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 – s  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 – L8 L8http:// L8  Law of Definite Proportions –A chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sample –Ex – H 2 O, CO 2

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 –Atoms of one element can differ from each other - ISOTOPES –An atom is made of smaller parts

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 (CRT) –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  structure-electrons-video.htm structure-electrons-video.htm structure-electrons-video.htm  Did experiments with CRT – –Found that the charge to mass ration was always the same ration was always the same

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

Composition of the nucleus  Protons –Positive charge atomic-structure-the-nucleus- video.htm atomic-structure-the-nucleus- video.htm atomic-structure-the-nucleus- video.htm  Neutrons –Neutral charge 07-atomic-structure-neutrons-video.htm 07-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  Based on distance electrons travel away from the nucleus  8-size-of-atoms-matter-video.htm 8-size-of-atoms-matter-video.htm 8-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 – fhydrogen.htm fhydrogen.htmhttp:// fhydrogen.htm

Counting Atoms  Designating Isotopes –Hyphen notation  Name-mass #  Uranium-235 – How many p, n, e-?  Ex – Neon with 12 neutrons? –Nuclear Symbol Notation  MN AN Element symbol  3 1 H  U How many p,n,e - in chlorine-37?

Relative Atomic Mass  Relative scale –Standard needed to be set –Carbon-12  All others compared to Carbon-12  Atomic mass unit –amu –The mass of an individual atom –Honors: 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 – number of particles in 1mol of substance –Molar mass  Mass of 1mol of substance – on P.T.

Conversions  Gram  MoleMole  Gram  Mole  ParticleParticle  Mole  Gram  ParticleParticle  Gram Facts (Conversion Factors): #g PT = 1 mol 6.02 x particles = 1 mol

Conversions  Gram  Mole; Mole  Gram

Conversions  Mole  Particle; Particle  Mole

Conversions  Gram  Particle; Particle  Gram