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ATOMIC THEORY Created by Campesi, SMS The smallest particle into which an element can be divided and still be the same substance is an ATOM An explanation for hypotheses and observations that have been supported by testing is a Theory Democritus, Greek philosopher, said that you would eventually end up with an “uncutable” particle that he called an ATOM Billard ball model Dalton developed the atomic theory based on experiments! Dalton Theory Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different. Dalton Theory Atoms join with other atoms to make new substances with new and different properties. Thomson Theory Thomson discovered that there are small particles inside the atom. Atoms can be divided into even smaller parts. Thomson Theory Thomson found the electron. Plum pudding model or chocolate chip ice cream. Rutherford Theory Rutherford presents a new atomic model Proposed that in the center of the atom is a tiny extremely dense positively charged region called the NUCLEUS . Bohr Theory Bohr suggested that electrons travel around the nucleus in definite paths. Electrons can jump levels. Modern Theory Electrons do not travel in definite paths as Bohr suggested. Regions inside the atom where electrons are likely to be found are called electron clouds. Inside an Atom Proton-positively charged particles inside the nucleus with a mass of 1 amu. Protons are what make an atom what it is. Atomic number is the number of protons. Neutron-neutral particle inside the nucleus with a mass of 1 amu. Neutrons just make an atom “fat.” Electrons-negative chargein the electron cloud-almost no mass. Atom is neutral-equal number of protons and electrons so they cancel each other out. If protons and electrons are not equal it becomes a charged particle called an ion. Isotopes are atoms that have the same number of protons but have different numbers of neutrons. The element does not change as long as it has the same number of protons. Isotopes can be unstable or radioactive. The isotopes of an element share similar properties. Mass number is the number of protons and neutrons in an atom. Naming isotopesHydrogen-1, hydrogen-2, carbon-12, carbon-14 Atomic mass is the weighted average of the masses of all the naturally occurring isotopes of an element. ATOMIC MASS IS NOT A WHOLE NUMBER. Number of protons Number of Electrons. Subtract atomic number To get # of neutrons Number of protons= 3 Number of electrons= 3 Round to nearest whole Number of neutrons= 4 Forces in the Atom Gravity between all objectssmall mass in an atom small gravity. Electromagnetic forceopposites attract, holds electrons in orbit around the nucleus. Strong force- hold the nucleus together despite the electromagnetic force. Weak force- plays a role in radioactive atoms.