Zumdahl’s Chapter 2

Atoms, Molecules, and Ions

Chapter Contents History of Chemistry Mass & Proportions Dalton Theory Subatomic Particles Structure of the Atom Molecules and Ions

Periodic Table Symbols and Organization

Naming Compounds Binary ionic molecule Binary covalent compounds Polyatomic ions

History of Chemistry Democritus (5th Century BC) atomic

postulate Lucretius (1st Century AD) “atoms

and the void” Priestly (18th Century AD) discovers

oxygen Lavoisier (18th) diamond=carbon

Conservation of Mass and Chemical Proportions Mass unchanged in chemical

reactions Implies atoms conserved in

reactions Elements combine in definite,

simple proportions by mass. Molecules are atoms in definite proportions! - Dalton

John Dalton (1808) Elements are collections of

identical, miniscule atoms. Different elements differ in their

atoms. Compounds are combinations of

different elements. Under reaction, compounds

rearrange their atoms.

Subatomic Components J.J. Thompson (1897) “cathode rays are electrons” (e–) and finds e/m ratio

Robert Millikan (1909) measures e and hence melectron known at 9.1110-31 kg

E. Rutherford (1906) bounces (He2+) off Au tissue proving protons (p+) in nucleus

F.A. Aston (1919) “weighs” atomic ions J. Chadwick (1939) observes neutrons

(no charge) by decomposition (to p+, e–, and ).

Structure of the Atom Nucleons (protons and

neutrons) of almost the same mass (1.6710-27 kg) live in nucleus (R~2 fm).

Electrons occupy the full atomic radius (R~50 pm), shielding the nucleus.

Electron and proton count identical in neutral atom.

Symbology of an Atom

3579Br Z=35 is bromine’s

atomic number (count of protons)

A=79 is its mass number (count of all nucleons)

So 3579Br has 79–35 or

44 neutrons 35

81Br exist too in equal #s.

So isotope average A=80

Molecules and Ions Atoms in molecules share

(covalent) or steal (ionic) electrons to bond.

Stolen electrons lead to attraction of unlike charged ions (ionic bonding)

Directional electron “clouds” lead to molecular shapes.

Molecules can be ionic as well as atoms.

Periodic Table Z increases linearly from 1H upper

left Groups (columns) have similar

chemistry Alkali metals, alkaline earths,

transition metals, halogens and noble gases

Naming Compounds IONIC

Cation named first. If atom 1 makes only one cation:

Strontium chloride SrCl2 If atom 1 makes several cations:

Iron(III) chloride FeCl3

COVALENT Less electronegative element named

first Most electronegative gets “anionic” –

ide Greek prefixes show proportions:

Dichlorine heptoxide Cl2O7 Mono prefix is never used for first atom.

Polyatomic Ions Few polyatomic cations

Most common: ammonium (NH4)+

Many polyatomic anions NO3

– nitrate, C2O42– oxalate, HSO4

– hydrogen sulfate, H2PO4

– dihydrogen phosphate, Cr2O7

2– dichromate ClO– hypochlorite, ClO2

– chlorite, ClO3–

chlorate, ClO4– perchlorate

Naming Exercise Al2(S2O3)3 P4O10 Cu(NO2)2 NaMnO4 CS2 Fe2(CrO4)3 HCl (gas) PH4BrO2

Aluminum thiosulfate Tetraphosphorous decaoxide Copper(II) nitrite Sodium permanganate Carbon disulfide Iron(III) chromate Hydrogen chloride Phosphonium bromite