Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were...

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Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes occur. Alchemy: Attempts to change cheap metals into gold. They invented the idea of atoms, that matter is not continuous. They discovered several elements and learned to prepare mineral acids.

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Transcript of Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were...

Page 1: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Chapter 2Atoms, Molecules and Ions

The Early History of Chemistry

Before 16th Century Greeks were the first to attempt to explain why

chemical changes occur. Alchemy: Attempts to change cheap metals into

gold. They invented the idea of atoms, that matter is not continuous. They discovered several elements and learned to prepare mineral acids.

Page 2: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

The Early History of Chemistry

16th Century German develop the systematic metallurgy

(extraction of metal from ores) Swiss develop the medicinal application of

minerals

17th Century Robert Boyle: First chemist to perform

quantitative experiments

Page 3: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Fundamental Chemical LawsLaw of Conservation of Mass (Antoine Lavoisier, 18th Century) – Mass is neither created nor destroyed

Law of Definite Proportion (Joseph Proust, 19th Century) – A given compound always contains exactly the same proportion of elements by mass. This principle of constant composition of compounds is a law of definite proportion. Carbon tetra chloride is always 1 atom carbon per 4 atoms chlorine

Page 4: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Fundamental Chemical Laws

Law of Multiple Proportions (John Dalton, 19th Century) – When two elements form a series of compounds, the ratio of the masses of the second element that combine with 1g of the first element can always be reduced to small whole numbers. The ratio of the masses of oxygen in H2O and H2O2 will be a small whole number (“2”).

Page 5: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Dalton’s Atomic Theory (1808)1. Each element is made up of tiny particles called atoms2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental

way or ways3. Chemical compounds are formed when atoms of

different elements combine with each other. A given compound always has the same relative numbers and types of atoms

4. Chemical reactions involve reorganization of the atoms – changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

Page 6: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Avogadro’s Hypothesis (1811)

At the same temperature and pressure, equal volumes of different gases contain the same number of particles

5 liters of oxygen and 5 liters of nitrogen contain the same number of particle

Page 7: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Thomson Atomic Model (1903) An atom consists of a diffuse cloud of positive

charge with the negative electrons embedded randomly in it. This model is often called plum (or raisin) pudding model.

Observed cathode ray (produced at the negative electrode and repelled by the negative pole of an applied electric field.

Cathode ray was a stream of negatively charged particles now called electrons

Page 8: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Deflection of Cathode Rays by an Applied Electric Field

Page 9: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

The Plum Pudding Model of the Atom

Page 10: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Rutherford Atomic Model (1911)

An atom with a dense center of positive charge (the nucleus) with electrons moving around the nucleus at a distance that is large relative to the nuclear radius. Nucleus is very small compared with the overall size of the atom. Nucleus is extremely dense, accounts for almost all of the atom’s mass.

Page 11: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Radioactivity

Spontaneous emission of radiation Gamma () rays: high energy light Beta () particles: high speed electron Alpha () particles (He2+): 2+ charge,

charge twice that of electron and with opposite sign. The mass of an -particle is 7300 times that of the electron

Page 12: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Rutherford’s Experiment on particle Bombardment of Metal Foil

Page 13: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Expected and Actual Results of Rutherford’s Experiment

Page 14: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

The Modern View of Atomic Structure

The atom contains: Electrons: move around the nucleus (mass:

9.11 X 10-31 kg, Charge 1-) Protons: found in the nucleus, they have a

positive charge equal in magnitude to the electron’s negative charge (mass: 1.67 X 10-

27 kg, charge 1+) Neutrons: found in the nucleus, virtually

same mass as a proton but no charge. (mass: 1.67 X 10-27 kg, charge: 0)

Page 15: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Nuclear Atom Viewed in Cross Section

Page 16: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

The Chemists’ Shorthand Atomic Symbols

Atomic number (Z): number of protons, gives the symbol of the element (X)Mass number (A): Total number of protons and neutronsElemental form = Zero net chargeTherefore, # electrons = # of protons

K Element Symbol

39

19

Mass number

Atomic number

Page 17: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Isotopes

Atoms with the same number of protons but

different number of neutrons. In nature most

elements contain mixtures of isotopes

2311Na : 11 protons, 11 electrons, and 12 neutrons

2411Na : 11 protons, 11 electrons, and 13 neutrons

Page 18: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Two Isotopes of Sodium

Page 19: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Molecules and Ions

Chemical Bonds: The forces that hold atoms together in compounds. H2O, NO, CO2

Covalent bonds: Covalent bonds result from atoms sharing electrons. Cl2

Ionic bonds: Force of attraction between oppositely charged ions.

Molecule: A collection of covalently-bonded atoms. H2, O2

Page 20: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Ions

Ions: An ion is an atom or group of atoms that has a net positive charge or negative charge particle (an unequal number of protons and electrons) is obtained by removing or adding electrons. Na+, Cl-

Cation: A positive ion (Na+, Mg2+, NH4+)

Anion: A negative ion (Cl-, SO42-)

Page 21: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Formulas Chemical Formula: In which the symbols for

the elements are used to indicate the types of atoms present and subscripts are used to indicate the relative numbers of atoms.

CO2 indicates each molecule contains 1 atom of carbon and 2 atoms of oxygen.

Structural Formula: In which the individual bonds are shown by lines. It may or may not indicates the actual shape of the molecules.

O=C=O

Page 22: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Periodic Table Periodic table is organized based on the

properties that elements have in common with one another.

Groups: Elements in the same vertical columns are in the same group have similar chemical properties.

Group 1A: Alkali metals: Li, Na, K, Rb, Cs, Fr Group 2A: Alkaline earth metals: Be, Mg, Ca, Sr, Ba,

Ra Group 7A: Halogens: F, Cl, Br, I, At (astatine) Group 8A: Noble gases: He, Ne, Ar, Kr, Xe, Rn (radon)

Page 23: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

The Periodic Table

Page 24: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Periodic Table Periods: The horizontal rows of elements in the

periodic table are called periods. First period: horizontal row one contains H and He Second period: row two contains Li through Ne Letters in the boxes are the symbols for the

elements Abbreviations are based on the current element

names or the original names. The number above each symbol is the atomic

number (number of protons)

Page 25: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Periodic Table Most of the elements are metals in the periodic

table. Metals: Conduction of heat and electricity,

malleability, ductility, lustrous, form positive ions

Nonmetals: appear in the upper right hand corner of the periodic table except hydrogen. Nonmetals lack the physical properties that characterize the metal, gain electrons in chemical reaction and form negative ions, form covalent bond to each other.

Page 26: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Naming Compounds Binary Compounds: Compounds composed of

two elements Binary Ionic Compounds (Type 1): contains a

positive ion (cation) always written first in the formula and a negative ion (anion)

Rules: 1. The cation is always named first and the anion

second2. A monatomic (meaning one atom) cation takes its

name from the name of the element3. A monatomic anion is named by taking the root of

the element name and adding –ide

Page 27: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Binary Ionic CompoundsCompound Ions Present Name

NaCl Na+, Cl- Sodium chloride

KI K+, I- Potassium iodide

CaS Ca2+, S2- Calcium sulfide

Li3N Li+, N3- Lithium nitride

CsBr Cs+, Br- Cesium bromide

MgO Mg2+, O2- Magnesium oxide

Page 28: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Naming compounds Binary Ionic Compounds (Type II): Metals that

form more than one type of positive ion. Fe2+ and Fe3+

Transition metals form several positive oxidation states

Charge on the metal ion must be specified Roman numeral indicates the charge of the cation.

Iron (II) chloride and iron (III) chloride The ion with the higher charge has a name ending

in –ic and the one with the lower charge has a name ending in –ous; ferrous chloride and ferric chloride

Page 29: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Naming Compounds

Ionic Compounds with Polyatomic Ions: Need to know the names of the polyatomic ions

(Table 2.5).

NH4+ ammonium, SO4

2- sulfate Na2SO4 Sodium sulfate KH2PO4 Potassium dihydrogen phosphate Fe(NO3)3 Iron(III) nitrate CsClO4 Cesium perchlorate NaOCl sodium hypochlorite Al2(Cr2O7)3 Aluminum dichromate Sr(CN)2 Strontium cyanide

Page 30: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Naming compoundsBinary Covalent Compounds (Type III):Formed between two nonmetalsRules: The first element in the formula is named first,

using the full element’s name Second element is name as if it were an anion Use prefixes to denote the number of atoms

present Never use mono – prefix for naming the first

element

Page 31: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

CO ==> carbon monoxide, not monocarbon monoxide

P2O5 ==> diphosphorus pentoxide

S2Cl4 ==> disulfur tetrachloride

NO2 ==> nitrogen dioxide

N2O5 ==> dinitrogen penoxide

Page 32: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Common Cations and Anions

Page 33: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Formulas from Names

Name Chemical FormulaDiphosphorus pentasulfide P2S5 (two non metals)

Cesium peroxide Cs2O2 (Cs1+, O22-)

Aluminum fluoride AlF3 (Al3+, F-1)

Vanadium (v) fluoride VF5 (V5+, F-1)

Dioxygen difluoride O2F2 (two non metals)

Gallium oxide Ga2O3 (Ga3+, O2-)

Ammonium dichromate (NH4)2Cr2O7 (NH4+, Cr2O7

2-)

Cupric phosphate Cu3(PO4)2 (Cu2+, PO43-)

Page 34: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Flowchart for Naming Binary Compounds

Page 35: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Acids

When dissolved in water produce a solution containing free H+ ions (protons)

An acid is a molecule with one or more H+ ions attached to an anion

If the anion does not contain oxygen, the acid is named with the prefix hydro – and the suffix –ic

HCl Hydrochloric acid

HCN Hydrocyanic acid

Page 36: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Acids If the anion contains oxygen, the acidic name is

formed from the root name of the anion with the suffix of –ic or –ous depending on the anion

HNO3 Nitric acid (Nitrate anion)

H2SO4 Sulfuric acid (Sulfate anion)

H3PO4 Phosphoric acid (Phosphate anion)

HC2H3O2 Acetic acid (Acetate anion)

H2SO3 Sulfurous acid (sulfite anion)

HNO2 Nitrous acid (nitrite anion)

Page 37: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Flowchart for Naming Acids

Page 38: Chapter 2 Atoms, Molecules and Ions The Early History of Chemistry Before 16 th Century Greeks were the first to attempt to explain why chemical changes.

Summary Laws Dalton’s atomic Theory Avogadros’ Hypothesis Various Atomic Models Radio Activity (, , rays) Atomic Symbol (atomic #, mass#, isotopes) Chemical Bonds (covalent bonds, Ionic bonds) Periodic Table Naming various types of compounds Formulas Acids


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