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Chapter 2 Atoms, Molecules, and Ions



Chemistry, The Central Science, 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

Chapter 2 Atoms, Molecules, and Ions
Atoms, Molecules, and Ions

>? 2009, Prentice-Hall, Inc.

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.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Dalton's Postulates
Each element is composed of extremely small particles called atoms.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Dalton's Postulates
All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Dalton's Postulates
Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Dalton’s Postulates
Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Law of Constant Composition
Joseph Proust (1754–1826)

? This is also known as the law of definite proportions. ? It states that the elemental composition of a pure substance never varies.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

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.

Atoms, Molecules, and Ions
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The Electron

? Streams of negatively charged particles were found to emanate from cathode tubes. ? J. J. Thompson is credited with their Atoms, discovery (1897). Molecules,
and Ions
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The Electron

Thompson measured the charge/mass ratio of the electron to be 1.76 ? 108 coulombs/g.
Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

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
? 2009, Prentice-Hall, Inc.

Millikan Oil Drop Experiment
Robert Millikan (University of Chicago) determined the charge on the electron in 1909.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

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
? 2009, Prentice-Hall, Inc.

Radioactivity
? Three types of radiation were discovered by Ernest Rutherford:
? ? particles ? ? particles ? ? rays

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

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
? 2009, Prentice-Hall, Inc.

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
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The Nuclear Atom
Since some particles were deflected at large angles, Thompson’s model could not be correct.

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

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
? 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 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.

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.

11 C 6

12 C 6

13 C 6

14 C 6
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 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
? It is a systematic catalog of the elements. ? Elements are arranged in order of atomic number.

Atoms, Molecules, and Ions
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Periodicity

When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.
Atoms, Molecules, and Ions
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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
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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
? 2009, Prentice-Hall, Inc.

Chemical Formulas
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
? 2009, Prentice-Hall, Inc.

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

Atoms, Molecules, and Ions
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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

? 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 Atoms, Molecules, on the right side of the periodic chart.
and Ions
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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 wholenumber ratio, divide them by the greatest common Atoms, factor. Molecules,
and Ions
? 2009, Prentice-Hall, Inc.

Common Cations

Atoms, Molecules, and Ions
? 2009, Prentice-Hall, Inc.

Common Anions

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; SO32? : 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 hypoand 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 acid – HBr: hydrobromic acid – HI: 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 acid – HClO2: 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 dioxide – CCl4: 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. Atoms,
– An alcohol ends in -ol.
Molecules, and Ions
? 2009, Prentice-Hall, Inc.



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