Download Chem 121 lecture notes in slides and more Slides Chemistry in PDF only on Docsity!
Atoms, Molecules and Ions (Ch. 2)
• 2.1 Early History of Chemistry
• 2.2 Fundamental Chemical Laws
• 2.3 Daltons Atomic Theory
• 2.4 Cannizzaros Interpretation
• 2.5 Early Expts: Characterizing the Atom
• 2.6 Atomic Structure
• 2.7 Molecules and Ions
• 2.8 The Periodic table
• 2.9 Naming Compounds
Atoms, Molecules, and Ions
(Zumdahl, Chapter 2)
- 400 BC: Greek Philosophers
- 4 elements fire, earth, water and air
- Democritus: early atomic theory- divisibility of matter - _______- ultimate particles - used shape as atomic distinctions Fake emeralds (early AD): Take white lead, one part, and of any glass you choose, two parts, fuse together in a crucible and then pour the mixture. To this crystal, add _______________and after forty days you will find emeralds.
- 2000 years of Alchemy
- attempts to turn metals into gold
- in the hunt, prepared mineral acids and isolated elements such as mercury and sulfur
- Daltons Atomic Theory (1808): marked the beginning of Modern Chemistry
- Each element is made up of tiny particles called atoms.
- The atoms of a given element are identical; the atoms of different elements are different in some fundamental way.
- Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative number and types of atoms.
- Chemical reactions involve the reorganization of atoms; changes in the way they are bound together. Atoms themselves are not changed in a chemical reaction
- Dalton (1766-1844):
Daltons Relative Atomic Masses
- prepared first table of atomic masses, based on the relative masses of elements in known compounds
- made many incorrect assumptions Known: water is 8 grams of oxygen for every 1 gram of hydrogen -assumed formula was OH -assigned hydrogen a mass of 1 and oxygen a mass of 8
Stanislao Cannizzaro (1826-1910) Accepted that:
- compounds contained whole #s of atoms as Dalton suggested
- Avogadros hypothesis was correct Presented his ideas:
- assigned the H 2 molecule a relative mass of 2 (and oxygen must be O 2 and water is H 2
O)
- measured the relative molecular masses of a large
of compounds
- led to approximate values of the relative atomic masses
8
- Early Experiments to Characterize the Atom: J.J. Thomson (1856-1940): - experimented with Cathode-ray tubes (Michael Faraday) - produced a beam of electrons in an evacuated tube - deflected beam with an applied electrical field - measured charge-to-mass ratio of an electron (negatively charged): 1. 76 x 10 C/ g m e (^8) = − C = Coulomb Fig.
Physics
- proposed the first atomic model:
- electrons distributed randomly in a diffuse positive cloud.
- ___________ model: raisins dispersed in pudding. __________ Model Fig 2. 02_
- Millikan (1868-1953):
- determined the charge of an electron Charge = -1.60 x 10 - C
- using e/m, the mass of an electron was determined: mass = 9.11 x 10 - kg Physics 1923
The Nuclear Atom
- Rutherford (1871-1937) -experiments to deduce something about the distribution of electrons in the atom -bombarded gold foil with high energy α particles (+ ve )
- Expectations :
- α particles would pass straight through with little or no deflection Plum pudding model Fig. 2.12a
Rutherford02_24 s gold foil experiment Beam of alpha particles Thin metal foil Luminescent screen to detect scattered alpha particles Some alpha particles are scattered Uranium source of alpha particles (embedded in a lead block to absorb most of the radiation) Most particles pass straight through foil α particles Figure 2.
proposed a centre of concentrated + ve charge in the atom
- this experiment led to the following conclusions:
- an atom is neutral (# e
= # p
)
CAPA #1:
The Mass–Density–Volume–Displacement Question Canadian $0.10 and $0.25 coins are made of pure nickel which has a density of 8.902 g/cm 3
. Suppose each dime weighs 2.02 g and each quarter weighs 5.05 g. A small collection of dimes and quarters are submerged in 10.00 mL of water in a graduated cylinder causing the water level to rise to the 15.11 mL mark. What is the combined monetary value (in Can$) of those coins? Example to be covered in tutorial
Atomic Structure: the Nucleus
Rutherford –
-collisions between α particles
and nitrogen nuclei released
positive particles - protons ,
with mass ~3600 x mass of
electron
-predicted existence of neutral
particles to account for total
mass of the atom
CHEMISTRY - 1908
