Development of the Periodic Table

• The periodic table displays all of the known elements. 

  A row of elements is called a period, while each column is called a group.
• True or false? Elements within a period show similar chemical properties to each other

  False

  Elements within the same group have similar chemical properties.
• The atoms of elements in the same group have the same number of:

  electrons in their outer shell
• True or false? Elements within a group show similar chemical properties to each other.

  True

  As they all have the same number of electrons in their outer shell, they all have similar chemical properties
• The alkali metals in group 1 of the periodic table all have how many electrons in their outer shell?

  1
• Remember the final column in the periodic table is called group 0, not group 8.

  The elemental atoms in this group have full outer shells of electrons, and so are stable and unreactive.
• Are there more metal or non-metal elements?

  Metal
• The atoms of elements in the same period have the same number of:

  Shells
• What name is given to the elements in group 1?

  Alkali Metals.
• What name is given to the elements in group 0?

  Noble gases
• Why did Mendeleev think there must be undiscovered elements?

  If the elements known about at the time were placed consecutively, some elements would be placed into groups where they had different chemical properties from the other elements in that group. This meant they would be in the 'wrong' group, and so Mendeleev thought some undiscovered element must go in that place instead
• What name is given to the elements in group 2?

  Alkali Earth Metals
• Why are elements put into groups?

  To group together the elements that have similar properties.
• What name is given to the elements in group 7?

  Halogens
• Why were elements often placed in the wrong group in early versions of the periodic table?

  Elements were placed in order of atomic weight rather than atomic mass, and didn't take into account the elements chemical properties.
• In the early 1800s, how were elements arranged in the periodic table?

  In the early 1800s, elements in the periodic table were arranged by atomic weight.
• What does the period tell you about the atoms of an element?

  The period tells us the number of shells an atom has. 

  E.g. all elements in period 2 have 2 energy shells
• Why did Mendeleev leave gaps in his table?

  To ensure that elements with similar properties stayed in the same group, and to leave space for elements that hadn't been discovered yet.
• How did the discovery of isotopes help to validate Mendeleev's periodic table?

  Some isotopes had different masses, but the same chemical properties - so he was correct in putting them in groups with other elements that had the same chemical properties.
• How did Mendeleev arrange his periodic table?

  1. He mainly ordered the elements by increasing atomic weight.
  2. He arranged elements that had similar properties into rows (periods), and columns (groups).
  3. He left gaps.
• What does the group number tell you about the atoms of an element?

  The group number tells you the number of electrons in the outer shell.

  E.g. all elements in group 3 will have 3 electrons in their outer shell. 
• Why do we use the word 'periodic' in the periodic table?

  Scientists noticed a 'periodic' pattern in the properties of elements, i.e. a pattern that repeats.
• How are elements arranged in the modern periodic table?

  1. Increasing atomic number.
  2. Patterns of chemical and physical properties (periods/groups)