Chapter 2 Atoms, Molecules, and Ions - Yolaholcombslab.yolasite.com/resources/WCU Inorganic Chemistry... · Chapter 2 Atoms, Molecules, and Ions ... Cottleville, MO Chemistry, The

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Atoms,

Molecules,

and Ions

© 2009, Prentice-Hall, Inc.

Chapter 2

Atoms, Molecules,

and Ions

John D. Bookstaver

St. Charles Community College Cottleville, MO

Chemistry, The Central Science, 11th edition

Theodore L. Brown; H. Eugene LeMay, Jr.;

and Bruce E. Bursten

Atoms,

Molecules,

and Ions


Chapter 2 Problems

• Problems 1,11, 17, 23, 25, 31, 45, 49,

55, 59, 63

Atoms,

Molecules,

and Ions


Contents

• Early chemical discoveries

• Electrons and the Nuclear Atom

• Chemical Elements

• Atomic Masses

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Atoms,

Molecules,

and Ions


Early Discoveries

Lavoisier 1774 Law of conservation of mass

Proust 1799 Law of constant composition

Dalton 1803 Atomic Theory

Atoms,

Molecules,

and Ions


Law of Conservation of Mass

Lavoisier (1774)

In an ordinary chemical reaction, matter is

neither created nor destroyed.

The sum of the masses of the reactants

equals the sum of the masses of the

products.

Atoms,

Molecules,

and Ions


Conservation of Mass

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Atoms,

Molecules,

and Ions


Proust’s Law of Constant Composition 1799

Joseph Proust (1754–1826)

In forming carbon monoxide, 1.33 g of oxygen combines with 1.0 g of carbon. (16 g of O to 12g of C)

Law of Definite Proportions (Constant Composition): The

elemental composition of a pure substance never varies.

Atoms,

Molecules,

and Ions


Law of Multiple Proportions

In forming carbon monoxide, 1.33 g of oxygen combines with 1.0 g of carbon. (16 g of O to 12g of C)

In forming carbon dioxide, 2.66 g of oxygen combines with 1.0 g of carbon. (32 g of O to 12g of C)

Law of Multiple Proportions: the same elements can be

combined to form different compounds by combining the

elements in different proportions in the rato of small whole

numbers

Atoms,

Molecules,

and Ions


Atomic Theory of Matter

The theory that atoms

are the fundamental

building blocks of

matter reemerged in

the early 19th century,

championed by John

Dalton.

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Atoms,

Molecules,

and Ions


Dalton’s Atomic Theory

Postulates (4)

• proposed in 1803

Atoms,

Molecules,

and Ions



Postulate 1

• An element is composed of tiny

particles called atoms.

• All atoms of a given element show the

same chemical properties.

Atoms,

Molecules,

and Ions



Postulate 2

• Atoms of different elements have

different properties.

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Atoms,

Molecules,

and Ions



Postulate 3

• Compounds are formed when atoms of

two or more elements combine.

• In a given compound, the relative

number of atoms of each kind are

definite and constant.

Atoms,

Molecules,

and Ions



Postulate 4

• In an ordinary chemical reaction, no

atom of any element disappears or is

changed into an atom of another

element.

• Chemical reactions involve changing

the way in which the atoms are joined

together.

Atoms,

Molecules,

and Ions


Law of Conservation of Mass

The total mass of substances present at

the end of a chemical process is the

same as the mass of substances

present before the process took place.

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Atoms,

Molecules,

and Ions


Electrons and the Nuclear

Atom

Atoms,

Molecules,

and Ions


Behavior of charges

Atoms,

Molecules,

and Ions


Cathode ray tube

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Atoms,

Molecules,

and Ions


Properties of cathode rays

Atoms,

Molecules,

and Ions


The Electron

• Streams of negatively charged particles were

found to emanate from cathode tubes.

• J. J. Thompson is credited with their

discovery (1897).

Atoms,

Molecules,

and Ions


The Electron

Thompson measured the charge/mass ratio

of the electron to be 1.76 108 coulombs/g.

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Atoms,

Molecules,

and Ions


Millikan Oil Drop Experiment

Once the charge/mass

ratio of the electron

was known,

determination of either

the charge or the mass

of an electron would

yield the other.

Atoms,

Molecules,

and Ions


Millikan Oil Drop Experiment

Robert Millikan

(University of Chicago)

determined the charge

on the electron in

1909.

Atoms,

Molecules,

and Ions


Millikin’s Oil Drop

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Atoms,

Molecules,

and Ions


Radioactivity

• Radioactivity is the spontaneous

emission of radiation by an atom.

• It was first observed by Henri

Becquerel.

• Marie and Pierre Curie also studied it.

Atoms,

Molecules,

and Ions


Radioactivity

• Three types of radiation were discovered by

Ernest Rutherford:

particles

particles

rays

Atoms,

Molecules,

and Ions


Radioactivity

Radioactivity is the spontaneous emission of radiation

from a substance.

X-rays and -rays are high-energy light.

-particles are a stream of helium nuclei, He2+.

-particles are a stream of high speed electrons

that originate in the nucleus.

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Atoms,

Molecules,

and Ions


Alpha Radiation

• composed of 2 protons and 2 neutrons

• thus, helium-4 nucleus

• +2 charge

• mass of 4 amu

• creates element with atomic number 2

lower

Atoms,

Molecules,

and Ions


Beta Radiation

• composed of a high energy electron

which was ejected from the nucleus

• “neutron” converted to “proton”

• very little mass

• -1 charge

• creates element with atomic number 1

higher

Atoms,

Molecules,

and Ions


Gamma Radiation

• nucleus has energy levels

• energy released from nucleus as the

nucleus changes from higher to lower

energy levels

• no mass

• no charge

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Atoms,

Molecules,

and Ions


The Atom, circa 1900

• The prevailing theory

was that of the “plum

pudding” model, put

forward by Thompson.

• It featured a positive

sphere of matter with

negative electrons

imbedded in it.

Atoms,

Molecules,

and Ions


Discovery of the Nucleus

Ernest Rutherford

shot particles at a

thin sheet of gold foil

and observed the

pattern of scatter of

the particles.

Atoms,

Molecules,

and Ions


The Nuclear Atom

Since some particles

were deflected at

large angles,

Thompson’s model

could not be correct.

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Atoms,

Molecules,

and Ions


The Nuclear Atom

• Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom.

• Most of the volume of the atom is empty space.

Atoms,

Molecules,

and Ions


Other Subatomic Particles

• Protons were discovered by Rutherford

in 1919.

• Neutrons were discovered by James

Chadwick in 1932.

Atoms,

Molecules,

and Ions


Subatomic Particles

• Protons and electrons are the only particles that

have a charge.

• Protons and neutrons have essentially the same

mass.

• The mass of an electron is so small we ignore it.

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Atoms,

Molecules,

and Ions


ATOM COMPOSITION

•protons and neutrons in

the nucleus.

•the number of electrons is equal to the

number of protons.

•electrons in space around the nucleus.

•extremely small. One teaspoon of water has

3 times as many atoms as the Atlantic Ocean

has teaspoons of water.

The atom is mostly

empty space

Atoms,

Molecules,

and Ions


Symbols of Elements

Elements are symbolized by one or two

letters.

Atoms,

Molecules,

and Ions


Atomic Number

All atoms of the same element have the same

number of protons:

The atomic number (Z)

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Atoms,

Molecules,

and Ions


Atomic Mass

The mass of an atom in atomic mass units

(amu) is the total number of protons and

neutrons in the atom.

Atoms,

Molecules,

and Ions


Isotopes

• Isotopes are atoms of the same element with

different masses.

• Isotopes have different numbers of neutrons.

11

6 C 12

6 C 13

6 C 14

6 C

Atoms,

Molecules,

and Ions


Atomic Weight (Mass)

• This tells us the mass of one atom of an

element relative to one atom of another

element.

• OR — the mass of 1000 atoms of one

relative to 1000 atoms of another.

• For example, an O atom is approximately

16 times heavier than an H atom.

• Define one element as the standard

against which all others are measured

• Standard = carbon

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Atoms,

Molecules,

and Ions


Masses of Atoms

Carbon-12 Scale

The Masses of the atoms of all elements

is compared to that of Carbon-12.

Carbon-12 is assigned a mass of 12.0000

amu.

Atoms,

Molecules,

and Ions


Mass Number, A • C atom with 6 protons and 6 neutrons is

the mass standard

• = 12 atomic mass units (u)

• Mass Number (A) = # protons + #

neutrons

• A boron atom can have

A = 5 p + 5 n = 10 u

A

Z

10

5B

Atoms,

Molecules,

and Ions


Isotopes

• Atoms of the same element (same Z) but

different mass number (A).

• Boron-10 has 5 p and 5 n: 105B

• Boron-11 has 5 p and 6 n: 115B

10B

11B

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Atoms,

Molecules,

and Ions


Atomic Mass

Atomic and

molecular masses

can be measured

with great accuracy

with a mass

spectrometer.

Atoms,

Molecules,

and Ions


Masses of Isotopes determined with a mass

spectrometer

Atoms,

Molecules,

and Ions


Average Mass

• Because in the real world we use large

amounts of atoms and molecules, we

use average masses in calculations.

• Average mass is calculated from the

isotopes of an element weighted by

their relative abundances.

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Atoms,

Molecules,

and Ions


Isotopes

• Because of the existence of isotopes, the

mass of a collection of atoms has an

average value.

• Average mass = ATOMIC WEIGHT

• Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth.

• For boron atomic weight

= 0.199 (10.0 u) + 0.801 (11.0 u) = 10.8 u

10B

11B

Atoms,

Molecules,

and Ions


Isotopes & Atomic Weight

• Because of the existence of isotopes, the

mass of a collection of atoms has an

average value.

• 6Li = 7.5% abundant and 7Li = 92.5%

• Atomic weight of Li = _________

• 28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10%

• Atomic weight of Si = ___________

Atoms,

Molecules,

and Ions


The Periodic Table

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Atoms,

Molecules,

and Ions


During the nineteenth century, chemists began to categorize the elements according to similarities

in their physical and chemical properties. The end result of these studies was our modern

periodic table.

Atoms,

Molecules,

and Ions


During the nineteenth century, chemists began to categorize the elements according to similarities

in their physical and chemical properties. The end result of these studies was our modern

periodic table.

Atoms,

Molecules,

and Ions


Dmitri Mendeleev

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

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Atoms,

Molecules,

and Ions


Modern Periodic Table

• It is a systematic

catalog of the

elements.

• Elements are

arranged in order

of atomic number.

Atoms,

Molecules,

and Ions


Periodic Law

Atoms,

Molecules,

and Ions


Periodicity

When one looks at the chemical properties of

elements, one notices a repeating pattern of

reactivities.

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Atoms,

Molecules,

and Ions


Periodic Table

• The rows on the

periodic chart are

periods.

• Columns are groups.

• Elements in the same

group have similar

chemical properties.

Atoms,

Molecules,

and Ions


Groups

These five groups are known by their names.

Atoms,

Molecules,

and Ions


Periodic Table

Nonmetals are

on the right

side of the

periodic table

(with the

exception of

H).

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Atoms,

Molecules,

and Ions


Periodic Table

Metalloids

border the

stair-step line

(with the

exception of

Al, Po, and

At).

Atoms,

Molecules,

and Ions


Periodic Table

Metals are

on the left

side of the

chart.

Atoms,

Molecules,

and Ions


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 chart.

– Anions are negative and are formed by elements

on the right side of the periodic chart.

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Atoms,

Molecules,

and Ions


Ionic Bonds

Ionic compounds (such as NaCl) are

generally formed between metals and

nonmetals.

Atoms,

Molecules,

and Ions


PREDICTING ION CHARGES

In general

• metals (Mg) lose electrons ---> cations

• nonmetals (F) gain electrons ---> anions

Atoms,

Molecules,

and Ions


Charges on Common Ions

+3

-4 -1 -2 -3 +1

+2

By losing or gaining e-, atom has same

number of e-’s as nearest Group 8A atom.

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Atoms,

Molecules,

and Ions


Predicting Charges on Monatomic Ions

Atoms,

Molecules,

and Ions


Rules for Oxidation States

1. The oxidation state (OS) of an individual atom in a free element is 0.

2. The total of the OS in all atoms in:

i. Neutral species is 0.

ii. Ionic species is equal to the charge on the ion.

3. In their compounds, the alkali metals and the alkaline earths have OS of +1 and +2 respectively.

4. In compounds the OS of fluorine is always –1

Atoms,

Molecules,

and Ions


Rules for Oxidation States

5. In compounds, the OS of hydrogen is usually +1

6. In compounds, the OS of oxygen is usually –2.

7. In binary (two-element) compounds with metals:

i. Halogens have OS of –1,

ii. Group 16 have OS of –2 and

iii. Group 15 have OS of –3.

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Atoms,

Molecules,

and Ions


What is the oxidation state of the underlined element in each

of the following? a) P4; b) Al2O3; c) MnO4-; d) NaH

a) P4 is an element. P OS = 0

b) Al2O3: O is –2. O3 is –6. Since (+6)/2=(+3), Al OS = +3.

c) MnO4-: net OS = -1, O4 is –8. Mn OS = +7.

d) NaH: net OS = 0, rule 3 beats rule 5, Na OS = +1 and

H OS = -1.

Assigning Oxidation States

Atoms,

Molecules,

and Ions


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.

Atoms,

Molecules,

and Ions


Common Cations

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Atoms,

Molecules,

and Ions


Common Anions

Atoms,

Molecules,

and Ions


Naming Compounds

Trivial names are used for common compounds.

H2O (water) NH3 (ammonia)

A systematic method of naming compounds is

known as a system of nomenclature.

Organic compounds

Inorganic compounds

Atoms,

Molecules,

and Ions


Inorganic Compounds:

Inorganic Chemistry

• field of chemistry in which are studied

the chemical reactions and properties of

all the chemical elements and their

compounds, with the exception of the

hydrocarbons (compounds composed of

carbon and hydrogen) and their

derivatives.

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Atoms,

Molecules,

and Ions


Inorganic Nomenclature:

Ionic Compounds (metal-

nonmetal)

• Write the name of the cation.

• 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.

• If the cation can have more than one

possible charge, write the charge as a

Roman numeral in parentheses.

Atoms,

Molecules,

and Ions


Inorganic Nomenclature

Binary Compounds of Metals and Nonmetals

NaCl = sodium chloride

name is unchanged “ide” ending electrically neutral

MgI2 = magnesium iodide

Al2O3 = aluminum oxide

Na2S = sodium sulfide

Atoms,

Molecules,

and Ions


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Atoms,

Molecules,

and Ions


Polyatomic Ions

Polyatomic ions are very common.

Here are a few:

ammonium ion NH4+ acetate ion C2H3O2

-

carbonate ion CO32- hydrogen carbonate HCO3

-

hypochlorite ClO- phosphate PO43-

chlorite ClO2- hydrogen phosphate HPO4

2-

chlorate ClO3- sulfate SO4

2-

perchlorate ClO4- hydrogensulfate HSO4

-

Atoms,

Molecules,

and Ions


Chemical Formulas of Molecular

Elements and Compounds The subscript to the right

of the symbol of an

element tells the number

of atoms of that element

in one molecule of the

compound.

Atoms,

Molecules,

and Ions


Chemical Formulas

Molecular compounds

are composed of

molecules and almost

always contain only

nonmetals.

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Atoms,

Molecules,

and Ions


Diatomic Molecules

These seven elements occur naturally as

molecules containing two atoms.

Atoms,

Molecules,

and Ions


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.

Atoms,

Molecules,

and Ions


Types of Formulas

• Structural formulas show the

order in which atoms are

bonded.

• Perspective drawings also

show the three-dimensional

array of atoms in a

compound.

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Atoms,

Molecules,

and Ions


Binary Compounds of Two

Non-metals Molecular compounds

usually write the positive OS element first.

HCl hydrogen chloride

mono 1 penta 5

di 2 hexa 6

tri 3 hepta 7

tetra 4 octa 8

Some pairs form more than one compound

Atoms,

Molecules,

and Ions


Nomenclature of Binary

Compounds

• The less electronegative atom is usually listed first.

• A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however.)

Atoms,

Molecules,

and Ions



Compounds

• The ending on the more

electronegative element is

changed to -ide.

– CO2: carbon dioxide

– CCl4: carbon tetrachloride

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Atoms,

Molecules,

and Ions



Compounds

If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one:

N2O5: dinitrogen pentoxide

Atoms,

Molecules,

and Ions


Atoms,

Molecules,

and Ions


Binary Acids

Emphasize the fact that a molecule is an acid by altering the name.

HCl hydrogen chloride hydrochloric acid

HF hydrogen fluoride hydrofluoric acid

Acids produce H+ when dissolved in water.

They are compounds that ionize in water.

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Atoms,

Molecules,

and Ions


Patterns in Oxyanion Nomenclature

• When there are two oxyanions involving

the same element:

– The one with fewer oxygens ends in -ite.

• NO2− : nitrite; SO3

2− : sulfite

– The one with more oxygens ends in -ate.

• NO3− : nitrate; SO4

2− : sulfate

Atoms,

Molecules,

and Ions


Patterns in Oxyanion

Nomenclature

• The one with the second fewest oxygens ends in -ite.

– ClO2− : chlorite

• The one with the second most oxygens ends in -ate.

– ClO3− : chlorate

Atoms,

Molecules,

and Ions


Patterns in Oxyanion Nomenclature

• The one with the fewest oxygens has the prefix hypo-

and ends in -ite.

– ClO− : hypochlorite

• The one with the most oxygens has the prefix per- and

ends in -ate.

– ClO4− : perchlorate

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Atoms,

Molecules,

and Ions


Acid Nomenclature

• If the anion in the acid

ends in -ide, change

the ending to -ic acid

and add the prefix

hydro- .

– HCl: hydrochloric acid

– HBr: hydrobromic acid

– HI: hydroiodic acid

Atoms,

Molecules,

and Ions


Acid Nomenclature


ends in -ite, change

the ending to -ous

acid.

– HClO: hypochlorous

acid

– HClO2: chlorous acid

Atoms,

Molecules,

and Ions


Acid Nomenclature


ends in -ate, change

the ending to -ic acid.

– HClO3: chloric acid

– HClO4: perchloric acid

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Atoms,

Molecules,

and Ions


Atoms,

Molecules,

and Ions


Organic Compounds

Organic Chemistry

• branch of chemistry in which carbon

compounds and their reactions are

studied.

• the chemistry of carbon-hydrogen

compounds

Atoms,

Molecules,

and Ions


Naming Organic Compounds

Organic compounds abound in nature

Fats, carbohydrates and proteins are foods.

Propane, gasoline, kerosene, oil.

Drugs and plastics

Carbon atoms form chains and rings and act as

the framework of molecules.

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Atoms,

Molecules,

and Ions


Nomenclature of Organic

Compounds

• Organic chemistry has its own system of

nomenclature.

Atoms,

Molecules,

and Ions



Compounds

The simplest hydrocarbons (compounds

containing only carbon and hydrogen) are

alkanes.

Atoms,

Molecules,

and Ions



Compounds

The first part of the names above correspond

to the number of carbons (meth- = 1, eth- = 2,

prop- = 3, etc.).

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Atoms,

Molecules,

and Ions


Atoms,

Molecules,

and Ions


Alkanes - CnH2n+2

• methane - CH4

• ethane - C2H6

• propane - C3H8

• butanes - C4H10

• pentanes - C5H12

• hexanes - C6H14

• heptanes - C7H16

• octanes - C8H18

• nonanes - C9H20

• decanes - C10H22

Atoms,

Molecules,

and Ions


Visualizations of some

hydrocarbons

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Atoms,

Molecules,

and Ions



Compounds

• When a hydrogen in an alkane is replaced with

something else (a functional group, like -OH in

the compounds above), the name is derived from

the name of the alkane.

• The ending denotes the type of compound.

– An alcohol ends in -ol.