element

Examples of element in the following topics:

• The Periodic Table

  • Everything in the universe is made of one or more elements.
  • In addition to providing the atomic number for each element, the periodic table also displays the element's atomic mass.
  • The elements at the boundary between the metallic elements (grey elements) and nonmetal elements (green elements) are metalloid in character (pink elements).
  • Within the p-block at the boundary between the metallic elements (grey elements) and nonmetal elements (green elements) there is positioned boron and silicon that are metalloid in character (pink elements), i.e., they have low electrical conductivity that increases with temperature.
  • Elements of the human body arranged by percent of total mass

• Essential Nutrients for Plants

  • These 20 elements are called essential nutrients.
  • For an element to be regarded as essential, three criteria are required:
  • The essential elements can be divided into macronutrients and micronutrients .
  • These micronutrients, or trace elements, are present in very small quantities.
  • For an element to be regarded as essential a plant cannot complete its life cycle without the element, no other element can perform the function of the element, and the element is directly involved in plant nutrition.

• Electron Shells and the Bohr Model

  • As previously discussed, there is a connection between the number of protons in an element, the atomic number that distinguishes one element from another, and the number of electrons it has.
  • Each element, when electrically neutral, has a number of electrons equal to its atomic number.
  • In comparison, the group 1 elements, including hydrogen (H), lithium (Li), and sodium (Na), all have one electron in their outermost shells.
  • Group 18 elements (helium, neon, and argon are shown) have a full outer, or valence, shell.
  • Elements in other groups have partially-filled valence shells and gain or lose electrons to achieve a stable electron configuration.

• Energy and Nutrient Requirements for Prokaryotes

  • Just a handful of elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
  • (A mnemonic for remembering these elements is the acronym CHONPS. )
  • Carbon is the major element in all macromolecules: carbohydrates, proteins, nucleic acids, lipids, and many other compounds.
  • In addition to these macronutrients, prokaryotes require various metallic elements in small amounts.
  • These are referred to as micronutrients or trace elements.

• Biogeochemical Cycles

  • The elemental components of organic matter are cycled through the biosphere in an interconnected process called the biogeochemical cycle.
  • The six most common elements associated with organic molecules (carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur) take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath the earth's surface.
  • The cycling of all of these elements is interconnected.

• The Chemical Basis for Life

  • Carbon is the most important element to living things because it can form many different kinds of bonds and form essential compounds.
  • Carbon is the fourth most abundant element in the universe and is the building block of life on earth.
  • The carbon atom has unique properties that allow it to form covalent bonds to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or "backbone," of the macromolecules.

• Vascular Tissue: Xylem and Phloem

  • The tissue consists of vessel elements, conducting cells, known as tracheids, and supportive filler tissue, called parenchyma .
  • The substances travel along sieve elements, but other types of cells are also present: the companion cells, parenchyma cells, and fibers.
  • Tracheids (top) and vessel elements (bottom) are the water conducting cells of xylem tissue.

• Genome Evolution

  • Processes such as mutations, duplications, exon shuffling, transposable elements and pseudogenes have contributed to genomic evolution.
  • There are various mechanisms that have contributed to genome evolution and these include gene and genome duplications, polyploidy, mutation rates, transposable elements, pseudogenes, exon shuffling and genomic reduction and gene loss.
  • Transposable elements are regions of DNA that can be inserted into the genetic code through one of two mechanisms.
  • The most common transposable element in the human genome is the Alu sequence, which is present in the genome over one million times.

• Transportation of Photosynthates in the Phloem

  • Photosynthates move through plasmodesmata to reach phloem sieve-tube elements (STEs) in the vascular bundles.
  • Phloem is comprised of cells called sieve-tube elements.
  • Neighboring companion cells carry out metabolic functions for the sieve-tube elements and provide them with energy.
  • Lateral sieve areas connect the sieve-tube elements to the companion cells.
  • Sucrose is actively transported from source cells into companion cells and then into the sieve-tube elements.

• Chemical Reactions and Molecules

  • According to the octet rule, elements are most stable when their outermost shell is filled with electrons.
  • However, since not all elements have enough electrons to fill their outermost shells, atoms form chemical bonds with other atoms, which helps them obtain the electrons they need to attain a stable electron configuration.
  • This is an example of a balanced chemical equation, wherein the number of atoms of each element is the same on each side of the equation.
  • Even though all of the reactants and products of this reaction are molecules (each atom remains bonded to at least one other atom), in this reaction only hydrogen peroxide and water are representative of a subclass of molecules known as compounds: they contain atoms of more than one type of element.
  • Molecular oxygen, on the other hand, consists of two doubly bonded oxygen atoms and is not classified as a compound but as an element .