Chapter 3Chapter 3

Atoms: the Building Blocks Atoms: the Building Blocks of Matterof Matter

The parts that make up an atom are called The parts that make up an atom are called subatomic particlessubatomic particles..

1) Protons (p1) Protons (p++) positively charged particle) positively charged particle

2) Neutron (n2) Neutron (noo) neutral particle (uncharged)) neutral particle (uncharged)

3) Electrons (e3) Electrons (e--) negatively charged particle) negatively charged particle Neutrons and Protons Neutrons and Protons

are located in the are located in the nucleusnucleus of an atom. of an atom.

Electrons orbit around Electrons orbit around the nucleus.the nucleus.

Q- How are atoms of different elements distinguished from Q- How are atoms of different elements distinguished from

one another? In other words, how do we distinguish a one another? In other words, how do we distinguish a

helium atom from a carbon atom?helium atom from a carbon atom?

A- Their number of A- Their number of pprotonsrotons, indicated by the , indicated by the atomic numberatomic number

Let’s look at helium, He.It has an atomic number of 2,

which means that is has 2protons in it’s nucleus.

Atomic StructureAtomic StructureHere are the basics; you need to know these.Here are the basics; you need to know these.

11

HH1.00761.0076

HydrogenHydrogen

Atomic Number (Atomic Number (ZZ)): the number of : the number of protonsprotons (p (p++))

Atomic MassAtomic Mass: the number of : the number of protonsprotons (p (p++) + the number of ) + the number of neutronsneutrons (n (n00))

▪ ▪ measured in measured in atomic mass unitsatomic mass units (amu) which is one twelfth (amu) which is one twelfth

the mass of a carbon-12 atom.the mass of a carbon-12 atom.

▪ ▪ the mass of electrons (1/1860 the mass of electrons (1/1860 pp++) is negligible.) is negligible.

Number of NeutronsNumber of Neutrons: the : the atomic massatomic mass - the - the atomic numberatomic number

Atomic Number

Atomic Symbol

Atomic Mass

Lets practice! Find the missing Lets practice! Find the missing information?information?

ElementElement Atomic Atomic ##

AtomicAtomic

MassMassProtonsProtons ElectronElectron

ssNeutronNeutronss

ArAr 1818 39.948 39.948 amuamu

HeHe 22 22

OO 15.999 15.999 amuamu

88

The Famous Gold Foil The Famous Gold Foil ExperimentExperiment

This showed us that the atom is made of mostlyThis showed us that the atom is made of mostly

empty spaceempty space..

IsotopesIsotopesAtoms of the same element with different Atoms of the same element with different

number of number of neutronsneutrons

Because they have the same number of protons, all Because they have the same number of protons, all isotopes of an element have the same chemical isotopes of an element have the same chemical

properties.properties.

Mass Numbers of Hydrogen IsotopesMass Numbers of Hydrogen Isotopes

What would the masses be?What would the masses be?

The Mole: A The Mole: A Measurement of Measurement of

MatterMatterAt the end of this section, you shouldAt the end of this section, you should

be able to:be able to:Describe how Avogadro’s Describe how Avogadro’s

number is related to a mole of number is related to a mole of any substanceany substance

Calculate the mass of a mole Calculate the mass of a mole of any substanceof any substance

The Mole The Mole (aka (aka Avagadro’s Number)Avagadro’s Number)::

6.02 x 1023

The Mole and Avogadro’s The Mole and Avogadro’s NumberNumber

SI unit that measures the amount of SI unit that measures the amount of substancesubstance

1 mole = 6.02 x 101 mole = 6.02 x 102323 representative representative particlesparticles

Representative particles are usually Representative particles are usually atoms, molecules, or formula units (ions) atoms, molecules, or formula units (ions)

But Why the Mole?But Why the Mole?Just as 12 = 1 dozen, or 63,360 inches = 1 mile,Just as 12 = 1 dozen, or 63,360 inches = 1 mile,

the mole allows us to count microscopic itemsthe mole allows us to count microscopic items

(atoms, ion, molecules) on a macroscopic scale.(atoms, ion, molecules) on a macroscopic scale.

So, So, 1 mole1 mole of any substance is a set number of of any substance is a set number of

Items, namely: Items, namely: 6.02 x 106.02 x 102323. .

Chemistry = awesomeChemistry = awesome

Examples:Examples:SubstanSubstancece

RepresentativRepresentative Particlee Particle

Chemical Chemical FormulaFormula

RepresentatiRepresentative Particles ve Particles in 1.00 molin 1.00 mol

Atomic Atomic nitrogennitrogen

AtomAtom NN 6.02 x 106.02 x 102323

WaterWater MoleculeMolecule HH22OO 6.02 x 106.02 x 102323

Calcium Calcium ionion

IonIon CaCa2+2+ 6.02 x 106.02 x 102323

SolveSolveSubstancSubstancee

Representative Representative

ParticleParticleFormulaFormula

UnitUnitRepresentatiRepresentative Particles ve Particles in 1.00 molin 1.00 mol

Nitrogen Nitrogen gasgas

NN22 MoleculeMolecule

Calcium Calcium FluorideFluoride

CaFCaF22 MoleculeMolecule

SucroseSucrose CC1212HH2222OO1111 MoleculeMolecule

CarbonCarbon CC MoleculeMolecule

AnswersAnswers

Nitrogen gas-molecule-NNitrogen gas-molecule-N22

Calcium fluoride-formula unit-CaFCalcium fluoride-formula unit-CaF22

Sucrose-molecule-CSucrose-molecule-C1212HH2222OO1111

Carbon-atom-C Carbon-atom-C

All have 6.02 x 10All have 6.02 x 102323 representative representative particles in 1.00 molparticles in 1.00 mol

How many atoms are in a How many atoms are in a mole?mole?

Determined from the chemical formulaDetermined from the chemical formula List the elements and count the atomsList the elements and count the atoms Solve for COSolve for CO2 2

C - 1 carbon atomC - 1 carbon atom

O - 2 oxygen atoms O - 2 oxygen atoms

Add: 1 + 2 = 3 Add: 1 + 2 = 3 Answer: 3 times Avogadro’s number of Answer: 3 times Avogadro’s number of

atomsatoms

Solve: How many atoms are in Solve: How many atoms are in a mole ofa mole of

1. Carbon monoxide – CO1. Carbon monoxide – CO 2. Glucose – C2. Glucose – C66HH1212OO66

3. Propane – C3. Propane – C33HH88

4. Water – H4. Water – H22OO

How many moles of How many moles of magnesium is 1.25 x 10magnesium is 1.25 x 102323

atoms of magnesium?atoms of magnesium? Refer to page 174 in textRefer to page 174 in text Divide the number of atoms or Divide the number of atoms or

molecules given in the example by molecules given in the example by 6.02 x 106.02 x 102323

Divide (1.25 x 10Divide (1.25 x 1023)23) by (6.02 x 10 by (6.02 x 1023)23)

Express in scientific notationExpress in scientific notation Answer = 2.08 x 10Answer = 2.08 x 10-1-1 mol Mg mol Mg

ObjectivesObjectives

Use the molar mass to convert Use the molar mass to convert between mass and moles of a between mass and moles of a substancesubstance

Use the mole to convert among Use the mole to convert among measurements of mass, volume, and measurements of mass, volume, and number of particlesnumber of particles

Molar massMolar mass

Mass (in grams) of one mole of a Mass (in grams) of one mole of a substancesubstance

Broad term (can be substituted) for Broad term (can be substituted) for gram atomic mass, gram formula gram atomic mass, gram formula mass, and gram molecular massmass, and gram molecular mass

Can be unclear: What is the molar Can be unclear: What is the molar mass of oxygen?mass of oxygen?

O or OO or O22 ? - element O or molecular ? - element O or molecular compound Ocompound O22 ? ?

Calculating the Molar Mass of Calculating the Molar Mass of Compounds (Molecular and Compounds (Molecular and

Ionic)Ionic) 1. List the elements1. List the elements 2. Count the atoms2. Count the atoms 3. Multiply the number of atoms of 3. Multiply the number of atoms of

the element by the atomic mass of the element by the atomic mass of the element (atomic mass is on the the element (atomic mass is on the periodic table)periodic table)

4. Add the masses of each element4. Add the masses of each element 5. Express to tenths place5. Express to tenths place

What is the molar mass (gfm) What is the molar mass (gfm) of ammonium carbonate of ammonium carbonate

(NH(NH44))22COCO33?? N 2 x 14.0 g = 28.0 gN 2 x 14.0 g = 28.0 g H 8 x 1.0 g = 8.0 gH 8 x 1.0 g = 8.0 g C 1 x 12.0 g = 12.0 gC 1 x 12.0 g = 12.0 g O 3 x 16.0 g = 48.0 gO 3 x 16.0 g = 48.0 g Add ________Add ________ Answer 96.0 g Answer 96.0 g

Practice ProblemsPractice Problems 1. How many grams are in 9.45 mol 1. How many grams are in 9.45 mol

of dinitrogen trioxide (Nof dinitrogen trioxide (N22OO33) ?) ? a. Calculate the grams in one molea. Calculate the grams in one mole b. Multiply the grams by the number b. Multiply the grams by the number of molesof moles 2. Find the number of moles in 92.2 2. Find the number of moles in 92.2

g g

of iron(III) oxide (Feof iron(III) oxide (Fe22OO33).). a. Calculate the grams in one mole a. Calculate the grams in one mole b. Divide the given grams by the b. Divide the given grams by the

grams in one mole grams in one mole

AnswersAnswers

1. 718 g N1. 718 g N22OO3 3 (one mole is 76.0g) (one mole is 76.0g)

2. 0.578 mol Fe2. 0.578 mol Fe22OO33 (one mole is (one mole is 159.6 g)159.6 g)

Volume of a Mole of GasVolume of a Mole of Gas

Varies with a change in temperature Varies with a change in temperature or a change in pressureor a change in pressure

At STP, 1 mole of any gas occupies a At STP, 1 mole of any gas occupies a volume of 22.4 Lvolume of 22.4 L

Standard temperature is 0Standard temperature is 0°°CC Standard pressure is 101.3 kPa Standard pressure is 101.3 kPa

(kilopascals), or 1 atmosphere (atm)(kilopascals), or 1 atmosphere (atm) 22.4 L is known as the molar volume22.4 L is known as the molar volume

22.4 L of any gas at STP contains 22.4 L of any gas at STP contains 6.02 x 106.02 x 102323 representative particles representative particles of that gasof that gas

One mole of a gaseous element and One mole of a gaseous element and one mole of a gaseous compound one mole of a gaseous compound both occupy a volume of 22.4 L at both occupy a volume of 22.4 L at STP (Masses may differ)STP (Masses may differ)

Molar mass (g/mol) = Density (g/L) x Molar mass (g/mol) = Density (g/L) x Molar Volume (L/mol) Molar Volume (L/mol)

ObjectivesObjectives

Define the termsDefine the terms Calculate the percent composition of Calculate the percent composition of

a substance from its chemical a substance from its chemical formula or experimental dataformula or experimental data

Derive the empirical formula and the Derive the empirical formula and the molecular formula of a compound molecular formula of a compound from experimental data from experimental data

Terms to KnowTerms to Know

Percent composition – relative Percent composition – relative amounts of each element in a amounts of each element in a compoundcompound

Empirical formula – lowest whole- Empirical formula – lowest whole- number ratio of the atoms of an number ratio of the atoms of an element in a compoundelement in a compound

An 8.20 g piece of magnesium An 8.20 g piece of magnesium combines completely with combines completely with 5.40 g of oxygen to form a 5.40 g of oxygen to form a

compound. What is the compound. What is the percent composition of this percent composition of this

compound?compound?1. Calculate the total mass1. Calculate the total mass

2.2. Divide each given by the total Divide each given by the total mass mass

and then multiply by 100%and then multiply by 100%

3.3. Check your answer: The Check your answer: The

percentages should total 100%percentages should total 100%

AnswerAnswer

The total mass is 8.20 g + 5.40 g = The total mass is 8.20 g + 5.40 g = 13.60 g13.60 g

Divide 8.2 g by 13.6 g and then multiply Divide 8.2 g by 13.6 g and then multiply by 100% = 60.29412 = 60.3%by 100% = 60.29412 = 60.3%

Divide 5.4 g by 13.6 g and then multiply Divide 5.4 g by 13.6 g and then multiply by 100% = 39.70588 = 39.7%by 100% = 39.70588 = 39.7%

Check your answer: 60.3% + 39.7% = Check your answer: 60.3% + 39.7% = 100%100%

Calculate the percent Calculate the percent composition of propane (Ccomposition of propane (C33HH88))

1. List the elements1. List the elements 2. Count the atoms2. Count the atoms 3. Multiply the number of atoms 3. Multiply the number of atoms

of the element by the atomic of the element by the atomic mass of the element (atomic mass of the element (atomic mass is on the periodic table)mass is on the periodic table)

4. Express each element as a 4. Express each element as a percentage of the total molar percentage of the total molar massmass

5. Check your answer5. Check your answer

AnswerAnswer

Total molar mass = 44.0 g/molTotal molar mass = 44.0 g/mol 36.0 g C = 81.8%36.0 g C = 81.8% 8.0 g H = 18.2%8.0 g H = 18.2%

Calculate the mass of carbon Calculate the mass of carbon in 52.0 g of propane (Cin 52.0 g of propane (C33HH88))

1.1. Calculate the percent composition Calculate the percent composition using the formula (See previous using the formula (See previous problem)problem)

2. Determine 81.8% of 82.0 g2. Determine 81.8% of 82.0 g

Move decimal two places to the Move decimal two places to the

left (.818 x 82 g)left (.818 x 82 g)

3. Answer = 67.1 g3. Answer = 67.1 g

1) Find the percent composition of 1) Find the percent composition of

Aluminum Oxide (AlAluminum Oxide (Al33OO22))

2) How much of a 5-g piece of Iron2) How much of a 5-g piece of Iron

Bromide (FeBrBromide (FeBr33) is iron?) is iron?

Calculating Empirical Calculating Empirical FormulasFormulas

Microscopic – atomsMicroscopic – atoms Macroscopic – moles of atomsMacroscopic – moles of atoms Lowest whole-number ratio may not Lowest whole-number ratio may not

be the same as the compound be the same as the compound formula formula

Example: The empirical formula of Example: The empirical formula of hydrogen peroxide (Hhydrogen peroxide (H22OO22) is HO) is HO

Empirical FormulasEmpirical Formulas The first step is to find the mole-to-mole The first step is to find the mole-to-mole

ratio of the elements in the compoundratio of the elements in the compound If the numbers are both whole numbers, If the numbers are both whole numbers,

these will be the subscripts of the these will be the subscripts of the elements in the formulaelements in the formula

If the whole numbers are identical, If the whole numbers are identical, substitute the number 1substitute the number 1

Example: CExample: C22HH22 and C and C88HH88 have an have an empirical formula of CHempirical formula of CH

If either or both numbers are not whole If either or both numbers are not whole numbers, numbers in the ratio must be numbers, numbers in the ratio must be multiplied by the same number to yield multiplied by the same number to yield whole number subscripts whole number subscripts

What is the empirical What is the empirical formula of a compound formula of a compound that is 25.9% nitrogen that is 25.9% nitrogen

and 74.1% oxygen?and 74.1% oxygen? 1. Assume 100 g of the compound, so 1. Assume 100 g of the compound, so

thatthat

there are 25.9 g N and 74.1 g Othere are 25.9 g N and 74.1 g O 2. Convert to mole-to-mole ratio:2. Convert to mole-to-mole ratio:

Divide each by mass of one mole Divide each by mass of one mole

25.9 g divided by 14.0 g = 1.85 mol N25.9 g divided by 14.0 g = 1.85 mol N

74.1 g divided by 16.0 g = 4.63 mol O74.1 g divided by 16.0 g = 4.63 mol O 3. Divide both molar quantities by the 3. Divide both molar quantities by the

smaller number of molessmaller number of moles

4. 1.85/1.85 = 1 mol N4. 1.85/1.85 = 1 mol N 4.63/1.85 = 2.5 mol O4.63/1.85 = 2.5 mol O 5. Multiply by a number that 5. Multiply by a number that

converts each to a whole number converts each to a whole number (In this case, the number is 2 (In this case, the number is 2 because 2 x 2.5 = 5, which is the because 2 x 2.5 = 5, which is the smallest whole number )smallest whole number )

2 x 1 mol N = 22 x 1 mol N = 2 2 x 2.5 mol O = 52 x 2.5 mol O = 5 Answer: The empirical formula is Answer: The empirical formula is

NN22OO55

Determine the Empirical Determine the Empirical FormulasFormulas

1. H1. H22OO22

2. CO2. CO2 2

3. N3. N22HH44

4. C4. C66HH1212OO66

5. What is the empirical formula of a 5. What is the empirical formula of a compound that is 3.7% H, 44.4% C, compound that is 3.7% H, 44.4% C, and 51.9% N?and 51.9% N?

AnswersAnswers

Compound Empirical FormulaCompound Empirical Formula 1. H1. H22OO22 HO HO

2. CO2. CO2 2 COCO2 2

3. N3. N22HH4 4 NHNH22

4. C4. C66HH1212OO66 CH CH22OO

5. HCN5. HCN

Calculating Molecular Calculating Molecular FormulasFormulas The molar mass of a compound The molar mass of a compound

is a simple whole-number is a simple whole-number multiple of the molar mass of the multiple of the molar mass of the empirical formulaempirical formula

The molecular formula may or The molecular formula may or may not be the same as the may not be the same as the empirical formula empirical formula

Calculate the molecular Calculate the molecular formula of the compound formula of the compound

whose molar mass is 60.0 g whose molar mass is 60.0 g and empirical formula is and empirical formula is

CHCH44N.N. 1. Using the empirical formula, calculate 1. Using the empirical formula, calculate

the empirical formula mass (efm)the empirical formula mass (efm) (Use the same procedure used to calculate (Use the same procedure used to calculate

molar mass.) molar mass.) 2. Divide the known molar mass by the 2. Divide the known molar mass by the

efm efm 3. Multiply the formula subscripts by this 3. Multiply the formula subscripts by this

value to get the molecular formulavalue to get the molecular formula

AnswerAnswer

Molar mass (efm) is 30.0 gMolar mass (efm) is 30.0 g 60.0 g divided by 30.0 g = 260.0 g divided by 30.0 g = 2 Answer: CAnswer: C22HH88NN22

Practice ProblemsPractice Problems 1) What is the empirical formula of a 1) What is the empirical formula of a

compounds that is 25.9% nitrogen and 74.1% compounds that is 25.9% nitrogen and 74.1% oxygen?oxygen?

2) Calculate the empirical formula of a 2) Calculate the empirical formula of a compound that is 32.00% C, 42.66% O, compound that is 32.00% C, 42.66% O, 18.67% N, and 6.67% H.18.67% N, and 6.67% H.

3) Calculate the empirical formula of a 3) Calculate the empirical formula of a compound that is 42.9% C and 57.1% O.compound that is 42.9% C and 57.1% O.

Practice ProblemsPractice Problems 4) What is the molecular formula for each 4) What is the molecular formula for each

compound:compound:

a) CHa) CH22O, 90 g/molO, 90 g/mol

b) HgCl, 472.2 g/molb) HgCl, 472.2 g/mol

c) Cc) C33HH55OO22, 146 g/mol, 146 g/mol