Atoms, Elements, Molecules and Compounds

7/28/2019 Atoms, Elements, Molecules and Compounds

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Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e

Topic 1:

Atoms,Elements,

Molecules andCompounds

Ms. Amira Raihana Adnan

Chemistry Unit, CFGS,

Universiti Tenaga Nasional (UNITEN).

1


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Law of Conservation of Mass

2

Antoine Lavoisier

1743-1794

Tro: Chemistry: A Molecular Approach, 2/e

Total mass of the materialsyou have before thereaction must equal the

total mass of the materialsyou have at the endtotal mass of reactants =

total mass of products


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Reaction of Sodium with Chlorine to

Make Sodium Chloride

3

7.7 g Na + 11.9 g Cl2 19.6 g NaCl



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4

Daltons Atomic Theory

Law of Multiple Proportions


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Daltons Atomic Theory

5Tro: Chemistry: A Molecular Approach, 2/e

1. Each element is composed of tiny, indestructibleparticles called atoms

2. All atoms of a given element have the samemass and other properties that distinguish themfrom atoms of other elements

3. Atoms combine in simple, whole-number ratios

to form molecules ofcompounds

4. In a chemical reaction, atoms of one elementcannot change into atoms of another element


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Practice Decide if each statement is correct

according to Daltons model of the atom

Copper atoms can combine with zinc atoms tomake gold atoms

Water is composed of many identicalmolecules that have one oxygen atom and two

hydrogen atoms



7/77Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e

J.J. Thomson

Measured the mass and charge of electronusing cathode ray tube



8/77Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e 8

Millikans Oil Drop Experiment


Measured mass of electron



Electrons

Electrons are tiny, negatively chargedparticles found in all atoms

The electron has a charge of1.60 x 1019 C

The electron has a mass of 9.1 x 1028 g




Thomsons Plum Pudding Atom

The structure of the atom containsmany negatively charged electrons

These electrons are held in theatom by their attraction for a

positively charged electric fieldwithin the atom

The mass of the atom is due to themass of the electrons within it




Predictions of the

Plum Pudding Atom

The mass of the atom is due to the mass ofthe electrons within it

electrons are the only particles in Plum Pudding

atoms, therefore the only source of mass

The atom is mostly empty spaceshould not have a bunch of negatively charged

particles near each other as they would repel




Rutherfords Interpretation

the Nuclear Model

1. The atom contains a tiny dense center calledthe nucleus

2. The nucleus has essentially the entire mass of

the atom

3. The nucleus is positively charged

4. The electrons are dispersed in the empty spaceof the atom surrounding the nucleus




Structure of the Nucleus Rutherford proposed that the nucleus

had a particle that had the sameamount of charge as an electron butopposite sign these particles arecalled protons

based on measurements of the nuclearcharge of the elements

protons are subatomic particles foundin the nucleus with a charge = +1.60 x

1019

C and a mass = 1.67262 x 1024

g Because protons and electrons have

the same amount of charge, for the atomto be neutral there must be equal

num bers of protons and elect rons14Tro: Chemistry: A Molecular Approach, 2/e



Neutron

Neutrons are subatomic particles with a mass= 1.67493 x 1024 g and no charge, and are

found in the nucleus

1 amu

slightly heavier than a proton

no charge




Elements

Each element has a unique number of protonsin its nucleus

The number of protons in the nucleus of anatom is called the atomic numberthe elements are arranged on the Periodic Table in

order of their atomic numbers

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

one capital letter or one capital letter and one

lowercase letter




Isotopes

Element have the same number of protons butdifferent masses and numbers of neutrons

Identified by theirmass numbers




Neon

9.25%221210Ne-22 or

0.27%211110Ne-21 or

90.48%201010Ne-20 or

Percent

Natural

Abundance

A, Mass

Number

Number of

Neutrons

Number of

ProtonsSymbol

Ne2010

Ne2110

Ne2210


E l 2 3b H t l t



Example 2.3b: How many protons, electrons,

and neutrons are in an atom of ?

for most stable isotopes, n0 p+Check:

Z = 24 = # p+

# e = # p+ = 24

Solution:

in neutral atom, # p+ = # e-

mass number = # p+ + # n0

Conceptual

Plan:

Relationships:

therefore A = 52, Z = 24

# p+, # e, # n0

Given:

Find:

Cr5224

symbol atomic

number# p+ # e

symbol atomic & mass

numbers

# n0

A = Z + # n0

52 = 24 + # n0

28 = # n0

21

Cr5224



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Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e 22

Charged Atoms

When atoms gain or lose electrons, theyacquire a charge

Charged atoms or groups of atoms arecalled ions

When atoms gain electrons, they becomenegatively charged ions, called anions

When atoms lose electrons, they becomepositively charged ions, called cations



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Ions and Compounds

Ions behave much differently than theneutral atoms

e.g., the metal sodium, made of neutral Na

atoms, is highly reactive and quite unstable;

however, the sodium cations, Na+, found in table

salt are very nonreactive and stable

Because materials such as table salt areneutral, there must be equal amounts ofcharge from cations and anions in them



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Atomic Structures of Ions

Nonmetals form anions For each negative charge, the ion has

one more electron than the neutral atom

F = 9 p+ and 9 e, F = 9 p+ and 10 e

P = 15 p+ and 15 e, P3 = 15 p+ and 18e

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

fluorine F + 1e F fluoride ionoxygen O + 2e O2 oxide ion



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Atomic Structures of Ions

Metals form cations For each positive charge, the ion has one less

electron than the neutral atom

Na atom = 11 p+ and 11 e, Na+ ion = 11 p+ and 10 eCa atom = 20 p+ and 20 e, Ca2+ ion = 20 p+ and 18e

Cations are named the same as the metal

sodium Na

Na+

+ 1e

sodium ioncalcium Ca Ca2+ + 2e calcium ion



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Practice Complete the table

26

3Al



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Practice Complete the table

27

2Mg

2S

Br

3Al



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About of the elements are classified as metals.

They have a reflective surface, conduct heat andelectricity better than other elements, and are

malleable and ductile

Most of the remaining elements are classified as

nonmetals. Their solids have a non-reflectivesurface, do not conduct heat and electricity well,

and are brittle.

A few elements are classified as metalloids.

Their solids have some characteristics of metalsand some of nonmetals.



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The Modern Periodic Table

Elements with similar chemical andphysical properties are in the same column

Columns are called Groups orFamiliesdesignated by a number and letter at top

Rows are called Periods

Each period shows the pattern ofproperties repeated in the next period



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Copyright 2011 Pearson Education, Inc.Tro: Chemistry: A Molecular Approach, 2/e 30Tro: Chemistry: A Molecular Approach, 2/e


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Practice What is the charge on each of

the following ions?

32

potassium cation

sulfide anion

calcium cation bromide anion

aluminum cation

K+

S2

Ca2+

Br

Al

3+



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Mass Spectrometry

Masses and abundances of isotopes are measured with amass spectrometer

Atoms or molecules are ionized, then accelerated down atube

some molecules are broken into fragments during the ionizationprocess

these fragments can be used to help determine the structure of the

molecule

Their path is bent by a magnetic field, separating them bymass

similar to Thomsons cathode ray experiment



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Mass Spectrometer



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Mass Spectrum

A mass spectrum is agraph that gives therelative mass and relativeabundance of each

particle Relative mass of the

particle is plotted in thex-axis

Relative abundance of theparticle is plotted in the y-axis


Example 2.5: If copper is 69.17% Cu-63 with a mass of 62.9396


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Example 2.5: If copper is 69.17% Cu 63 with a mass of 62.9396amu and the rest Cu-65 with a mass of 64.9278 amu, find

coppers atomic mass

the average is between the two masses,

closer to the major isotope

Check:

Solution:

Conceptual

Plan:

Relationships:

Cu-63 = 69.17%, 62.9396 amu

Cu-65 = 100-69.17%, 64.9278 amuatomic mass, amu

Given:

Find:

isotope masses,

isotope fractionsavg. atomic mass


Practice Ga 69 with mass 68 9256 amu and


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PracticeGa-69 with mass 68.9256 amu and

abundance of 60.11% and Ga-71 with mass 70.9247

amu and abundance of 39.89%. Calculate the

atomic mass of gallium.



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Chemical Bonds

Chemical bonds are forces of attractionbetween atoms

The bonding attraction comes fromattractions between protons and electrons



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Bond Types Two general types: ionic and covalent

Ionic bondsresult when electrons have beentransferred between atoms, resulting in oppositelycharged ions that attract each othergenerally found when metal atoms bond to nonmetal

atoms Covalent bondsresult when two atoms share

some of their electronsgenerally found when nonmetal atoms bond together



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Chemical Formula


To represent the compounds


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Types of Formula:

Empirical Formula

An empirical formulagives the relative numberof atoms of each elementin a compound

The empirical formula for the ionic compound fluorspar is CaCl2.

This means that there is 1 Ca

2+

ion for every 2 Cl

ions in thecompound.



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Types of Formula:

Molecular Formula

Amolecular formulagives the actual numberof atoms of each element in a molecule of a

compound

The molecular formula is C2H2O4. This does not tell you that the

carbon atoms are attached together in the center of the molecule,

and that each is attached to two oxygen atoms.



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Types of Formula:

Structural Formula

A structural formulauses lines to representcovalent bonds and shows how atoms in a

molecule are connected or bonded to each other

single line = two shared electrons, a single covalent bond

double line = four shared electrons, a double covalent bond

triple line = six shared electrons, a triple covalent bond



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Structural Formula of Oxalic Acid

O C

O

C

O

O HH



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Representing Compounds:

Molecular Models

Models show the 3-dimensional structurealong with all the other information given in the

structural formula

Ball-and-stick models use balls to representthe atoms and sticks to represent the

attachments between them

Space-filling models use interconnectedspheres to show the electron clouds of atoms

connecting together



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Models of Oxalic Acid

Ball and stickSpace filling



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Classifying Elements & Compounds


Atomic elements = elements whose particles aresingle atoms

Molecular elements = elements whose particlesare multi-atom molecules

Molecular compounds = compounds whoseparticles are molecules made of only nonmetals

Ionic compounds = compounds whose particlesare cations and anions


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Classify Each of the Following as Either an

Atomic Element, Molecular Element,

Molecular Compound, or Ionic Compound

Aluminum, Al

Aluminum chloride, AlCl3Chlorine, Cl2

Acetone, C3H6O

Carbon monoxide, COCobalt, Co

49

atomic element

ionic compoundmolecular element

molecular compound

molecular compoundatomic element



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Ionic Compounds

Compounds of metals with nonmetals aremade of ions

Have a 3-dimensional array of cations andanions made offormula units

Many contain polyatomic ionsseveral atoms attached together by covalent

bonds into one ion


E l 3 3 W i h f l f d


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Example 3.3: Write the formula of a compound

made from aluminum ions and oxide ions

1. Write the symbol for themetal cation and its charge

2. Write the symbol for thenonmetal anion and its

charge3. Charge (without sign)becomes subscript for other

ion

4. Reduce subscripts tosmallest whole number ratio

5. Check that the total chargeof the cations cancels the

total charge of the anions

Al3+ column 3A

O2 column 6A

Al+3 O2

Al2O3

Al = (2)(+3) = +6

O = (3)(2) = 6



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Practice What are the formulas for

compounds made from the following ions?

Potassium ion with a nitride ion

Calcium ion with a bromide ion

Aluminum ion with a sulfide ion



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K+ with N3 K3N

Ca2+ with Br CaBr2

Al3+

with S2

Al2S3


Naming Metal Cations


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Metals with variable

Chargesmetals whose ions

can have more than

one possible charge




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Metals with invariant chargemetals whose ions can only

have one possible charge


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Naming Monatomic Nonmetal Anion


To name anion, change ending on the elementname toide

1. KCl

2. MgBr2

3. Al2S3

potassium chloride

magnesium bromide

aluminum sulfide


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Practice Find the charge on the cation

1. TiCl4

2. CrO3

3. Fe3N2

4 Cl = 4, Ti = 4+

3 O = 6, Cr = 6+

2 N = 6, 3 Fe = 6+, Fe = 2+


Example: Naming binary ionic


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p g y

with variable charge metal

CuF2


1. Identify cation and anion

F = F because it is Group 7

Cu = Cu2+ to balance the two () charges from 2 F

2. Name the cationCu2+ = copper(II)

3. Name the anion

F = fluoride

4. Write the cation name first, then the anion name

copper(II) fluoride


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Name the following compounds

1. TiCl4

2. PbBr2

3. Fe2S3

titanium(IV) chloride

lead(II) bromide

iron(III) sulfide



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copper(II) ion with a nitride ion

iron(III) ion with a bromide ion

Cu

2+

with N

3

Cu3N2

Fe3+ with Br FeBr3



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Compounds Containing Polyatomic Ions


Polyatomic ions are single ions that containmore than one atom

Often identified by parentheses around ion informula

Name and charge of polyatomic ion do not change

Name any ionic compound by naming cation firstand then anion

P i di P tt f P l t i I


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Periodic Pattern of Polyatomic Ions

-ate groups



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Name the Following Compounds

1. NH4Cl

2. Ca(C2H3O2)2

3. Cu(NO3)2

ammonium chloride

calcium acetate

copper(II) nitrate


Example Writing formula for ionic


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Example Writing formula for ionic

compounds containing polyatomic ion

Iron(III) phosphate

1. Write the symbol for the

cation and its charge


anion and its charge

3. Charge (without sign)

becomes subscript for other

ion

4. Reduce subscripts to

smallest whole number ratio

5. Check that the total charge

of the cations cancels the


Fe3+

PO43

Fe3+ PO43 Fe3(PO4)3

Fe = (1)(3+) = +3

PO4= (1)(3) = 3

FePO4



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aluminum ion with a sulfate ion

chromium(II) with hydrogen carbonate

Al3+ with SO42 Al2(SO4)3

Cr2+ with HCO3 Cr(HCO3)2


Hydrates are ionic compounds containing a


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specific number of watersfor each formula unit

CoCl2

6H2

O = cobalt (II) chloride hexahydrate

CaSO4H2O = calcium sulfate hemihydrate

MgSO47H2O = magnesium sulfate heptahydrate

NiCl26H2O = nickel (II) chloride hexahydrate

Example: Naming binary molecular


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Example: Naming binary molecular

BF3


1. Name the first element

boron

2. Name the second element with anide

fluorine

fluoride3. Add a prefix to each name to indicate the subscript

monoboron, trifluoride

4. Write the first element with prefix, then the second

element with prefixa) drop prefix monofrom first element

boron trifluoride


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Name the Following

NO2

PCl5

I2F7

nitrogen dioxide

phosphorus pentachloride

diiodine heptafluoride


E l Bi M l l


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Example: Binary Molecular

dinitrogen pentoxide


Identify the symbols of the elements

nitrogen = N

oxide = oxygen = O Write the formula using prefix number for subscript

di = 2, penta = 5

N2O5


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Write Formulas for the Following

dinitrogen tetroxide

sulfur hexafluoride

diarsenic trisulfide

N2O4

SF6

As2S3


Example: Naming binary acids


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Example: Naming binary acids

HCl(aq)


1. Identify the anion

Cl = Cl, chloride because Group 7A

2. Name the anion with anicsuffix

Cl = chloride chloric

3. Add a hydro-prefix to the anion name

hydrochloric

4. Add the word acidto the endhydrochloric acid

E l N i id


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Example: Naming oxyacids

H2SO4(aq)



SO4 = SO42 = sulfate

2. If the anion hasatesuffix, change it toic. If the

anion hasi tesuffix, change it to -ousSO4

2 = sulfate sulfuric

3. Write the name of the anion followed by the wordacid

sulfuric acid

(kind of an exception, to make it sound nicer!)



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H2SO3(aq)



SO3 = SO32 = sulfite

2. If the anion hasatesuffix, change it toic. If the

anion hasi tesuffix, change it to -ousSO3

2 = sulfite sulfurous

3. Write the name of the anion followed by the wordacid

sulfurous acid


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Name the Following

H2S

HClO3

HNO2

hydrosulfuric acid

chloric acid

nitrous acid



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Writing Formulas for Acids

When name ends in acid, formulas starts with H

Write formulas as if ionic, even though it ismolecular

Hydro prefix means it is binary acid, no prefixmeans it is an oxyacid

For oxyacid, if ending is ic, polyatomic ion

ends in

ate; if ending is

ous, polyatomic ionends in ous


Example: Oxyacids


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Example: Oxyacids

sulfurous acid

1. Write the symbol for thecation and its charge


anion and its charge

3. Charge (without sign)becomes subscript for other

ion

4. Add (aq) to indicate

dissolved in water

5. Check that the total charge

of the cations cancels the


H+

SO32

H+ SO32 H2SO3

H = (2)(1+) = +2

SO3= (1)(2) = 2

H2SO3(aq)

in all acids thecation is H+

no hydro means

polyatomicion

-ous means -ite ion


P ti Wh t th f l f th


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Practice What are the formulas for the

following acids?

H+ with ClO2 HClO2

H+ with PO43 H3PO4

H+ with Br HBr

chlorous acid

phosphoric acid

hydrobromic acid

Atoms, Elements, Molecules and Compounds

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