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Exploring Atomic Structure: Modern Atomic Theory Overview

Learn about atoms, subatomic particles (protons, neutrons, electrons), nucleons, atomic number, mass number, isotopes, weighted average atomic mass, ions, cations, anions, and more in the world of atomic science. Understand the importance of atomic mass and nuclear symbols.

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Exploring Atomic Structure: Modern Atomic Theory Overview

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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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