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Modern Atomic Theory

Modern Atomic Theory. Modern Atomic Theory States:. Atoms are composed of protons, neutrons and electrons. Atoms/Ions/Isotopes. An atom’s identity comes from the number of protons in the nucleus. this number is called the atomic number. The atomic number can be found on

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Modern Atomic Theory

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  1. Modern Atomic Theory

  2. Modern Atomic Theory States: Atoms are composed of protons, neutrons and electrons.

  3. Atoms/Ions/Isotopes

  4. An atom’s identity comes from the number of protons in the nucleus. this number is called the atomic number. The atomic number can be found on the periodic table. It is usually located in the upper right hand corner.

  5. If an atom is neutral (has no charge), the number of electrons will be the same as the number of protons. Positive charge = negative charge Ex. Helium has an atomic number of 2. So it has 2 protons and if neutral has 2 electrons. So if an atom is neutral, you can use the atomic number to find the number of electrons as well.

  6. Mass Number To find the number of neutrons, you use the mass number of the element. Mass number = number of protons + number of neutrons The mass number can be found by rounding the average atomic mass of an element to a whole number. Ex. Hydrogen has an average atomic mass of 1.00794 so its mass number would be 1.

  7. Finding the number of neutrons.. Number of neutrons = mass number – atomic number Example: The mass number of sodium is 23. Sodium has 11 protons… so it has 12 neutrons (23-11).

  8. More examples... Protons Electrons Neutrons 0 1 1 Hydrogen 20 Calcium 20 20 Chlorine 17 17 18

  9. Na +1 Ions Ba +2 O-2 Cl -1 Atoms can lose and gain electrons. An ion is an atom that has lost or gained electrons to take on a net electrical charge. Charge of ion = # of protons - # electrons Example: Mg+2 always has 12 protons but because it has a charge of +2 it only has 10 electrons (12-10 = 2).

  10. More examples: Ion Protons Electrons K+1 18 19 38 36 Sr +2 35 36 Br-1 S-2 16 18

  11. Isotopes (Hyperlink) In nature, elements can be found with different numbers of neutrons. An isotope is an atom that has the same number of protons but has different numbers of neutrons. Because of the differing number of neutrons-isotopes differ in mass. Example: All chlorine atoms have 17 protons-but some chlorine nuclei have 18 neutrons while others have 20 neutrons.

  12. Protons Neutrons Electrons Iron-56 30 26 26 Examples 35 Cl 17 17 18 17 29 36 27 Cu+2-65

  13. Practice Ga+3 List the following: 1.Atomic number 2.Average atomic mass 3.Mass number 4.# protons 5.# electrons 6.# neutrons

  14. Calculating Average Atomic Mass • The average atomic mass of an element takes into account all of an elements isotopes. Remember… because isotopes differ in #’s of neutrons, their masses will differ • Avg. Atomic Mass = the sum of each elements fractional abundance multiplied by its mass

  15. Examples: Mass Abundance Carbon Isotope 1 Isotope 2 Chlorine Isotope 1 Isotope 2 Silicon Isotope 1 Isotope 2 Isotope 3 12 98.89% 13.003 1.11% 34.969 75.53% 36.966 24.47 27.977 92.21% 28.976 4.70% 29.974 3.09% 11.8668 .14433 Average atomic mass 12.011 amu 26.412 9.046 Average atomic mass 35.45 amu 25.798 1.3619 .9262 Average atomic mass 28.09 amu

  16. Practice • Calculate average atomic mass Copper-63 62.929601amu 69.15% Copper-65 64.927794amu 30.85%

  17. Forces in the atom • Generally like charges repel • It would be expected that since like particles are so close together, the nucleus would fly apart. • NUCLEAR FORCES hold the nucleus together: proton-proton • neutron-neutron • neutron-proton

  18. Forces that hold atom together • Strong force • Weak force • Electromagnetic force • Gravity http://www.youtube.com/watch?v=DZGINaRUEkU (song about 4 forces in nature)

  19. Electric repulsion between protons Strong nuclear force which overcomes the repulsion between protons in the nucleus and keeps it together. ***The presence of neutrons adds to the net attractive force in the nucleus. In the nucleus, two forces exist: If the strong nuclear force is not sufficient to overcome the repulsion between protons, the nucleus begins to fall apart. This is what causes an element to be radioactive.

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