Naming Compounds

1. Naming Compounds Lesson Objective: Distinguish between ionic and molecular compounds, and describe the properties of some common examples of each.

2. Hmmm… Not all Scientists 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.

3. Review from last class… • Element Symbol and Name: for most elements, the symbol is an abbreviation derived from the element’s 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.

4. Not all elements are named for Latin Words. • 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).

5. Atomic Number • Number above element’s symbol on the left… shows how many protons are in the nucleus of one atom of the element. • Oxygen atom always has 8 protons. • If you found 6 protons in an atom, which element would you be looking at? (page 126-127)

7. Atoms are neutral • The number of protons equals the number of electrons. • The atomic number also tells you how many electrons are in an atom of a particular element. • Protons = positive • Electrons = negative • Metals- shiny, happy people… they all lose electrons to form positive ions. • Non-metals-go all emo… they accept electrons to form negative ions.

8. Notice that the atomic number increases by one for each element as you read across the periodic table from left to right.

9. Atomic Mass • Below the element’s name. • Tells you total mass of all the protons and neutrons in an atom. • Electrons 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.

10. 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.

11. Patterns: • 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.

12. Alkaline-earth metals (group 2): react to air and water as well, but reactivity not as strong as that of the alkali metals.

13. Halogens (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).

14. Noble Gasses (Group 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.

16. Remember from your timeline… • Atom comes from the Greek word atomoswhich 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.

17. Combining elements to make compounds. • Water, soap, shampoo, toothpaste, ammonia, bleach, salt, baking soda, baking powder… all chemicals. • 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.

18. Table Salt • Chemical Name: Sodium Chloride • Chemical Formula: NaCl

19. Baking Soda Chemical Name: Sodium Bicarbonate Chemical Formula: NaHCO3

20. Nomenclature • Rules for naming compounds. • Until the 18th century, no standardized system for naming chemicals existed. • Created confusion as chemical names varied from country to country, and scientist to scientist. • For example, hydrochloric acid and muriatic acid are the same thing/chemical. • Some compounds are better known by their common name: Bleach VS Aqueous Sodium Hypochlorite?

21. 1787, Guyton de Morveau • Created a naming system, or nomenclature, for compounds. • He decided to use the chemical name for each element in the compound, always putting the metal element first. • Zinc + Oxygen = Zinc Oxide

22. 1920, IUPAC • International Union of Pure and Applied Chemistry… Is the body responsible for agreeing on the appropriate name for every chemical compound discovered. • http://www.iupac.org/

23. If 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. • Sodium Chloride… Indicates the compound is made of one atom of sodium, and one atom of chlorine. • Chemical Formula… NaCl, indicates this too.

24. Water: H20 • 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.

26. Indicating the Physical State of a Compound: • State of chemical at room temperature? • H2O (l) – the “2” and the “l” are subscripts • NaCl(s) • NaCl(aq)?

27. Ionic Compounds • Table salt is formed when a very reactive metal-sodium- is placed in a container with a poisonous, green non-metal, chlorine gas. • When 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)

28. Sodium Chloride 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.

29. Other properties of ionic compounds: • High melting point. • Good electrical conductivity. • Distinct crystal shape.

30. All ionic compounds are solid at room temperature. • Table salt will not melt until it is heated to 801degrees Celcius. • When 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.

31. Ions • When an ionic compound is dissolved in water, the metal and non-metal form an aqueous solution of ions. • An 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.

32. Ion Charges • To indicate ions, us a plus sign (+) or a minus sign (-) • Na+ (superscript… means “above”) and Cl- • Polyatomic ions: poly means many. Polyatomic ions are a group of atoms acting as one. • E.g. One atom of Carbon and three atoms of Oxygen form the polyatomic ion called carbonate or CO32-

33. Naming Ionic Compounds • 2 rules to remember. • First: 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.

34. One exception to these naming rules • Where negative ions are polyatomic ions, the name remains unchanged. • Calcium carbonate, not Calcium carbonide. • CaCO3

35. Ion Charge Chart, 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: Fe2+O

36. Using Ion Charges and Chemical names to write formulas (page 126) • Step 1: Print the metal element’s 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 element’s symbol with its ion charge. • Ca2+ Cl1-

37. 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. • Ca2+ Cl1- Cl1-

38. 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 element’s symbol. If there is one atom, no number (subscript) is used. • CaCl2(s)

39. Ion Charges and the Periodic Table • 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! Look at

40. Still 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: AlBr3(s) PbS2(s) Fe2O3(s)

41. Li2O(s) • FeCl3(s) • Cu3P2(s) • Aluminum bromide • Lead(IV) sulfide • Iron(III) oxide

42. Molecular Compounds • 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.

43. When 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).

44. 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.

45. Writing Formulas For Molecular Compounds • 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: NH3(g)

46. Naming of Molecular Compounds • 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.)

47. 1. • The first element in the compound uses the element name- just like ionic compounds.

48. 2. • The second element in the compound uses the suffix “ide” – just like ionic compounds.

49. 3. • When there is more than one atom in the formula, a prefix is used which specifies the number of atoms.

50. 4. • An exception to rule 3 is when the first element has only one atom, the prefix mono is not used.