The Nuclear Atom Rutherford modified Thomson’s model: –assume the atom is spherical but the positive charge must be located at the center (it’s small and dense), with a diffuse negative charge surrounding it –Read section 2.2 for all of the details on the experiments! Text, P. 40

The Modern View of Atomic Structure The atom consists of positive, negative, and neutral entities (protons, electrons, and neutrons) Nucleus: Small Dense (Protons and neutrons) Massive (Protons and neutrons) Isotopes have the same number of protons but different numbers of neutrons Electrons are located outside of the nucleus Most of the volume is due to the electron cloud

31 Text, P. 42

41 Isotopes, Atomic Numbers, and Mass Numbers Atomic number (Z) = number of protons in the nucleus Mass number (A) = total number of protons and neutrons in the nucleus For element X, we write X Isotopes have the same Z but different A

51 Atomic Number Average Atomic Mass (Mass Number = 24)

61 Sample Problems: # 15 & 19

Atomic Weights The Atomic Mass Scale 1 atom of 1 H weighs x g and 1 atom of 16 O weighs x g We define: mass of 12 C = exactly 12 amu Using atomic mass units: 1 amu = x g 1 g = x amu

81 Sample Problem: # 73 a and 75

91 Average Atomic Masses Relative atomic mass: average masses of isotopes: –Naturally occurring C: % 12 C % 13 C Average mass of C: ( )(12 amu) + (0.0108)( ) = amu Atomic weight (AW) is also known as average atomic mass

101 Sample Problem: # 23

The Periodic Table The Periodic Table is used to organize the elements in a meaningful way Dimitri Mendeleev: Periodic properties IUPAC: governing body of chemistryIUPAC

The Periodic Table 92 naturally occurring elements Others are synthetic Metalloids have the appearance of metals and the behavior of nonmetals

131 Metals, Nonmetals, and Metalloids Increasing Metallic Character

141 Groups Alkali metals (no H) Alkaline Earth metals Halogens Noble Gases Transition metals No Group #s Innertransition metals Chalcogens Lanthanides Actinides

151 Periods Period #

Molecules and Molecular Compounds Molecules and Chemical Formulas Molecules: two or more atoms bonded together The chemical formula indicates the type and number of atoms in the molecule Compounds formed from molecules are molecular compounds Molecules that contain two atoms bonded together are called diatomic molecules 2 of the same element

171 The Diatomic Molecules Text, P. 50 “Oh I have nice closets for brooms!” ~ Mat Golden, 10/3/06

181 Molecular and Empirical Formulas Molecular formulas –give the actual numbers and types of atoms in a molecule –Examples: H 2 O, CO 2, CO, CH 4, H 2 O 2, O 2, O 3, and C 2 H 4

191 Empirical formulas –give the lowest whole number ratio of atoms in a molecule –Examples: H 2 O, CO 2, CO, CH 4, HO, CH 2

201 Picturing Molecules Text, P. 51 (nothing to copy from this slide)

211 Sample problems # 37, 41