NIS – PHYSICAL SCIENCE Lecture 88 – Lecture 89 – Lecture 90 Writing Formulas and Naming Compounds Ozgur Unal

Writing Formulas and Naming Compounds What is alchemy?

Binary Ionic Compounds A binary compound is a compound that is composed of two elements. Example: KI, NaCl, H2O … and more? Oxidation number: In an ionic compound: Metals always lose electrons  positive ions Nonmetals always gain electrons  negative ions The charge on an ion is known as the oxidation number. Cl-  oxidation number = -1 Na+  oxidation number = +1 What are the oxidation numbers of the ions of Ca, O, Mg, P, F, I, Li, N etc? Check out Figure 20!!

Binary Ionic Compounds Some elements can have more than one oxidation number! Check out Table 3!! Like all compounds, ionic compounds are neutral. Example: CaCl2 Ca+2 has +2 charge 2 Cl- has -2 charge  net charge is +2-2=0!! Perform the same exercise for Al2O3.

Binary Ionic Compounds Writing formulas: 1- Write the symbol of the element that has the positive oxidation number of charge. 2- Write the symbol of the element with the negative number. 3- To have a neutral compound, the positive charges have to balance negative charges. Exercise 1: Write the formula for the binary ionic compound formed by Lead (IV) and Phosphorus Exercise 2: Write the formula for the binary ionic compound formed by Iron (II) and Oxygen

Binary Ionic Compounds Writing names: 1- Write the name of the positive ion. 2- If the positive ion has more than one oxidation number write the oxidation number using Roman numerals in parenthesis. 3- Write the root name of the negative ion. 4- Add the ending –ide to the root. Example: NaCl  Sodium Chloride Example: Fe2O3  Iron (III) Oxide Example: Al2S3  Aluminum Sulfide How about FeO? How about CO2?

Compounds With Polyatomic Ions Not all ionic compounds are binary! Baking soda has the chemical formula NaHCO3  not binary! Some ionic compounds are composed of more than two elements  polyatomic A polyatomic ion is a positively or negatively charged, covalently bonded group of atoms. A polyatomic ion contains two or more elements Example: HCO3- Check out Table 5!!

Compounds With Polyatomic Ions In order to name a polyatomic ionic compound, we use the names of the positive and negative ions. Example: K2SO4  Potassium sulfate Name the following compounds: Na2CO3 AgNO3 KOH (NH4)3PO4 How do we write the formulas of these compounds? Check out Figure 21!! http://www.ausetute.com.au/namiform.html

Compounds with Added Water Some ionic compounds have water molecules as part of their structure  hydrates A hydrate is a compound that has water chemically attached to its ions and written into its chemical formula. Example: MgSO4 . 7H2O  Magnesium Sulfate Heptahydrate Check out Table 6!! How do you read CoCl2 . 6H2O? You can remove water from these crystals by heating them  anhydrous CuSO4 . 5H2O  ??

Naming Binary Covalent Compounds Remember binary covalent compounds? Some pairs of nonmetals can form more than one compound with each other. Example: NO, N2O, NO2, N2O5 etc.. Scientists use the Greek prefixes to indicate how many atoms of each element are in a binary covalent compound. NO  Nitrogen monoxide N2O  Dinitrogen monoxide NO2  Nitrogen dioxide N2O5  Dinitrogen pentoxide Name the followings: CO2 CO PH3 N2O3 http://www.cstephenmurray.com/onlinequizes/chemistry/namingcompounds/Namingcompounds.htm