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Chemistry Atomic Theory

Chemistry Atomic Theory. Atomic Structure, Isotopes, Ions, Atomic Mass Do Now – Take out HW to check. CALCULATORS REQUIRED PERIODIC TABLES REQUIRED. Atoms. Atoms contain three subatomic particles Protons (p + ) Neutrons (n 0 ) Electrons (e - )

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Chemistry Atomic Theory

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  1. ChemistryAtomic Theory Atomic Structure, Isotopes, Ions, Atomic Mass Do Now – Take out HW to check. CALCULATORS REQUIRED PERIODIC TABLES REQUIRED

  2. Atoms • Atoms contain three subatomic particles • Protons (p+) • Neutrons (n0) • Electrons (e-) • Protons and neutrons are located in the nucleus. • Electrons surround the atom in an electron cloud. • How big is the atom?

  3. Periodic Table Information • Atomic Number – number of protons • Protons determine the identity of the element • Atomic Mass – the average mass of an atom of that element. • Measured in amu (atomic mass units)

  4. Isotopes • Isotopes are atoms of the same element that have different masses. • Carbon has three naturally occurring isotopes. • Carbon-12 (98.9%), carbon-13 (1.1%), carbon-14 (less than 0.1%) • The weighted average of these isotopes gives the atomic mass seen on the periodic table. • The average of C-12, C-13, and C-14gives the atomic mass on the periodic table: 12.0107 amu

  5. Mass Number • Each subatomic particle has a certain mass: • Protons: 1 amu • Neutrons: 1 amu • Electrons: 1/1837 amu • The mass of an electron is so small that we usually ignore it. • The mass number of an isotope is the sum of the protons and neutrons. • Carbon-12 has a mass number of 12. • 6 protons, 6 neutrons

  6. Atomic Charge Since atoms are neutral, the number of protons must equal the number of electrons. How many protons, neutrons, and electrons are in an atom of nitrogen-15? Nitrogen-14?

  7. Isotopic Symbol For helium-4, this is the proper isotopic symbol: How many protons, neutrons, & electrons does this represent?

  8. Practice • For sulfur-32… • How many protons? • How many neutrons? • How many electrons? • What is the atomic number? • What is the mass number? • What is the isotopic symbol?

  9. Changing Subatomic Particles Changing protons changes the element. Changing neutrons makes an isotope. Changing electrons makes an ion.

  10. Ions • An ion is a charged version of an atom, due to having unequal protons and electrons. • The charge of an ion is written on the upper right of the atomic symbol. • Ex: Na+ (+1 charge) • O2- (-2 charge) • F- (-1 charge) • These charges can also be placed on isotopic symbols: (oxygen-16 ion)

  11. Cations & Anions • Ions with a positive charge have lost electrons, and are called cations. • “Cats have pluses in their eyes” • Na+, Al3+, Fe2+ • Ions with a negative charge have gained electrons, and are called anions. • “Anti” – negative • S2-, F-, N3-

  12. Cations & Anions

  13. Sample Problem • For a +2 ion of cobalt-60… • Is this a cation or anion? • What is the atomic number? • What is the mass number? • How many protons, neutrons, and electrons? • What is the charge? • What is the isotopic symbol?

  14. Atomic Mass vs. Mass Number • Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. • Atomic mass is calculated from all of the natural isotopes of an element averaged together from their relative abundances. • Like a class’s test average • Mass number is the mass, in amu, of one specific atom or isotope. • Like a single student’s test grade

  15. Calculating Atomic Mass • Calculating the atomic mass of an element involves using a weighted average. • A weighted average takes into account how much of each component there is. • Example – test scores • If 70% of the class gets a 90, 20% gets an 80, and 10% gets a 70, what score would you expect the class average to be closest to?

  16. Calculating Atomic Mass We use this concept to determine atomic mass. Atomic Mass = (%)(mass number of isotope 1) + (%)(mass number of isotope 2) + … The number of isotopes used determines how many terms in your equation! The percentages must be converted to decimals for this to work! (99% = 0.99)

  17. In-Class Example Naturally occuring chlorine is 75.78% chlorine-35, and 24.22% chlorine-37. Calculate the average atomic mass of chlorine.

  18. In-Class Example (Algebra Connection) If the average atomic mass of carbon is 12.0107 amu, and we assume that the only possible isotopes are carbon-12 and carbon-13, what are the percent abundances of each?

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