Chapter 6.3 “Ionic Bonding”

Electron Dot diagrams are… A way of showing & keeping track of valence electrons. How to write them? Write the symbol - it represents the nucleus and inner (core) electrons Put one dot for each valence electron (8 maximum) They don’t pair up until they have to (Hund’s rule) X

The Octet Rule The noble gases are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stable Each noble gas (except He, which has 2) has 8 electrons in the outer level

Ionic Bonding Anions and cations are held together by opposite charges (+ and -) Ionic compounds are called salts. Simplest ratio of elements in an ionic compound is called the formula unit. The bond is formed through the transfer of electrons (lose and gain) Electrons are transferred to achieve noble gas configuration.

Properties of Ionic Compounds Crystalline solids - a regular repeating arrangement of ions in the solid: Ions are strongly bonded together. Structure is a rigid crystal lattice. High melting points Coordination number- number of ions of opposite charge surrounding it

Do they Conduct? Conducting electricity means allowing charges to move. In a solid, the ions are locked in place. Ionic solids are insulators. When melted, the ions can move around. Melted ionic compounds conduct. NaCl: must get to about 800 ºC. Dissolved in water, they also conduct (free to move in aqueous solutions)

- Page 198 The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

Atoms and Ions Atoms are electrically neutral. Because there is the same number of protons (+) and electrons (-). Ions are atoms, or groups of atoms, with a charge (positive or negative) Cations (+) and anions (-) They have different numbers of protons and electrons. Only electrons can move, and ions are made by gaining or losing electrons.

Predicting Ionic Charges Many transition elements have more than one possible oxidation state. Note the use of Roman numerals to show charges iron (II) = Fe2+ iron (III) = Fe3+

Naming cations Two methods can clarify when more than one charge is possible: Stock system – uses roman numerals in parenthesis to indicate the numerical value Classical method – uses root word with suffixes (-ous, -ic) Does not give true value

Naming cations We will use the Stock system. Cation - if the charge is always the same (like in the main group of metals) just write the name of the metal. Transition metals can have more than one type of charge. Indicate their charge as a roman numeral in parenthesis after the name of the metal

Predicting Ionic Charges Some of the post-transition elements also have more than one possible oxidation state. tin (II) = Sn2+ lead (II) = Pb2+ tin (IV) = Sn4+ lead (IV) = Pb 4+

Predicting Ionic Charges Some transition elements have only one possible oxidation state, such as these three: (memorize these) silver = Ag+ zinc = Zn2+ cadmium = Cd2+

Anions are always the same charge Naming Anions Anions are always the same charge Change the monatomic element ending to – ide F- a fluorine atom will become a fluoride ion.

This group of charged species is called polyatomic ions. Many common ionic compounds contain ions that are themselves composed of a group of covalently bonded atoms with an overall charge. This group of charged species is called polyatomic ions. NaNO3 contains Na+ and NO3–. CaCO3 contains Ca2+ and CO32–. KClO Contains K+ and ClO–.

Naming Ionic Compounds Containing Polyatomic Ions We name ionic compounds that contain a polyatomic ion in the same way as other ionic compounds, except that we use the name of the polyatomic ion whenever it occurs. For example, NaNO2 is named according to its cation, Na+, sodium, and its polyatomic anion, NO2–, nitrite. Hence, NaNO2 is sodium nitrite.

If there are two ions in the series, Oxyanions Most polyatomic ions are oxyanions, anions containing oxygen and another element. Notice that when a series of oxyanions contains different numbers of oxygen atoms, they are named according to the number of oxygen atoms in the ion. If there are two ions in the series, the one with more oxygen atoms has the ending -ate, and the one with fewer has the ending -ite. For example, NO3– is nitrate SO42– is sulfate NO2– is nitrite SO32– is sulfite

Oxyanions If there are more than two ions in the series then the prefixes hypo-, meaning less than, and per-, meaning more than, are used. ClO– hypochlorite BrO– hypobromite ClO2– chlorite BrO2– bromite ClO3– chlorate BrO3– bromate ClO4– perchlorate BrO4– perbromate

Polyatomic ions are… YOU MUST KNOW THESE POLYATOMIC IONS! Groups of atoms that stay together and have an overall charge, and one name. Usually end in –ate, -ite, (few –ide) A table is found in Ch. 7, Sec. 1. It is Table 2 on page 226. YOU MUST KNOW THESE POLYATOMIC IONS!

In Ionic compounds it is helpful to remember... 1. In an ionic compound, the net ionic charge is zero (criss-cross method) 2. An -ide ending generally indicates a binary compound (nonmetal anion) 3. An -ite or -ate ending means there is a polyatomic ion that has oxygen 4. A Roman numeral after the name of a cation is the ionic charge of the cation