Writing Formulas and Names of Compounds PDF

Given the names of different substances inside the box, classify them according to elements, compounds or mixture. copper wire sand and gravel chicken meat air lemon juice cologne oxygen gas paper ink liquid water ice...

Given the names of different substances inside the box, classify them according to elements, compounds or mixture. copper wire sand and gravel chicken meat air lemon juice cologne oxygen gas paper ink liquid water ice aluminum foil salt metal spoon baking soda Zonrox bleach shampoo dust chlorine vinegar alcohol monosodium glutamate (vitsin) ELEMENTS Elements do not usually exist as single atoms in nature. Helium, neon, argon, krypton, xenon, and radon are the only elements that exist as a single atom in nature. Matter most often exists as a group of atoms. COMPOUNDS Some compounds are covalent, which are formed from two or more nonmetals. Covalent compounds exist as molecules. MOLECULE is a particle that consist of at least two atoms Some elements exist in nature as molecules. EXAMPLES: OXYGEN NITROGEN CHLORINE GAS All of them exist as diatomic molecules- their molecules contain two atoms. MOLECULE A molecule can also contain more than one type of atom. EXAMPLE: 1. A water molecule is composed of one oxygen atom and two hydrogen atoms. 2. Carbon dioxide also a molecule consisting of one carbon atom and two oxygen atoms. ION is an atom or a group of atoms having a positive or a negative charge CATION - A positive ion results from the loss of one or more electrons. Example: Mg+ K+ ION is an atom or a group of atoms having a positive or a negative charge ANION - a negative ion results from the gain of one or more electrons. Example: Cl- S2− Let’s Check! A.Determine whether the following are molecules or ions. _______________1. Fluorine gas (F2) _______________2. Lithium fluoride (LiF) _______________3. Glucose (C6H12O6) _______________4. Cr3+ _______________5. PO43- Let’s Check! B. Indicate the number of electrons lost or gained in forming these ions: _______________1. NH4+ _______________2. CO32- _______________3. OH- _______________4. SO42- _______________5. Ni +2 CHEMICAL FORMULAS Chemical formulas are used to express the composition of molecules and ionic compounds in terms of chemical symbols. Molecular formulas Empirical formulas Structural formula Lewis electron formula CHEMICAL FORMULAS A. Empirical formulas give the exact number of elements present in the smallest unit of a substance. the ratio is at its smallest whole- number value CHEMICAL FORMULAS B. Molecular formulas are formulas that show which elements are present and in what ratio they exist in the substance. shows the actual number of each element in the substance. Table 1. Comparison of Molecular and Empirical Formulas of Different Compounds Molecular Empirical Name of Lowest ratio (actual) (simplest) Compound of elements formula formula Set C2H2 CH 1:1 Benzene C6H6 CH 1:1 Formaldehyde CH2O CH2O 1:2:1 Glucose C6H12O6 CH2O 1:2:1 Hydrogen H2O2 HO 1:1 peroxide Water H2O H2O 2:1 CHEMICAL FORMULAS C. Structural formula consists of symbols to represent atoms, and lines to represent chemical bonds. CHEMICAL FORMULAS D. Lewis electron formula also known as the electron-dot formula, shows the distribution of electrons (represented by dots) in the outermost shell of the atom. Bonded electrons are symbolized by dots drawn between two atoms while a pair of dots outside the atom stand for nonbonding electrons.  Example The formulas for hydrogen peroxide are given below: Molecular formula: H2O2 Empirical formula: HO O H Structural formula: H O O H Lewis electron formula: H O Atoms combine to achieve a stable configuration resembling noble gas configuration (eight valence electrons). There are two ways to achieve stable configuration. These are: Electron transfer Electron sharing 1.Electron transfer An atom gaining electrons becomes negatively charged and is called anion. An atom losing electron/s becomes positively charges and is called cations. You can predict if an atom has a tendency to gain or lose electron based on its position in the periodic table. In general, metals lose electrons (group 1 to 3) and nonmetals gain electrons (group 5 to 7). 2. Electron sharing The bond formed by sharing electrons is called covalent bond. It is shared only by nonmetal to another nonmetal. Examples are CO2 or carbon dioxide and NH3 or ammonia. A chemical formula may have a subscript and/or parenthesis ( ). A subscript is a number appearing after the chemical symbol of an element. It indicates the number of atoms of the element. If no subscript appears, one atom of the element is present. A chemical formula may have a subscript and/or parenthesis ( ). A subscript is a number appearing after the chemical symbol of an element. It indicates the number of atoms of the element. If no subscript appears, one atom of the element is present. HOW TO WRITE CHEMICAL FORMULAS AND NAME COMPOUNDS IONIC COMPOUND metal + nonmetal = ionic compound BINARY IONIC COMPOUND Inorganic compounds composed of just two elements – metal cations and nonmetal anions 1. Elements with ions of only one charge 2. Metals with ions of more than one charge Guidelines for Binary Ionic Compounds 1. The cation is always listed before the anion. 2. The cation-anion ratio must give a net charge of zero. 3. The ratio is always expressed in the smallest whole number. 4. The unchanged English name of the metals is used. 5. The name of the anion includes only the English root plus –ide. Example: Write the formula of the given compounds. a. Potassium bromide K+ + Br- KBr (+1) + (-1) = 0 b. Zinc oxide Zn 2+ + O 2- ZnO (+2) + (-2) = 0 BINARY IONIC COMPOUND Subscripts are used in formulas when the ratios of atoms are not 1:1. BINARY IONIC COMPOUND Cross-charge method To represent the compound, first write the ions side by side with their appropriate charges. Then write the subscripts. The numerical value of the charge on the cation becomes the subscript on the anion and vice versa. Example: Write the formula of the given compounds. a. Sodium sulfide Na1+ + S2- Na2S (2)(+1) + (1)(-2) = 0 2-2 = 0 Example: Write the formula of the given compounds. b. Calcium phosphide Ca 2+ + P 3- Ca3P2 (3)(+2) + (2)(-3) = 0 6–6 = 0 Table 1-2 Common Roots for Naming Compounds Element Root Element Root Element Root As arsen- Cr chrom- N nitr- Br brom- F flour- O ox- C carb- H hydr- P phosph- Cl chlor- I iod- S sulf- Here are some examples of binary compounds and their names. NaBr sodium bromide Ca2C calcium carbide MgCl2 magnesium chloride KI potassium iodide ZnO zinc oxide BaS barium sulfide METALS WITH IONS OF MORE THAN ONE CHARGE STOCK METHOD CLASSICAL METHOD STOCK METHOD The charge on the metal ion follows the name of the metal in Roman numerals and in parenthesis STOCK METHOD Example: CuCl copper (I) chloride CuCl2 copper (II) chloride CLASSICAL METHOD The name of the metal ion that has the lower charge ends in –ous and that with higher charge ends in -ic CLASSICAL METHOD If the symbol of the element is derived from a Latin word, the Latin root is generally used rather than the English root. CLASSICAL METHOD Example: CuCl cuprous chloride CuCl2 cupric chloride  STOCK METHOD {(number of metal cation) x (+charge of metal cation)} + {(number of nonmetal anion)x(-charge of nonmetal anion)} = 0 Example: a. Name the compound Fe2S3 The equation is {2 x (Fe charge)} + {3 x (S charge)} = 0 x -2 Fe2 S3 Therefore, the name of the 2x + 3(-2) = 0 compound is iron (III) sulfide. 2x + (-6) = 0 2x = +6 = +3 (III) Example: Write the formula for lead (IV) oxide. Pb 4+ + O 2- Pb2O4 Since 2 and 4 are divisible by 2, the formula is reduced to PbO2 LET’S CHECK! A. Name the given compounds (in two ways). 1. Hg2Cl2 2. Sb2S5 3. CuO 4. NiCl3 LET’S CHECK! B. Write the formula for the given compounds. 1. stannic fluoride 2. chromium (II) oxide 3. platinous sulfide 4. gold (III) chloride POLYATOMIC IONS The metal is written (or named) first When the formula contains more than one group of atoms that occurs as an ionic unit, a parenthesis () is placed around the group, and the number of units of the group is indicated by a subscript placed after the parenthesis. POLYATOMIC IONS Since these ionic compounds are also electrically neutral, the number of charges equals the number of negative charges. Cross-over method may be used to facilitate formula writing a polyatomic compound. POLYATOMICS IONS Example: NH4 + + CO3 -2 → (NH4)2CO3 ammonium carbonate POLYATOMICS IONS Example: Mg +2 + SO4 -2 → Mg2(SO4)2 magnesium sulfate POLYATOMICS IONS Note: A parenthesis shows that the polyatomic ion is doubled, tripled, etc. For polyatomic anions, use the given name. (Note: the name of the polyatomic anion/cation can be found in your periodic table) LET’S CHECK! A. Name the given ionic compounds: 1. Ca(ClO)2 2. Sr2(CO3)2 B. Write the formula of the given compounds: 1. sodium oxalate 2. barium hydroxide MOLECULAR COMPOUNDS Naming molecular compounds is the same as naming ionic compounds. The first element in the formula is named first; then, the second element, with the suffix “-ide”, is named next. Ex: HBr hydrogen bromide SiC silicon carbide MOLECULAR COMPOUNDS there are compounds which contains the same elements Greek prefixes are employed to denote the number of atoms prefix di- and tri- Ex: SO2 sulfur dioxide SO3 sulfur trioxide MOLECULAR COMPOUNDS However, some compounds of hydrogen do not follow these rules H2S hydrogen sulfide MOLECULAR COMPOUNDS The prefix ‘mono-’ may be omitted for the first element. If there is no prefix in the name of the first element, it means that there is only one atom of that element in the molecule. CO2 carbon dioxide PCl3 phosphorous trichloride Greek prefixes used in naming molecular compounds PREFIX MEANING mono- 1 di- 2 tri- 3 tetra- 4 penta- 5 hexa- 6 hepta- 7 octa- 8 nona- 9 Greek prefixes used in naming molecular compounds PREFIX MEANING mono- 1 di- 2 tri- 3 tetra- 4 hexa- 5 Hepta 6 octa- 7 nona- 8 deca- 9