⭐️SC4 - The Periodic Table
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How many elements were discovered by 1869?
63
How did Mendeleev arrange the elements?
In order of increasing atomic mass in vertical columns and in order of chemical property in horizontal columns
What did mandeleev do differently to other chemists?
He left gaps in the table
When did Mendeleev swap the positions of elements?
If he thought that better suited their chemical properties and those of their compounds.
What elements did Mendeleev swap to fit their chemical properties?
Iodine was placed after tellurium so it lined up with fluorine despite it having a lower relative atomic mass than tellurium
Why did Mendeleev switch the two elements?
As iodine and fluorine both are non metals that don’t easily react with oxygen but tellurium us a metal that burns in air to form tellurium dioxide
What did Mendeleev use the gaps in his table for?
To make predictions about future elements e.g his predictions for eka-aluminium closely fit the chemical properties of how gallium
What was discovered in the end of the 19th century?
a group of Inert (unreactive) elements
Who began to address the gaps still left in the periodic table after Mendeleev?
Henry Moseley
How did Moseley show that an elements atomic number was a physical property?
By firing high energy electrons at different elements which made them give off x rays
What did Moseley realise from his atomic number experiment?
Atomic number = number of protons in the nucleus
In what order are the elements in a period?
Increasing atomic number
How are elements in a group organised?
They all have similar properties
Where are non- metals?
On the right
When were the seven elements between hydrogen and uranium discovered?
Between 1917 and 1945. The first element being neptunium with an atomic number above 92 was discovered in 1940
What is the configuration of electrons?
2.8.8 (for the 1st 20 elements)
What is the electronic configuration of sodium?
2.8.1
What does the period number tell you?
The number of occupied shells an element has
What does the group number tell you?
The number of electrons in the outer shell (except 0 which has a full outer shell)
How can you tell sodium and chlorine are in the same period from electronic configurations?
They both have 3 electron shells that are occupied