1. CH 3 Atoms: The Building Blocks of Matter 3
CH 3 Atoms: The Building Blocks of Matter 3.1 The Atom: from Philosophical Idea to Scientific Theory
Atom: a- not; -tomos cutting
Molecules made of combining 2+ atoms
3 basic laws describe chemical reactions:
Law of conservation of mass
Law of definite proportions
Law of multiple proportions

2. Law of conservation of mass
Mass cannot be created or destroyed during chemical reactions or physical changes
Coefficients in chemical reaction show this relationship

3. Law of definite proportions: chemical compound has the same element in the same proportions no matter the sample
Law of multiple proportions: same elements even with diff #’s atoms have same ratio of masses of elements

4. Dalton’s Theory Atomic Theory
All matter is composed of extremely small particles called atoms.
Atoms of an element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created or destroyed.
Atoms of different elements combine in simple whole-number ratios to for chemical compounds.
In chemical reactions, atoms are combined, separated or rearranged.
Atomic Theory
All matter is composed of atoms
Atoms of one or more element differ in properties from atoms of another element

5. 3.2 The Structure of the Atom
Democritus
atom indivisible and indestructible; 1st, not based on scientific method
2000yrs pass
Dalton’s Atomic Theory
Thomson
Experiment
Particles move from cathode (-) to anode (+)
Cathode rays were deflected by a magnetic field
Plum Pudding Atomic model
Negative parts spread evenly thought positive

6. Goldstein Chadwick Rutherford
exp showed canal rays/ positive particles, mass p+ 1840x that of e-
Chadwick
Discovered neutrons
Rutherford
Exp-alpha particles (He atoms lost e-) being double + charge should pass thru gold foil easily
most did pass straight but some bounced off at large angles and some bounced straight back!
Rutherford Atomic Model (aka nuclear atom) atom is mostly empty space, + charge and mass is concentrated in nucleus (very small)

7. Nuclear forces Short range hold nuclear particles together
Proton-neutron
Proton-proton
Neutron-neutron

8. 3.3 Counting Atoms Atomic number: # p+ Mass number: p+ and neutrons
Isotope: different # neutrons
Atomic mass unit: 1/12 of C-12 atom
Avg atomic mass: weighted for isotopes and elements

9. Counting atoms Mole Avogrado’s number Molar mass
SI unit for substance
Amount of particles = to atoms in 12g of C-12
Avogrado’s number
6.02x1023
Particles in 1 mole
Molar mass
Mass of 1 mole of the substance
Use conversion factors!

10. 1 step 2 step Gram-mole Mole-gram Mole-atom Atom-mole Mass-atom
Atom-mass
*Use fraction conversion factors!