ATOMS: The Building Blocks of Matter Objectives 1.Law of conservation of mass 2.Law of definite proportions 3.Law of multiple proportions 4.Dalton’s Atomic Theory 5.How Dalton’s Atomic Theory relates to 1, 2, & 3

Atomic Theory Foundations Law of Conservation of Mass – mass is neither created or destroyed during a chemical or physical change Law of Definite Proportions – a compound contains the same proportions by mass regardless of the size of the sample Example: NaCl – always 39.34% Na & 60.66% Cl

Atomic Theory Foundations Law of Multiple Proportions – if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers Example CO 2 and CO : ratio of oxygen is always 2:1

Dalton’s Atomic theory 1.All matter is composed of atoms 2.Atoms of an element have the same size, mass and properties; atoms of a different element have different sizes, masses and properties 3.Atoms cannot be divided, created or destroyed 4.Atoms of different elements combine in simple whole number ratios 5.Chemical reactions combine, separate, or rearrange atoms

Modern Atomic Theory Atoms can be divided Atoms of the same element can have different masses All else remains the same

Structure of the Atom Objectives Discovery of the Electron Rutherford’s Experiments Protons, Neutrons, Electrons

Atomic Structure Electron = no mass; negative charge Proton mass = hydrogen atom; positive Neutron mass = hydrogen atom; no charge Dalton’s Model JJ Thompson’s Plum Pudding Model

Rutherford Shoots alpha particles (Helium atoms) at gold foil Expected to pass right through Particles are deflected Leads to idea of a dense positively charged center with e- orbiting around it

The electron Mass of x kg Negative charge

The Proton Mass = x kg Positive charge

The neutron Mass = x kg No charge

Comparing Theories Dalton See notes Solid sphere Thompson Plum pudding model Electrons scattered thru positively charged cloud Rutherford Concept of the nucleus Positively charged

Counting Atoms Objectives Explain isotopes Define atomic number, atomic mass Determine number of protons, neutrons & electrons Define mole and molar mass Convert between grams, moles, and atoms

Atomic Number –# of protons in nucleus Element Symbol Element Name Atomic Weight Electron Configuration 3 Li Lithium [He]2s 1

Isotopes Def: atoms of the same element that have different masses Example: hydrogen protium – 1 proton in nucleus deuterium – 1 proton; 1 neutron tritium – 1 proton; 2 neutrons *Nuclide – general term for any isotope

Mass Number Def: the number of protons and neutrons in the nucleus of an isotope mass # - atomic # = # of neutrons Example – oxygen Mass # (16) – atomic # (8) = # of neutrons (8)

Writing Isotopes Example – Uranium 235