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Atomic Structure

Atomic Structure. Standards. 1a. Students know how to relate the position of an element in the periodic table to its atomic number and atomic mass. 1b. Students know how to use the periodic table to identify metals, semi-metals {metalloids}, non-metals, and halogens

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Atomic Structure

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  1. Atomic Structure

  2. Standards • 1a. Students know how to relate the position of an element in the periodic table to its atomic number and atomic mass. • 1b. Students know how to use the periodic table to identify metals, semi-metals {metalloids}, non-metals, and halogens • 1e. Students know the nucleus of the atom is much smaller than the atom yet contains most of its mass.

  3. Purpose • We will use this information to build our chemistry knowledge. • We will use this information as the foundation to calculate limiting reagent problems. • The standardized exams in the spring will test you on this information.

  4. Objectives • Know the 3 particles of the atom and where they reside • Know the difference between atomic number and mass number • Know how to write nuclide symbols • Know the three isotopes of hydrogen • Know how to calculate atomic mass • Know how to calculate percent composition

  5. First Some Questions… • What are atoms made up of? • Protons, Neutrons and Electrons • Where do you find these particles? • Protons and Neutrons are located in the nucleus • Electrons are located in the outer rings, outside the nucleus.

  6. Vocabulary • Atom- from the Greek atomos=indivisible. The atom is the smallest particle of an element that retains the properties of that element. • Nucleus: the center of the atom; composed of neutrons and protons. Because the mass of the proton and the neutron is much larger than that of electrons, almost all the mass is located in the nucleus. • Ion: a charged particle; # protons ≠ # electrons • Electrons occupy most of the volume of an atom outside/around the nucleus.

  7. Fundamental Particles • Proton • A positively charged particle located in the nucleus. • Neutron • A neutral particle located in the nucleus. • Electron • A negatively charged particle located outside the nucleus.

  8. Question • What differentiates one atom from another atom? • The number of PROTONS

  9. Atomic Number (Z) • Number of protons in the nucleus of an atom • This number is found on the Periodic Table • Atomic Number identifies an element • Always a positive number (b/c it is a counting #) • Tells number of electrons in a neutral atom • An atom is electrically neutral

  10. What does it mean to be electrically neutral? • The atom has no charge • The number of protons = the number of electrons

  11. Question • What observations can you make about atomic numbers on the periodic table? • Atomic Number increases as you go across the rows from left to right.

  12. Questions • What is the atomic number of Chlorine? • What can you tell me about its protons and electrons? • What element has 20 protons? • What is the relationship between the # protons and the atomic number? • They’re equal.

  13. Complete the Chart K 19 19 Boron B 5 Sulfur S 16 Yttrium 39 39

  14. Mass Number (A) • Total number of protons and neutrons in the nucleus of an atom • Always a positive number • You can determine the nuclear composition of an atom from its mass number and atomic number

  15. Question • What do the atomic number and the mass number have in common? • Both Positive integers • Both havethe same # of protons

  16. How to find # of Neutrons • Mass # - Atomic#= # Neutrons • Or • # protons + # neutrons= Mass # • (atomic number + # neutrons)=Mass #

  17. Complete the Chart 19 9 9 F 14 29 14 Si 22 22 25 Ti 25 30 25 Mn 6 12 6 6

  18. Isotopes • Atoms of the same element with differing numbers of neutrons • Atoms with the same atomic number but different mass number • Isotopes of an element have different masses • Chemical properties of different isotopes are virtually the same

  19. Nuclide Symbol • A=Mass # • Z= Atomic #

  20. Nuclide • A specific kind of atom • Specification of an element in terms of its nuclear composition/structure • Tells number of protons and number of neutrons

  21. Complete the Chart 19 9 9 F 14 29 14 Si 22 22 25 Ti 25 30 25 Mn 6 12 6 6

  22. 3 Isotopes of Hydrogen Protium 1 0 1 Deuterium 1 1 1 Tritium 1 2 1

  23. Nuclides • By specifying the nuclear structure, then you call it a nuclide. • But if you say Carbon atom, you do not know which Carbon atom it is, therefore you don’t know how many neutrons it has • Example: Brothers and Sisters- • You are members of the Jones family, but you have not specified which Jones member you are referring to.

  24. Write the nuclide name and nuclide symbol Chlorine-37 Anion Calcium-40 Cation Uranium-238

  25. Atomic Mass • A weighted average of the atoms in a naturally occurring sample of the element. • Naturally occurring: no matter where you get the sample from, it will have the same percentages of isotopes.

  26. Construct a Fruit Basket • Fruit TypeWeight of Each Piece 2 grapefruit 14 oz 4 apples 10 oz 3 pears 7 oz 1 kiwi 3 oz • What is the Average Weight?

  27. Fruit Basket • Average weight=9.2oz • Each type of fruit makes a different contribution to the overall weight • How many pieces of fruit actually weigh 9.2 ounces? • None! • What does 9.2 oz mean? • Fictitious non-existent piece of fruit

  28. Atomic Mass • If you have a recipe, you could count items to put in, say 200 chocolate chips, 3 eggs, etc. • But suppose I have a recipe to make a compound. • I need 100 hydrogen atoms and 50 oxygen atoms-you cannot count atoms or pluck them out with atomic tweezers! • So instead they mass them (weigh them) • Careful here, the mass of an object is completley different from the weight of an object.

  29. Question • What accounts for the mass of the atom? • # protons & # neutrons in the nucleus

  30. Atomic Mass • Know that 1.0 amu is defined as exactly 1/12 the mass of a atom. • Carbon-12 has 6 protons and 6 neutrons, therefore 1 proton or 1 neutron = ~1 amu • 1 amu = 1.6606 x 10 -24 grams • Since the mass mostly depends on # protons and # neutrons, you’d think atomic mass would be a whole number, but it isn’t. How come?

  31. Atomic Mass • In nature, most elements exist as a mixture of 2 or more isotopes. • Each isotope of an element has a fixed, constant mass and fixed constant relative abundance. • Relative abundance- (amount) X 100=% (how much of each isotope is present) • Sample of carbon from anywhere in the world; coal from S. Africa, W. Virginia or Pennsylvania → 99% C-12 and 1% C-13 • Atomic Mass of periodic table takes into account the larger and smaller masses of the isotopes, just like the average piece of fruit accommodated the larger and smaller masses. • → Idea of weighted average

  32. Calculating Atomic Mass • To calculate atomic mass you need to know 3 things: • # of stable isotopes • Mass of each isotope • % abundance of each isotope • Each isotope is a piece of fruit and the isotope’s mass is the weight of each piece of fruit.

  33. Example: Chlorine Calculation • mass of isotope X relative abundance + mass of isotope X relative abundance =_______amu • (34.969)(.7553) + (36.935)(.2447) = • That’s the same value on the periodic table! 35.4500amu

  34. Question • How many chlorine atoms actually have a mass of 35.45 amu? • NONE • So the atomic mass, in amu, is the average of a fictitious non-existent atom of an element.

  35. Example: Copper Calculation (62.9298)(.6909)+(64.9278)(.3091)= 63.5464 amu

  36. Calculating Relative Abundance • To Calculate % Abundance: • Make a Chart • Isotopic Mass X %Abundance of each isotope • Set-up equation • Solve for “x” • Plug in “x” value to solve for “y”

  37. Example x 1- x 1.00 x + y = 1.00 y = 1 – x 10.103 (x) + 11.009 (1 –x) = 10.811 10.103x + 11.009 -11.009x = 10.811 -0.996x = -0.198 x = .1987 y= 1-.1987 y= .8013 B-10 = 19.87% B-11 = 80.13%

  38. The End

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