atoms, molecules, and ions chapter 2 atoms, molecules, and ions

Atoms,Molecules,

and Ions

Chapter 2Atoms, Molecules,

and Ions

Atoms,Molecules,

and Ions

Historical Discovery of Atom• Democritus – Laughing Philosopher

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• John Dalton – solid sphere, combine• Thomson – Plum Pudding Model• Rutherford – Gold Foil Experiment• Millikan – Oil Drop Experiment• Bohr – Orbital Model• Chadwick – Neutrons• Wave Mechanical Model

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Atoms,Molecules,

and Ions

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Atomic Theory of MatterThe theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.

• 4 Postulate Theory

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Dalton's Postulates

1. Each element is composed of extremely small particles called atoms.

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Dalton's Postulates

2. All atoms of a given element are identical in mass and properties, but the atoms of one element are different from the atoms of another element.

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Dalton's Postulates3. Atoms of an element are not changed by chemical reactions; atoms are neither created nor destroyed in chemical reactions – just REARRANGED.

Supports the Law of Conservation of Mass

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Dalton’s Postulates4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Supports the Law of Constant Composition

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Law of Constant CompositionJoseph Proust (1754–1826)

• also known as the law of definite proportions• states that the elemental composition of a

pure substance never varies.

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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.

Atoms,Molecules,

and Ions

Subatomic Particles• Landmark Discoveries lead to the current model

of atomic theory

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• Streams of negatively charged particles were found to emanate from cathode (- electrode) tubes.

• J. J. Thompson is credited with their discovery (1897).

The Busy Electron

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The Busy Electron

Thompson measured the charge/mass ratio of the electron to be 1.76 108 coulombs/g.

Electron Charge (C) = 1.76 108 coulombs

Electron Mass (g) 1 gram

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Millikan Oil Drop Experiment

He examined the relationship between voltage of plates affected rate of electron fall.

Open text to pg. 40

Fig. 2.5 Explanation

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Millikan Oil Drop Experiment

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

Charge of Electron = 9.10 x 10 -28 g

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Subatomic Particles Relative Mass and Charge

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Relative Mass Image

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Radioactivity• Radioactivity is the spontaneous emission of

radiation by an atom.• It was first observed by Henri Becquerel• Followed by Marie and Pierre Curie.• Shared 1903 Nobel Prize in Physics

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Radioactivity• Three types were discovered by Rutherford:

– particles, Alpha, bent by electric field, +2 charge– particles, Beta, bent by electric field, - 1 charge– rays, Gamma, unaffected by electric field, no charge

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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.

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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.

Particles were deflected by foil.

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The Nuclear Atom

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

Rutherford proposed the positive nucleus containing protons.

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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.

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Other Subatomic Particles

• Protons discovered by Rutherford, 1919.• Neutrons discovered by James Chadwick,1932.

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and Ions

Subatomic Particles• Protons and electrons are 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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and Ions

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Symbols of Elements

• Nuclear Symbol

• Hyphen NotationC -12

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Atomic Number

Atoms of the same element have the same number of protons: the atomic number (Z)

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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.

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and Ions

Isotopes

• Isotopes are atoms have different masses.• Isotopes have different numbers of neutrons.

116

C 126

C 136

C 146

C

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Atomic Mass

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

Turn to pg. 48 in text

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and Ions

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Average Atomic 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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Calculating Average Atomic Mass

EX. You have a box containing two sizes of marbles.

25% of the marbles have a mass of 2.0 g.

75% of the marbles have a mass of 3.0 g.

Calculate the average weight of the marble.

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and Ions

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EX. Copper has two naturally occurring isotopes:• Cu-63 (69.17% abundant) with amu = 62.929 • Cu-65 (30.83% abundant) with amu =

64.927• Calculate the average atomic mass.

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and Ions

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Periodic Table

• It is a systematic catalog of the elements.

• Elements are arranged in order of atomic number.

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Periodicity or Periodic Law

Notices a repeating pattern of reactivities!

Function of the atomic number called periodicity.

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Periodic Table

• The rows on the periodic chart are periods.

• Columns are groups or families.

• Elements in the same group have similar chemical properties.

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Groups

These five groups are known by their names.

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Periodic Table

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

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Periodic Table

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

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Periodic Table

Metals are on the left side of the chart.

80% of elements are metals.

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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.

Naming and Writing Inorganics

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Chemical Formulas

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

- covalent compounds

- NM + NM

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Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.

Br2 I2 N2 Cl2 H2 O2 F2

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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.

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and Ions

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Types of Formulas• Structural formulas show the order

in which atoms are bonded.

• Perspective drawings show the three-dimensional array of atoms in a compound.

• Ball+Stick models show the atoms as spheres and bonds as sticks.

• Space filling model shows relative sizes of atoms.

Atoms,Molecules,

and Ions

Ions

When atoms lose or gain electrons, they become ions.– Ca+ions are positive, formed as atoms lose e-, metals– Anions are negative, formed as atoms gain e-, nonmetals

Atoms,Molecules,

and Ions

Ionic BondsIonic compounds = Metal + Nonmetal

Ionic compounds = cation + anion

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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.

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and Ions

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RIP Kris Kross

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and Ions

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Writing Chemical Formulas• Assign Charges then criss x cross the numbers• DO NOT criss x cross the charges, just the #s

Ex. Magnesium Chloride

Assign Charges Mg +2 Cl-1

Criss-Cross Mg Cl2

Chemical Formula MgCl2

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and Ions

Common Cations

Pg. 62 or on back fold of text

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and Ions

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Common Anions

Pg. 64 or on back fold of text

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and Ions

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Inorganic Nomenclature• Write the name of the metal cation.

• If the metal cation can have more than one charge, write the charge as a Roman Numeral in parentheses. (CLIMT)

• 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.

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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

-ate is GREAT and –ite is LIGHT

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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

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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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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

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Acid Nomenclature

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

HClO3: chloric acid

HClO4: perchloric acid

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Acid Nomenclature

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

HClO: hypochlorous acid

HClO2: chlorous acid

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Molecular Nomenclature

• 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) .

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

– CO2: carbon dioxide– CCl4: carbon tetrachloride

Molecular Nomenclature

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• 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

Molecular Nomenclature

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Nomenclature of Organic Compounds

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

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Nomenclature of Organic Compounds

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

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Nomenclature of Organic 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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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.