Unit 2 Intro toQuantitative Chemistry

CDO CP CHemistry Trimble

PERIODIC TABLE

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ELEMENTS ON THE PERIODIC TABLE

• The elements on the periodic table are classified into one of three categories:

• METALS

• NONMETALS

• METALOIDS

A. Metallic Character

1

2

3

4

5

6

7

• Metals

• Nonmetals

• Metalloids

B

Si

Ge As

Sb Te

Po At

Amounts of a Substance

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What is a mole?

• An amount of substance that contains the same number of particles as 12 g of C-12

• Analogy

• A dozen is 12

• A ream is 500

• A mole is 6.02 x 10 23

Avogadro’s Number

• 6.02 x 1023 (L)

• Example: Determine the number of atoms in 12 g of C-12 if the mass of 1 atom of C -12 is 1.99252 x 10 -23

g.

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Molar Mass (Mr)

• By definition, Mr is the mass of 1 mol of a substance (i.e., g/mol).

• The molar mass of an element is the average mass for the element that we find on the periodic table.

• The Mr of a compound is the sum of each of the relative molecular mass of each element multiplied by the number of the atoms in the formula

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Example: Calculating Molar Mass

Calculate the molar mass for each of the following elements/compound:

1. CO2

2. H2SO4

3. S

4. Ca(C2H3O2)2CDO IB Chemistry SL9

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White Board Practice

• Find the Mr for each of the following compounds or atoms:

• HNO3

• H2O

• O2

• Mg

Using Moles

• Moles provide a bridge from the molecular scale to the real-world scale.

• If the substance is an element we will count atoms using Avogadro's number if the substance is a compound we will count molecules, formula units or ions

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Converting to Determine number of Particles

• Equation:

n = N

NA

Where

n = moles

N = # of particls

NA = Avogadros #

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N

n NA

Examples: Using Avogadro’s Number

• How many atoms of Au are there in 0.36 moles of Au?

• How many moles are there in 3.46 x 1028 molecules of water?

CDO IB Chemistry SL13

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Converting Between Mass and Moles

• Equation:

n = m

Mr

Where

n = moles

m = grams

Mr = molar mass

m

n Mr

Example: Using Moles in Calculations – Molar Mass

• How many moles of tin are there in 250 grams of tin?

• How many moles of SO2 is present in 0.45 grams of sulfur dioxide?

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White Board Practice

• How many moles are there in 36 g of Sulfur?

• How many grams are there in 3.2 moles of CO2?

• How many atoms are there in 1.62 moles of Calcium?

• How many moles is 3.61 x 10 23 molecules of sulfuric acid?

Mole Relationships

• One mole of atoms, ions, or molecules contains Avogadro’s number of those particles.

• One mole of molecules or formula units contains Avogadro’s number times the number of atoms or ions of each element in the compound.

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Molecules and Chemical Formulas18

Molecules

• Molecules are groups of atoms chemically bonded together.

• Molecules may be elements or compounds.

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Molecular Elements and Allotropes

• Some Elements exist as molecules• Diatomic elements (molecules)

• Phosphorus exists as a tetratomic molecule

• Some elements exist in a variety of forms (Allotropes)• Carbon: graphite; diamond; buckminsterfullerine

• Phosphorus - red and white

• Sulfur - S6 and S4

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Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.

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Molecules and Molecular Compounds

• Molecular compounds - molecules containing atoms from two or more different elements

• Covalent bonds - the force holding the atoms together in a molecular compound by the sharing of electrons

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Formulas

• A compound is represented by using the symbols for the elements of which it is composed

• Subscripts are used to indicate how many atoms of a particular element exist in the compound

• If there is only one atom of a particular element, the one is assumed

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Formulas, con’t

• Changing the subscripts changes the compound

• consider H2O and H2O2

• Two different compounds can, however, share the same chemical formula

• dimethyl ether and ethyl alcohol both have the formula C2H6O

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Ions

• When atoms lose or gain electrons, they become ions.

• Cations are positive and are formed by elements on the left side of the periodic table

• Anions are negative and are formed by elements on the right side of the periodic table

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How charged species arise

• Neutral atoms and molecules have the same number of protons and electrons

• Cations have more protons than electrons resulting from the loss of an electron

• Anions have more electrons than protons resulting from the gain of an electron

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Common Monatomic Ions

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• Main Group Elements

• Group 1, 2 – All Metals – Group # = Charge of the Cation

• Group 3 – Metals (doesn’t include B) – Group # = Charge of Cation

• Group 5 – Non Metals – Group # - 8 = Charge of Anion

Metal – Bi – Group # = Charge

• Group 6, 7 – Non Metals Group # - 8 = Charge of Anion

• Group 0 – Doesn’t Form Ions!!

Common Variable Charge Cations

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• Copper – Cu 1+ and Cu 2+

• Iron – Fe 2+ and Fe 3+

• Lead – Pb 2+ and Pb 4+

• Gold – Au 1+ and Au 3+

• Tin – Sn 2+ and Sn 4+

Ionic Bonds

• Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. (Cation and Anions) due to electrostatic attraction

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Writing Formulas

• Because compounds are electrically neutral, one can determine the formula of a compound this way:

• The charge on the cation becomes the subscript on the anion.

• The charge on the anion becomes the subscript on the cation.

• If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.30 CDO IB Chemistry SL

Examples: Writing the Formula for Ionic Compounds

• Ca and Cl

• Ba and F

• Na and S

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Polyatomic ions

• Cations or anions consisting of groups of atoms that are covalently bonded to each other

• When more than one appears in a formula unit - the polyatomic ion is put in between parentheses, and a subscript is used to indication the number of the ions that appear in the formula unit

• example: Ba(ClO3)2

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Polyatomic Ions to Memorize

• Ammonium

• Hydrogen Carbonate (Bicarbonate)

• Carbonate

• Nitrate

• Hydroxide

• Sulfate

• Acetate (Ethanoate)

• Phosphate

Types of Ionic Compounds

• Ionic compounds will always consist of one of the following combinations:

• a metal and a nonmetal

• a polyatomic ion and a nonmetal

• a metal and a polyatomic ion or

• two polyatomic ions

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Properties of Ionic Compounds

• High melting points that correlate with charges on ions

• Most ionic solids do not conduct electricity but molten ionic compounds do.

• Most ionic compounds dissolve in water

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Properties cont.

• Solutions of ionic compounds in water conduct electricity (electrolytes)

• In ionic substances, each ion has its own characteristics, and these are different from the characteristics of the atom from which the ion was derived (NaCl)

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Binary Compound Nomenclature

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Ionic Nomenclature

• Write the name of the cation.

• If the cation is a polyatomic ion, write the name of the polyatomic ion

• If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses.

• If the anion is an element, change its ending to -ide;

• If the anion is a polyatomic ion, simply write the name of the polyatomic ion.

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Examples Formula to Name

• NaCl

• MgCl2

• KBr

• CuCl

• CuCl2

• Al(NO3)3

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Example Name to Formula

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White Board Practice

Binary Molecular Nomenclature42

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Nonmetals + nonmetals

• Name nonmetal further to the left of the periodic table first with no changes

• Name nonmetal further to the right of the periodic table second with the -ide suffix

• Use Greek prefixes to indicate the number of each one

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Greek prefixes

Number Prefix1 Mono

2 Di

3 Tri

4 Tetra

5 Penta

6 Hexa

7 Hepta

8 Octa

9 Nona

10 Deca

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Examples

• N2O3

• CO2

• P2O5

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Acids

• Binary acids – H with one other non metal• name begins with hydro

• then add stem of nonmetal plus -ic

• end with acid

• Examples

• HCl –

• H2S -

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Oxyacids

• Take polyatomic suffix and convert

• change -ate to -ic

• change -ite to -ous

• Do not use hydro- in the beginning

• Examples

• H2SO4 –

• H2SO3 -

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Hydrates

• Some ionic compounds can have water molecules attached within the structure

• These compounds are termed hydrates and have properties distinct from the unhydrated form

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Naming Hydrates

• Hydrates are named by naming the ionic compound and then using a Greek prefix to indicate the number of water molecules followed by the word hydrate

• Example

CuCl2 5H20

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Formula Calculations

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Types of Formulas

•Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.

•Molecular formulas give the exact number of atoms of each element in a compound.

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Empirical Formula

• Simplest whole number ratio of atoms in the compound

• All ionic formulas are empirical

• Molecular formulas are either equal to the empirical or a whole number multiple

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The composition of compounds

• Mole composition is the number of moles of each of the elements that make up the compound

• CO2 - one mole of C and two moles of O

• Mass composition is the mass of each element in the compound

• CO2 - 12.0 g of C and 32.0 g of O

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Percent composition

• Equation

x(Molar Mass of Element A) x 100

Molar Mass Compound

• Example

Find the mass % of each element in CH2O (formaldehyde)

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White Board Practice

• Find the percent by mass of carbon in CO2

Calculating Formulas

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Determination of Empirical formula

• Problem Solving Process:

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Example

• Example: A compound contains 63.6% N and 36.4% O, determine the compounds empirical formula

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Example

• Determine the empirical formula for a compound which is 26.6% K, 35.4% Cr, 38.0% O

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White Board Practice

• What is the empirical formula of a compound which is 26.4% N, 5.66% H and 67.9 % C

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Molecular formula

• The actual number of each atom in a formula unit

• Consider acetylene and benzene

• both have the empirical formula CH

• acetylene is actually C2H2

• benzene is actually C6H6

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Molecular Formula from Empirical

• Molecular formula must be integral multiple of empirical formula

• Therefore the mass of the molecular formula must be the same integral multiple of the mass of the empirical formula.

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Example

• A compound has the following composition

20.0% C, 2.2 % H, 77.8 % Cl. The molar mass of the compound is 545 g/mol. What is the molecular formula of the compound

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White Board Practice

• A compound is composed f 1.65 g N and 3.78 g S, its molar mass is 184 g/mol, what is the molecular formula?

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