9/19/07. Chemistry 6A Fall 2007 Dr. J. A. Mack. Molar Masses. Avagagro s s Number. Avogadro s Number and the Mole

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Chemistry 6A Fall 007 Dr. J. A. Mack Avogadro s Number and the Mole The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole).

1 Chemistry 6A Fall 007 Dr. J. A. Mack Avogadro s Number and the Mole The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole). The Standard is based upon the C-1 isotope. The atomic mass of 1 C is defined as exactly 1 u. The atomic mass of 1 C is g. 9/19/07 1 amu = (the mass of one 1 C atom 1) = g = kg CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack Avagagro s s Number Since one mole of 1 C has a mass of 1g (exactly), 1g of 1 C contains 6.01 x 10 1 C-atoms. But carbon exists as isotopes: C-1, C-1 &C-1 The average atomic mass of carbon is u. From this we conclude that 1.011g of carbon contains 6.01 x 10 C-atoms Molar Masses Since we can equate mass (how much matter) with moles (how many particles) we now have a conversion factor that relates the two. mols molar mass (g/mol) = grams The Molar Mass of a substance is the amount of matter that contains one-mole or particles. aka: Avogadro's number (N A ) Is this a valid assumption? Yes, since N A is so large, the statistics hold. The atomic masses on the Periodic Table also represent the molar masses of each element in grams per mole (g/mol) CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack

So if you have 1.011g of carbon you have 6.0 10 carbon atoms! So if you have 1.011g of carbon you have 6.0 10 carbon atoms! So if you have 9.95g of argon you have 6.0 10 argon atoms!

0 10 avocados you have a guacamole 9-19-07 CSUS Chem 6A F07 Dr. Mack 5 if you have a mole of dollar bills you are Bill Gates you have 6.0 10 bucks! and if you have 6.

2 So if you have 1.011g of carbon you have carbon atoms! So if you have 1.011g of carbon you have carbon atoms! So if you have 9.95g of argon you have argon atoms! So if you have 9.95g of argon you have argon atoms! if you have a mole of dollar bills you are Bill Gates you have bucks! and if you have avocados you have a guacamole CSUS Chem 6A F07 Dr. Mack 5 if you have a mole of dollar bills you are Bill Gates you have bucks! and if you have avocados you have a guacamole CSUS Chem 6A F07 Dr. Mack 6 Grams, moles and the number of atoms: Since atoms are extremely small individual particles, even small masses (grams) will have huge quantities of them! How many argon atoms are there in g of argon? Solution: Use the molar masses of the element and Avogadro's number as conversion factors g Ar 1 mole Ar Ar atoms 9.95g Ar 1 mole Ar = Ar atoms sf CSUS Chem 6A F07 Dr. Mack 7 How many chlorine atoms are there in 5.01g of elemental chlorine? Solution: Use the molar masses of the element and Avogadro's number as conversion factors. Recall that chlorine in its elemental state is diatomic! Cl The molar mass is therefore the molar mass of atomic chlorine. Cl = 5.5 g/mol = g/mol CSUS Chem 6A F07 Dr. Mack 8

3 How many chlorine atoms are there in 5.01g of elemental chlorine? Solution: Use the molar masses of the element and Avogadro's number as conversion factors. What do you know! Cl = g/mol N A = particles / mole what else do we know? for every one mole of Cl, there are moles of Cl atoms Conversion factor! 1 mole Cl mole Cl 5.01g Cl Cl atoms = g Cl 1 mole Cl 1 mole Cl Cl Cl-atoms sf CSUS Chem 6A F07 Dr. Mack 9 What mass of argon will have the same number of particles as 5.01 g of sodium? Solution: Use the molar masses of the two elements as conversion factors. Na =.99 g/mol Ar = 9.95 g/mol 1 mol 9.95g Ar 5.01g Cl.99 g Na 1mol = 8.71g Ar ( sf) CSUS Chem 6A F07 Dr. Mack 10 How many protons are there in 1.05g of carbon? Use the molar mass and atomic number and Avogadro's number to determine the result. 1.05g C 1 mole C C atoms 6 protons g C 1 mole C 1 C atom = protons sf CSUS Chem 6A F07 Dr. Mack 11 Compounds: A compound is a distinct substance that contains two or more elements combined in a definite proportion by weight. Atoms of the elements that constitute a compound are always present in simple whole number ratios. They are never present as fractional parts. Examples: Never: AB A B AB A ½ B CSUS Chem 6A F07 Dr. Mack 1

Molecules and Ionic Compounds: A molecule is the smallest uncharged individual unit of a compound formed by two or more atoms.

Ionic compounds are held together by attractive forces between their positive and negative charges. Molecular compounds are held together by covalent bonds.

An ionic compound is represented by a formula unit that describes the simplest ratio of cations to anions. 9-19-07 CSUS Chem 6A F07 Dr.

4 Molecules and Ionic Compounds: A molecule is the smallest uncharged individual unit of a compound formed by two or more atoms. Ionic compounds are made of positively and negatively charged ions. Compounds can be classified as molecular or ionic. Ionic compounds are held together by attractive forces between their positive and negative charges. Molecular compounds are held together by covalent bonds CSUS Chem 6A F07 Dr. Mack 1 A molecule can exist as an entity on its own. An ionic compound is represented by a formula unit that describes the simplest ratio of cations to anions CSUS Chem 6A F07 Dr. Mack 1 1 Inorganic Compounds: Metals and Nonmetals 1 IA IIA 1 IIIA 1 IVA 15 VA 16 VIA 17 VIIA 18 VIIIA Ions: If one or more electrons are removed from a neutral atom a positive ion is formed. A positive ion is called a cation IIIB IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB Metals IB 1 IIB Nonmetals remove e CSUS Chem 6A F07 Dr. Mack 15 neutral atom cation CSUS Chem 6A F07 Dr. Mack 16

If one or more electrons are added to a neutral atom a negative ion is

A positively charged ion is called a cation.

add e Cl - Chloride ion neutral atom anion 9-19-07 CSUS Chem 6A F07 Dr.

Mack 18 Ionic Compounds Ionic compounds consist of ions (charged particles).

5 If one or more electrons are added to a neutral atom a negative ion is formed. A negative ion is called an anion. A positively charged ion is called a cation. Na + Sodium ion metals form cations An anion is a negatively charged ion. add e Cl - Chloride ion neutral atom anion CSUS Chem 6A F07 Dr. Mack 17 non-metals form anions CSUS Chem 6A F07 Dr. Mack 18 Ionic Compounds Ionic compounds consist of ions (charged particles). The oppositely charged ions (positive and negative) are held together by strong electrostatic forces. The crystalline structure of sodium chloride is held together by the attractive forces between the positive sodium ions and the negative chloride ions CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 0

The actual chemical formulas of ionic compounds express the smallest whole number ratio that exists between these cations and the anions. The more electrons lost, the more positive the cation becomes.

6 The actual chemical formulas of ionic compounds express the smallest whole number ratio that exists between these cations and the anions. The more electrons lost, the more positive the cation becomes. Na Na + + e - Na Cl Wrong! NaCl Correct! Ca Ca + + e - Al Al + + e CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack Naming ions: Cations All metal cations are named after there representative element followed by the word ion. The metals in the center of the periodic table (including the transition metals) often form more than one type of cation. sodium barium silver Na Na + sodium ion Ba Ba + Barium ion Ag Ag + silver ion CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack

Example: Cu Cu + copper (I) ion Cu Cu + copper (II) ion Example: chlorine oxygen nitrogen Cl Cl - chloride ion O O - oxide ion N N - nitride ion 9-19-07 CSUS Chem 6A F07 Dr.

7 All variable transition metal cations are named by their element followed by the number of their oxidation (charge) state. All simple anions are named by the root name of the element followed by the suffix (ending) -ide. Example: Cu Cu + copper (I) ion Cu Cu + copper (II) ion Example: chlorine oxygen nitrogen Cl Cl - chloride ion O O - oxide ion N N - nitride ion CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 6 Predicting Ion charges: The charge on an ion can be predicted from its position in the periodic table. All group 1A elements form +1 Cations H + Li + Na + etc All group A elements form + Cations Be + Mg + Ca + etc Group A: Aluminum forms a + cation CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 8

8 Group 7A non-metals form 1 anions F - Cl - etc Group 6A forms anions O - S - etc All chemical compound must have a net charge of zero. (neutral) Since inorganic compounds (metal and a non-metal) contain ions, then the charge on the cations must cancel the charge on the anions. (equal zero) Group 5A forms anions N - etc charge from cation (+) + charge from anion ( ) = CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 0 Chemical Formulas: Since we are large (macroscopic) and atoms and compounds are small (microscopic), we need a symbolism to communicate the identity of an atom or compound. CaCl The formula tells us that there are two chlorine ions for every calcium ion in the compound A chemical formula tells us not only which elements make up a compound, but also their proportions. We pronounce the name: Calcium Chloride A compound made of calcium and chlorine has the formula: CaCl The metal atom is written first followed by the anion. The subscript indicates the number of each element (1 s are not shown) CSUS Chem 6A F07 Dr. Mack 1 One does not use the prefixes mono, di, tri etcetera for ionic compounds We ll get into that later CSUS Chem 6A F07 Dr. Mack

9 Binary Compounds: Metal & non-metal Metal of fixed oxidation (charge) state combined with a non-metal. Examples: Al + + S - Al S since the charges on the cation and anion don t match we must have multiples of both Cation Anion Formula Name K + Cl KCl Potassium chloride Ca + O - CaO Calcium Oxide Na + S - Na S Sodium sulfide Al + S - Al S Aluminum sulfide + = +6 Al S - = = CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack Or one can use the Chris-Cross method: Al + S - Al S Metals of variable charge with a non-metal Examples: Cation Anion Formula Name Pb + Cl PbCl lead (II) chloride pronounced: lead - two - chloride Fe + O Fe O Iron (III) oxide Pb + Cl PbCl lead (IV) chloride CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 6

10 Two complex anions are named like simple ions with the suffix (ending) -ide. Example: OH - hydroxide ion More examples: Ion: NO Name: nitrite CN - cyanide ion SO sulfite Most other complex ions end in -ate or -ite. SO SO See table 6.6 page 117 sulfate ion sulfite ion HCO MnO bicarbonate or hydrogen carbonate permanganate CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 8 Ternary Compounds: Those with three different elements metal of fixed charge with a complex ion Cation Anion Formula Name Al (SO ) K + Ca + Na + Al + OH KOH Potassium hydroxide OH Ca(OH) Calcium hydroxide SO Na SO Sodium sulfate SO Al (SO ) Aluminum sulfate spoken as: Al - two, sulfate, taken three times or Al -two, parenthesis, sulfate, three CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 0

11 indicates the element hydrogen (H) H PO indicates the element oxygen (O) indicates indicates O atoms H atoms indicates the element phosphorous (P) CSUS Chem 6A F07 Dr. Mack 1 indicates the element barium Ba (PO ) indicates two - phosphate (PO ) groups indicates three Ba atoms indicates the phosphate group composed of one phosphorous atom and four oxygen atoms CSUS Chem 6A F07 Dr. Mack Metal of variable charge with a complex ion Type I Acids: Acids derived from ide anions. Cation Anion Formula Name The names for these acids follows the formula: Pb + SO PbSO lead (II) sulfate Pb + SO Pb(SO ) lead (IV) sulfate Fe + NO Fe(NO ) Iron (III) nitrate hydro + the root of the ide anion + ic acid Anion: Acid: Name: chloride HCl hydrochloric acid Fe + NO Fe(NO ) Iron (II) nitrite fluoride HF hydrofluoric acid CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack

12 H + and S - An acid must be an aqueous (in water) species: it takes H + to cancel one S - Later on will differentiate acids from molecules by: H S HCN(aq) hydrocyanic acid hydro sulfuric acid Vs. HCN(g) hydrogen cyanide gas CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 6 Oxy-acids contain hydrogen, oxygen and one other element. Example: H SO The other element is usually a nonmetal, but it can be a metal. Its first element is hydrogen. Its remaining elements include oxygen in the form of a polyatomic ion. Oxy Acids: Those derived from ate anions. The names for these acids follows the formula: root name of the anion with ic replacing the -ate One student remembered it this way: I ate something icky! CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 8

Examples: Anion: Acid: Name: (nitrate) NO HNO nitric acid (chlorate) ClO HClO chloric acid (sulfate) SO H SO sulfuric acid (acetate) CHO HC H O acetic acid vinegar Additional Acids: Those derived

13 Examples: Anion: Acid: Name: (nitrate) NO HNO nitric acid (chlorate) ClO HClO chloric acid (sulfate) SO H SO sulfuric acid (acetate) CHO HC H O acetic acid vinegar Additional Acids: Those derived from ite anions. root name of the anion with ous replacing the -ite The ite forma of a complex anion usually has one less oxygen atom than the ate form. NO NO nitrate nitrite One can remember the ous acids by: one less (oxygen atom) is the ous acid CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 50 Anion: Acid: Name: (nitrite) NO HNO nitrous acid (chlorite) ClO HClO chlorous acid (sulfite) SO H SO sulfurous acid CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 5

and oxygen. 9-19-07 CSUS Chem 6A F07 Dr. Mack 5 9-19-07 CSUS Chem 6A F07 Dr. Mack 5 A diatomic molecule contains exactly two atoms of the same or different elements.

14 Molecular Compounds: Nonmetals and Nonmetals A water molecule consists of two hydrogen atoms and one oxygen atom. 1 1 IA IIA 1 IIIA 1 IVA 15 VA 16 VIA 17 VIIA 18 VIIIA 5 IIIB IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB IB 1 IIB Nonmetals 6 7 If it is decomposed, the water molecule will be destroyed liberating hydrogen and oxygen CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 5 A diatomic molecule contains exactly two atoms of the same or different elements. Some elements exist in nature as diatomic molecules. Molecular compounds: non-metal with a non-metal When non-metals combine, they form molecules. They may do so in multiple forms: CO CO Because of this we need to specify the number of each atom by way of a prefix. 1 = mono = di = tri = tetra 5 = penta 6 = hexa 7 = hepta CSUS Chem 6A F07 Dr. Mack CSUS Chem 6A F07 Dr. Mack 56

15 Examples: Formula Name: BCl SO NO we don t write: N O boron trichloride sulfur trioxide nitrogen monoxide nitrogen monooxide or mononitrogen monoxide dinitrogen tetraoxide CSUS Chem 6A F07 Dr. Mack 57

EIT Review S2007 Dr. J.A. Mack.

EIT Review S2007 Dr. J.A. Mack www.csus.edu/indiv/m/mackj/ Part 1 Atom: The smallest divisible unit of an element Compound: A substance made of two or more atoms Ion: A charged atom or molecule Cation: