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Chapter 3 Notes – Atomic Theory and Structure Atoms An ________ is the smallest unit of an _____________ that still has all the _____________of that element. Atoms are very, very ____________. However, atoms are visible with the proper tools. A ______________ _______________ ________________ can be used to visualize atoms. The idea of atoms was first suggested by the Greek philosopher _________________ in the 4th century B.C. He stated that atoms ________________, _________________, fundamental units of matter. Democritus did not do any _____________ to back up his ideas, so they never became a _____________. Dalton’s ideas were ignored for the next ____________ years for two reasons: o _________________, who was much more famous and influential, refuted the idea of atoms. o Most scientists were preoccupied with the field of ________________. Alchemy The first chemists were ______________. Alchemy began in ____________ and _____________ in 400 B.C. The goal of alchemists was to The alchemists did not accomplish this goal, but they did do many things that spurred the development of science. o They performed the first . o They discovered many . o They designed the first , , and many types of ______________________. o They developed procedures like and . Their experiments led to the development of two laws: 1. The law of 2. The law of The Law of Conservation of Mass Developed by in 1792. Lavoisier observed many chemical reactions occurring inside sealed containers. He noticed that the mass of the was always the same as the mass of the . This observation is now known as the . This law states that in any chemical reaction, mass is not ________ or ____________, only ________________. The Law of Definite Proportions Proposed by in 1799. Proust studied the composition of many He found that compounds always contained the same . in the same _______________________. For example, water is always ________ oxygen and ________ hydrogen. The led to the law of This law states that compounds always contain the same elements in the same proportions. . Dalton’s Atomic Theory In the 1800s, an English schoolteacher named Unlike Democritus, Dalton performed Based on his results, he proposed the first Dalton’s atomic theory included the following key points: 1. All also studied atoms. in 1803. are composed of . and . 2. Atoms are 3. Atoms of the same element are . Atoms of one element are _______________ from any other element. 4. Atoms of different elements can in small whole-number ratios to form . 5. When chemical reactions occur, atoms are , , or . But atoms of one element can never be changed to atoms of ________________ ________________. Most of Dalton’s theory is still accepted today. But two important changes have been made. 1. One is that atoms of the same element are not always 2. The other is that atoms are not Atoms can be divided into three subatomic particles: 1. ________________ 2. _______________ 3. ________________ Electrons Can be abbreviated __________ __________________ charged. . . Discovered by _______________________ in 1897 through a series of ___________________ _______ experiments. Have a mass that is about ______________ of the smallest known atom. The discovery of the electron allowed scientists to make two important assumptions: 1. Because the e- is so ____________, atoms must contain other particles to account for the rest of their _______________ 2. Because atoms are ______________, they must contain some sort of ______________ charge to balance out the _____________ electron. Protons Abbreviated ________. ______________ charged subatomic particle. The discovery of the proton is not credited to any one person. Have a mass that is about ___________ times greater than the electron. Neutrons Abbreviated ______ ______________ subatomic particle. Discovered by ____________ _______________ in 1932. The mass of the neutron is about the same as the mass of the _____________. Atomic Structure Dalton imagined atoms as . Thomson imagined that atoms looked like a : a solid sphere with _______________ scattered throughout. In 1911, Ernest Rutherford performed his famous . This experiment led to an entirely new view of the atom. At this time, scientists knew that atoms contained both ___________ and ____________. However, they did not know how these particles were _____________. Rutherford’s work showed that atoms are mostly with a very dense at the center. Rutherford realized that the must be located in the We now know that are also located in the He proposed that the must float somewhere in the . . around the nucleus. Many scientists were reluctant to accept this model however, because it had one very obvious flaw. Since protons are and electrons are particles should But according to Rutherford’s model, they do not. , the oppositely charged In 1913, a scientist named proposed a new model of the atom. He suggested that electrons could only be found in certain places in the atom. He called these places ___________, or ____________ ___________. Bohr believed electrons orbit the _________ much like planets orbit the sun. His model of the atom is also called the In Bohr’s model, electrons filled the energy levels in an orderly manner. _____ electrons fit into the first energy level. _____ fit in the 2nd and 3rd. The 4th and 5th could hold ________. . Atomic Number Number of ____________ in an atom. All atoms of an element have the same Atomic numbers are used to an element. Can be found on the , above the element’s symbol. Ex: The atomic number of carbon is 6. There are 6 p+ in carbon. Atoms are . . So they must contain the same number of _________________ as ______________. Ex: carbon also has 6 electrons. Mass numbers can also be written: You can determine the composition of an atom using its mass # and atomic #. o Atomic # = # protons o # of protons = # of electrons o Mass # = protons + neutrons o Neutrons = mass # - protons Isotopes Isotopes are atoms of the same element with different __________. They have different masses because they have different numbers of They also have different Ex: Hydrogen has three isotopes: o Hydrogen 1 – protium o Hydrogen 2 – dueterium o Hydrogen 3 - tritium . . Ions Sometimes, atoms can gain or lose . When this happens, the atom is no longer . The atom becomes an An ion has a or If the atom electrons, it becomes a If it Ex: If a Lithium atom loses an electron, it becomes an ion with a charge of +1. This is written Li+1. A positive ion is called a . A negative ion is called an . To determine the # of protons, neutrons, and electrons in an ion: . charge. electrons, it becomes o p+ = atomic # o no = mass # - p+ o e- = atomic # - charge of ion ion. .