Democritus Democritus He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided? 400 B.C. His theory: thought matter could not be divided indefinitely There was a limit to how far you could divide matter. You would eventually end up with a piece of matter that could not be cut
He named the smallest piece of matter atomos, meaning not to be cut Aristotle Very famous Greek philosopher Believed matter could be divided smaller and smaller pieces forever
Believed that matter was made of a combination of four elements: earth, fire, water, air Aristotle was wrong. However, his theory persisted for 2000 years. PIECES OF CARBON An atom is the smallest particle that an element
can be divided and still be that element. For example the smallest particle of carbon is a single atom of carbon. If you divide it is no longer carbon anymore. CARBON ATOM 1800 -Dalton proposed a modern atomic model based on experimentation not on pure reason
All matter is made of atoms Atoms of the same element are identical Each element has different atoms Atoms of different elements combine in constant ratios to form compounds. Atoms are rearranged in reactions. His ideas account for the law of conservation of mass (atoms are neither
created nor destroyed) and the law of constant composition (elements combine in fixed ratios). Accidental discovery of the cathode ray Discovery led to the development of the television Joseph John Thompson
What particle did Thompson discover? found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere This sphere contained a soup of positive charge to balance the electron's charge electrons similar to plums in a pudding or
chocolate chips in ice cream. PLUM PUDDING MODEL Negative electron Positive charge spread over sphere Developed the charge of an atom e- Rutherford shot alpha () particles at gold foil Zinc sulfide screen
Thin gold foil Lead block Radioactive substance path of invisible particles Most particles passed through So, atoms are mostly empty space Some positive -particles deflected or bounced back! Thus, a nucleus is positive & holds most of an atoms mass
Electrons orbit the nucleus in shells Electrons can be bumped up to a higher shell if hit by an electron or a photon of light There are 3 types of subatomic particles. electrons (e) protons (p+) neutrons (n0) They have: no charge Elements are often symbolized with their mass number and atomic number
The periodic table give you all this information For now, round the mass # to a whole number # of protons = # of electrons = atomic number Mass number atomic number = # of protons E.g. Oxygen:
16 8O Nuclear Symbol Particle Charge Mass Proton + charge 1
Neutron No charge 1 Electron - Charge nil ATOMIC STRUCTURE EXAMPLE Atomic mass
the number of protons and neutrons in an atom 4 Atomic number the number of protons in an atom 2 He All of these pieces of information (numbers) are obtained from your
periodic table Atomic number = number of electrons = number of protons Practice Atomic Ca Ar Br Mass p+ n0 e
Copy the table right below your notes and fill in the information that is required of you. Use the periodic table to fill in this information. Symbol Calcium Neon Magnesi um Sodium Lithium Oxygen Carbon Potassiu m Silicon Chlorine
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