ion or Ferrous ion the Fe3+ ion is called Iron (III) ion or Ferric ion This Roman numeral system is called the stock system.

Anions Become NEGATIVELY charged because they GAIN electrons Nonmetals have MORE than 3 valence electrons so they gain them to become anions. 1- means one electron was gained 2- means 2 electrons were gained 3- means 3 were gained

Metalloids Have 3, 4, or 5 valence electrons Sometimes they gain electrons to become anions Sometimes they lose to become cations CARBON usually does not Ionize by itself, can form polyatomic ions. Reference Table E, p. 2

Ionic compounds When a positively charged cation is attracted to a negatively charged anion they form a relationship because opposites attract. VIDEO

Example, table salt or sodium chloride Na has one valence electron, which it loses easily (think the exploding water) Chlorine wants one because it have seven already (deadly gas, reacts with the water in your lungs, don’t breathe it).

Na Cl ONE VALENCE ELECTRON SEVEN VALENCE ELECTRONS

Na Cl ZERO VALENCE ELECTRONS EIGHT VALENCE ELECTRONS

Lewis Structure are ALWAYS on the exam in some form!! Na Cl Lewis structure for Ionics: NaCl KF CaCl2 MgO

Salt (chemistry definition) an ionic compound made between a metal and a nonmetal. Although they are composed of ions, ionic compounds are electrically neutral. The total positive charge of the cations equals the total negative charge of the anions.

Properties of Ionic Compounds (yes, you must know all these) very stable structure. high melting points. (NaCl has a melting point of about 800°C.) Are crystalline solids at room temperature. (Crystal - a solid in which the atoms, ions, or molecules are arranged in repeating, three-dimensional patterns called a crystal lattice) can conduct an electric current when dissolved in water.

Properties of Ionic Compounds When dissolved, the ions are free to move about in the aqueous (water) solution. Solvation - a process that occurs when an ionic solute dissolves; in solution, solvent molecules surround the positive and negative ions.

Metallic Bonds Metals are best thought of as positive nuclei floating in a “sea of electrons”. The valence electrons can drift freely from one part of the metal to another. Metallic bonds consist of the attraction of the free-floating valence electrons for the positively charged nuclei video

Metallic Properties Metals are good conductors of electrical current because electrons can flow freely in them. Metals are ductile—that is, they can be drawn into wires. Metals are also malleable, which means that they can be hammered or forced into shapes.

Alloys Alloys are mixtures composed of two or more elements, at least one of which is a metal. Most of the metals you encounter are alloys. Brass is an alloy of copper and zinc. Sterling silver (92.5% silver and 7.5% copper) is harder and more durable than pure silver but still soft enough to be made into jewelry and tableware. Bronze is an alloy of seven parts of copper to one part of tin. Bronze is harder than copper and more easily cast. Non-iron alloys, such as bronze, copper-nickel, and aluminum alloys, are commonly used to make coins.

Amalgam (rarely asked on exam) Liquid mercury has the ability to dissolve other metals to produce alloys and these alloys are called amalgams. Amalgam examples are gold/mercury, silver/mercury and copper/mercury all of which are used in dentistry.

Covalent Bonds Atoms held together by sharing a pair of electrons diatomic molecule - a molecule consisting of two atoms…

Lewis dot for Diatomics: H2 N2 F2 Br2 I2 Cl2

Covalent Continued on next presentation.