Download Chemistry applications and more Lecture notes Chemistry in PDF only on Docsity!
Activity 1 : Formula Naming and Writing
17
1.1 WRITING CHEMICAL FORMULAS
The study of formula writing covers a bewildering array of chemical formulas that students encounter much confusion as so many new names come up in the discussion. A lack of understanding of the fundamental principles and basic rules is another contributing factor. The names and formulas of inorganic compounds are written in such a way that every compound can be named from its formula and each formula has a name peculiar to that compound. An organization of chemists called the International Union of Pure and Applied Chemistry (IUPAC) has developed a simplified way of writing and naming chemical formulas. A chemical formula is a representation of the number and kind of atoms in a molecule of a substance and is used in place of the name of the substance. Types of Formulas Molecular formulas give the actual number of atoms per molecule or per mole of a compound. Example: Hydrogen Peroxide MF: H 2 O 2
- Empirical formulas give the simplest whole number ratios in which atoms combine to form a compound. These ratios are always expressed as whole numbers to conform to the assumption that fractions of atoms cannot combine. Example: Hydrogen Peroxide EF: HO
- Structural formulas show the bonding arrangement of the atoms within a molecule. Example: Hydrogen Peroxide SF:
ACTIVITY 1 CHEMICAL FORMULA^ NAMING AND WRITING
O O
H
H
Activity1: Formula Naming and Writing
2
- Lewis electronic formulas (electron dot formulas) show how the electron pairs are arranged in the molecule. Example: Hydrogen Peroxide LEF:
The derivation of formulas of compounds consisting of two elements permits a generalization for writing the formulas of other compound elements is present. Examine the following compounds given on the next page.s where either of these
HCl 1 H atom combines with 1 Cl atom NaCl 1 Na atom combines with 1 Cl atom Na 2 O 2 Na atoms combine with 1 O atom H 2 O 2 H atoms combine with 1 O atom NH 3 3 H atoms combine with 1 N atom SiH 4 4 H atoms combine with 1 Si atom CaH 2 2 H atoms combine with 1 Ca atom
These formulas show that more than one atom of hydrogen can combine with one atom of the other element. By convention, the valence of hydrogen is 1+. Therefore, the common valence of an element can be defined as the number of hydrogen atoms that combine with atom of that element. The common valences of the elements in the above formulas are: Na, 1+ Cl, 1− N, 3− Ca, 2+ O, 2− Si, 4+ The common valence of an element expresses only its combining capacity, not the presence or absence of ions. Common valences make it possible to predict the formulas of binary compounds which are compounds consisting of two elements. It is convenient to consider valence as a sort of an electrical or magnetic phenomenon. Thus a metal almost always has a positive
H O O
H
Activity1: Formula Naming and Writing
4
(c) Make a total oxidation number equal to zero by applying the “criss- cross” method. Example: NaCl Na 2 SO 4 (NH 4 ) 3 PO 4
Note: The subscript “1” is never written. The radicals should be enclosed in parenthesis. Same valence number cancels out.
1. 2 NAMING CHEMICAL FORMULAS Communication is impossible without a rational system of naming substances. Each discipline finds it necessary to develop its own systematic language. Modern rules of nomenclature issued by the IUPAC make possible the naming of more than 4 million substances with a minimum of memorization.
I. BINARY COMPOUNDS are substances consisting of two types of elements
- Covalent Compounds which usually involve 2 non-metallic elements use the Greek prefixes, mono, di, tri, tetra, penta …etc, to indicate the number of atoms of each element present in the compound. The second non-metal usually ends in – ide. Examples: CO carbon monoxide CO 2 carbon dioxide N 2 O dinitrogen monoxide N 2 O 4 dinitrogen tetroxide PCl 3 phosphorus trichloride PCl 5 phosphorus pentachloride Note: The prefix “mono” is never written for the first element.
Activity 1 : Formula Naming and Writing
17
- Binary Acids: Aqueous solutions of acids (aq) are distinguished by the prefix hydro - and ending – ic. Examples: HCl(aq) hydrochloric acid H 2 S(aq) hydrosulfuric acid HI(aq) hydroiodic acid HBr(aq) hydrobromic acid Note: For the combination of these elements in the gaseous form, the rules for naming binary salts apply.
- Salts: These consist of a metallic cation and non-metallic anion. The element which forms a positive ion is written first and the second element is abbreviated and given the suffix - ide Examples: NaCl sodium chloride K 2 S potassium sulfide LiH lithium hydride CaO calcium oxide MgBr 2 magnesium bromide BaF 2 barium fluoride
When metals with variable valences are involved, it is necessary to distinguish the various salts by one of the following systems.
A. OUS – IC system: It is the traditional system not recommended by IUPAC. It applies the suffix – ic for the element with the higher oxidation state and – ous for that with the lower oxidation state.
Activity 1 : Formula Naming and Writing
17
Examples: H 2 O water HCl muriatic acid NH 3 ammonia Al 2 O 3 alumina PH 3 phosphine NaHCO 3 baking soda AsH 3 arsine CaCO 3 marble CH 4 marsh gas N 2 O laughing gas CaO lime NaOH lye NaCl table salt NaClO Chlorox
- Peroxides are oxygen atoms with a single covalent bond between them. Care must be taken to distinguish between peroxides and normal oxides. Examples: BaO 2 barium peroxide BaO barium oxide Na 2 O 2 sodium peroxide Na 2 O sodium oxide
II. TERNARY COMPOUNDS
Ternary Acids and Salts The oxides of non-metals react with water to form solutions, which are acidic. In some cases, there may be a series of oxyacids, each one containing the non–metal in a different oxidation state. In order to distinguish between these acids and their respective salts, the following system has been devised.
Activity1: Formula Naming and Writing
8
Oxidation state of Cl Acid Name 1+ HClO Hypochlorous acid 3+ HClO 2 Chlorous acid 5+ HClO 3 Chloric acid 7+ HClO 4 Perchloric acid
Oxidation state of Cl Acid Name 1+ NaClO Sodium hypochlorite 3+ NaClO 2 Sodium chlorite 5+ NaClO 3 Sodium chlorate 7+ NaClO 4 Sodium perchlorate
Note that for acids ending in ous , the corresponding salt ends in ite , and for acids ending in ic , the salts end in ate. In addition the prefix hypo , Greek for under, is used to denote the lowest oxidation state of the non–metal. The prefix per , from the Greek hype r, meaning above, is used to denote highest oxidation state of the non–metal.
Activity1: Formula Naming and Writing
10
Part 1 and 2 will be discussed as Examples in Class (Synchronous Session).
Part 3 Answers will be the submitted using the Treatment of Data Template for Activity 1 (Asynchronous Session).
Part 1. Name the following compounds
1. SO 2
- PBr 5
- SnCl 4 *
- MgCl 2
- PbS 2 *
- Ca(CN) 2
- HCN (aq)
- Al(OH) 3
- H 2 SO 4 (in water)
- Ca 3 (PO 4 ) 2
Activity 1 : Formula Naming and Writing
17
Part 2. Formula Writing
- calcium nitrate
- iron (III) sulfate
- ammonium phosphate
- tin (II) sulfite
- silver phosphate
- zinc cyanide
- lead (IV) oxide
- ferric ferrocyanide
- cuprous sulfide
- chlorine gas
Activity 1 : Formula Naming and Writing
17
DATA SHEET Activity No. 1 FOMRULA WRITING AND NAMING
Name: _____________________________ Instructor: _______________________
_____________________________
_____________________________
Sec.: _______ Group No.: _______ Date: ___________________________
Activity1: Formula Naming and Writing
14
LIST OF COMMON CATIONS
Name Formula Other name(s) Aluminum Al+ Ammonium NH 4 + Barium Ba+ Calcium Ca+ Chromium(II) Cr+2^ Chromous Chromium(III) Cr+3^ Chromic Copper(I) Cu+^ Cuprous Copper(II) Cu+2^ Cupric Iron(II) Fe+2^ Ferrous Iron(III) Fe+3^ Ferric Hydrogen H+ Hydronium H 3 O+ Lead(II) Pb+ Lithium Li+ Magnesium Mg+ Manganese(II) Mn+2^ Manganous Manganese(III) Mn+3^ Manganic Mercury(I) Hg 2 +2^ Mercurous Mercury(II) Hg+2^ Mercuric Nitronium NO 2 + Potassium K+ Silver Ag+ Sodium Na+ Strontium Sr+ Tin(II) Sn+2^ Stannous Tin(IV) Sn+4^ Stannic Zinc Zn+
Activity1: Formula Naming and Writing
16
LIST OF COMMON NAMES FOR CHEMICAL COMPOUNDS
Common Name Chemical Name Formula baking soda sodium hydrogen carbonate / sodium bicarbonate
NaHCO 3
bleach (liquid) sodium hypochlorite or hydrogen peroxide
NaClO H 2 O 2 bleach (solid) sodium perborate NaBO 3 Borax sodium tetraborate decahydrate Na 2 B 4 O 7 .10 H 2 O brimstone sulfur S cream of tartar potassium hydrogen tartrate KHC 4 H 4 O 6 Epsom salt magnesium sulfate heptahydrate MgSO 4 .7 H 2 O Freon dichlorodifluoromethane CF 2 Cl 2 galena lead (II) sulfide PbS grain alcohol ethanol C 2 H 5 OH graphite carbon C gypsum calcium sulfate dihydrate CaSO 4 .2 H 2 O hypo sodium thiosulfate Na 2 S 2 O 3 laughing gas dinitrogen oxide N 2 O lime calcium oxide CaO limestone calcium carbonate CaCO 3 lye sodium hydroxide NaOH marble calcium carbonate CaCO 3 MEK ethyl methyl ketone CH 3 COC 2 H 5 milk of magnesia magnesium hydroxide Mg(OH) 2 muriatic acid hydrochloric acid HCl
Activity 1 : Formula Naming and Writing
17
oil of vitriol sulfuric acid H 2 SO 4 plaster of paris calcium sulfate hemihydrate CaSO 4.^ ½ H 2 O potash potassium carbonate K 2 CO 3 iron pyrite (fools gold) iron disulfide FeS 2 quartz silicon dioxide SiO 2 quicksilver mercury Hg rubbing alcohol isopropyl alcohol (CH 3 ) 2 CHOH sal ammoniac ammonium chloride NH 4 Cl salt sodium chloride NaCl salt substitute potassium chloride KCl Saltpeter potassium nitrate KNO 3 slaked lime calcium hydroxide Ca(OH) 2 sugar sucrose C 12 H 22 O 11 washing soda sodium carbonate decahydrate Na 2 CO 3 .10 H 2 O wood alcohol methyl alcohol CH 3 OH
