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Notes: Atomic Structure (Chapters 4) Essential questions: 1. What components make up an atom? 2. How are atoms of one element different from atoms of another element? 3. How does the quantum mechanical model of the atom describe the arrangement of electrons in atoms? 4. What happens when electrons in atoms absorb or release energy? Equations: # Neutrons = Mass # - Atomic # 4.1 DEFINING THE ATOM A. Early Models of the Atom Key Question: How did the concept of the atom change from the time of Democritus to the time of John Dalton? Answer:_______________________________________________________________________ Atomic Theory Main Ideas (1803) 1. __________________________________________________________________________ 2. __________________________________________________________________________ 3. __________________________________________________________________________ 4. ___________________________________________________________________________ See Figure 4.1. How does a mixture of different atoms of elements differ from a compound? _________________________________________________________ B. Sizing up the Atom Key Question: What instruments are used to observe individual atom? ______________________________________________________________________________ Using a ruler, draw a line 1 centimeter long: _____________________________ atoms of copper = 1 cm _____________________________________________________________________________________ 4.2 STRUCTURE OF THE NUCLEAR ATOM ____________________________________________________________________________________ A. Subatomic Particles Atom _________________________________________________________________________ Key Question: What are the three kinds of subatomic particles? ________________________________________________________________________________ ______________________________________________________________________________ Derived from Greek work __________________ meaning ____________________ Electrons _________________________________________________________________ Democritus (Greek philosopher ___________BC- __________BC) a) Discovered by English physicist __________________________ in reasoned _____________________________________________________ _____________ using a ______________________________________. John Dalton (English chemist & schoolteacher, _____________) using _______________________________________________________________ _____________________________________________________________________ How was John Dalton able to study atoms even though he was unable to see them directly? What evidence did he use to form his theory? ___________________________________________________________________ ___________________________________________________________________ List two reasons why the ideas of Democritus were not useful in a scientific sense._______________________________________________ _____________________________________________________________ The diagram above shows electrons moving from left to right in a cathode-ray tube. Draw an arrow showing how the path of the electrons will be due to the negative and positive plates. b) Robert A Millikan (American physicist) in 1909 experimented with Complete the following table: oil drops. What two properties of an electron did he find? 1. __________________________________________________ Properties of Subatomic Particles Particle Symbol 2. ___________________________________________________ B. Atomic Nucleus Key Question: How can you describe the structure of the nuclear atom? ____________________________________________________________________ ___________________________________________________________________________ Nucleus _________________________________________________________________ A. Protons _______________________________________________________ Relative charge Relative mass (proton = 1) Actual mass (g) Electron e- 9.11 x 10-28 Proton p+ 1.67 x 10-24 Neutron n0 1.67 x 10-24 4.3 DISTINGUISHING AMONG ATOMS A. Atomic number and Mass number Evidence found by ________________________ in a cathode-ray Key Question: What makes one lement different from another? tube found positive “canal rays”. Answer: ______________________________________________________________ B. Neutrons ______________________________________________________ Discovered byEnglish physicist ______________________ in 1932; they are composed of ___________________. Models of an atom: 1. J.J. Thomson called his model the ____________________________model where _____________________ were evenly distributed through an atom with ______________________charged material (not protons). Atomic number ____________________________________________________ The atomic number defines the element! The symbol for the atomic number is Z. Mass number ________________________________________________________ The mass number defines the isotope of that element. The symbol for mass number is A. Nuclear Symbol: 2. Ernest Rutherford (JJ Thomson's student) devised the ____________ example: A X foil experiment. Circle the letter of each sentence that is true about the nuclear theory of atoms suggested by Rutherford’s experimental results. a. An atom is mostly empty space. b. All the positive charge of an atom is concentrated in a small central region called the nucleus. c. The nucleus is composed of protons. d. The nucleus is large compared with the atom as a whole. e. Nearly all the mass of an atom is in its nucleus. affected by the placement of the negatively and positively charged plates. 12 C Z 6 This is example is C-12. Carbon-12 has 6 protons and 6 neutrons, totaling 12 amu. Complete the following table: Isotope Atomic Number Mass Number Protons Neutrons 5 5 S-34 V -51 Electrons B. Isotopes Key Question: How do isotopes of an element differ? b. Isotopes of an element do not have a specific natural percent abundance. Answer: ______________________________________________________________ c. The average atomic mass of an element is usually closest to that of the isotope with the highest natural abundance. Practice problems: d. Because hydrogen has three isotopes with atomic masses of about 1 amu, 2 amu, and 3 amu, respectively, the average atomic mass of natural hydrogen is 2 amu. 1. Three isotopes of oxygen exist: O-16, O-17, and O-18. Write the nuclear symbol for each, including the atomic number and mass number. O-16 O-17 O-18 2. Three isotopes exist for chromium: Cr-50, Cr-52, and Cr-53. How many neutrons are in each isotope, given the atomic number of chromium is 24? 3. How do atoms of Neon-20 and Neon-22 differ? C. Atomic Mass Key Question: How do you calculate the atomic mass of an element? Answer: ____________________________________________________ _________________________________________________________________________ Atomic mass unit (amu) What isotope of carbon has been chosen as the reference isotope for atomic mass units? ____________________ What is the defined atomic mass in amu of this isotope? ____________ Atomic mass _________________________________________________________ _________________________________________________________________________ Circle the letter of each statement that is true about the average atomic mass of an element and the relative abundance of its isotopes. a. In nature, most elements occur as a mixture of two or more isotopes. Example problem: Calculating Atomic Mass Element X has two naturally occuring isotopes. The isotope with a mass of 10.012 amu (10X) has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu (11X) has a relative abundance of 80.09%. Calculate the atomic mass of element X. Knowns isotope 10X mass = 10.012 amu relative abundance = 19.91% = 0.1991 iostope 11X mass = 11.009 amu relative abundance = 80.09% = 0.8009 Unknown atomic mass of X = ? Solve for 10X 10.012 amu x 0.1991 = 1.993 amu for 11X 11.009 amu x 0.8009 = 8.817 amu for element X, atomic mass = 1.993 amu + 8.817 amu = 10.810 amu (Answer) Practice problem: Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%). Compare your answer to the atomic mass of bromine on a periodic table. Knowns Unknown Essential Questions: 1. How does the quantum mechanical model describe the arrangement of electrons in atoms? 2. What happens when electrons in atoms absorb or release energy?