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Atomic Structure

Atomic Structure. Modern Atomic Theory. Atom – smallest particle of an element that retains the properties of the element Subatomic Particles Protons Neutrons Electrons. Protons. Positive Charge (+1) Located in the nucleus Mass = 1 amu (atomic mass unit) 1 amu = 1.66 x 10 -24 grams

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Atomic Structure

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  1. Atomic Structure

  2. Modern Atomic Theory • Atom – smallest particle of an element that retains the properties of the element • Subatomic Particles • Protons • Neutrons • Electrons

  3. Protons • Positive Charge (+1) • Located in the nucleus • Mass = 1 amu (atomic mass unit) • 1 amu = 1.66 x 10-24 grams • Symbol: p+ or H+

  4. Neutrons • Neutral Charge • Located inside the nucleus • Mass = approximately 1 amu • Symbol: n

  5. Electrons • Negative Charge (-1) • Located outside the nucleus • Mass = 1/1836 of a proton (basically mass less) • Symbol: e- or e-1

  6. Nucleons • Particles located inside the nucleus • Protons and Neutrons • All mass is located in the center of the atom (inside the nucleus), nucleus is very dense

  7. Atomic Number • The number of protons in an atom • Bold number on the periodic table • For a neutral atom: • Number of protons = number of electrons Why???

  8. Atomic Mass/Mass Number • The mass of an atom (expressed in amu) • Equal to the number of protons + the number of neutrons in an atom Why aren’t electrons included in the mass?

  9. Nuclear Symbol • The nuclear symbol consists of three parts • the symbol of the element • the atomic number of the element • the mass number of the specific isotope

  10. Examples Indicate how many protons, neutrons and electrons are in each of the following atoms. • Aluminum-27 • Xe-131 • 56Fe

  11. Gram Atomic Mass • The mass of 1 mole of the element • 1 mole = 6.02 x 1023 particles • Expressed in grams instead of amu

  12. Mass Examples • 1 atom of K = • 1 mole of K = • 1 CO2 molecule = • 1 mole of CO2 =

  13. Isotopes • Same element, same atomic number, number of protons are the same • Different masses, because the number of neutrons varies Example: indicate the number of protons, neutrons, and electrons in carbon-12 and carbon-14

  14. Weighted Average Atomic Mass • Mass found on the periodic table is the weighted average of the naturally occurring isotopes • Accounts for the percent abundance and mass of each of the elements isotopes

  15. How to Calculate • Each exact atomic mass is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures. Example: Nitrogen

  16. Examples • Calculate the weighted average atomic mass for Magnesium.

  17. Ions • Occur when a neutral atom gains or loses a electrons • Caused by the transfer of electrons • Results in a charged atom • Protons are never lost or gained

  18. Cation • Positive Ion • Results from the loss of an electron • Elements on the left side of the table (metals) tend to lose electrons to form cations

  19. Anion • Negative ion • Results from the gain of an electron • Elements on the right side of the table (nonmetals) tend to gain electrons to form anions

  20. Ion Examples Indicate the number of protons, neutrons and electrons in each: • 35Cl atom: • 35Cl- ion: • 39K atom: • 39K+ ion: • 40Ca atom: • 40Ca2+ ion:

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