N AMING C OMPOUNDS Lesson Objective: Distinguish between ionic and molecular compounds, and describe the properties of some common examples of each. S AME L ANGUAGE, S AME THING, DIFFERENT W ORDS ? How could scientists understand each others work of there were not common rules? R ULES Always fair and equal? H MMM N OT ALL S CIENTISTS WHO CONTRIBUTE TO THE UNDERSTANDING OF ELEMENTS ARE RECOGNIZED Canadian Harriet Brooks She studied the radioactive element thorium, and was able to measure what was thought to be a gas given off by thorium. She proved that this gas was in fact a new element, and it was given the name radon. R EVIEW Element Symbol and Name: For most elements, the symbol is an abbreviation derived from the elements modern chemical name. Symbol for silicon is Si, and the symbol for manganese is Mn. Some exceptions Symbol for gold is Au, which is from Aurum, the Latin word for gold. N OT ALL ELEMENTS HAVE A L ATIN C ONNECTION : Some elements are named for the place they were discovered Californium (discovered in 1950 at U of California). Some are named after scientists who made important contributions to their field of study Einsteinium (Albert Einstein) Fermium (Albert Fermi), Curium (Marie Curie). A TOMIC N UMBER Number above elements symbol on the left shows how many protons are in the nucleus of one atom of the element. Oxygen atom always has 8 protons. I F YOU FOUND 6 PROTONS IN AN ATOM, WHICH ELEMENT WOULD YOU BE LOOKING AT ? ( PAGE ) A TOMS ARE NEUTRAL ( NO CHARGE ) The number of protons equals the number of electrons. Protons are Electrons are T HE ATOMIC NUMBER Also tells you how many electrons are in an atom of a particular element. M ETALS : Shiny, happy people They all lose electrons to form positive ions. N ON - METALS : Go all emo They accept electrons to form negative ions. T HE ATOMIC NUMBER Increases by one for each element as you read across the periodic table from left to right. A TOMIC M ASS Below the elements name. Tells you total mass of all the protons and neutrons in an atom. E LECTRONS : So tiny they have very little effect on the total mass of an element. Not all atoms of an element have the exact same mass different number of neutrons from atom to atom. AMU Atomic mass is measured by atomic mass unit (amu) Defined as 1/12 the mass of a carbon-12 atom. Mass number: represents the sum of the number of protons and neutrons in an atom. P ATTERNS : Alkali Metals (group 1, not including hydrogen): Most reactive of the metals; react when exposed to air or water. As you move down the group, reactivity increases. Alkaline-earth metals (group 2): react to air and water as well, but reactivity not as strong as that of the alkali metals. H ALOGENS ( GROUP 17) Most reactive non-metals. Chlorine Bromine (gas so corrosive can burn skin). Elements in this group can combine with other elements to form substances with useful properties: Sodium + Fluorine = Sodium Fuloride (chemical found in toothpaste). N OBLE G ASSES (G ROUP 18) Most stable and un-reactive elements inert. Long thought that they could NEVER combine with other elements. 1962, Canadian Chemist, Neil Bartlett & colleagues at U of BC synthesized the first noble gas compound containing xenon, platinum, and fluorine. R EMEMBER FROM YOUR TIMELINE Atom comes from the Greek word atomos which means indivisible People once thought the atom was the smallest particle possible. Today we know that the atom is made of several much smaller particles. M OVING ON TO NEW STUFF AKA: W HY DO WE HAVE TO LEARN THIS ? 10 P LACES IN C ANADA S TUDENTS CAN DRINK FOR CREDIT : University of Alberta, NUFS 402: Brewing, Enology and Food Fermentations. Students brew and ale and a lager, and make wine. HOW CAN SCIENCE BE FUN? C OMBINING ELEMENTS TO MAKE COMPOUNDS : Water, soap, shampoo, toothpaste, ammonia, bleach, salt, baking soda, baking powder all chemicals. CHEMICAL FORMULA Each of these compounds has a chemical name and a chemical formula. The formula identifies which elements, and how much of each are in the compound. T ABLE S ALT Chemical Name: Sodium Chloride Chemical Formula: NaCl B AKING S ODA Chemical Name: Sodium Bicarbonate Chemical Formula: NaHCO 3 N OMENCLATURE Rules for naming compounds. Until the 18 th century, no standardized system for naming chemicals existed. C REATED CONFUSION As chemical names varied from country to country, and scientist to scientist. F OR EXAMPLE : Hydrochloric acid and muriatic acid are the same thing/chemical. Some compounds are better known by their common name: Bleach or Aqueous Sodium Hypochlorite? 1787, G UYTON DE M ORVEAU Created a naming system, or nomenclature, for compounds. H E DECIDED : To use the chemical name for each element in the compound, always putting the metal element first. Zinc + Oxygen = Zinc Oxide Why the ide? 1920, IUPAC International Union of Pure and Applied Chemistry Is the body responsible for agreeing on the appropriate name for every chemical compound discovered. I F YOU KNOW ONLY THE FORMULA OF A CHEMICAL COMPOUND : You can determine its chemical name. If you know only its name: You can determine its chemical formula. S ODIUM C HLORIDE : Indicates the compound is made of one atom of sodium, and one atom of chlorine. Chemical Formula, NaCl: Indicates this too. W ATER : H 2 0 Next to the H is a subscript (sub means below). The 2 indicates there are two atoms of hydrogen to go with every atom of oxygen. Subscript numbers in a chemical formula indicate the number of atoms of the elements that must combine to form the compound. No subscript number indicates that only one atom of that element is needed. I NDICATING THE P HYSICAL S TATE OF A C OMPOUND : How do scientists indicate the state of chemical at room temperature? H 2 O (l) the 2 and the l are subscripts NaCl (s) ? NaCl (aq) ? I ONIC C OMPOUNDS Table salt is formed when a very reactive metal, sodium, is placed in a container with a poisonous, green non-metal, chlorine gas. W HEN THE TWO CHEMICAL ELEMENTS ARE COMBINED : The sodium metal explodes in a bright yellow flame. As the sodium burns, a white, course powder is produced Salt or Sodium Chloride NaCl (s) S ODIUM C HLORIDE : Is an ionic compound. Ionic compounds are pure substances formed as the result of the attraction between particles of opposite charges, called ions. Table salt is formed from positively charged sodium ions and negatively charged chorine ions. O THER PROPERTIES OF IONIC COMPOUNDS : High melting point. Good electrical conductivity. Distinct crystal shape. A LL IONIC COMPOUNDS ARE SOLID AT ROOM TEMPERATURE. Table salt will not melt until it is heated to 801degrees Celsius. W HEN AN IONIC COMPOUND IS MELTED : Or dissolved in water, it will conduct electricity. This property of ionic compounds led to the study of electrochemical cells (cells that convert chemical energy into electrical energy or vice versa) And eventually to the invention of batteries. I ONS When an ionic compound is dissolved in water, the metal and non-metal form an aqueous solution of ions. A N ION IS AN ATOM Or group of atoms that has become electrically charged through the loss or gain of electrons. Review chart on page 146 in text. I ON C HARGES To indicate ions, us a plus sign (+) or a minus sign (-) Na + (superscript means above) and Cl - P OLYATOMIC IONS : Poly means many. P OLYATOMIC IONS : Are a group of atoms acting as one. E.g. One atom of Carbon and three atoms of Oxygen form a polyatomic ion called carbonate or CO 3 2- N AMING I ONIC C OMPOUNDS 2 rules to remember. F IRST : The chemical name of the metal or positive ion goes first, followed by the name of the non-metal or negative ion. Second: The name of the non-metal negative ion changes its ending to ide. NaCl is not sodium chlorine, but sodium chloride. O NE EXCEPTION TO THESE NAMING RULES Where negative ions are polyatomic ions, the name remains unchanged. Calcium carbonate, not Calcium carbonide. CaCO 3 I ON C HARGE C HART, PAGE 146 Some elements have more than one ion charge. Iron 2+ or 3+ Show clearly which ion is being used in a chemical name. Iron Oxide: Fe 2+ O U SING I ON C HARGES AND C HEMICAL NAMES TO WRITE FORMULAS ( PAGE 126) Step 1: Print the metal elements symbol with its ion charge (remember that the ion charge is found in the top right hand corner). Next to it, print the non-metal elements symbol with its ion charge. Ca 2+ Cl 1- S TARTED OF WITH : C A 2+ C L 1- Step 2: Balance the ion charges. The positive ion charge must balance the negative ion charges. In our example, this means that there must be 2 chlorine atoms each with an ion charge of 1- to balance the 2+ ion charge of one calcium atom. Now you know how many of each element you need to include in the formula. Ca 2+ Cl 1- Cl 1- Step 3: Write the formula by indicating how many atoms of each element are in it as shown. Do not include the ion charge in the in the formula. Place the number of atoms of each element in a subscript after the elements symbol. If there is one atom, no number (subscript) is used. CaCl 2(s) I ON C HARGES AND THE P ERIODIC T ABLE Take another look at the periodic table on pages 126/127. Do you see a pattern in the ion charges? Group 1, Alkali metals, have an ion charge of 1+ Group 17, Halogens, have an ion charge of 1- Generally, all the elements in a group form ions with the same charge. Pattern is most consistent at extreme ends of the periodic table A little iffy in the middle! S TILL LOOKING AT THE PERIODIC TABLE ON PAGES 126/127 Write the formula for: Lithium oxide Iron(III) cloride Copper(II) phosphide Write the chemical name for: AlBr 3(s) PbS 2(s) Fe 2 O 3(s) Li 2 O (s) FeCl 3(s) Cu 3 P 2(s) Aluminum bromide Lead(IV) sulfide Iron(III) oxide M OLECULAR C OMPOUNDS Scientists have discovered more than 10 million compounds. At least 9 million are molecular compounds containing carbon We are a carbon- based life form, and most molecules from living systems contain carbon. W HEN NON - METALS COMBINE, A PURE SUBSTANCE CALLED A MOLECULE Or molecular compound is formed. Molecular compounds differ from ionic compounds in several ways : They can be solids, liquids, or gases at room temp (recall that ALL ionic compounds are solid at room temp). They are usually insulators, and are poor conductors of electricity (recall that an ionic compound melted or dissolved in water will conduct electricity). They have relatively low melting and boiling points because the forces between the molecules are weak. Examples of molecular compounds include sugar, acetylene, and water. W RITING F ORMULAS F OR M OLECULAR C OMPOUNDS It is hard to predict how non-metals combine there are no ions present and the ion charge is not used in the formula. The formulas for molecular compounds still clearly show what elements are present, and how many of each type of element make up the molecule. E.g. Ammonia: NH 3(g) N AMING OF M OLECULAR C OMPOUNDS All molecular compounds, except those containing hydrogen, can be named using the following rules: (common names are used for molecular compounds containing hydrogen water, ammonia, etc. R ULE 1: The first element in the compound uses the element name- just like ionic compounds. R ULE 2: The second element in the compound uses the suffix ide just like ionic compounds. R ULE 3: When there is more than one atom in the formula, a prefix is used which specifies the number of atoms. R ULE 4: An exception to rule 3 is when the first element has only one atom, the prefix mono is not used. S O P REFIX + F IRST ELEMENT /P REFIX + S ECOND E LEMENT ( ENDING IN IDE) CO 2 carbon dioxide N 2 O dinitrogen monoxide N 2 O 3 dinitrogen trioxide NF 3 nitrogen trifluoride CCl 4 carbon tetrachloride PF 5 phosphorus pentafluoride