History of the periodic table

• Early Periodic Tables


  In the early 1800s, elements were primarily organised by ATOMIC WEIGHT and their PHYSICAL AND CHEMICAL PROPERTIES.
• Early periodic table


  ATOMIC WEIGHT was the only measurable data early scientists could use, as the sub-atomic particles was not yet discovered, which led to where PROPERTIES kept repeating PERIODICALLY, (hence the term periodic table).
• Early Periodic Table

  It was INCOMPLETE and some elements were placed in INAPPROPRIATE GROUPS if the strict order of ATOMIC WEIGHTS was followed.
• Mendeleev's Periodic Table

  In 1969, DMITRI MENDELEEV, improved earlier tables by arranging 50 known elements by ATOMIC WEIGHT but also their PROPERTIES to maintain consistency within groups.
• Mendeleev's Periodic Table

  Mendeleev left GAPS for elements that he thought would fit the groups but had NOT been DISCOVERED yet.

  E.g. Mendeleev PREDICTED the existence and PROPERTIES of EKA-ALUMINIUM (now known as GALLIUM)

  
• Mendeleev's Periodic Table

  Mendeleev CHANGED the ORDERS of some elements, even though their atomic weights did not fit this order.

  
  

  E.g. Usually, elements are lined up by their weight, and Iodine (I) should be before Tellurium (Te) because it's lighter. But Mendeleev switched them, because its properties were more similar to the other elements in its column.
• Mendeleev's changes were right because:

  The elements he left gaps for were discovered later and Filled the gaps.

  Mendeleev had predicted properties of missing elements.

  properties matched Mendeleev's predictions.
• In the modern periodic table, the elements are arranged in order of atomic number.
• The Modern Periodic Table

  METALS are located to the left and NON-METALS to the right, with a staircase line usually marking the division between them.

  
• The Modern Periodic Table

  The VERTICAL COLUMNS are called GROUPS.
• The Modern Periodic Table

  the HORIZONTAL ROWS are called PERIODS.
• The Modern Periodic Table

  GROUP NUMBER equals to the number of ELECTRONS in the outer shell.

  
• The Modern Periodic Table

  Elements in the same group have SIMILAR CHEMICAL PROPERTIES because they have the SAME number of ELECTRONS in their OUTER SHELL.
• The Modern Periodic Table

  The PERIOD NUMBER equals to the NUMBER OF SHELLS an atom has.

  
• Group and Period Trends

  Elements in the same group have similar properties and react in SIMILAR ways due to having the same number of electrons in their outer shell.

  • GROUP 1 elements (alkali metals) have one electron in their outer shell, making them highly reactive.
• Group and Period Trends

  Reactivity trends can be observed, such as Group 1 elements becoming MORE REACTIVE as you move down the group.
• Predicting Element Properties

  If you know one element's properties, you can make predictions about others in the same group.

  • For example, knowing the properties of Lithium (Li) helps predict the behaviour of Sodium (Na) and Potassium (K).
• explain why the early periodic tables placed iodine (I) before tellurium (Te), but then Mendeleev placed tellurium before iodine.

  early periodic tables were arranged with elements in order of their atomic weights and iodine has a lower atomic weight than tellurium, so Mendeleev placed iodine with elements with similar properties.

  
• Differences between group 1 of Newlands' table and the periodic table:

  hydrogen, fluorine and chlorine are not in the same group of the periodic table.

  Lithium, sodium, potassium are in group 1 of the periodic table.

  
• atomic number is the number of protons and protons were not discovered until later.

  Correct reason was so their properties matched the rest of the group.