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Molecules, Ions and Their Compounds

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1 Molecules, Ions and Their Compounds
AP Notes Chapter 2 Molecules, Ions and Their Compounds

2 Chemical Compounds Chemical compounds result from the joining together of atoms Chemical Bonds are the forces that hold atoms together. Chemical formulas are used to describe the number and kind of atoms in a compound There are two major types of compounds that differ mostly by the way the atoms hold on to each other or the type of bond.

3 Ionic Compounds Ionic compound are held together with an Ionic bond joining metal ions and non metal ions Transfer of electrons cause the formation of ions or charged particles

4 Ions & Ionic Compounds Atoms or groups of atoms with a charge.
Cations- positive ions - get by losing electrons(s). Metallic Anions- negative ions - get by gaining electron(s). Nonmetallic It is these opposite charges that define an ionic compound and an ionic bond Solid Ionic compounds are called salts.

5 +1 +2 -3 -2 -1

6 Ionic Compounds Law of Definite Proportion- compounds have a constant composition. Ions react in specific ratios by mass and charge. Ionic compounds do not have a charge Positive and negative charges balance Ions exist in small whole number ratios. Get charges from table, name of metal ion, or memorized from the list. Use parenthesis to indicate multiple polyatomics.

7 Naming Ionic Compounds
Cation is wrtiten first in name and formula. If the cation is monoatomic- Name the metal (cation) just write the name. If the cation is polyatomic- name it. THEN If the anion is monoatomic- name it but change the ending to –ide. If the anion is poly atomic- just name it Practice Ion names and formula w/charge

8 Naming Ionic Compounds
Have to know what ions they form off table, polyatomic, or figure it out CaS K2S AlPO4 K2SO4 FeS CoI3 Calcium sulfide Potassium sulfide Aluminum phosphate Potassium sulfate Iron II sulfide or Ferrous sulfide Cobalt III iodide or Cobaltic iodide

9 Naming Ionic Compounds
Fe2(C2O4) MgO MnO KMnO4 NH4NO3 Hg2Cl2 Cr2O3

10 Writing Ionic Formulas
Sodium nitride sodium- Na is always +1 Nitride - ide tells you it comes from the table nitride is N-3 Doesn’t add up to zero. Na+1 N-3

11 Writing Ionic Formulas
Sodium nitride sodium- Na is always +1 nitride - ide tells you it comes from the table nitride is N-3 Doesn’t add up to zero Need 3 Na Na+1 N-3 Na3N

12 Ionic Compound Formulas
Sodium sulfite calcium iodide Lead (II) oxide Lead (IV) oxide Mercury (I) sulfide Barium chromate Aluminum hydrogen sulfate Cerium (IV) nitrite Na2S CaI2 PbO Pb2O4 or PbO2 Hg2S BaCrO4 Al(HSO4)3 Ce(NO3)4

13 Covalent Compounds Composed of Molecules
Law of Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers. Chemical formula- the number and type of atoms in a molecule. C2H6 - 2 carbon atoms, 6 hydrogen atoms Structural formula shows the connections, but not necessarily the shape.

14 Molecules differ by the number and kind of elements that make them up
Speculate on the formula of two oxides of carbon and oxygen Carbon monoxide = Carbon dioxide = Show that these compounds follow the law of multiple proportion. Sometimes formula is not enough to get an adequate picture of a compound CO CO2

15 There are also other models that attempt to show three dimensional shape.
Ball and stick. H H H C C H H H Ball and stick.

16 Covalent compounds Two words, with prefixes.
Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, deca First element whole name with the appropriate prefix, except mono. Second element, -ide ending with appropriate prefix. Practice

17 Naming Covalent Compounds
Two words, with prefixes Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, deca First element whole name with the appropriate prefix, except mono Second element, -ide ending with appropriate prefix Practice

18 Naming Covalent Compounds
CCl4 N2O4 XeF6 N4O4 P2O10

19 Covalent compounds The name tells you how to write the formula
Sulfur dioxide difluorine monoxide nitrogen trichloride diphosphorus pentoxide

20 Summary for Writing Formulas and Names of Compounds
Two sets of rules, ionic and covalent To decide which to use, decide what the first word is. If is a metal or polyatomic use ionic. If it is a non-metal use covalent.

21 Acids Substances that produce H+ ions when dissolved in water.
All acids begin with H. Two types of acids: Oxyacids Non-oxyacids

22 Naming acids If the formula has oxygen in it
write the name of the anion, but change ate to -ic acid ite to -ous acid Watch out for sulfuric and sulfurous H2CrO4 HMnO4 HNO2

23 Naming acids If the acid doesn’t have oxygen add the prefix hydro-
change the suffix -ide to -ic acid HCl H2S HCN

24 Formulas for acids Backwards from names.
If it has hydro- in the name it has no oxygen Anion ends in -ide No hydro, anion ends in -ate or -ite Write anion and add enough H to balance the charges.

25 Formulas for acids hydrofluoric acid dichromic acid carbonic acid
hydrophosphoric acid hypofluorous acid perchloric acid phosphorous acid

26 Percent Composition Percent of each element a compound is composed of.
Find the mass of each element, divide by the total mass, multiply by a 100. Easiest if you use a mole of the compound. Find the percent composition of CH4 Al2(Cr2O7)3 CaSO4 · 2H2O

27 Working backwards From percent composition, you can determine the empirical formula. Empirical Formula the lowest ratio of atoms in a molecule. Based on mole ratios. A sample is 59.53% C, 5.38%H, 10.68%N, and 24.40%O what is its empirical formula.

28 Sample Problem A gram sample of a compound (vitamin C) composed of only C, H, and O is burned completely with excess O g of CO2 and g of H2O are produced. What is the empirical formula?

29 Empirical To Molecular Formulas
Empirical is lowest ratio. Molecular is actual molecule. Need Molar mass. Ratio of empirical to molar mass will tell you the molecular formula. Must be a whole number because...

30 Sample Problem A compound is made of only sulfur and oxygen. It is 69.6% S by mass. Its molar mass is 184 g/mol. What is its formula?

31 Hydrates Some salts trap water crystals when they form crystals.
These are hydrates. Both the name and the formula needs to indicate how many water molecules are trapped. In the name we add the word hydrate with a prefix that tells us how many water molecules.

32 Hydrates In the formula you put a dot and then write the number of molecules. Calcium chloride dihydrate Chromium (III) nitrate hexahydrate CaCl2·2H2O Cr(NO3)3· 6H2O

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