electron

Examples of electron in the following topics:

• Ions and Ionic Bonds

  • This movement of electrons from one element to another is referred to as electron transfer.
  • As illustrated, sodium (Na) only has one electron in its outer electron shell.
  • When sodium loses an electron, it will have 11 protons, 11 neutrons, and only 10 electrons.
  • Therefore, it tends to gain an electron to create an ion with 17 protons, 17 neutrons, and 18 electrons.
  • In the formation of an ionic compound, metals lose electrons and nonmetals gain electrons to achieve an octet.

• Electron Shells and the Bohr Model

  • These orbits form electron shells or energy levels, which are a way of visualizing the number of electrons in the various shells.
  • Electrons fill orbit shells in a consistent order.
  • The innermost shell has a maximum of two electrons, but the next two electron shells can each have a maximum of eight electrons.
  • As shown, helium has a complete outer electron shell, with two electrons filling its first and only shell.
  • An atom may gain or lose electrons to achieve a full valence shell, the most stable electron configuration.

• Electrons and Energy

  • In living systems, a small class of molecules functions as electron shuttles: they bind and carry high-energy electrons between compounds in cellular pathways.
  • These compounds can be easily reduced (that is, they accept electrons) or oxidized (they lose electrons).
  • It is noteworthy that NAD+must accept two electrons at once; it cannot serve as a one-electron carrier .
  • When electrons are added to a compound, the compound is reduced.
  • When electrons are removed from a compound, the compound is oxidized.

• Electron Orbitals

  • Electron orbitals are three-dimensional representations of the space in which an electron is likely to be found.
  • Helium has two electrons; therefore, it can completely fill the 1s orbital with its two electrons.
  • The second electron shell may contain eight electrons.
  • Two electrons fill the 1s orbital, and the third electron then fills the 2s orbital.
  • Its electron configuration is 1s22s1.

• Electron Transport Chain

  • The electron transport chain uses the electrons from electron carriers to create a chemical gradient that can be used to power oxidative phosphorylation.
  • Once it is reduced to QH2, ubiquinone delivers its electrons to the next complex in the electron transport chain.
  • This enzyme and FADH2 form a small complex that delivers electrons directly to the electron transport chain, bypassing the first complex.
  • Cytochrome c is the acceptor of electrons from Q; however, whereas Q carries pairs of electrons, cytochrome c can accept only one at a time.
  • The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen.

• Processes of the Light-Dependent Reactions

  • Because this state of an electron is very unstable, the electron is transferred to another molecule creating a chain of redox reactions called an electron transport chain (ETC).
  • The electron flow goes from PSII to cytochrome b6f to PSI; as electrons move between these two photosystems, they lose energy.
  • The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor.
  • The excited electron must then be replaced.
  • In (b) photosystem I, the electron comes from the chloroplast electron transport chain.

• The Two Parts of Photosynthesis

  • Each photosystem plays a key role in capturing the energy from sunlight by exciting electrons.
  • The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor.
  • The excited electron must then be replaced.
  • In photosystem I, the electron comes from the chloroplast electron transport chain.
  • The two photosystems oxidize different sources of the low-energy electron supply,    deliver their energized electrons to different places, and respond to different wavelengths of light.

• Chemiosmosis and Oxidative Phosphorylation

  • During chemiosmosis, electron carriers like NADH and FADH donate electrons to the electron transport chain.
  • The electrons cause conformation changes in the shapes of the proteins to pump H+ across a selectively permeable cell membrane.  
  • The overall result of these reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms.
  • At the end of the pathway, the electrons are used to reduce an oxygen molecule to oxygen ions.
  • The extra electrons on the oxygen attract hydrogen ions (protons) from the surrounding medium and water is formed.

• Covalent Bonds and Other Bonds and Interactions

  • Covalent bonds result from a sharing of electrons between two atoms and hold most biomolecules together.
  • The octet rule can be satisfied by the sharing of electrons between atoms to form covalent bonds.
  • In return, the oxygen atom shares one of its electrons with the hydrogen atom, creating a two-electron single covalent bond.
  • To completely fill the outer shell of oxygen, which has six electrons in its outer shell, two electrons (one from each hydrogen atom) are needed.
  • The relative attraction of an atom to an electron is known as its electronegativity: atoms that are more attracted to an electron are considered to be more electronegative.

• Microscopy

  • In contrast to light microscopes, electron microscopes use a beam of electrons instead of a beam of light.
  • The method used to prepare the specimen for viewing with an electron microscope kills the specimen.
  • Electrons have short wavelengths (shorter than photons) that move best in a vacuum, so living cells cannot be viewed with an electron microscope.
  • In a scanning electron microscope, a beam of electrons moves back and forth across a cell's surface, creating details of cell surface characteristics.
  • In a transmission electron microscope, the electron beam penetrates the cell and provides details of a cell's internal structures.