Unit 2 Intro to Quantitative Chemistry CDO CP CHemistryTrimble.

Unit 2 Intro toQuantitative Chemistry

CDO CP CHemistry Trimble

PERIODIC TABLE

CDO IB Chemistry SL2


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

CP Chemistry5

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.

7 CDO IB Chemistry SL

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


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


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


Converting to Determine number of Particles

• Equation:

n = N

NA

Where

n = moles

N = # of particls

NA = Avogadros #


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?



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?




• 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.


Molecules and Chemical Formulas18

Molecules

• Molecules are groups of atoms chemically bonded together.

• Molecules may be elements or compounds.


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


Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.


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


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


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


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


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


Common Monatomic Ions


• 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


• 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


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


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



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


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


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)


Binary Compound Nomenclature

37CDO IB Chemistry SL

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.


Examples Formula to Name

• NaCl

• MgCl2

• KBr

• CuCl

• CuCl2

• Al(NO3)3



Example Name to Formula

Binary Molecular Nomenclature42

CDO IB Chemistry SL

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


Greek prefixes

Number Prefix1 Mono

2 Di

3 Tri

4 Tetra

5 Penta

6 Hexa

7 Hepta

8 Octa

9 Nona

10 Deca


Examples

• N2O3

• CO2

• P2O5


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 -


Oxyacids

• Take polyatomic suffix and convert

• change -ate to -ic

• change -ite to -ous

• Do not use hydro- in the beginning

• Examples

• H2SO4 –

• H2SO3 -


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


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


Formula Calculations

50

CDO IB Chemistry SL

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.


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


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


Percent composition

• Equation

x(Molar Mass of Element A) x 100

Molar Mass Compound

• Example

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




• Find the percent by mass of carbon in CO2

Calculating Formulas

56

CDO IB Chemistry SL

Determination of Empirical formula

• Problem Solving Process:


Example

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


Example

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



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


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


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.


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



• 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?


Unit 2 Intro to Quantitative Chemistry CDO CP CHemistryTrimble.

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