The periodic table of elements: order in nature

• An element tends to gain, lose, or share electrons to achieve a full outer shell of eight electrons and a stable electron configuration.
• Fourteen elements were discovered in antiquity to the Middle Ages, including gold, silver, and copper
• During this period, 20 recorded elements were discovered, such as phosphorus, oxygen, nitrogen, hydrogen, mercury, zinc, and sulfur
• Johann Wolfgang Dobereiner in 1817 attempted to classify elements into groups of three with related properties, called Triads
• Alexander-Emile Beguyer de Chancourtois discovered that arranging elements in a spiral form by increasing atomic weights resulted in elements with similar properties lining up vertically
• John Newlands arranged elements by atomic mass, where every 8th element had similar properties
• Dmitri Mendeleev created a table in atomic mass order, grouping elements based on properties and predicting the existence of unknown elements
• Lothar Meyer proposed a table to organize elements by atomic mass
• Henry Mosley rearranged the sequence of elements by atomic number instead of atomic weight
• Glenn Seaborg proposed an additional series called actinide in the periodic table
• Modern Periodic Table of Elements has horizontal rows (periods) and vertical columns (groups)
• There are seven periods in the modern periodic table: Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium, Francium
• Based on sublevels being filled, the periodic table may be divided into blocks: s, p, d, f
• Trends in the Periodic Table include systematic variations called periodic trends
• Atomic Radius decreases across a period and increases down a group
• Electronegativity is the ability of an atom in a compound to attract electrons toward itself
• Ionization Energy is the minimum amount of energy required to remove an electron from a gaseous atom
• Electron Affinity describes the ability of an atom to accept an electron, tending to increase across a period and decrease down a group
• Metallic Character is related to an element's ability to lose an electron, while Nonmetallic Character is related to its ability to gain electrons
• Roles of Cell Cycle

  • Continuity of life
  • Reproduction of cells or cell division
• Cytokinesis

  Animal Cell: a cleavage furrow separates the daughter cells
• Prophase

  1. Nuclear envelope disappears

  2. Chromatin materials thicken and shorten into double-stranded chromosomes with two chromatids joined by centromere

  3. Centrioles move to the opposite poles of the cell

  4. Spindle fibers are formed
• Interphase - S Stage

  1. Synthesis stage

  2. DNA is copied or replicated
• Stages of Mitosis

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Telophase

  1. Chromosomes arrive at the opposite pole and begin to decondense

  2. Nuclear envelope reappears

  3. Chromosomes uncoil into chromatin form

  4. Nucleolus reappears

  5. Mitotic spindle breaks down
• Interphase - G1 Stage

  1. 1st growth stage after cell division

  2. Cells mature by making more cytoplasm & organelles

  3. Cell carries on its normal metabolic activities
• Cell Cycle

  • Based upon the reproduction of cells, or cell division
  • Sequence of events being repeated from one mitotic cell division to the next
• Interphase - G2 Stage

  1. 2nd Growth Stage

  2. Occurs after DNA has been copied

  3. All cell structures needed for division are made (e.g., centrioles)

  4. Both organelles & proteins are synthesized
• Unicellular organisms


  • Reproduce by cell division
• Metaphase

  1. Double-stranded chromosome align themselves at the equatorial region

  2. Spindle attach to the kinetochore fibers

  3. Shortest stage of mitosis
• Multicellular organisms depend on cell division for

  • Development from a fertilized cell
  • Growth
  • Repair
• Mitosis

  1. Cell division that involves somatic cells or body cells

  2. Process of forming identical daughter cells by replicating and dividing the original chromosomes
• Anaphase

  1. Centromere separate

  2. Spindle fibers pull the chromosomes to the opposite pole

  3. Single-stranded chromosome migrate to the opposite pole
• Did you know how "Gametes" are being produced in our body?
• The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced
• Cleavage furrow
• Meiosis - chromosome that same size and shape which carry the same type of gene
• SPERM Cell
• Sister Chromatids align at the Equatorial Region
• Meiosis is the exchange of genetic material between two homologous chromosomes non-sister chromatids that result in recombinant chromosomes during sexual reproduction