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Friday, Oct. 25 th : “A” Day Monday, Oct. 28 th : “B” Day Agenda Finish section 3.2: “Structure of Atoms” Atomic number, mass number, isotope Movie: “Writing Nuclear Symbols” and worksheet Homework: Sec. 3.2 review, pg. 89: #1-8 Finish movie worksheet Concept Review: “Structure of Atoms”
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Atomic Number is the Number of Protons in the Nucleus Atomic Number: the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element. No two elements can have the same atomic number.
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The Atomic Number Also Tells the Number of Electrons The atomic number also reveals the number of electrons in an atom. Why? For atoms to be electrically neutral, the number of positively charged protons must equal the number of negatively charged electrons. If you know the number of protons in an atom, you automatically know the number of electrons too!
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Mass Number is the Number of Particles in the Nucleus Mass Number: the sum of the numbers of protons and neutrons of the nucleus of an atom. (also called atomic mass ) Protons + Neutrons Mass Number Unlike the atomic number, the mass number can vary between atoms of a single element.
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Atomic Number/Mass Number
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Sample Problem A, pg. 86 How many protons, electrons, and neutrons are there in an atom of copper whose atomic number is 29 and whose mass number is 64? Atomic number = number of protons = 29 Protons = electrons = 29 Mass number = protons + neutrons 64 = 29 + Neutrons Neutrons = 35
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Practice Problem #3, pg. 86 Calculate the mass number for an atom that has 45 neutrons and 35 electrons. Mass number = protons + neutrons Protons = electrons = 35 Mass number = 35 + 45 Mass number = 80 Which element is this? Bromine (Br)
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Atomic Structures Can Be Represented by Symbols (nuclear symbols) Each element has a name and symbol that is listed in the periodic table of elements. Sometimes, atomic numbers and mass numbers are written with an element’s symbol. Atomic #: whole number Mass #: has decimal point
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Atomic Structures Can Be Represented by Symbols The atomic number always appears on the lower left side of the element’s symbol: 1 H 2 He 3 Li 4 Be 5 B Mass numbers are written on the upper left side of the symbol: 1 1 H 2 4 He 3 7 Li 4 9 Be 5 11 B **mass number = protons + neutrons**
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Isotopes of an Element Have the Same Atomic Number All atoms of an element have the same atomic number and the same number of protons. However, atoms of the same element do not necessarily have the same number of neutrons. Isotope: an atom that has the same number of protons (atomic number) as other atoms of the same element, but has a different number of neutrons (atomic mass).
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Two Ways of Identifying Isotopes 1.Write the mass number with a hyphen after the symbol for the element: He-3 This is a helium atom with a mass number of 3. 2.Write the nuclear symbol for the isotope: 2 3 He This is also a helium atom with a mass number of 3. *Remember: all isotopes of an element have the same atomic number and the same number of protons!*
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Sample Problem B, pg. 89 Calculate the number of protons, electrons, and neutrons in oxygen-17 and in oxygen-18. These are both isotopes of oxygen, whose atomic number is 8. Atomic number = number of protons = 8 Protons = electrons = 8 Mass number = proton + neutrons For oxygen-17: 17 = 8 + neutrons Neutrons = 9 For oxygen-18: 18 = 8 + neutrons Neutrons = 10
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Movie: “Writing Nuclear Symbols” The movie is really short, about 8 minutes. Worksheet Complete the front side of the worksheet that goes along with the movie The back side is homework
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Homework Section 3.2 review, pg. 89: #1-8 Finish “Writing Nuclear Symbols” worksheet Concept Review: “Structure of Atoms ” *Be ready for a quiz over section 3.2 next time*
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