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Chapter 2

Atoms, Molecules, and Ions

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Atoms and Atomic Structure• Dalton’s Atomic Theory - 1808

1. -Elements are composed of small, nondivisible particles called atoms

2. -Atoms of an element have identical properties and differ from those of other elements

3. -Atoms cannot be created, destroyed, or transformed into other atoms

4. -Compounds are formed when atoms of different elements combine in whole-number ratios

5. -Atom ratios are constant in a given compound6. -Chemical reactions rearrange and recombine

atoms but do not destroy them

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Structure of the Atom1. -atom is mostly empty space2. -consists of a very small, dense center called

the nucleus3. -nearly all of the atom’s mass is in the

nucleus4. -the nuclear diameter is 1/10,000 to

1/100,000 times less than the atom’s radius

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Particle Mass (amu) Charge

Electron (e-) 0.00054858 -1

Proton (p,p+) 1.0073 +1

Neutron(n,n0) 1.0087 0

Structure of the Atom• -Sir John Joseph Thompson and Ernest

Rutherford established a model of the atom still in use today

• -Three fundamental particles make-up atoms:

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Elements• substances that cannot be

decomposed into simpler substances via chemical reactions

• Elemental symbols-abbreviation representing each element on periodic table– -First letter capital, second letter lower

case– ie: C, Ca, Co

– CO is not an element (it’s a compound) because there are two capital letters

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The Periodic Table• 1869 - Mendeleev & Meyer

– Discovered the periodic law• -Organized based on related chemical

reactivities, physical properties, other behaviors and trends

• -The properties of the elements are periodic functions of their atomic numbers (not atomic masses)

Law of Chemical Periodicity

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The Periodic Table• Groups or families

– Vertical group of elements on periodic table– Similar chemical and physical properties

•Period–Horizontal group of elements on periodic table–Transitions from metals to nonmetals •Three regions–Metals, nonmetals and metalloids

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•Period– Horizontal group of elements on

the periodic table•-Transition from metals to nonmetals

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•Groups (families)– Vertical group of elements on the

periodic table•-similar chemical and physical

properties

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•Metalloids• separate metals from nonmetals

• Metals are to the left of stair step– -Approximately 80% of the

elements• Nonmetals are to the right

of stair step– -Approximately 20% of the

elements• Elements box on the stair

step have properties between metals and nonmetals

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The Periodic Table• Chemical properties of metals

1. -Outer (valence) shells contain few electrons2. -Form cations by losing electrons3. -Form ionic compounds with nonmetals4. -Solid state characterized by metallic

bonding-Conductors of electricity and heat-Malleable: can be hammered-Ductile: drawn into wire-Typically solids (except mercury)

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The Periodic Table• Chemical properties of

nonmetals1. -Outer shells contain four or more electrons2. -Form anions by gaining electrons (- charge)3. -Form ionic compounds with metals and

covalent compounds with other nonmetals4. -Form covalently bound molecules; noble

gases are monatomic and have full electron shells

5. -Insulators meaning poor conductors6. -Typically gasses or solids (Br2 liquid I2 solid)

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The Periodic Table:• Periodic trends

PeriodicChart

More MetallicMoreMetallic

Periodic Table

Atomic number increase

Size decreases

Atomic number increase

Size increases

Form compounds with similar formulas

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Metals • Group IA metals:

– Alkali metals- Li, Na, K, Rb, Cs, Fr– -solids, reactive, and never found in nature as free

elements– -chemical formula from top-to-bottom are the same

• Group IIA metals:– Alkaline earth metals- Be, Mg, Ca, Sr, Ba, Ra– -solids, reactive, and mostly found in nature as

compounds– -chemical formula from top-to-bottom are the same

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Group IIIA: B, Al, Ga, In, Tl• -Aluminum (Al) most abundant metal in the earth’s

crust• -Boron (B) is the only nonmetal• -forms compounds of analogous chemical formulas

Group IVA: C, Si, Ge, Sn, Pb -most variation in their properties -Carbon (C) is the “element of life”

CO2 carbonate-limestone, coral, shellsfossil fuels-coal, petroleum, natural gas

-Silicon (Si) is found as gemstones, glass, and sand -Lead (Pb) was used as water pipes, paint, and in

gasoline -form compounds of analogous chemical formulas

Metals

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Allotropes

• elements (nonmetals) that exist in several different and distinct forms each having its own properties

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Group VA: N, P, As, Sb, Bi• Nitrogen (N) • -makes up ~75% of the earth’s atmosphere • -used to make fertilizer (NH3)• -found in biological systems in proteins and

DNA

• Phosphorous (P)• -has several allotropes most common are white

and red phosphorus • -white ignites spontaneously in air and used to

make phosphoric acid• -red phosphorus is used in striking strips of

matchbooks• -form similar types of chemical compounds

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•Group VIA: nonmetals– Chalcogens– O, S, Se, Te

-Oxygen (O) is the power source of life on earth by combining with other substances, and has allotropes-Sulfur (S) (and even Selenium, Se) is fowl smelling, and S appears as allotropes-these elements are considered poisonous, but essential for human diets-Some variations is chemistries, but form analogous formulas

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•Group VIIA nonmetals– halogens– F, Cl, Br, I

-All exist in the form of diatomic molecules-At room temperature, Fluorine (F) and Chlorine (Cl) are gases where Bromine (Br) is a liquid and Iodine (I) is a solid-Some of the most reactive of all elements they react with metals and nonmetals to form compounds

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•Group VIIIA nonmetals– noble, inert or rare gases– He, Ne, Ar, Kr, Xe, Rn

-least reactive elements and for a long time considered unreactive-all are gases and none are abundant on earth-He is the second most abundant element in the universe

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Transition Metals• Most are found as compounds in

nature – -Ag, Au, Pt are less reactive and can be

found as pure substances– -These elements are commercially useful

as building materials, in paints, catalytic converters, coins, batteries, and fireworks

– -Play important roles in biological processes

– -Bottom two rows of the periodic table are used in television picture tubes, atomic fuel, smoke detectors

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Atomic Number (Z)

the number of protons in the nucleus•-numbered consecutively on the periodic

table

• atomic number determines the element:•-elements differ from one another by the

number of protons in the nucleus •-the number of electrons in a neutral atom

(no charge) is equal to the atomic number•-negatively charged species have more

electrons•-positively charged species have less

electrons

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Mass Number (A)• sum of the number of protons and

neutrons– Z = atomic number (number of protons) – N = number of neutrons– A = Z + N

• One common symbolism used to show mass and proton numbers is:

AuCa, C, example for E 19779

4820

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AZ

?Cu, N, 188

63?

14?

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Mass Number (A)•How many protons and neutrons are in

the following?

U

U

O

O

23692

23892

188

168

23216

8235

24020

2311

S

Br

Ca

Na

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Mass Number (A)

Give the number of protons, neutrons and electrons and the correct element symbol:

?

?

?

157

20079

2412

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Isotopes• Atoms of the same element but with different

numbers of neutrons (or same atomic number, but different mass numbers)

Isotopes have different masses and mass number(A) values but are the same element

• Example: hydrogen isotopes or protium is the most common hydrogen isotope

• -one proton and no neutrons or deuterium (D) is the second most abundant hydrogen isotope

• -one proton and one neutron or tritium (T) is a radioactive hydrogen isotope

• -one proton and two neutrons

H

H

H

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11

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Atomic Weights• How do we know what

the values of these atomic weights are?

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Atomic Weight• the weighted average of the masses of

the elements stable isotopes

• Example: Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63Cu with a mass of 62.9 amu, and 30.9% 65Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place.

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Atomic Mass• weighted average of the masses of

an elements stable isotopes as listed on the periodic table– For example: hydrogen (H) = 1.008

amu– calcium (Ca) = 40.078

amu

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Moleculessmallest unit of a pure substance that can be

divided and still retain the composition and chemical properties of the substance

Examples of molecules:– H2

– O2

– S8

– H2O– CH4

– C2H6OMolecular formulas: describe the composition of

substances, but provide no structural information

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Classes of Substances:

monatomic elementsHe, Au, Na

diatomic elements (binary molecules)O2, H2, Cl2, F2, I2, N2,Br2

complex elementsO3, S4, P8

Compounds (molecules)H2O, C12H22O11

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Molecular (Chemical) FormulasCompound Contains

HCl H2O NH3

C3H8

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Chemical bondsAttractive forces that hold atoms together in compounds Chemical bond types:

1. Ionic bonding: resulting from electrostatic attractions between ions -formed by the transfer of one or more electrons from one atom to

another -attraction of cations for anions typically form solids -most often formed by interactions between metals and nonmetals

2. Covalent bonding: results from sharing one or more electron pairs between two atoms - typically formed by interactions between nonmetals and

nonmetals

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Ionic CompoundsAn ion is an atom or a group of atoms

possessing a net electrical charge

positive (+) ions or cationsThese atoms have lost 1 or more electronsMetals lose electrons to form cations (monoatomic

cations)Consider Group IA and IIA metals

negative (-) ions or anionsThese atoms have gained 1 or more electrons.Nonmetals gain electrons to form anions

(monoatomic anions)Consider the nonmetals-groups IVA through VIIA

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Ionic Compounds• Coulomb’s Law: dictates the strength

of ionic bonds – it is an inverse square law

ions ofcenter between distance dionson charge of magnitude q

ionsbetween attraction of force Fwhere

d

qqkF 2

=

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Ionic CompoundsCations:

Na+, Ca2+, Al3+ (monoatomic cations)NH4

+ (polyatomic cation)Anions:

F-, O2-, N3- (monoatomic anions)SO4

2-, PO43-, HCO3

- (polyatomic anions)Transition metals forming cations

No pattern exists for determining the chargeMany metals form several different ions (charge

states)H and noble gases are special cases

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Ionic FormulasFormulas of ionic compounds are

determined by the charges of the ions-total charge of the cations must equal the total charge of the anions-The compound must be neutral

NaCl sodium chloride (Na1+ & Cl1-)KOH potassium hydroxide (K1+ & OH1-)CaSO4 calcium sulfate (Ca2+ & SO4

2-)Al(OH)3 aluminum hydroxide (Al3+ & OH1-)

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Writing binary chemical formulasCharge becomes subscript. Then give the

subscript as lowest common denominator

??

??

??

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2

2332

2222

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1

OFe

ICu

ClK

NBaNBa

MgOOMgOMg

AlBrBrAl

CaFFCa

LiClClLi

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Naming Ionic Compoundsmetal cation and a nonmetal anion

1. Name the cation2. Name the anion, nonmetal stem with –

ide ending

LiBr lithium bromide magnesium chloride

Li2S lithium sulfideAl2O3 You do it!You do it!

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Naming Ionic CompoundsLiBr lithium bromideMgCl2 magnesium chlorideLi2S lithium sulfideAl2O3 aluminum oxideNa3P Mg3N2 Notice that binary ionic compounds with

metals having one oxidation state They do not use prefixes or Roman numerals!!!

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Naming CationsMonoatomic cations

use the name of the metal plus the word “cation”Examples: Al3+, Li+, Ca2+

Transition metals that have multiple charges:Two methods are used1. Older method: -add suffix “ic” to element’s Latin name for higher

oxidation state (higher positive charge) -add suffix “ous” to element’s Latin name for lower

oxidation state (lower positive charge)2. Modern method: use Roman numerals in parentheses to indicate

metal’s oxidation state

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Naming Ionic Compoundsionic compounds containing metals

with more than one oxidation state (charge)

memorize them on your handout

Metals exhibiting multiple oxidation states are:1. most of the transition metals2. metals in groups IIIA (except Al), IVA, &

VA on the periodic table

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Compound Old System Modern SystemFeBr2 ferrous bromide iron(II) bromide

ferric bromide iron(III) bromideSnO tin(II) oxideSnO2 tin(IV) oxideCoCl2 cobaltous chlorideCoCl3 cobaltic chloride

plumbous sulfide lead(II) sulfideplumbic sulfide lead(IV) sulfide

Naming Ionic Compounds

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Naming Ionic CompoundsThere are polyatomic ions that form binary

ionic compounds

1. OH- hydroxide2. CN- cyanide3. NH4

+ ammonium

KOH potassium hydroxidebarium hydroxideAl(OH)3 aluminum hydroxideFe(OH)2 You do it!You do it!

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Naming Ionic CompoundsKOH potassium hydroxideBa(OH)2 barium hydroxideAl(OH)3 aluminum hydroxideFe(OH)2 iron (II) hydroxide

iron (III) hydroxideBa(CN)2

ammonium sulfideNH4CN

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Naming AnionsMonoatomic anions

use the name of the nonmetal plus the word “-ide” at the end

Examples: F-, Cl-, S2- Polyatomic anions

Some guidelines for oxoanions (contain Oxygen)• If only 2 similar formula type anions exist, the one containing the

greater number of oxygen atoms have an “–ate” ending, and the smaller number of oxygen atoms have an “-ite” ending

NO3- NO2

-

SO42- SO3

2-

• If more than two exist, the one with the largest number of oxygen atoms have a prefix “per-” and an “-ate” ending, and the smallest number of oxygen atoms have a prefix “hypo-” and an “-ite” ending ClO4

- ClO3-

ClO2- ClO-

• Oxoanions containing H are named with the word hydrogen in front, if more than one H is contained in the oxoanion, then prefixes are used to indicate the number of hydrogen atoms HPO4

2- H2PO4-

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Naming Ionic CompoundsOn Your Own

NaNO2 sodium nitritesodium nitrate

Na2SO3sodium sulfate

Na3PO4 MgSO4Ca(NO3)2BaCO3

potassium phosphate

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Ionic FormulasWhat is the name of K2SO3?

Potassium sulfiteWhat is charge on sulfite ion?

-2What is the formula of ammonium sulfide?

(NH4)2SWhat is charge on ammonium ion?

+1What is the formula of aluminum sulfate?

Al2(SO4)3What is charge on both ions?

+3 -2

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Name or Write the formula: Formula Name1.Cu(OH)2 2.CuOH3.MgCl24.Li2O 5.Zn3N26. calcium bromide7. sodium hydroxide8. aluminum phosphide9. barium iodide10. magnesium cyanide

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Name or Write the formula:

Formula Name1. iron(II) bromide2. iron(III) hydroxide3. copper(II) oxide4. lead(IV) cyanide

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Commonly Found Ionic Compounds

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Covalent Compounds

Covalent Bonds: Sharing of one or more electron pairs between atoms

Representation of the formation of a H2 molecule from 2 H atoms

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Naming Molecular (Covalent) Compounds

molecular formulas for these compounds are generally written with increasing group number

– Use the first nonmetal’s name with the appropriate prefix di-, tri-, tetra-, etc (excluding mono-)

– Followed by the next nonmetal: use this nonmetal’s stem with “-ide” ending and the appropriate prefix mono-, di-, tri-, etc

Exception: hydrogen – write the word hydrogen– then the following nonmetal: use the nonmetal stem

with the “-ide” ending

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Naming NonmetalsElement StemBoron (B) borCarbon (C) carbSilicon (Si) silicNitrogen (N) nitrFluorine (F) fluorChlorine (Cl) chlor

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Naming NonmetalsElement StemBromine (Br) bromIodine (I) iodOxygen (O) oxSulfur (S) sulfSelenium (Se) selenPhosphorus (P) phosphHydrogen (H) hydr

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Naming Molecular Compounds

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Naming Covalent CompoundsFormula NameHF hydrogen fluoride(hydrofluoric acid)HCl hydrogen chloride (hydrochloric acid)HBr hydrogen bromide (hydrobromic acid)H2S You do it!You do it!

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Names and Formulas • What is the formula of nitric acid?

• What is the formula of sulfur trioxide?

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Naming Covalent CompoundsFormula NameCO _________________ carbon dioxideSO3

oxygen difluorideP4O6

tetraphosphorus decoxide

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Naming Covalent CompoundsFormula Modern NameN2O dinitrogen monoxideNO nitrogen monoxideN2O3

NO2

dinitrogen tetroxide dinitrogen pentoxide

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Describing Compound Formulas

% composition = mass of an individual element in a compound divided by the total mass of the compound x 100

% comp = x 100component

masstotal mass

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Percent Composition

What is the percent composition of H in C3H8?

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Percent Composition

What is the percent composition of H in H2O?

Ans: 11.21%

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Percent CompositionCalculate the percent composition of

each component in Fe2(SO4)3 to 3 sig. fig.

On your own27.9% Fe24.1% S48.0% OTotal = 100%

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Empirical and Molecular Formulas

Empirical Formula: smallest whole-number ratio of atoms present in a

compound

Molecular Formula: actual numbers of atoms of each element present in a

molecule of the compound

We determine the empirical and molecular formulas of a compound from the percent composition

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Empirical And Molecular Formulas

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Empirical FormulasA compound contains 24.74% K, 34.76%

Mn, and 40.50% O by mass. What is its empirical formula?

Make the simplifying assumption that we have 100.0 g of compound

In 100.0 g of compound there are:24.74 g of K34.76 g of Mn40.50 g of O

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Empirical FormulasA sample of a compound contains

6.541g of Co and 2.368g of O. What is empirical formula for this compound?

You do it!You do it!

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Molecular Formulas

A compound is found to contain 85.63% C and 14.37% H by mass. In another experiment its molar mass is found to be 56.1 g/mol. What is its molecular formula?

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More PracticeWhat mass of ammonium phosphate,

(NH4)3PO4, would contain 15.0 g of N? MW = 149.08626

g/mol

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The Mole• an amount of a substance that

contains as many elemental entities as there are atoms in exactly 12.000g of carbon-12 isotope

– -This number is an amount of atoms, ions, or molecules that is large enough to see and easier to handle

– -A mole (mol) = some number of things• Just like a dozen = 12 things• One mole = 6.022 x 1023 things

– -Avogadro’s number (NA) = 6.022 x 1023

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The Mole

• Molar mass: mass in grams that is equal to the atomic weight of the element (in grams)

• H has an atomic weight of 1.00794 g 1.00794 g of H atoms = 6.022 x 1023 H atoms (= 1 mol)

• Mg has an atomic weight of 24.3050 g 24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms (= 1

mol)

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The Mole

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The Mole

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The Mole• Calculate the mass of a single Mg

atom, in grams, to 3 significant figures.

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The Mole• Calculate the number of atoms in

one-millionth of a gram of Mg to 3 significant figures.

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The Mole• How many atoms are contained in

1.67 moles of Mg?

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The Mole• How many moles of Mg atoms are

present in 73.4 g of Mg?

YOU MUST KNOWHOW TO DO THESE PROBLEMS

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Molecular WeightsAdd atomic weights of each atom

in the molecule

molar mass (molecular weight) of propane (C3H8):

amu 44.11 mass Molar

amu 8.08 amu 1.01 8H 8amu 36.03amu 12.01 3C 3

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Molecular Weightsmolar mass of calcium nitrate,

Ca(NO3)2:

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Formula Weights, Molecular Weights, and Moles

One Mole of: ContainsCl2 = 70.90g 6.022 x 1023 Cl2 molecules

2(6.022 x 1023 ) Cl atoms= 1.204 x 1024 Cl atoms

C3H8 = 44.11 g 6.022 x 1023 C3H8 molecules 3 (6.022 x 1023 ) C atoms 8 (6.022 x 1023 ) H atoms

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Formula Weights, Molecular Weights, and Moles

Calculate the number of C3H8 molecules in 74.6 g of propane:

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Formula Weights, Molecular Weights, and Moles

Calculate the number of O atoms in 26.5 g of Li2CO3: