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Atoms, Ions and Isotopes

Atoms, Ions and Isotopes. Subatomic Particles. Particle Symbol Charge Relative Mass Electron e - 1- 0 Proton p + + 1 Neutron n 0 1. Atomic Number. Counts the number of protons in an atom. Atomic Number on the Periodic Table. 11 Na. Atomic Number.

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Atoms, Ions and Isotopes

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  1. Atoms, Ions and Isotopes

  2. Subatomic Particles Particle Symbol Charge Relative Mass Electron e- 1- 0 Proton p+ + 1 Neutron n 0 1

  3. Atomic Number Counts the number of protons in an atom

  4. Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

  5. All atoms of an element have the same number of protons 11 Na 11 protons Sodium

  6. Number of Electrons • An atom is neutral • The net charge is zero • Number of protons = Number of electrons • Atomic number = Number of electrons

  7. Mass Number Counts the number of protons and neutrons in an atom *Mass number is not on the periodic table

  8. Atomic Symbols • Show the mass number and atomic number • Give the symbol of the element mass number 23 Nasodium-23 atomic number11

  9. More Atomic Symbols 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15e- 30 e-

  10. Isotopes • Atoms with the same number of protons, but different numbers of neutrons. • Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 1717 chlorine - 35 chlorine - 37

  11. Ions • An atom that has gained or lost electrons • An atom that loses electrons has a positive charge (+) • Positive ions are called cations • ex. Na+, Mg+2 • An atoms that gains electrons has a negative charge • Negative ions are called anions • Ex. Cl-, O-2 • How many protons, neutrons, and electrons are there in the Calcium ion (Ca+2)? • How many protons, neutrons, and electrons are there in the Fluoride ion (F -)?

  12. Learning Check AT 5 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is 1) 14 2) 16 3) 34 C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1)34X 2)34X 3)36X 16 14 14

  13. Masses of Atoms • A scale designed for atoms gives their small atomic masses in atomic mass units (amu) • An atom of 12C was assigned an exact mass of 12.00 amu • Relative masses of all other atoms was determined by comparing each to the mass of 12C • An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu.

  14. Calculating Average Atomic Mass • You need to know… • Percent(%) abundance of isotopes • Mass of each isotope • Weighted average = (mass of isotope 1)(% abundance/100) +(mass of isotope 2)(% abundance/100) + …

  15. 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% (.7870 x 24.0) + (.1013 x 25.0) + (.1117 x 26.0) Atomic mass (average mass) Mg = 24.3 amu Mg 24.3

  16. Learning Check AT7 Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the average atomic mass of gallium?

  17. Solution AT7 Ga-69 68.9 amu x 60.2 = 41.5 amu for 69Ga 100 Ga-71 (%/100) 70.9 amu x 39.8 = 28.2 amu for 71Ga 100 Atomic mass Ga = 69.7 amu

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