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Name_________________________ Date________ Class_______ Chapter 14.1 Notes The Structure of the Atom Lesson Objectives Define the atom. Explain how Democritus and John Dalton described atoms. Identify the instruments used to observe individual atoms Vocabulary atom Dalton’s atomic theory proton nucleus electron atomic mass mass number neutron cathode ray Atoms Atoms are the smallest particles of an element that still have the chemical properties of that element. Scientists once believed atoms were the smallest particles of matter. With the advancement of technology, it has become clear that atoms themselves are made up of simpler (sub-atomic) particles. Sub-atomic Particles Atoms have positively charged protons and neutral neutrons inside a nucleus, and negatively charged electrons outside the nucleus. Atoms of the same element have the same number of protons, which is equal to an atom’s atomic number. Atomic number also describes the location of the element on the periodic table. All the known elements are arranged on the periodic table based on increasing atomic number. Because atoms are neutral, the atomic number equals the number of electrons in the atom. Some atoms may have more electrons or fewer electrons than protons, such atoms are called ions. Ions with more electrons are negatively charged, while those with fewer electrons, positively charged. Atoms of the same element may have different numbers of neutrons. Such atoms are called isotopes. Isotopes of a given element have the same atomic number, but different mass numbers. Democritus and the Atom The concept of the atom intrigued a number of scholars, both scientists and philosophers. Although they could not observe individual atoms, they were still able to propose ideas about the structure of the atom. The Greek philosopher was among to suggest the existence of atoms. He reasoned that atoms were both indivisible and indestructible. Democritus however could not: Explain chemical behavior of elements. Did not have experimental support (not based on scientific method). Dalton’s Atomic Theory By using experimental methods, Dalton (1766-1844), an English chemist and schoolteacher transformed Democritus ideas on atoms into a scientific theory. Dalton studied the ratios in which elements combined in chemical reactions. Based on the results, he formulated his now famous Dalton’s Atomic Theory. Chemical reactions occur when atoms are separated from each other, join, or re-arranged in a different combination. Atoms of one element can never be changed into atoms of another element. Sizing up the Atom Atoms are very small. A pure copper coin / penny contains 2 x 10 22 atoms of copper. The world population is currently 7 x 10 9people There are 3 x 1012 (3 000 000 000 000) many atoms in the small coin as there are people on the planet. 10 000 000 (1x 107) copper atoms lined up side by side would only be 1 cm. long. Individual atoms have been observed using scanning electron microscopes (SEM) With the help of electron microscopes, individual atoms can be manipulated to form new patterns. This new technology (nanotechnology) has great potential in medicine, communication, energy and even space exploration. Name____________________________________ Date_______ Ch. 14-1Lesson Check 1. How did Democritus characterize atoms? __________________ 2. How did Dalton advance the atomic philosophy proposed by Democritus__________________________________________ ___________________________________________________ 3. What instrument can be used to observe individual atoms? ___________________________________________________ 4. Explain the main ideas of Dalton’s theory____________________ ___________________________________________________ ___________________________________________________ 5. Why do the ideas on atoms proposed by Dalton are considered a theory while those proposed by Democritus are not? ___________ ___________________________________________________ 6. According to Dalton’s theory, is it possible to convert atoms of one element into atoms of another? Explain._____________________ ___________________________________________________ 7. A dozen of eggs have a mass of 635 g. Calculate the mass of a single egg. (Show your work). 8. A sample of copper with a mass of 63.5 g contains 6.02 x 10 23 atoms. Calculate the mass of a single copper atom. (Show your work). 9. What are the three subatomic particles? What are the relative charges and masses of each particle? Particle Symbol Relative charge Relative mass 10. Complete the table below Name Symbol Atomic Protons Electrons Neutrons Mass number H number 1 0 Sulfur 32 Ne Sodium 10 11 12 Fe Calcium 56 20