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Unit 2-5 Ions and isotopes

Unit 2-5 Ions and isotopes. Ions: losing or gaining electrons. In an atom, protons (+) are in the center and electrons (-) are on the outside. only electrons can be added or taken away. +. +. +. +. +. this is an atom with 5 electrons and 5 protons the atom is neutral

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Unit 2-5 Ions and isotopes

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  1. Unit 2-5 Ions and isotopes

  2. Ions: losing or gaining electrons • In an atom, protons (+) are in the center and electrons (-) are on the outside. • only electrons can be added or taken away.

  3. + + + + + • this is an atom with 5 electrons and 5 protons • the atom is neutral • 5 e- and 5 p+ = zero charge (neutral)

  4. + + + + + • charge = 1- (one minus) Now the atom gains one electron from outside • charge = ?

  5. + + + + +

  6. + + + + charge = ? 2+ (two plus)

  7. WHEN AN ATOMLOSES ELECTRONS THE RESULTING CHARGE IS POSITIVE Li+ (plus 1 charge) Li (neutral)

  8. WHEN AN ATOM GAINS ELECTRONS THE RESULTING CHARGE IS NEGATIVE N3- N (neutral)

  9. An atom with positive or negative charge is called an ION Positively charged ion is called cation Negatively charged ion is called anion

  10. IMPORTANT: Cation: electrons are lost. Example: Na+ (one electron lost) Ca2+ Al3+

  11. IMPORTANT: Anion: Ions with a negative charge. In an anion, electrons are gained. Example: Cl-(one electron gained) O2- N3- S2-

  12. AND... Notice that ONLY the number of e- changes (Only electrons are added or subtracted) The number of protons in an Atom NEVER changes, except for nuclear reaction (why?)

  13. What do IONS have to do with anything??

  14. ions make up the salt you put on your eggs in the morning ions are required for your brain to function (ions allow you to see and understand this presentation) ions are an essential ingredient in soap ions are required for cellular respiration ions make up acids and bases

  15. Homework • Page 79, question 59 and 60. Page 80, question 98 and 99. • Due tomorrow.

  16. Isotopes

  17. Isotopes • atoms of the same element with different numbers of neutrons and so have different mass number • most elements exist as a mixture of isotopes in nature • some isotopes are stable and some are not (radioactive) • an unstable (radioactive)isotope will undergo a nuclear reaction to make it’s nucleus stable

  18. There are 3 isotopes of hydrogen • Each is found in water • protium – H2O • deuterium – D2O (heavy water) • tritium – T2O (radioactive) • What is the atomic number of • protium? • deuterium? • tritium?

  19. Naming Isotopes • Hyphen notation: • Name - mass number • ex. Carbon – 13 or C-13 • Symbol

  20. Examples • 7 protons, 8 neutrons Nitrogen-15 or N-15 • 17 electrons, 19 neutrons Chlorine-36 or Cl-36

  21. Masses of Atoms: amuv.s. molar mass • A unit designed for atoms gives their small atomic masses in atomic mass units (amu) • One atom of C-12 was assigned an exact mass of 12.00 amu. One mole of C-12 was assigned an exact mass of 12.00 g. 1 amu= 1 g/mol • The mass of proton or neutron = 1 amu = 1 g/mol • Relative masses of all other atoms was determined by comparing each to the mass of C-12

  22. Average atomic Mass Na 22.99 • This is what is given on the periodic table • Why is it not a whole number? • Average atom based on all the isotopes and their abundance (% in nature) • Average atomic mass is not a whole number • Mass number of each isotope is.

  23. Calculating Average Atomic Mass • Must know 2 things to calculate average atomic mass 1. Percent(%) abundance of isotopes 2. Mass of each isotope of that element Average Atomic Mass = mass isotopeA(%A) + mass isotopeB(%B) + … Remember that % is not a “number” and must be converted to a decimal

  24. Average atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70% 25Mg = 25.0 amu 10.13% 26Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu = 24.3 g/mol Mg 24.3 HOW is this calculated????

  25. Average Atomic Mass Example 1 • Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.

  26. Average Atomic Mass Example 2 A sample of boron consists of 10B and 11B. If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope? This is different …. how?

  27. Assign x and y values: x = % 10B % 11B = 1-x 10(x) + 11(1-x) = 10.8 10x + 11 – 11x = 10.8 - 1x = -.2 x = .2 or 20 % 10B  % 11B = 100 - 20% = 80% 11B

  28. Assign x and y values: x = % 10B y = % 11B Determine y in terms of x x + y = 100 y = 100 - x Solve for x: x (10.0) + (100 - x )(11.0) = 10.8 100 100 Multiply by 100 10.0 x + 1100 - 11.0x = 1080 - 1.0x = -20 x = 20 or 20 % 10B y = 100 - x % 11B = 100 - 20% = 80% 11B

  29. Homework • Page 79, question 53, 54, 55, 74, 77 and 78 • Due tomorrow.

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