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Delve into the world of atomic shells and bonding in chemistry with this detailed guide. Learn about electron levels, occupancy, stability, and the periodic table. Understand ionic, metallic, and covalent bonds, along with examples like sapphire and ruby. Discover how atoms achieve stability and bond types to achieve electron configurations. Explore topics such as molecular attractions, the Earth's atmosphere, polar molecules, and life on other planets. Gain insights into radioactive dating methods like carbon dating and solar neutrons. This comprehensive overview provides a deep understanding of chemistry concepts.
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Other Atoms Only 2 electrons fit in the lower shell. The 3rd electron must fit in the next shell.
Atomic Shells The discrete electron levels are arranged in shells. Each shell has a maximum occupancy. The first electronic shell can have at most 2 electrons, the second shell has room for 8 electrons and so on. The 1st shell has the lowest energy. Thus, elements, in their lowest energy state fill the 1st level first, and then fill the 2nd level next. These elements are listed in the 1st and 2nd rows of the periodic table. Atoms are most stable if their outer shell is full. The electrons in outer shells are shielded by the inner shells from the full attraction of the nucleus. These electrons participate most readily in chemical reactions.
Atomic Shells How many electrons does neutral Carbon (6 protons) have in its outer shell? How many electrons does neutral Neon (10 protons) have in its outer shell?
Periodic or Mendelev Table 1 e- missing to fill shell (Halogens) # protons Full outer shell (Noble Gases) 1 e- in outer shell (Alkali Metals) Li: solid, Cs: liquid, Ar: gas, Tc: synthetic
Bonding There are three major ways that elements bond to form molecules.
Ionic Bonds Atoms with filled shells, the Noble Gases, are highly inert. Atoms with one electron in the outer shell, and atoms with one electron missing are, on the other hand, highly reactive. These atoms form ionic bonds. The alkali gives up an electron. The halogen takes the electron. Elements are bonded by the electric force between the ions.
Example of ionic bonds Sapphire Aluminum oxide, Al2O3 Ruby
Metallic Bonds Atoms in a metals also give up electrons, however the electrons are not transferred to the other atom. Instead, they are shared by all atoms. The electron sea allows current to flow through metal. Metals thus make good conductors. In sodium, for example, 1 out of the 11 electrons is released so that Na has two filled shells. The extra electrons move around the metal in a “sea” of negative charge. This negatively charged sea moves around a regular structure of positive Na ions.
Covalent Bonds Certain molecules are formed by sharing electrons. The covalent bond that forms resembles metallic bonds in that electrons are shared. Yet, like ionic bonds the electrons are shared in discrete shells of the atoms and don’t run willy nilly throughout the material.
Question How would you covalently bond two oxygen atoms to make O2? Oxygen has 8 protons & electrons. How many electrons would each O have to share with the other?
Periodic or Mendelev Table 1 e- missing to fill shell (Halogens) # protons Full outer shell (Noble Gases) 1 e- in outer shell (Alkali Metals) What kind of bonding does KBr have?
Question How would you expect KF to be bonded?
Periodic or Mendelev Table 1 e- missing to fill shell (Halogens) # protons Full outer shell (Noble Gases) 1 e- in outer shell (Alkali Metals) What kind of bonding does KBr have?
Answer Ionic Bond: K+F-
Earth’s Atmosphere Multiple Covalent Bonds Gases in Earth’s atmosphere are mainly covalently bonded molecules or noble gases. Combining C6, N7, O8
Molecular attractions Polar molecules are more positively charged on one side and more negative on the other. This provides a cohesion.
Iron Oxides are present e.g. Hematite or Fe2O3
Summary Atoms have discrete energy levels, specific to that atom. A photon is absorbed when an electron jumps to a higher energy level. A photon is emitted when an electron drops to a lower energy level. The emitted/absorbed photon’s energy equals the difference between the atomic levels involved. Atomic levels can only fit a certain number of electrons (2 in the 1st level, 8 in the 2nd …) The periodic table is arranged according the electronic shells and the number of protons/electrons in the atom. Atoms with filled shells are most stable. Atoms bond in order to achieve this configuration. Ionic bonding involves the transfer of electrons from one atom to another. Covalent bonding involves the sharing of electrons by one or several atoms. Metallic bonding involves the sharing of electrons by the entire material/metal.
Radioactive Dating *Time that it takes wood to have half the C14 of a living plant.
Carbon Dating • Solar neutrons enter Earth’s atmosphere. • Neutrons collide with N14 (7p, 7n), creating C14 (6p,8n) [n + N14 p + C14 ] • Living bodies continually absorb C14 (e.g. as CO2 in photosynthesis). • When the plant or animal dies, it no longer assimilates C14. • The C14 decays (half life of 5730 yrs). [C14 N14 + e- + ve ] (n p + e- + ve ) • The e- emission rate reveals the age. Measure ages < 70,000 yrs
