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Atomic structure and History Notes Democritus- 440 B.C. He proposed that if you kept cutting something in half you would eventually end up with an “________________” particle. Which he called an atom Greek: Atomos - ________________ Aristotle- 338-322 B.C He disagreed with Democritus. He believed you would never end up with an indivisible particle. Dalton- 1808 In search of understanding why elements combine in specific ratios he discovered through his experiments that this happens because they are made of___________ atoms. His theory states 3 things Atoms are small and cannot be ___________,___________ or___________. Atoms of the___________ element are all alike 3-Atoms join with other atoms to make ___________ substances ___________ discovered electrons. His plum-pudding model described the atom as a lump of positively charged material with negative electrons scattered throughout. ___________ discovered that atoms contain a small, dense, positively charged center called the nucleus. ___________ suggested that electrons move around the nucleus at only certain distances. According to the current atomic theory, electron clouds are where electrons are most likely to be in the space around the nucleus. Atoms are extremely ________________. Atoms contain a ________________. Atoms are made of subatomic particles : ________________ , ________________, ________________ Protons ________________ charged particles (+). Found in the nucleus. All protons are identical Each proton= 1________________ (atomic mass unit) Every atom of the same element has the ________________number of protons. Neutrons Particles that have ________________ Found in nucleus All neutrons are identical Protons & Neutrons are the most massive particles in the atom but located in ________________small area (nucleus) Electrons ________________ charged particles (e-) Located outside of the nucleus in ________________ or levels called atomic clouds Their mass is so small that it is usually considered________________ . It takes more than 1,800 electrons to equal the mass of one proton. However electrons occupy most of an atoms ________________. In an atom, the number of protons equals the number of electrons. As a result, the positive charge from protons equals the number of electrons which makes the atom ________________. Force of Attraction The four forces at work in an atom are ________________, the electromagnetic force, the strong force, and the ________________. • • • • The _________ ring can only hold ____ electrons The _________ring can hold up to ____ electrons The _________ ring can hold up to ____electrons _________ can hold up to ____. • • Isotopes of hydrogen and uranium are shown as examples of the isotope notation method illustrated in the previous image. ______________________________________________ ________________________________________________________________________ Isotopes are atoms that have the ___________________ but have different number of neutrons •
