Chemistry and Society

1. Chemistry and Society Bonding Dr. Victor H. Vilchiz Fall 2011

2. Chemical Substances; Formulas and Names • Ionic compounds • Most ionic compounds contain metal and nonmetal atoms; for example, NaCl. • You name an ionic compound by giving the name of the cation followed by the name of the anion. • A monatomic ion is an ion formed from a single atom. • Table lists some common monatomic ions of the main group elements.

3. Chemical Substances; Formulas and Names • Rules for predicting charges on main group monatomic ions • Most of the main group metals form cations with the charge equal to their group number. • Example: Aluminum is in group IIIA; therefore an aluminum ion will be Al3+ • The charge on a monatomic anion for a nonmetal equals the group number minus 8. • Example: Nitrogen is in group VA; therefore a nitrogen ion will be N(5-8),N3-

4. Common Ions of the Main Group Elements Return to Lecture

5. Transition Metal Ions • A lot of the transition metal ions are confused as to how many electrons they wish to donate; therefore, they form more than one ion, each with a different charge. (see Table). • You should know the ones for Cu, Fe, Pb, and Hg.

6. Common Ions of the transition metals Return to Lecture

7. 0 Naming Cations • Rules for naming cations • There are two types of cations: elemental (Monatomic) and Ammonium Ion • Monatomic cations are named after the element and the word Ion is appended. For example, Al3+ is called the aluminum ion. • If there is more than one cation of an element, a Roman numeral in parentheses denoting the charge on the ion is used. This often occurs with transition elements. Example: Fe2+ and Fe3+; Iron(II) ion and Iron(III) ion

8. Naming Anions • Rules for naming anions • Monatomic Anions: Use the root of the element’s name and change ending to – ide and append the word ion. • example, Br Br – Bromine becomes Bromide ion. • Polyatomic Anions: Use the table provided.

9. 0 List of Polyatomic Ions Return to Lecture

10. Naming Ionic Compounds • NaF - • LiCl - • MgO -

11. 0 Naming Ionic Compounds • NaF- Sodium Ion and Fluoride ion • LiCl- Lithium Ion and Chloride Ion • MgO- Magnesium Ion and Oxide Ion

12. 0 Naming Ionic Compounds • NaF - Sodium Fluoride • LiCl - Lithium Chloride • MgO - Magnesium Oxide

13. Cd(OH)2 Cadmium Hydroxide Ca3(PO4)2 Calcium Phosphate AgCN Silver Cyanide Na2SO4 Sodium Sulfate Na2SO3 Sodium Sulfite KNO3 Potassium Nitrate 0 More Practice

14. 0 Ionic Compounds Formulas • How do we know how many atoms of each ion we need? • A simple crossing of the charges can answer that question about 90% of the time. • Example: Mg2+ and PO43- Mg3(PO4)2 Check the charges… 3 x (+2) = +6 2 x (-3) = -6 • When they combined they cancel to yield a neutral compound.

15. 0 Ionic Compounds Formulas • The crossing technique does not work if the magnitude of the charges is the same • Example: Mg2+ and CO32- Mg2(CO3)2 This is incorrect since we want the lowest ratio possible which is 1:1 to yield MgCO3

16. 0 Naming Covalent Compounds • A covalent compound as we said before is formed by sharing electrons between 2 nonmetals or metalloids. • These compounds are usually molecular and are named using a prefix system. • When naming these compounds name the element further to the left (in the periodic table) first, then the one on the right.

17. Naming Covalent Compounds • You name the first element using the exact element name. • Name the second element by writing the root of the element’s name and add the suffix “–ide.” • If there is more than one atom of any given element, you add the Greek prefix denoting how many atoms of that element are present. Table lists the Greek prefixes used. • If only one atom of the second element is present it gets the prefix “mono”

18. Greek Prefixes for Covalent Compounds Nomenclature Return to Lecture

19. Naming Covalent Compounds • Here are some examples of prefix names for binary molecular compounds. • PF5 phosphorus pentafluoride • SO2 sulfur dioxide • SF6 sulfur hexafluoride • N2O4 dinitrogen tetroxide • CO carbon monoxide

20. Bonding • I mentioned earlier that the periodic table was arranged according to how many electrons were in the outer shell. • It is the same electrons in the outer shell that dictate how a compound interacts with the rest of the substances. • It is the electrons that are involved in bonding and determine how a compound is held together.

21. Electrons in Bonding • Electrons in an atom feel an attraction towards the nucleus, where the positive charged molecules are found. • However, there are other electrons in the outer shell as well as inner shells that will repel each other due to the similar charge. • The same is true of protons feeling the proximity of other protons in the nucleus.

22. Bonding • At the end what we have is a tug-o-war between the electrostatic attraction between the electrons and protons on one side and the proton-proton and electron-electron repulsion on the other. • Once those three forces are balanced we end up with a bond between atoms.

23. How does bonding take place? • Sometimes in order to learn how something happens it is easier to look at the case of when it does not happen. • Lets look at the case of the noble gases which rarely form compounds covalent or otherwise. • What is it that noble gases have that the rest of the elements do not. • First notice their position in the periodic table. • They are at the very far right of the table.