CHEMISTRY

• Johann Wolfgang Dobereiner


  attempted to classify the existing elements into groups of three with related properties
• Robert Boyle


  defined an elemnt as a substance that cannot be broken down into simpler substance through chemical reactions.
• Alexandre-Emile-Beguyer de Chancourtois


  He discovered that if the elements are arranged in a spiral form by order of increasing atomic mass, the elements with similar properties line up vertically.
• John A.R. Newlands


  he classified 56 known elements into 2 groups based on similarities in their physical properties.
• Law of Octaves

  John Newlands' system of groupings
• Lothar Meyer


  worked on a periodic table that included 28 elements arranged based on atomic volume
• Henry Moseley


  found a relationship between an element's X-ray wavelength and its atomic number.
• Henry Moseley


  his discovery led to the rearrangement of the element in the periodic table based on atomic number instead of atomic mass. He summarized hus discoveries by stating the modern periodic law: the properties of the elements are periodic function of their atomic number.
• Glen Seaborg


  proposed an additional series of elements called "Actinide Series".
• Dimitry Mendeleev


  Father of the modern periodic table.
• Period 1

  contains only 2 elements, H and He. The electrons of the elements occupy the first energy level.
• Period 2

  contains 8 elements, whose outermost electrons occupy the second energy level. 2s and 2p are filled up.
• Period 3


  contains 8 elements. The elements have electrons fill up the third energy level. 3s and 3p orbitals are filled up.
• Period 4


  first period to have more than 8 elements; contains 18 elements. Corresponds tp the fourth energy level occupied by the outermost electrons of the elements. Contains s, p, and d blocks.
• Period 6

  contains 32 elements. Consistd of s, p, d, f blocks. The electrons fill the 4f orbitals only after the 5d orbitals are fully occupied. Includes the lathanide series.
• Period 7


  includes the four newly named elements. Occupies s,p,d,f blocks. Actinide series belongs to this group.
• Group A

  Consists of several groups called "REPRESENTATIVE ELEMENTS"
• Group B

  called "Transition elements". Metallic elements with electrons in d orbital
• Inner Transition elements


  elements that are metallic in nature and have partially of complete filled f orbitals. These elements are also metals that are grouped into the lanthanide and actinide series.
• Atomic Radius


  the total distance from the nucleus of an atom to the outermost orbital or its electron.
• Covalent Radius


  can be measured as one-half the distance between the nuclei of two bonded atoms. also called Atomic Radius.
• Electrons Shielding


  the blocking of valence shell electron attraction by the nucleus, due to the presence of inner- shell electrons.
• Ionization Energy (IE)


  The amount of energy required to remove an electron from a neutral atom in the gaseous state.
• Ionization Potential


  measured in electron electron vol (eV) in which 1 eV atom is equal to 96.49 kJ/mol.
• Electron Affinity (EA)


  describes the ability of an atom to accept an electron. It is the energy released or absorbed when a gaseous atom gains an electron.
• Ionic Radius


  the radius of an atom's ion found in a crystal lattice.
• Electronegativity


  refers to the ability of an atom in a molecule to attract electrons towards itself.
• Sanderson Line


  line that separates metal from non-metal
• Type 7 the properties of metal

  shiny(lustrous), solid at room temperature except mercury), high melting point, high density, malleable, ductile, high heat and electrical conductivity.
• Type the 5 properties of non-metal

  dull (not lustrous), very low or zero heat and electrical conductivity, may be solid, liquid, or gas at room temperature, not ductile, brittle.
• type the 4 properties of metalloids

  good semiconductors, have both metallic and nonmetallic properties, brittle, solids at room temperature.
• Period 5

  2nd period to contain d block elements. Has 18 elements, outermost electron fill the fifth energy level. s,p,d blocks