Transcript CHAPTER 5
CHAPTER 6 CHEMICAL NAMES and FORMULAS THE PERIODIC TABLE Dmitri Mendeleev (1834-1907) Russian chemist Listed elements in columns in order of increasing atomic mass. Arranged columns so that elements with similar properties were side by side. THE PERIODIC TABLE Medeleev left blank spaces where there were no known elements with the appropriate properties or mass. Predicted the properties of the missing elements. THE PERIODIC TABLE Henry Mosely (1887-1915) British Physicist Determined the atomic number of the atoms of the elements. Arranged elements in table by atomic number instead of mass. THE MODERN PERIODIC TABLE Each horizontal row is a period Seven periods From 2 to 32 elements in a period Properties of the elements change as you move across a period. This pattern repeats from period to period The Periodic Law THE MODERN PERIODIC TABLE Each column is a group or family Elements in a group have similar physical and chemical properties Groups are identified by a number and the letter A or B Group A are the representative elements Group A can be divided into three broad classes THE MODERN PERIODIC TABLE METALS HIGH ELECTRICAL CONDUCTIVITY HIGH LUSTER DUCTILE MALLEABLE THE MODERN PERIODIC TABLE METALS ALKALI METALS ALKALINE EARTH METALS TRANSITION METALS INNER TRANSITION METALS THE MODERN PERIODIC TABLE NON-METALS POOR ELECTRICAL CONDUCTIVITY NON-LUSTRIOUS THE MODERN PERIODIC TABLE NON-METALS HALOGENS NOBLE GASES THE MODERN PERIODIC TABLE METALLOIDS Elements with properties that are intermediate between those of metals and non-metals. Introduction to Chemical Bonding Review Elements Atom - Smallest particle of an element that retains the properties of that element Building blocks of all matter Approximately 100 elements Molecules and Molecular Compounds Only the noble gases exist as single atoms Two or more atoms combine together to form a molecule When atoms of different elements combine they form molecular compounds. Molecules A molecule is two or more atoms acting as a unit. A molecule is the smallest electrically neutral unit that retains the properties of a substance. Molecules Atomic Oxygen monatomic Molecular Oxygen O2 diatomic Ozone O3 triatomic Molecular Compounds Most molecular compounds are made up of atoms of 2 or more non-metals. Most molecular compounds are gas or liquid at room temperature. If in the solid state they have low melting points Ions and Ionic Compounds Many compounds are not molecular – they are composed of Ions Ions are atoms or groups of atoms that have a positive or negative charge Ions form when an atom or group of atoms loses or gains electrons Formation of Ions Sodium has 11 protons and 11 electrons. Sodium loses 1 electron to form a sodium ion Formation of Ions Most metals tend to lose electrons, taking on a positive charge. The positively charged ions are called cations. Written Na+ or Mg2+ For metallic elements, the cation name is the same as the name of the element Formation of Ions The properties of the ion are very different from the properties of the element. What cations are formed by: K, Li, Al, Cs, Ba, Sn? Formation of Ions Formation of Ions Most non-metals tend to gain electrons, taking on a negative charge. The negatively charged ions are called anions. Written Cl- or O2What ions are formed by F, P, S, N? Formation of Ions The name of an anion typically ends in -ide. Sulfur (S) Sulfide (S2-) Bromine (Br) Bromide (Br-) Formation of Ionic Compounds Ionic compounds are composed of a cation and an anion Usually a metal and a non-metal Although they are formed from electrically charged ions, ionic compounds are neutral Ionic Compounds Ionic compounds are usually crystalline solids at room temperature They have very high melting points Ionic Compounds Characteristics of Molecular and Ionic Compounds Characteristic Molecular Compound Ionic Compound Representative Unit Molecule Formula Unit Type of element Non-metallic Metallic Physical state Solid, liquid, gas Solid Melting point Low – below 300 °C High – above 300 °C Representing Chemical Compounds Chemical Formulas More than 10 million chemical compounds No two have identical properties Representing Chemical Compounds Chemical Formula Represents the composition of a chemical substance Shows the kind and number of atoms in the smallest representative unit of a substance Representing Chemical Compounds Monatomic Use the Atomic symbol If a molecule has more than one atom of an element, the number is shown as a subscript: O2, Br2, H2O, CH4 Representing Chemical Compounds The chemical formula of a molecular compound is called the molecular formula. It shows composition, but doesn’t provide information about molecular structure – arrangement of the atoms. Molecules Molecules Representing Chemical Compounds The chemical formula can be written for ionic compounds Not a molecule A balance of +/- charge in a continuous array of ions Representing Chemical Compounds Ionic compounds Formula unit Lowest whole number ratio of ions in the compound Representing Chemical Compounds Sodium Chloride Na+, Cl-, ration 1:1 Formula unit NaCl Magnesium Chloride Mg2+, Cl-, ration 1:2 Formula unit MgCl2 What would the formula unit be for Aluminum Chloride? Law of Definite Proportion Magnesium Sulfide has one atom of Mg per atom of S Mg atomic mass 24.305 amu S atomic mass 32.06 amu Mass ratio 24.305:32.06 = 0.7584:1 Law of Definite Proportion A mass of a molecule of MgS is 43.13% Mg, and 56.87% S If I have 100 g of MgS? 43.13 g Mg, 56.87 g S If I have 50g of MgS? 21.57 g Mg, 28.43 g S Ratio is constant 0.7584:1 Law of Definite Proportion For any chemical compound, the masses of the elements are always in the same proportions. Consistent with Daltons Theory Atoms combine in whole number ratios Proportions by mass are always the same Law of Multiple Proportion When two elements form more than one compound, the different masses of one element that combine with the same masses of the other element are in whole number ratios. Law of Multiple Proportion Hydrogen and Oxygen combine to form both water H2O, and hydrogen peroxide H2O2 H2O H 2O 2 2 g H and 16 g O 2 g H and 32 g O 8 16 ;1 : 2 1 2 1:8 1:16 Polyatomic Ions Tightly bound groups of atoms that behave as a unit and carry a charge. Most end in –ite or –ate Exceptions NH4+ – ammonium CN- - cyanide OH- - Hydroxide Polyatomic Ions Polyatomic Ions -ite/-ate pairs Same charge -ite has one less O atom Polyatomic Ions When polyatomic ions begin with H, it is actually (H+) combined with another polyatomic ion. HCO3- is a combination of H+ and CO32HPO42- is a combination of H+ and PO43- What’s in a name? Before current standards were in place, a new material was named by the inventor or founder. What problems could this cause? Naming Substances A systematic method was developed for naming compounds Added consistency and clarity universal Binary Ionic Compounds Binary – composed of two elements (+) charge must balance (-) charge Net charge = 0 Cation is written first Writing Formulas for Binary Ionic Compounds Potassium Chloride K+ and ClCharge ratio 1:1 KCl Writing Formulas for Binary Ionic Compounds Calcium Bromide Ca+2 and BrCharge ratio 2:1 CaBr2 Writing Formulas for Binary Ionic Compounds Use criss cross method Charge on one ion becomes the subscript on the other Reduce to lowest whole number ratio. Formulas and Names Write formulas from ions Ba2+, S2Li+, O2Ca2+, N3Cu2+, I- Write formulas from names Sodium iodide Stannous chloride Potassium sulfide Calcium iodide Naming Binary Ionic Compounds Can you write a name given the formula CuO? Copper Oxide would be incomplete. Why? Ternary Ionic Compounds Contain three different elements. Usually contain a polyatomic ion. Balance charge like binary compound – treat polyatomic ion as single unit. Ternary Ionic compounds Calcium Carbonate Ca2+ and CO32CaCO3 Ternary Ionic Compounds Lithium Carbonate Li+ and CO32- Li2CO3 Ternary Ionic Compounds Magnesium Hydroxide Mg2+ and OH- Mg(OH)2 Formulas and Names Write formulas from ions Al3+, (OH)Sn2+, (PO4)3Na+, (CrO4)2K+, (MnO4)- Write formulas from names Calcium Oxylate Potassium hypochlorite Lithium cyanide Lead acetate Naming Binary Molecular Compounds Non-metallic elements Can combine in more than one way No charges involved Naming Binary Molecular Compounds Prefixes are used to denote multiple ions of one element in a molecule. The second element in the name ends in –ide. Naming Binary Molecular Compounds Prefixes used in naming binary molecular compounds Prefix Number mono- 1 di- 2 tri- 3 tetra- 4 penta- 5 hexa- 6 hepta- 7 octa- 8 nona- 9 deca- 10 Naming Binary Molecular Compounds CO2 – carbon dioxide CO – carbon monoxide N2O – dinitrogen monoxide Cl2O8 – dichlorine octoxide Naming Binary Molecular Compounds Write names from formulas OF2 N 2O 5 Cl2O8 SO3 Write formulas from names Nitrogen trifluoride Disulfur dichloride Dinitrogen tetroxide Carbon tetrachloride Acids Compounds which produce H+ ions when dissolved in water. Common acids – HCl, H2SO4, HNO3, HC2H3O2, H3PO4, H2CO3 Acids Think of acids as polyatomic anions with enough (H+) cations to produce a neutral charge. (H+and Cl-) (2H+ and SO42-) (H+ and NO3-) Acids Naming Acids Anion ending Example Acid Name Example -ide Cl- Hydro-(stem)-ic acid Hydrochlori c acid SO32- (stem) – ous acid Sulfurous NO3 (stem) – ic acid Nitric acid chloride -ite sulfite -ate nitrate acid Naming Compounds from Formulas Writing Formulas from Chemical Names In an ionic compound, the net charge is zero. An –ide ending generally indicates a binary compound. An –ite or –ate ending means there is a polyatomic ion that includes oxygen in the formula. Writing Formulas from Chemical Names Prefixes in the name generally indicate that the compound is molecular. They show the number of each kind of atom in the molecule A Roman numeral after the cation shows the ionic charge of the cation.