CHAPTER 3 Atoms: The Building Blocks of Matter CHEMISTRY

Foundations of Atomic Theory History Greek Democritus – “atom” – could not be divided anymore Aristotle and Plato - argued 1600-1700s Natural Philosophers Experimentation – balances – quantitative measurements Atom Comes from Greek “a” – not “tomos” – cutting indivisible

Foundations of Atomic Theory Chemical Reaction Transformation of substances into one or more new substances Chemical change Law of Conservation of Mass Mass is neither created nor destroyed in ordinary chemical reactions http://search.msn.com/video/results.aspx?q=law+of+conservation+of+mass&docid=1616197255512&FORM=VIVR3 Law of Definite Proportions A chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sample Ex – H2O, CO2

Foundations of Atomic Theory Law of Multiple Proportions If two or more compounds are composed of the same 2 elements, the masses can be expressed as ratios of small whole numbers

Dalton’s Atomic Theory John Dalton English School Teacher 1803

Dalton’s Atomic Theory 5 Points in his theory All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole number ratios to form compounds In chemical reactions, atoms are combined, separated, or rearranged

Dalton’s Atomic Theory

Modern Atomic Theory There have been some changes since Dalton’s Theory Important concepts of modern theory All matter is composed of atoms Atoms of one element differ in properties from atoms of another element

Structure of the Atom Atom – smallest particle of an element that can exist alone Two regions of an atom Nucleus Center of atom Protons and neutrons Electron “cloud” Area surrounding nucleus containing electrons

Discovery of the electron Symbol  e- Cathode ray tubes Vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen. Used in TV, computer monitors

Discovery of the electron Charge and mass of the electron JJ Thomson – 1897 Discovered the electron 1907 Nobel Prize in Physics http://videos.howstuffworks.com/hsw/6298-atomic-structure-electrons-video.htm Did experiments with CRT – Found that the charge to mass ration was always the same

Discovery of the atomic nucleus Ernest Rutherford – 1908 Gold Foil Experiment

Composition of the nucleus Protons Positive charge http://videos.howstuffworks.com/hsw/5806-atomic-structure-the-nucleus-video.htm Neutrons Neutral charge http://videos.howstuffworks.com/hsw/5807-atomic-structure-neutrons-video.htm

Forces in Nucleus Nuclear forces Forces that hold nuclear particles together Binds protons and neutrons into the atomic nucleus

Sizes of Atoms http://videos.howstuffworks.com/hsw/5788-size-of-atoms-matter-video.htm

Summary

Counting Atoms Atomic Number Symbol  Z Number of protons in nucleus The number of protons determines identity of the element!!

Counting Atoms Isotopes Atoms of the same element with varying number of neutrons Nuclide – general term for any isotope of any element Mass Number – total number of protons + neutrons

Counting Atoms The isotope of hydrogen Protium – one proton only; 1e- Deuterium – one proton, one neutron, one electron Tritium – one proton, two neutrons, one electron; radioactive http://www.citycollegiate.com/isotopesofhydrogen.htm

Counting Atoms Designating Isotopes Hyphen notation Name-mass # Uranium-235 Ex – Neon with 12 neutrons? Nuclear Symbol Notation MNAN Element symbol 31H 23592U How many p,n,e- in chlorine-37?

Relative Atomic Mass Relative scale Atomic mass unit Standard Way to compare Carbon-12 All others compared to Carbon-12 Atomic mass unit amu Approximate mass of a proton or a neutron

Average Atomic Mass Weighted average of the atomic masses for all known isotopes Calculating average atomic mass:

Relating mass to the number of atoms “Particle” – a generic term Mole – SI unit for amount of substance, counting unit Symbol – mol Avogadro’s number 6.02 x 1023 – number of particles in 1mol of substance Molar mass Mass of 1mol of substance = atomic mass

Calculating Molar Mass H2O CO2 C6H12O6

Conversions Gram  Mole Mole  Gram Mole  Particle Particle  Mole Gram  Particle Particle  Gram

Conversions Gram  Mole; Mole  Gram

Conversions Mole  Particle; Particle  Mole

Conversions Gram  Particle; Particle  Gram