ATOMIC COMPOSITION• Protons (p+)– + electrical charge– mass = 1.672623 x 10-24 g– relative mass = 1.007 atomic mass units(amu) but we can round to 1• Electrons (e-)– negative electrical charge– relative mass = 0.0005 amubut we can round to 0• Neutrons (no)– no electrical charge– mass = 1.009 amu but we can round to 1
Atomic Number, ZAll atoms of the same element havethe same number of protons in thenucleus, Z13Al26.981Atomic numberAtom symbolAVERAGE Atomic Mass
Mass Number, A• Mass Number (A)= # protons + # neutrons• NOT on the periodic table…(it is the AVERAGEatomic mass on the table)• A boron atom can haveA = 5 p + 5 n = 10 amuAZ105B
Atomic Symbols Show the mass number and atomic number innuclear symbol formmass number23 Naatomic number 11
Counting Protons, Neutrons, andElectrons• Protons: Atomic Number (from periodic table)• Neutrons: Mass Number minus the number ofprotons (mass number is protons and neutronsbecause the mass of electrons is negligible)• Electrons:– If it’s an atom, the protons and electrons must be the SAMEso that it is has a net charge of zero (equal numbers of + and-)– If it does NOT have an equal number of electrons, it is notan atom, it is an ION. For each negative charge, add anextra electron. For each positive charge, subtract anelectron (Don’t add a proton!!! That changes the element!)
Isotopes• Atoms of the same element (same Z) butdifferent mass number (A).• Boron-10 (10B) has 5 p and 5 n• Boron-11 (11B) has 5 p and 6 n10B11B
AVERAGEATOMIC MASS• Because of the existence of isotopes, the mass of acollection of atoms has an average value.• Boron is 20% 10B and 80% 11B. That is, 11B is 80percent abundant on earth.• For boron atomic weight= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu10B11B
• 1895 – discovered how to use electromagneticradiation to create x-rays• Led to significant advances in medicine,especially on the battlefields of World War I• In the 1900’s the damaging qualities of x-rayswere studied and proven useful in fighting somecancers.The first x-ray ofRoentgen’swife’s hand
Radiation was discovered purely by chance ……….He put a couple of photographicplates in a drawer next to a rock.Days later he discovered that theplates had patches on them wherethey had been developed.WHAT DO YOU BELIEVE HAPPENED HERE?The “rock” in his desk contained URANIUM in it.Becquerel discovered that it gave off invisible rays whichdeveloped the film plates.
• Defined and studied radioactivity• Trained by her father, worked with herhusband Pierre• Isolated polonium and radium• Nobel Prize for Physics and Chemistry• Died of leukemia after never receivingfinancial gain from her work• Oldest daughter, Irene continued work andearned Nobel Prize in Chemistry
All nuclear energy begins in the area of the atom calledthe ……The central “core” of the atom.Contains PROTONS andNEUTRONS.Reactions that involve the nucleusof an atom are called NUCLEARREACTIONS, and produce atremendous amount of energy.
THERE ARE THREE TYPES OF PARTICLES ANDENERGY GIVEN OFF BY RADIOACTIVE ELEMENTS1.ALPHA PARTICLES-Type of radiation where theparticles possess a positivecharge, cannot even penetratepaper, has the most mass, andmoves slowly.If you could see an alpha particle, it would look just like a heliumnucleus. Two protons, two neutrons.
THERE ARE THREE TYPES OF PARTICLES ANDENERGY GIVEN OFF BY RADIOACTIVE ELEMENTSBETA PARTICLES -Type of radiation where theparticles have a negativecharge, penetrates living tissue,and has less mass but movesquicker than an alpha particle.If you could actually see a beta particle it would appearto be one “free” electron capable of moving anywhere.
THERE ARE THREE TYPES OF PARTICLES ANDENERGY GIVEN OFF BY RADIOACTIVE ELEMENTSGAMMA RAYS -The only type of radiation which is“energy” instead of particles.Travels at the speed of light, hasno mass, is neutral in charge, andpenetrates just about everysubstance. POWERFUL!!!!!!Since Gamma rays are energy only and travel soquickly, you would not see them even if you could!
The time it takes for 1/2 of a radioactive elementto decay. Every radioactive element has a uniquehalf-life. (some are in seconds and some arebillions of years!)On the island of Bikini Atoll, scientistsback in the 1950’s tested nuclearbombs for the government. Today,nobody is still allowed to return therebecause it is STILL RADIOACTIVE!!
Half-life formula:Amount remaining = (initial amount) (1/2) nWhere n is number of half-lives.If you need to find the number of half-lives that havepassed,elapsed timeNumber of half-lives (n) = half-life