Chemical Formulas and Compounds. Chapter 7

Transcription

1 Chemical Formulas and Compounds Chapter 7

2 Chemical Nomenclature

3 Chemical Nomenclature

4 Binary Ionic Compounds The nomenclature, or naming system, of binary ionic compounds involves combining the names of the compound s positive and negative ions. The name of the cation is given first, followed by the name of the anion. For most simple compounds, the ratio of the ions is not indicated in the compound s name because it is understood based on the relative charges of the compound s ions.

5 Binary Ionic Compounds For example NaCl is named sodium chloride. Name of metal ion is stated first Name of non-metal ion is stated second The ratio of 1 to 1 is understood because sodium tends to lose 1 electron and form a +1 ion while chlorine tends to gain 1 electron and form a -1 ion. These two therefore combine in a 1:1 ratio.

6 Binary Ionic Compounds Name the following binary ionic compounds. BaF 2 K 3 N CaO NaI AgF AlBr 3 CdO

7 Binary Ionic Compounds Write the formula for the binary ionic compound formed between each of the following pairs of elements. Magnesium and sulfur Potassium and sulfur Aluminum and chlorine Zinc and bromine Cesium and sulfur Strontium and oxygen Calcium and nitrogen

8 Binary Ionic Compounds For all of the examples we have discussed thus far, the metal atom tends to lose a specific number of valence electrons. For example, calcium will always lose two and aluminum will always lose three. But for many other metals on the periodic table, there is more than one possibility and therefore more than one compound can be formed when a metal and non-metal combine.

9 Binary Ionic Compounds For example, iron has the ability to lose either 2 or 3 valence electrons, forming a +2 or +3 ion. If iron were to combine with chlorine (which gains 1 electron) two different compounds could result. If iron were to lose 2 electrons and combine with chlorine the resulting compound would be FeCl 2. If iron were to lose 3 electrons and combine with chlorine, the resulting compound would be FeCl 3.

10 Binary Ionic Compounds FeCl 2 and FeCl 3 have very different properties and thus there is a need to somehow distinguish between them in their names. We can t simply name them iron chloride because we would not know which one we were referring to. Unfortunately iron dichloride and iron trichloride won t suffice either. Its turns out that the important part of the compound is how many electrons were lost by the metal. To distinguish between the multiple ions that may be formed by the metals, the Stock system of nomenclature is used.

11 Binary Ionic Compounds Since in FeCl 2, the iron has lost 2 electrons it is called iron (II) chloride. Since in FeCl 3, the iron has lost 3 electrons it is called iron (III) chloride.

12 Binary Ionic Compounds Write the formula and give the name for the compound formed between each of the following pairs of ions. Cu + and O 2- Hg +2 and O 2- Fe +3 and S 2- Sn +4 and S 2- Cu +2 and Cl - V +2 and F - Sn +2 and Cl - V +3 and F -

13 Binary Ionic Compounds Give the names of the following compounds using the stock system. CoI 2 CuBr 2 PbS 2 Fe 2 O 3

14 Polyatomic Ions Table E in your reference tables list some common polyatomic ions All but 3 are negatively charged and most are classified as oxyanions polyatomic ions that contain oxygen Compounds containing polyatomic ions are named in the same manner as other ionic compounds Name of cation first Name of anion second

15 Polyatomic Ions Write the formula for the following ionic compounds. Lithium nitrate Sodium carbonate Calcium nitrite Copper (II) hydroxide

16 Polyatomic Ions Give the names for the following ionic compounds. KClO 3 NH 4 OH FeCrO 4 Ca(SCN) 2

17 Molecular Compounds Unlike ionic compounds, molecular compounds are composed of individually bonded units or molecules Important thing to chemists is the number of each atom in the molecule so naming system changes

18 Molecular Compounds Naming Molecular Compounds Less electronegative element goes first Use prefix only if more than one is present Second element gets an ide suffix Number Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

19 Molecular Compounds P 4 O 10 Less electronegative element goes first Prefix needed because there is more than one Prefix is used to denote number present Second element gets an ide suffix Tetraphosphorous decoxide

20 Molecular Compounds Name the following binary molecular compounds CO 2 CO SF 6 As 2 O 5

21 Molecular Compounds Write the formulas for the following binary molecular compounds carbon tetrachloride oxygen difluoride trisilicon tetranitride nitrogen monoxide

22 Naming Compounds Name the following compounds. SiC NaI TiO 2 N 2 O 3 Al(NO 3 ) 3 FeSO 4

23 Naming Compounds Give the formula of the following compounds. carbon tetraiodide calcium oxide cobalt (II) bromide disulfur dichloride potassium permanganate lead (II) phosphate

24 Oxidation Numbers The charges on the ions that make up an ionic compound reflect the actual electron distribution In NaCl, the sodium has physically lost one electron and the chlorine has gained one. In order to indicate the general electron density of electrons in molecules, where atoms are covalently bonded to one another, oxidation states are used Unlike charges, oxidation numbers do not have a physical meaning

25 Assigning Oxidation Numbers As a general rule, shared electrons are assumed to belong to the most electronegative atom in the bond. Here are some more specific rules. 1. Atoms in a pure element are assigned an oxidation state of zero 2. The more electronegative element in a binary compound is assigned an oxidation state equal to the negative charge it would have as an anion. The less electronegative atom is assigned the number equal to what it would have as a cation

26 Assigning Oxidation Numbers 3. The sum of all of the oxidation states of the atoms in a compound is equal to zero. 4. The sum of all of the oxidation states of the atoms in a polyatomic ion is equal to the charge of the ion. 5. Although rules 1-4 apply to covalently bonded atoms, oxidation states can be assigned to ions as well.

27 Assigning Oxidation Numbers UF 6 H 2 SO 4 ClO 3 - O 2 Mg 2+ S 8

28 Molar Masses In Chapter 3 you learned that the molar mass of a substance is equal to the mass in grams of one mole, or about 6.02 x particles, of the substance. For example, the molar mass of pure magnesium is 24.3 g because one mole of Mg atoms has a mass of 24.3 g The molar mass of a compound is calculated in a similar fashion.

29 Molar Masses One mole of water molecules contains two moles of hydrogen atoms and one mole of oxygen atoms. Molar mass of water is 18.0 g/mol

30 Molar Masses Find the molar mass of each of the following compounds. NaNO 3 K 2 SO 4 C 6 H 12 O 6 Fe(OH) 3

31 Molar Mass as a Conversion Factor Molar mass can be used as a conversion factor to relate the amount in moles of a substance to a mass in grams. What is the mass in grams of 2.50 mol of O 2 gas?

32 Molar Mass as a Conversion Factor Ibuprofen, C 13 H 18 O 2, is the active ingredient in many over-the-counter pain relievers. What is the molar mass of ibuprofen? A tablet of ibuprofen is found to contain 200 mg of ibuprofen. How many moles of ibuprofen are in the tablet? How many molecules of ibuprofen are in the tablet?

33 Percent Composition It is often useful to know the percent composition by mass of the elements in a compound. To find the mass % of an element in the compound, divide the mass of the element in the compound by the total mass of the compound, then multiply by 100% Mass % = Mass of part Mass of whole x 100%

34 Percent Composition For many years chloroform (CHCl 3 ) was used as an inhalation anesthetic in spite of the fact that it also is a toxic substance that may cause severe liver, kidney, and heart damage. Calculate the mass % composition of chloroform.

35 Percent Composition Monosodium glutamate (MSG), a flavor enhancer, has been blamed for Chinese restaurant syndrome, the symptoms of which are chest pains and headaches. MSG has the following composition by mass: 35.51% C 4.77 % H 37.85% O 8.29 % N 13.60% Na What is its empirical formula? If the molar mass of MSG is about 169 grams, what is its molecular formula?