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Isotopes and Ions

Isotopes and Ions. Quotes about atoms. From A Short History of Nearly Everything by Bill Bryson “protons give an atom its identity, electrons its personality” p. 140

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Isotopes and Ions

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  1. Isotopes and Ions

  2. Quotes about atoms • From A Short History of Nearly Everything by Bill Bryson • “protons give an atom its identity, electrons its personality” p. 140 • “if an atom were expanded to the size of a cathedral, the nucleus would be only about the size of a fly- but a fly many thousands of times heavier than the cathedral” p. 141

  3. Parts of the atom: • Proton: • + charge • Located in nucleus • Role: identifies the atom • Neutron: • no charge • Located in nucleus • Role: space out nucleus and add mass (stabilize the nucleus) • Electron: • - charge • Located in orbital's outside of nucleus (energy levels) • Role: perform all bonding of atom, give it charge

  4. Atom Model

  5. Atomic Number • Found at top of each element square • Represents the number of protons in atom • If atom is “neutral” number of protons = number of electrons

  6. Atomic Mass • # at bottom of each element box • = # of protons + # of neutrons • To find # neutrons, subtract atomic number from atomic mass • Ex) C: atomic mass = 12, atomic # = 6, • # of protons = 6, • # of neutrons = 6, (12-6) • # of electrons = 6 (= to # of protons)

  7. Atomic Symbols • Shorthand way of writing information • Write symbol for element • Put atomic number in subscript in front of symbol • Put atomic mass in superscript in front of symbol • BASICALLY FLIPPED FROM P.T.

  8. Atomic Symbol Example

  9. What is an ion? • Ion - an atom or group of atoms that has a positive or negative charge • An ion forms when an atom gains or loses electrons (protons identify atom) How does an atom become an ion?

  10. What is the charge on an electron? • negative • If you have more electrons than protons the charge would be? • negative • If you have more protons than electrons? • positive (extra protons)

  11. Cation • Positive charge • Cat-ions are pawwwwwsitive • Formed by the atom losing electrons • Metals (left side of periodic table) form cations Ca Ca2+ + 2e- How many electrons did Ca start with? How many did it end with? 20 18

  12. Anion • Negative charge • An-ion is anegative ion • Formed by the atom gaining electrons • Non-metals (right side of periodic table) form anions O + 2e-O2- How many electrons did O start with? How many did it end with? 8 10

  13. Key Point • If atom has more p+ than e-, it will be a cation, have a + charge • If atom has more e- than p+, it will be anion, have a - charge

  14. Ion atomic Symbol • Can always tell p+, no, e- from atomic symbol, • Must include charge for ion! • Atomic # & atomic mass go on the LEFT • Charge goes on the RIGHT • Ex: Al+3 • How many protons, electrons and neutrons?

  15. What is an isotope? • Isotopes are atoms of the same element with different atomic masses. • They have different masses because they have different numbers of neutrons in the nucleus (remember, neutrons add mass and stability to the atom)

  16. How do you write isotopes? • There are different types of isotope notation: • Carbon-14 C C • These all tell us that we are dealing with an isotope of carbon with an atomic mass of 14. • How many protons and neutrons are in these isotopes? • Protons = 6 • Neutrons = 14 – 6 =8

  17. How many protons and neutrons in these? O N Hydrogen-3 protons = 8, neutrons = 16 – 8 = 8 protons = 7, neutrons = 15 - 7 = 8 protons = 1, neutrons = 3 -1 = 2

  18. Ions & Isotopes • Both ions and isotopes can be shown in the same symbol. • Atomic # & atomic mass go on the LEFT • Charge goes on the RIGHT • How many protons, neutrons and electrons S Protons= 16 Neutrons = 34-16 = 18 Electrons = 16 +2 = 18

  19. Write your own • Write symbols for the following: • The ion with 17 protons, 18 electrons, 20 neutrons: • The ion with 92 protons, 88 electrons, 146 neutrons: Cl- U+4

  20. Key Points (atomic symbols) • Mass Number (# on top) – use to find neutrons • Atomic Number (# on bottom) – use to find protons • Charge Symbol (to right) – use to find electrons

  21. Average atomic mass • So far all the atomic masses we have used have been whole numbers • BUT there are not whole number masses on the periodic table • WHY??? The numbers on the periodic table are AVERAGE atomic masses

  22. Calculating average atomic mass • Average atomic mass is calculated by taking the average of all the different isotope masses • For example, if these were the only 5 atoms of carbon we had: • Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14 • What would the average mass be? • 12+12+12+14+14 / 5 = 12.8

  23. We can’t possibly weigh every atom in the world though… • So we have to average their abundances • How much of them exists in relation to total • Using our example from before: • Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14 • Abundance of carbon-12 = 3/5 = (0.60 relative abundance) 60% • Abundance of carbon-14 = 2/5 = (0.40 relative abundance) 40% • Calculate average mass: 12g(0.60) + 14g(0.40) = 12.8g • SAME ANSWER!!! LESS WORK!!

  24. Practice Problem #1 • Calculate the average atomic mass of magnesium using the following data for three magnesium isotopes. • Isotope mass (amu) % abundance • Mg-24 23.985 78.70 • Mg-25 24.986 10.13 • Mg-26 25.983 11.17

  25. Practice Problem #2 • Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic masses and abundances in nature: • Lithium-6, 6.017 amu, 7.30% • Lithium-7, 7.018 amu, 92.70%

  26. Key Points • % of all isotopes has to add up to 100! • Make sure to take %’s and convert to relative abundance (move decimal 2 places to right)

  27. What happens when you change… • Protons: number of protons is the same as the atomic number, protons are what define an element. • change the protons you change the element • Neutrons: The neutrons add to the mass and stability to the element. • change the mass of the element (make an isotope) • Electrons: The electrons balance the charge of the protons. • change the charge of the element (make an ion)

  28. Marshmallium Lab • On the BACK: • Calculate average marshmallow mass using the LONG way • Find the mass of each marshmallow, add them all up and divide by the total number of marshmallows • Write a sentence about why the way on the front (read directions) is easier.

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