Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 4 Atoms and Elements.

Introductory ChemistryIntroductory Chemistry, 2, 2ndnd Edition EditionNivaldo TroNivaldo Tro

Chapter 4Atoms and Elements

Tro's Introductory Chemistry, Chapter 4Tro's Introductory Chemistry, Chapter 4 22

Experiencing AtomsExperiencing Atoms

Atoms are very small; they are building Atoms are very small; they are building blocks of matter.blocks of matter.

Atom = smallest particle of an element that Atom = smallest particle of an element that retains its characteristicsretains its characteristics


Dalton’s Atomic TheoryDalton’s Atomic Theory1.1. Elements are composed of tiny Elements are composed of tiny

indivisible particles called indivisible particles called atomsatoms

2.2. All atoms of an element are All atoms of an element are identical; atoms of different identical; atoms of different elements are differentelements are different

– every carbon atom is identical to every carbon atom is identical to every other carbon atomevery other carbon atom

they have the same chemical and they have the same chemical and physical propertiesphysical properties

– but carbon atoms are different but carbon atoms are different from sulfur atomsfrom sulfur atoms

they have different chemical and they have different chemical and physical propertiesphysical properties

John Dalton(1766-1844)


Dalton’s Atomic TheoryDalton’s Atomic Theory

3.3. Atoms combine in simple, whole-Atoms combine in simple, whole-number ratios to form molecules of number ratios to form molecules of compounds compounds

– each molecule of a compound contains each molecule of a compound contains the exact same types and numbers of the exact same types and numbers of atomsatoms

Law of Constant Composition or Definite Law of Constant Composition or Definite ProportionsProportions

Chemical FormulasChemical Formulas


Dalton’s Atomic TheoryDalton’s Atomic Theory

4.4. In chemical reactions, atoms are not In chemical reactions, atoms are not broken or changed into other atoms.broken or changed into other atoms.

– atoms are not created or destroyed, just atoms are not created or destroyed, just rearrangedrearranged

total mass will remain the same total mass will remain the same

Law of Conservation of MassLaw of Conservation of Mass

– atoms of one element do not change into atoms of one element do not change into atoms of another element in a chemical atoms of another element in a chemical reactionreaction

cannot turn Lead into Gold by a chemical cannot turn Lead into Gold by a chemical reactionreaction


Dalton’s Atomic TheoryDalton’s Atomic TheoryLaw of Law of multiple proportionsmultiple proportions : if two elements A : if two elements A and B combine to form more than one and B combine to form more than one compound, masses of B which combine with compound, masses of B which combine with mass of A, is a ratio of small whole numbers. mass of A, is a ratio of small whole numbers. Ex: CO, (1.33 g O/1g C); COEx: CO, (1.33 g O/1g C); CO2 2 (2.67 g O/g)(2.67 g O/g)

The mass of O in COThe mass of O in CO22 is twice that in CO: 2.67g is twice that in CO: 2.67g O in COO in CO22/1.33 g O in CO/1.33 g O in CO22 = 2.00 = 2.00

Thus, when 2 elements combine to form 2 Thus, when 2 elements combine to form 2 different compounds, they combine in different different compounds, they combine in different ratios or proportions: ratios or proportions:

CO, COCO, CO22 ;; SOSO22, SO, SO33


Modern Evidence for AtomsModern Evidence for Atoms

Atoms can be seen through a special instrument Atoms can be seen through a special instrument called the scanning tunneling microscope (STM)called the scanning tunneling microscope (STM)


Mass of AtomsMass of Atoms

Using compositions of compounds Using compositions of compounds and assumed formulas, Dalton and assumed formulas, Dalton determined determined relativerelative masses of atoms masses of atoms

Dalton based his scale on H = 1 amuDalton based his scale on H = 1 amu

we now base it on C-12 = 12 amu we now base it on C-12 = 12 amu exactlyexactly

unit = unit = atomic mass unit, amuatomic mass unit, amu


The Atom is Divisible!The Atom is Divisible!

Work done by J.J. Thomson and others proved that the atom had particles called electronselectrons

Thomson found that electrons are much Thomson found that electrons are much smaller than atoms and carry a negative smaller than atoms and carry a negative chargecharge

The mass of the electron is 1/1836The mass of the electron is 1/1836thth the mass the mass of a hydrogen atomof a hydrogen atom


Rutherford’s ExperimentRutherford’s Experiment

Lead Box

RadioactiveSample

GoldFoil

FluorescentScreen

Alpha ParticlesStriking Screen


Conclusions from Rutherford’s Conclusions from Rutherford’s ExperimentExperiment

Atom mostly empty space Atom mostly empty space

– because most particles went throughbecause most particles went through

Atom contains a dense particle that was small Atom contains a dense particle that was small in volume compared to the atom but large in in volume compared to the atom but large in mass mass

– because of the few particles that bounced backbecause of the few particles that bounced back

This dense particle was positively chargedThis dense particle was positively charged

– because of the large deflections of some of the because of the large deflections of some of the particlesparticles

1212

Rutherford’s Interpretation – Rutherford’s Interpretation – the Nuclear Modelthe Nuclear Model

1)1) Atom contains a tiny dense center called the Atom contains a tiny dense center called the nucleusnucleus

2)2) The nucleus has essentially the entire mass The nucleus has essentially the entire mass of the atomof the atom

– the electrons weigh so little they give practically the electrons weigh so little they give practically no mass to the atomno mass to the atom

3)3) The nucleus is positively charged The nucleus is positively charged – the amount of positive charge balances the the amount of positive charge balances the

negative charge of the electronsnegative charge of the electrons

4)4) The electrons move around in the empty The electrons move around in the empty space of the atom surrounding the nucleus space of the atom surrounding the nucleus


The Modern AtomThe Modern Atom

Atoms are composed Atoms are composed of three particles - of three particles - protonsprotons, , neutronsneutrons and and electronselectrons

The The nucleusnucleus contains contains protons and neutronsprotons and neutrons

The electrons move The electrons move outside the nucleusoutside the nucleus

Neutral atom has same Neutral atom has same # protons and # protons and electrons.electrons.


+

+

The Nuclear Atom:The Nuclear Atom:

protonsprotons

neutronsneutrons

-

NucleusNucleus

electronselectrons

-


Subatomic Particles:Subatomic Particles:

neutrons (n)neutrons (n)

protons (p)protons (p)

electrons (e)electrons (e)

Charge?Charge? Location?Location?



00 nucleus nucleus

+1+1 nucleus nucleus

-1-1 outside outside

neutronneutron

protonproton

electronelectron

Charge?Charge? Location?Location?


11

11

00 (1/1837) (1/1837)

neutronneutron

protonproton

electronelectron

Mass (amu)Mass (amu)



ElementsElements

Each element has a unique number of Each element has a unique number of protons in its nucleusprotons in its nucleus

Number of protons in the nucleus of an atom Number of protons in the nucleus of an atom is called the is called the atomic numberatomic number– the elements are arranged on the Periodic the elements are arranged on the Periodic

Table in order of their atomic numbersTable in order of their atomic numbers

Each element has a unique name and Each element has a unique name and symbolsymbol– symbol either one or two letterssymbol either one or two letters

one capital letter or one capital letter + one one capital letter or one capital letter + one lower caselower case


How many?How many?

protons = depends on elementprotons = depends on element

neutrons = variable for each neutrons = variable for each elementelement

electrons = same as protons electrons = same as protons


atomic numberatomic number - -

The number of protons in one atom; The number of protons in one atom; each element has a different atomic each element has a different atomic numbernumber

The number on top of the element The number on top of the element symbol in the periodic tablesymbol in the periodic table


The Periodic Table of ElementsThe Periodic Table of Elements


ReviewReviewWhat is the atomic number of boron, B?What is the atomic number of boron, B?What is the atomic mass of silicon, Si?What is the atomic mass of silicon, Si?How many protons does a chlorine atom have?How many protons does a chlorine atom have?How many electrons does a neutral neon atom How many electrons does a neutral neon atom have? have? Will an atom with 6 protons, 6 neutrons and 6 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral?electrons be electrically neutral?Will an atom with 27 protons, 32 neutrons and Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? 27 electrons be electrically neutral? Will a Na atom with 10 electrons be electrically Will a Na atom with 10 electrons be electrically neutral?neutral?


ReviewReviewWhat is the atomic number of boron, B? What is the atomic number of boron, B? 55What is the atomic mass of silicon, Si? What is the atomic mass of silicon, Si? 28.09 28.09 amuamuHow many protons does a chlorine atom have? How many protons does a chlorine atom have? 1717How many electrons does a neutral neon atom How many electrons does a neutral neon atom have? have? 1010Will an atom with 6 protons, 6 neutrons and 6 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? electrons be electrically neutral? YesYesWill an atom with 27 protons, 32 neutrons and Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? 27 electrons be electrically neutral? YesYesWill a Na atom with 10 electrons be electrically Will a Na atom with 10 electrons be electrically neutral? neutral? NoNo

Three Types of ElementsThree Types of Elements

= Metal

= Metalloid

= Nonmetal


MetalsMetals

Solids at room temperature, Solids at room temperature, except Hgexcept HgShinyShinyConduct heat, electricityConduct heat, electricityMalleable: can be shapedMalleable: can be shapedDuctile = drawn or pulled into Ductile = drawn or pulled into wireswiresLose electrons and form cations Lose electrons and form cations (+ charge) in reactions(+ charge) in reactionsAbout 75% of the elements are About 75% of the elements are metalsmetals


NonmetalsNonmetals

Found in all 3 statesFound in all 3 states

Poor conductors of heat & Poor conductors of heat & electricityelectricity

Solids are brittleSolids are brittle

Gain electrons in reactions Gain electrons in reactions to become anions (- charge)to become anions (- charge)Only a few on the right of Only a few on the right of periodic tableperiodic table


MetalloidsMetalloids

Show some Show some properties of properties of metals and some metals and some of nonmetalsof nonmetals

Also known as Also known as semiconductorssemiconductors Properties of Silicon

shinyconducts electricity

does not conduct heat wellbrittle


The Modern Periodic TableThe Modern Periodic Table

Elements with similar chemical and Elements with similar chemical and physical properties are in same columnphysical properties are in same column

Columns are called Columns are called GroupsGroups or or FamiliesFamilies– designated by a number and letter at topdesignated by a number and letter at top

Rows are called Rows are called PeriodsPeriods

Each period shows the pattern of Each period shows the pattern of properties repeated in the next periodproperties repeated in the next period


The Modern Periodic Table The Modern Periodic Table

Main Group = Representative Elements Main Group = Representative Elements = ‘A’ groups= ‘A’ groupsTransition Elements = ‘B’ groupsTransition Elements = ‘B’ groups– all metalsall metals

Bottom rows = Inner Transition Bottom rows = Inner Transition Elements = Rare Earth ElementsElements = Rare Earth Elements– metalsmetals– really belong in Period 6 & 7really belong in Period 6 & 7


= Alkali Metals

= Alkali Earth Metals

= Noble Gases

= Halogens

= Lanthanides

= Actinides

= Transition Metals


Important Groups - HydrogenImportant Groups - Hydrogen

nonmetalnonmetal

colorless, diatomic gascolorless, diatomic gas– very low melting point & densityvery low melting point & density

reacts with nonmetals to form molecular reacts with nonmetals to form molecular compoundscompounds– HCl is acidic gasHCl is acidic gas

– HH22O is a liquidO is a liquid

reacts with metals to form hydridesreacts with metals to form hydrides– metal hydrides react with water to form Hmetal hydrides react with water to form H22

HX dissolves in water to form acidsHX dissolves in water to form acids

3232

Important Groups – IA, Alkali MetalsImportant Groups – IA, Alkali Metals

hydrogen usually placed hydrogen usually placed here, though it doesn’t here, though it doesn’t belongbelongsoft, low melting points,low soft, low melting points,low densitydensityvery reactive, never find very reactive, never find uncombined in natureuncombined in naturetend to form water soluble tend to form water soluble compoundscompoundsreact with water to form react with water to form basic (alkaline) solutions basic (alkaline) solutions and Hand H22 releasing a lot of releasing a lot of

heatheat

lithium

sodium

potassium

rubidium

cesium


Important Groups – IIA, Alkali Earth MetalsImportant Groups – IIA, Alkali Earth Metals

harder, higher melting, harder, higher melting, and denser than alkali and denser than alkali metals metals

reactive, but less than reactive, but less than corresponding alkali corresponding alkali metalmetal

form stable, insoluble form stable, insoluble oxides from which they oxides from which they are normally extractedare normally extracted

oxides are basic = oxides are basic = alkaline earthalkaline earth

magnesium

calcium

beryllium

strontium

barium


Important Groups – VIIA, HalogensImportant Groups – VIIA, Halogens

nonmetalsnonmetals

FF22 & Cl & Cl22 gases; Br gases; Br22 liquid; liquid;

II22 solid solid

all diatomicall diatomic

very reactivevery reactive

react with metals to form react with metals to form ionic compoundsionic compounds

HX all strong acids HX all strong acids except HFexcept HF

bromine

iodine

chlorine

fluorine


Important Groups – VIIIA, Noble GasesImportant Groups – VIIIA, Noble Gases

all gases at room all gases at room temperature, temperature, – very low melting and very low melting and

boiling pointsboiling points

very unreactive, very unreactive, practically inertpractically inert

very hard to remove very hard to remove electron from or give electron from or give an electron toan electron to


Charged Atoms = IonsCharged Atoms = Ions

Number of Number of protonsprotons (atomic #) identifies the (atomic #) identifies the element!element!

– all sodium atoms have 11 protons in the all sodium atoms have 11 protons in the nucleusnucleus

In chemical change, number of protons in In chemical change, number of protons in nucleus of atom doesn’t change!nucleus of atom doesn’t change!

Atoms can lose or gain electrons becoming Atoms can lose or gain electrons becoming electrically charged, these are called electrically charged, these are called ionsions


IonsIons

Atoms acquire a charge by gaining or Atoms acquire a charge by gaining or losing electronslosing electrons– not protons!!not protons!!

Ion Charge = Ion Charge = ## protonsprotons – – # electrons# electrons

ions with a ions with a + charge+ charge are called are called cationscations– more protons than electronsmore protons than electrons– form by losing electronsform by losing electrons

ions with a ions with a – charge– charge are called are called anionsanions– more electrons than protonsmore electrons than protons– form by gaining electronsform by gaining electrons


Atomic Structures of IonsAtomic Structures of Ions

MetalsMetals form form cationscationsFor each positive charge the ion has 1 less For each positive charge the ion has 1 less electron than the neutral atomelectron than the neutral atom– Na atom = 11 pNa atom = 11 p+ + and 11 eand 11 e--, Na, Na+ + ion = 11 pion = 11 p+ + and 10 eand 10 e--

– Ca atom = 20 pCa atom = 20 p+ + and 20 eand 20 e--, Ca, Ca2+2+ ion = 20 p ion = 20 p+ + and 18and 18 ee--

Cations are named the same as the metalCations are named the same as the metalsodiumsodium Na Na Na Na+ + + 1e+ 1e-- sodium ionsodium ioncalciumcalcium Ca Ca Ca Ca2+ 2+ + 2e+ 2e-- calcium ioncalcium ion

The charge on a cation can be determined from The charge on a cation can be determined from the Group number on the Periodic Tablethe Group number on the Periodic Table– Group 1A Group 1A +1, Group 2A +1, Group 2A +2, (Al, Ga, In) +2, (Al, Ga, In) +3 +3


Atomic Structures of IonsAtomic Structures of IonsNonmetalsNonmetals form form anionsanionsFor each negative charge the ion has 1 more For each negative charge the ion has 1 more electron than the neutral atomelectron than the neutral atom– F = 9 eF = 9 e--, F, F-- = 10 e = 10 e--

– P = 15 eP = 15 e--, P, P3-3- = 18 = 18 ee--

Anions are named by changing the ending of Anions are named by changing the ending of the name to the name to -ide-ide

fluorinefluorine F + 1eF + 1e-- F F-- fluoride ionfluoride ionoxygenoxygen O + 2eO + 2e-- O O-2-2 oxide ion oxide ion

Charge on an anion can be determined by Charge on an anion can be determined by subtracting 8 from the Group number on the subtracting 8 from the Group number on the Periodic TablePeriodic Table– Group 7A Group 7A 7- 8 = -1; Group 6A 7- 8 = -1; Group 6A 6 – 8 = -2 6 – 8 = -2

Example 4.5:Example 4.5:Determining the Number of Determining the Number of

Protons and Electrons in an IonProtons and Electrons in an Ion


Example:Example:

Find the number of protons and electrons in the CaFind the number of protons and electrons in the Ca2+2+ ion. ion.


Example:Example:Find the number of protons Find the number of protons and electrons in the Caand electrons in the Ca2+2+ ion ion

Write down the given quantity and its units. Write down the given quantity and its units.

Given: Given: Ca Ca2+2+



Write down the quantity to find and/or its units. Write down the quantity to find and/or its units.

Find: #p and #eFind: #p and #e

InformationInformation



Design a Solution Map. Design a Solution Map.

ion symbol

element

#p

atomic number




Find:Find: #p and #e#p and #e

#e and #e

Ion charge = #p - #e


Apply the Solution Map.Apply the Solution Map.– Determine the Name of the Element Determine the Name of the Element



Given: Given: CaCa2+2+


Solution Map: ion symbol Solution Map: ion symbol element element atomic number atomic number #p #p #e #e

Ca = calciumCa = calcium


Apply the Solution Map.Apply the Solution Map.– Determine the Atomic Number of the Element Determine the Atomic Number of the Element



Given: Given: CaCa2+2+ = calcium = calcium



Ca = calciumCa = calciumAtomic Number = 20Atomic Number = 20


Apply the Solution Map.Apply the Solution Map.– Determine the Number of Protons in an Atom of the Determine the Number of Protons in an Atom of the

Element Element



Given: Given: CaCa2+2+ = calcium, Z = 20 = calcium, Z = 20




#p = atomic number = 20#p = atomic number = 20


Apply the Solution Map.Apply the Solution Map.– Determine the Number of Electrons in an Ion of the Determine the Number of Electrons in an Ion of the

Element Element



Given: Given: CaCa2+2+ = calcium, Z = 20 = calcium, Z = 20

Find:Find: #p = 20 and #e#p = 20 and #e




Ion Charge = #p - #eIon Charge = #p - #e+2 = 20 - #e+2 = 20 - #e-18 = - #e-18 = - #e18 = #e18 = #e



Ion p+ e-

Cl-1

K+1

S-2

Sr+2



Ion p+ e-

Cl-1 17 18

K+1 19 18

S-2 16 18

Sr+2 38 36


Ion Charge & the Periodic TableIon Charge & the Periodic Table

Charge on an ion can often be Charge on an ion can often be determined from an element’s position determined from an element’s position on the Periodic Tableon the Periodic Table

MetalsMetals are always are always positivepositive ions, ions, nonmetalsnonmetals are are negativenegative ions ions

For many main group metals, the For many main group metals, the charge = the group numbercharge = the group number

For nonmetals, the charge = the group For nonmetals, the charge = the group number - 8number - 8


LiLi+1+1

NaNa+1+1

KK+1+1

RbRb+1+1

CsCs+1+1

BeBe++2

MgMg+2+2

CaCa+2+2

SrSr+2+2

BaBa+2+2

AlAl+3+3

GaGa+3+3

InIn+3+3

OO-2-2

SS-2-2

SeSe-2-2

TeTe-2-2

FF-1-1

ClCl-1-1

BrBr-1-1

II-1-1

NN-3-3

PP-3-3

AsAs-3-3

IA

IIA IIIA VIIAVIA

VA

Charges of Main Group IonsCharges of Main Group Ions


IsotopesIsotopes

IsotopesIsotopes = atoms of an element that have = atoms of an element that have same # of protons but different # of neutronssame # of protons but different # of neutrons

Isotopes of an element have different massesIsotopes of an element have different masses

isotopes are identified by their isotopes are identified by their

– mass numbersmass numbers = = protons + neutronsprotons + neutrons

All isotopes of an element are chemically All isotopes of an element are chemically identicalidentical

– undergo the exact same chemical undergo the exact same chemical reactionsreactions


• Atomic NumberNumber of protonsZ (symbol)

• Mass NumberProtons + NeutronsWhole numberA (symbol)

Abundance = relative amount found in a sample

IsotopesIsotopes


NeonNeon

9.25%9.25%222212121010Ne-22 Ne-22

0.27%0.27%212111111010Ne-21 Ne-21

90.48%90.48%202010101010Ne-20 Ne-20

Percent Percent Natural Natural AbundanceAbundance

A, Mass A, Mass NumberNumber

Number Number of of NeutronsNeutrons

Number Number of Protonsof ProtonsSymbolSymbol

Ne2010

Ne2110

Ne2210


Isotope SymbolsIsotope Symbols• Cl-35Cl-35 makes up about 75% of chlorine makes up about 75% of chlorine

atoms in nature, and atoms in nature, and Cl-37Cl-37 makes up the makes up the remaining 25%remaining 25%

• Average Average atomic massatomic mass of of ClCl = 35.45 amu = 35.45 amu• Cl-35Cl-35 has a mass number = 35, 17 protons has a mass number = 35, 17 protons

and 18 neutrons (35 - 17)and 18 neutrons (35 - 17)

X = Atomic SymbolA = mass numberZ = atomic number

AXZ

Cl3517

or or Cl-35Cl-35

Example 4.8:Example 4.8:Determining the Number of Determining the Number of Protons and Neutrons fromProtons and Neutrons from

Isotope SymbolsIsotope Symbols


Example:Example:

How many protons and neutrons in the chromium How many protons and neutrons in the chromium isotope isotope

Cr5224


Example:Example:How many protons and How many protons and neutrons in the chromium neutrons in the chromium isotope isotope

Write down the given quantity and its units. Write down the given quantity and its units.

Given: Given:

Cr5224

Cr5224


Write down the quantity to find and/or its units. Write down the quantity to find and/or its units.

Find:Find: #p and #n#p and #n


Given: Given:


Cr5224

Cr5224


Design a Solution Map. Design a Solution Map.

ion symbol

element

#p

atomic number


Given: Given:


#n


Cr5224

Cr5224

Mass # = #p + #n


Apply the Solution Map.Apply the Solution Map.– Determine the Name of the Element Determine the Name of the Element


Given: Given:


Solution Map: ion symbol Solution Map: ion symbol element element atomic number atomic number #p #p #n #n

Cr = chromiumCr = chromium


Cr5224

Cr5224


Apply the Solution Map.Apply the Solution Map.– Determine the Atomic Number of the Element Determine the Atomic Number of the Element


Given: Given: = calcium = calcium



Cr = chromiumCr = chromiumAtomic Number = 24Atomic Number = 24


Cr5224

Cr5224


Apply the Solution Map.Apply the Solution Map.– Determine the Number of Protons in an Atom of the Determine the Number of Protons in an Atom of the

Element Element








Cr5224

Cr5224


Apply the Solution Map.Apply the Solution Map.– Determine the Number of Neutrons in an Atom of the Determine the Number of Neutrons in an Atom of the

Element Element



Mass Number = #p + #nMass Number = #p + #n52 = 24 + #n52 = 24 + #n

28 = #n28 = #n






Cr5224

Cr5224


Practice - Complete the following tablePractice - Complete the following table

Atomic Number

Mass Number

Number of

Protons

Number of

Electrons

Number of

Neutrons Calcium-40

Carbon-13

Aluminum-27+3


Practice - Complete the following tablePractice - Complete the following table

Atomic Number

Mass Number

Number of

Protons

Number of

Electrons

Number of

Neutrons Calcium-40 20 40 20 20 20

Carbon-13 6 13 6 6 7

Aluminum-27+3 13 27 13 10 14


Mass Number is Not the SameMass Number is Not the Sameas Atomic Massas Atomic Mass

The atomic mass is an experimental The atomic mass is an experimental number determined from number determined from allall naturally naturally occurring isotopesoccurring isotopes

The mass number refers to the number The mass number refers to the number of protons + neutrons in one isotopeof protons + neutrons in one isotope– natural or man-madenatural or man-made

Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 4 Atoms and Elements.

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Transcript of Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 4 Atoms and Elements.