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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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
Symbols of Elements
Elements are symbolized by one or two letters.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Atomic Number
All atoms of the same element have the same number of protons:
The atomic number (Z)
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
Periodicity
When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
Groups
These five groups are known by their names.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Periodic Table
Nonmetals are on the right side of the periodic table (with the exception of H).
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Periodic Table
Metalloids border the stair-step line (with the exception of Al, Po, and At).
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
Chemical FormulasMolecular compounds are composed of molecules and almost always contain only nonmetals.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Diatomic Molecules
These seven elements occur naturally as molecules containing two atoms.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
Ionic Bonds
Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
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
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
Acid Nomenclature
• If the anion in the acid ends in -ite, change the ending to -ous acid.HClO: hypochlorous
acidHClO2: chlorous acid
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
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,
and Ions© 2009, Prentice-Hall, Inc.
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© 2009, Prentice-Hall, Inc.
Nomenclature of Binary Compounds
• The ending on the more electronegative element is changed to -ide.
CO2: carbon dioxideCCl4: carbon tetrachloride
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Nomenclature of Binary 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© 2009, Prentice-Hall, Inc.
Nomenclature of Organic Compounds
• Organic chemistry is the study of carbon.• Organic chemistry has its own system of
nomenclature.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Nomenclature of Organic Compounds
The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes.
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Nomenclature of Organic Compounds
The first part of the names above correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.).
Atoms,Molecules,
and Ions© 2009, Prentice-Hall, Inc.
Nomenclature of Organic 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.
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
Example:Find the number of protons and electrons in the Ca2+ ion
• 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
Example:Find the number of protons and electrons in the Ca2+ ion
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
Example:Find the number of protons and electrons in the Ca2+ ion
Information
Given: Ca2+
Find: #p and #e
Solution Map: ion symbol element atomic number #p #e
Ca = calcium
Atoms,Molecules,
and IonsPart 4 58
• Apply the Solution Map.
Determine the Atomic Number of the Element
Example:Find the number of protons and electrons in the Ca2+ ion
Information
Given: Ca2+ = calcium
Find: #p and #e
Solution Map: ion symbol element atomic number #p #e
Ca = calciumAtomic Number = 20
Atoms,Molecules,
and IonsPart 4 59
• Apply the Solution Map.
Determine the Number of Protons in an Atom of the Element
Example:Find the number of protons and electrons in the Ca2+ ion
Information
Given: Ca2+ = calcium, Z = 20
Find: #p and #e
Solution Map: ion symbol element atomic number #p #e
Ca = calciumAtomic Number = 20
#p = atomic number = 20
Atoms,Molecules,
and IonsPart 4 60
• Apply the Solution Map.
Determine the Number of Electrons in an Ion of the Element
Example:Find the number of protons and electrons in the Ca2+ ion
Information
Given: Ca2+ = calcium, Z = 20
Find: #p = 20 and #e
Solution Map: ion symbol element atomic number #p #e
Ca = calciumAtomic Number = 20
#p = atomic number = 20
Ion Charge = #p - #e+2 = 20 - #e-18 = - #e18 = #e
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
Example:How many protons and neutrons in the chromium isotope Cr52
24
Cr5224
Atoms,Molecules,
and IonsPart 4 75
• Apply the Solution Map.
Determine the Name of the Element
Information
Given:
Find: #p and #n
Solution Map: ion symbol element atomic number #p #n
Cr = chromium
Example:How many protons and neutrons in the chromium isotope Cr52
24
Cr5224
Atoms,Molecules,
and IonsPart 4 76
• Apply the Solution Map.
Determine the Atomic Number of the Element
Information
Given: = calcium
Find: #p and #n
Solution Map: ion symbol element atomic number #p #n
Cr = chromiumAtomic Number = 24
Example:How many protons and neutrons in the chromium isotope Cr52
24
Cr5224
Atoms,Molecules,
and IonsPart 4 77
• Apply the Solution Map.
Determine the Number of Protons in an Atom of the Element
Cr = chromiumAtomic Number = 24
#p = atomic number = 24
Information
Given: = calcium
Find: #p and #n
Solution Map: ion symbol element atomic number #p #n
Example:How many protons and neutrons in the chromium isotope Cr52
24
Cr5224
Atoms,Molecules,
and IonsPart 4 78
• Apply the Solution Map.
Determine the Number of Neutrons in an Atom of the Element
Cr = chromiumAtomic Number = 24
#p = atomic number = 24
Mass Number = #p + #n52 = 24 + #n
28 = #n
Information
Given: = calcium
Find: #p and #n
Solution Map: ion symbol element atomic number #p #n
Example:How many protons and neutrons in the chromium isotope Cr52
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
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