atoms, molecules, and ions chapter 2 atoms, molecules, and ions kr chemistry, the central science,...

Atoms,Molecules,

and Ions

Chapter 2Atoms, Molecules,

and Ions

kr

Chemistry, The Central Science, 12th editionTheodore L. Brown; H. Eugene LeMay, Jr.;

and Bruce E. Bursten

Atoms,Molecules,

and Ions

Roadmap chapter 2:

• Basic material building blocks/things (electrons, neutrons, protons ) and electromagnetic radiation

• Basic material structures: atoms, ions, isotops, molecules , etc.

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

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© 2009, Prentice-Hall, Inc.

The Modern 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.

1 Angstrom = 0.1nm

Atoms,Molecules,


Other Subatomic Particles

• Protons were discovered by Rutherford in 1919.

• Neutrons were discovered by James Chadwick in 1932.

Atoms,Molecules,

and IonsPart 4 7

Subatomic

Particle

Mass

g

Mass

amu

Location

in atom

Charge Symbol

Proton 1.67

x 10-24

1 nucleus +1 p, p+, H+

Electron 0.0009

x 10-24

~0 empty space -1 e, e-

Neutron 1.67

x 10-24

1 nucleus 0 n, n0

Atoms,Molecules,


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.

1 amu = 1.66 10-24g

Atoms,Molecules,

and Ions

Atoms and elements

• Atoms of different elements have different number of protons

All atoms of an element have the same number of protons, but different numbers of electrons (ions) or neutrons (isotopes).

Atoms,Molecules,


Symbols of Elements

Elements are symbolized by one or two letters.

Atoms,Molecules,


Atomic Number

All atoms of the same element have the same number of protons:

The atomic number (Z)

Atoms,Molecules,


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,


Isotopes

• Isotopes are atoms of the same element with different masses.

• Isotopes have different numbers of neutrons.116C 12

6C13

6C14

6C

Atoms,Molecules,

and Ions

Neutrals vs. Ions

• Ions: positive are ca+ions

• Cation is missing electron(s)

• p>e

• Ne +

• Ions: negative are anions

• Anion has extra electrons

• p<e

• O2-

Atoms,Molecules,


Atomic Mass

Atomic and molecular masses can be measured with great accuracy with a mass spectrometer.

Atoms,Molecules,

and IonsPart 4 16

Mass Number is Not the Sameas Atomic Mass

• the atomic mass is an experimental number determined from all naturally occurring isotopes

• the mass number refers to the number of protons + neutrons in one isotopenatural or man-made

Atoms,Molecules,

and IonsPart 4 17

FYI: Calculating Atomic MassGallium has two naturally occurring isotopes: Ga-69 with mass 68.9256 amu and a natural abundance of 60.11% and Ga-71 with mass 70.9247 amu and a natural abundance of 39.89%. Calculate the atomic mass of gallium.

Solution: 1) Convert the percent natural abundance into decimal form.

Ga-69 0.6011Ga-71 0.3989

2) Determine the Formula to Use

Atomic Mass = (abundance1)∙(mass1) + (abundance2)∙(mass2) + ...3) Apply the Formula:

Atomic Mass = 0.6011 (68.9256 amu) + 0.3989 (70.9247 amu) = 69.72 amu

Atoms,Molecules,


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.

Atoms,Molecules,


Periodic Table as databankHave your own PT !!!

• It is a systematic catalog of the elements.

• Elements are arranged in order of atomic number.

• Find what data are in your PT for each element!!!!

Atoms,Molecules,

and Ions

PT

• Find what data are in your PT for each element!!!!

• What is the unit of the average mass?

• What is mole?

Atoms,Molecules,


Periodicity

When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

Atoms,Molecules,


Periodic Table

• The rows on the periodic chart are periods.

• Columns are groups.• Elements in the same

group have similar chemical properties.

Atoms,Molecules,


Groups

These five groups are known by their names.

Atoms,Molecules,


Periodic Table

Nonmetals are on the right side of the periodic table (with the exception of H).

Atoms,Molecules,


Periodic Table

Metalloids border the stair-step line (with the exception of Al, Po, and At).

Atoms,Molecules,


Periodic Table

Metals are on the left side of the chart.

Atoms,Molecules,

and Ions

Elements, Molecules, Compounds

• What is a molecule?

• What is N2?

• What is a compound?

• What is a molecular compound?

• What is ionic compound?

Atoms,Molecules,


Chemical FormulasThe 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,


Chemical FormulasMolecular compounds are composed of molecules and almost always contain only nonmetals.

Atoms,Molecules,


Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.

Atoms,Molecules,


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,


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.

Atoms,Molecules,


Ions –common charges

• 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.

Atoms,Molecules,


Ionic Bonds

Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

Atoms,Molecules,


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,


Common Cations

Atoms,Molecules,


Common Anions

Atoms,Molecules,


Inorganic Nomenclature

• 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,


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; SO42− : sulfate

Atoms,Molecules,



• 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,



• 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

Atoms,Molecules,


Acid Nomenclature

• If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- .HCl: hydrochloric acidHBr: hydrobromic acidHI: hydroiodic acid

Atoms,Molecules,


Acid Nomenclature

• If the anion in the acid ends in -ite, change the ending to -ous acid.HClO: hypochlorous

acidHClO2: chlorous acid

Atoms,Molecules,


Acid Nomenclature

• If the anion in the acid ends in -ate, change the ending to -ic acid.HClO3: chloric acid

HClO4: perchloric acid

Atoms,Molecules,


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,



• The ending on the more electronegative element is changed to -ide.

CO2: carbon dioxideCCl4: carbon tetrachloride

Atoms,Molecules,



• 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,


Nomenclature of Organic Compounds

• Organic chemistry is the study of carbon.• Organic chemistry has its own system of

nomenclature.

Atoms,Molecules,



The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes.

Atoms,Molecules,



The first part of the names above correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.).

Atoms,Molecules,



• 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.

Atoms,Molecules,

and Ions

Example :Determining the Number of

Protons and Electrons in an Ion

Atoms,Molecules,

and IonsPart 4 53

Example:• Find the number of protons and electrons in the Ca2+ ion.

Atoms,Molecules,

and IonsPart 4 54

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

• Write down the given quantity and its units.

Given: Ca2+

Atoms,Molecules,

and IonsPart 4 55


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

Find: #p and #e

Information

Given: Ca2+

Atoms,Molecules,

and IonsPart 4 56

• Design a Solution Map.

ion symbol

element

#p

atomic number


Information

Given: Ca2+

Find: #p and #e

#e#p and #e

Atoms,Molecules,

and IonsPart 4 57

• Apply the Solution Map.

Determine the Name of the Element


Information

Given: Ca2+

Find: #p and #e

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

Ca = calcium

Atoms,Molecules,

and IonsPart 4 58


Determine the Atomic Number of the Element


Information

Given: Ca2+ = calcium

Find: #p and #e


Ca = calciumAtomic Number = 20

Atoms,Molecules,

and IonsPart 4 59


Determine the Number of Protons in an Atom of the Element


Information

Given: Ca2+ = calcium, Z = 20

Find: #p and #e



#p = atomic number = 20

Atoms,Molecules,

and IonsPart 4 60


Determine the Number of Electrons in an Ion of the Element


Information

Given: Ca2+ = calcium, Z = 20

Find: #p = 20 and #e




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

Atoms,Molecules,

and IonsPart 4 61

Atomic Structures of Ions

Ion p+ e-

Cl-1

K+1

S-2

Sr+2

Atoms,Molecules,

and IonsPart 4 62

Atomic Structures of Ions

Ion p+ e-

Cl-1 17 18

K+1 19 18

S-2 16 18

Sr+2 38 36

Atoms,Molecules,

and IonsPart 4 63

Ion Charge & the Periodic Table

• the charge on an ion can often be determined from an elements position on the Periodic Table

• metals are always positive ions, nonmetals are negative ions

• for many main group metals, the charge = the group number

• for nonmetals, the charge = the group number - 8

Atoms,Molecules,

and IonsPart 4 64

Li+1

Na+1

K+1

Rb+1

Cs+1

Be+2

Mg+2

Ca+2

Sr+2

Ba+2

Al+3

Ga+3

In+3

O-2

S-2

Se-2

Te-2

F-1

Cl-1

Br-1

I-1

N-3

P-3

As-3

IA

IIA IIIA VIIAVIA

VA

Atoms,Molecules,

and IonsPart 4 65

Structure of the Nucleus• Soddy discovered that the same element

could have atoms with different masses, which he called isotopesthere are 2 isotopes of chlorine found in

nature, one that has a mass of about 35 amu and another that weighs about 37 amu

• The observed mass is a weighted average of the weights of all the naturally occurring atomsthe atomic mass of chlorine is 35.45 amu

Atoms,Molecules,

and IonsPart 4 66

Isotopes• all isotopes of an element are chemically

identicalundergo the exact same chemical reactions

• all isotopes of an element have the same number of protons

• isotopes of an element have different masses• isotopes of an element have different

numbers of neutrons• isotopes are identified by their mass

numbersprotons + neutrons

Atoms,Molecules,

and IonsPart 4 67

• Atomic NumberNumber of protonsZ

• Mass NumberProtons + NeutronsWhole numberA

Abundance = relative amount found in a sample

Isotopes

Atoms,Molecules,

and IonsPart 4 68

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

Atoms,Molecules,

and IonsPart 4 69

Isotopes• Cl-35 makes up about 75% of chlorine

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

• the average atomic mass of Cl is 35.45 amu

• Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17)

Atomic SymbolA = mass numberZ = atomic number

AXZ

= X-ACl35

17

Atoms,Molecules,

and Ions

Example:Determining the Number of Protons and Neutrons from

Isotope Symbols

Atoms,Molecules,

and IonsPart 4 71

Example:• How many protons and neutrons in the chromium isotope Cr52

24

Atoms,Molecules,

and IonsPart 4 72

Example:How many protons and neutrons in the chromium isotope

• Write down the given quantity and its units.

Given:

Cr5224

Cr5224

Atoms,Molecules,

and IonsPart 4 73

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

Find: #p and #n

Information

Given:

Example:How many protons and neutrons in the chromium isotope Cr52

24

Cr5224

Atoms,Molecules,

and IonsPart 4 74

• Design a Solution Map.

ion symbol

element

#p

atomic number

Information

Given:

Find: #p and #n

#n#p and #n


24

Cr5224

Atoms,Molecules,

and IonsPart 4 75


Determine the Name of the Element

Information

Given:

Find: #p and #n

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

Cr = chromium


24

Cr5224

Atoms,Molecules,

and IonsPart 4 76


Determine the Atomic Number of the Element

Information

Given: = calcium

Find: #p and #n


Cr = chromiumAtomic Number = 24


24

Cr5224

Atoms,Molecules,

and IonsPart 4 77


Determine the Number of Protons in an Atom of the Element



Information

Given: = calcium

Find: #p and #n



24

Cr5224

Atoms,Molecules,

and IonsPart 4 78


Determine the Number of Neutrons in an Atom of the Element



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

28 = #n

Information

Given: = calcium

Find: #p and #n



24

Cr5224

Atoms,Molecules,

and IonsPart 4 79

Practice - Complete the following table

Atomic Number

Mass Number

Number of

Protons

Number of

Electrons

Number of

Neutrons Calcium-40

Carbon-13

Aluminum-27+3

Atoms,Molecules,

and IonsPart 4 80

Practice - 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

atoms, molecules, and ions chapter 2 atoms, molecules, and ions kr chemistry, the central science,...

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