Building blocks of matter ATOMIC THEORY Building blocks of matter

DEMOCRITUS IN 400 BC,DEMOCRITUS SAID: ALL MATTER IS MADE UP OF TINY PARTICLES CALLED “ATOMOS”

The Greek Periodic Table - Aristotle: Matter had no properties itself, but that various combinations of simple properties made every substance known. 4 properties were: moist, cold, dry, hot 4 elements: Water, earth, fire, air

300 BC, Aristotle: The Greek periodic table

Greek theories were philosophical and moralistic Did nothing to suggest a direction for experimental work

1808 Dalton’s atomic theory 1. All matter is made up of atoms 2. Atoms of the same element are alike. 3. Atoms of different elements are different. 4. Compounds have a definite composition and combine in small whole number ratios. 5. Chemical Reactions involve the reshuffling of the atoms in a compound to make new compounds. 6. Atoms cannot be subdivided.

LAWS FROM ATOMIC THEORY 1. Law of conservation of matter Mass of reactants = mass of products mass cannot be created nor destroyed For example, if you were told that 4 grams of hydrogen reacted with some oxygen to make 36 grams of water then you could figure out how much oxygen must have been used by applying the law of conservation of mass. hydrogen + oxygen = water 4 g + ? = 36 g ? = 36 - 4 = 32 So 32 grams of oxygen were used

LAWS FROM ATOMIC THEORY 2. Law of definite proportions AKA Law of constant composition Every pure sample of a particular compound always contains the same proportion by mass of the elements in the compound the relative amount of each element in a particular compound is always the same H2O, will always have the same percent by weight, e.g. 11.2% H and 88.8% O

LAWS FROM ATOMIC THEORY 3. Law of multiple proportions when elements combine, they do so in the ratio of small whole numbers carbon and oxygen react to form CO or CO2, but not CO1.6

PARTICLES OF THE ATOM ELECTRON- JJ THOMPSON/1897 (plum pudding) Atoms contain – charged particles (corpuscles) - electrons Atoms contain + charged particles later called protons An atom is electrically neutral Atoms need – and + Thought of the atom as a positive charged ball with negative charges throughout. (Plum pudding/Chocolate chip cookie)

How did Thompson do it? a cathode ray tube consists of a gas-filled glass tube in which two metal plates, one negatively charged (the cathode) and the other positively charged (the anode), have been placed. When a very large voltage is placed across the electrodes, the neutral gas inside the tube will ionize into a conducting plasma, and a current will flow as electrons travel from the cathode to the other side.

Rutherford - Bohr PROTON AND NUCLEUS- RUTHERFORD/ 1911 (gold foil experiment)

Rutherford Alpha, beta and gamma particles

Alpha particles – Helium atoms Beta particles – high energy electrons emitted directly from the nucleus Gamma particles is high energy radiation given off by the nucleus

Rutherford’s accomplishments Identified alpha, beta, and gamma particles Showed that new elements were formed as a result of radio active decay of an element Showed that alpha particles were really helium ions (He2+)

Discovered the atomic nucleus (Gold foil) Most alpha particles pass through (atom is mainly space) Some bounce straight back (hit something heavy) – the nucleus Nucleus contained all the protons and most of the mass of an atom Predicted the existence of the neutron – Neutron found by Chadwick in 1932

The atom Particle Symbol Charge Molar Mass Found

Particle Symbol Charge Molar Mass Found Electron e- -1 0.000 549 Outside nucleus Proton p +1 1.007 825 Inside nucleus Neutron n 1.008 665

Borh explained behaviour of electrons outside the nucleus He explained that the electrons orbited the nucleus of an atom Therefore Rutherford-Bohr model Couldn’t make model work with atoms with more than 1 electron, but it is still a good model for understanding atomic structure

NEUTRON-CHADWICK / 1932 Electron Shells/ Bohr / 1913