The Periodic Table Flashcards
(37 cards)
What so the odeon periodic table?
It’s a chart that arranges these elements in a way that’s useful to chemists
Thanks to the periodic table what can chemists do?
Can make sense of patterns and trends which lets them predict the properties of elements
In early 1869 What was the problem Russian chemist Dmitri Mendeleev (1834-1907) faced and how did he solve it?
He was busy writing the second volume of his chemistry textbook and could not decide which elements it made sense to write about next. His solution was to construct a table that led to the periodic table we know today
How many elements had chemists discovered by 1869?
63 and Mendeleev arranged these elements in order of increasing relative atomic masses (called atomic weights then)
Unlike other chemists who had tried to arrange elements in order of relative atomic mass what did Mendeleev do in his table
He left gaps
What did Mendeleev sometimes do to the elements if he thought that better suited their chemical properties and those of their compounds?
Swapped some elements around
Turn to page 26
And look at paragraph 3
What did Mendeleev assume?
That elements would continue to be discovered so he left gaps for them
How did Mendeleev leaving gaps help him to position the existing elements?
So that vertical columns contained elements with increasing relative atomic mass, and horizontal rows contained elements with similar chemical properties
Mendeleev continued to work on his periodic table. By 1871 what had he settled on?
A table in which elements with similar properties were arranged into vertical columns, just as today
Turn to page 27
And look at Mendeleev’s periodic table
What did Mendeleev use the gaps in his table for?
To make predictions about the properties of u discovered elements, based on the properties a out the properties of nearby elements. One set of predictions was for an element in 1875, it’s properties closely fitted those Mendeleev had predicted for eka-aluminium
Turn to page 27
And look at the table
How many known elements are there?
Over 100
Development of the periodic table continued after Mendeleev’s first tables and what was discovered near the end of the 20th century?
An entire group of inert or very unreactive elements
Even though the chemists had not predicted the existence of the group of unreactive elements what group in the periodic table did they easily fit into but what was the problem?
Group 0, however pair reversals were not properly explained and there were still gaps. This began to change in 1913 due to a physicist called Henry Mosley
When scientists were. Beginning to accept the periodic table what was a elements atomic number?
It was just its position in the table
Instead of an elements atomic number just its position in the table what did mostly show?
It is a physical property of an elements atoms
What did Moseley fire at different elements and what did he discover?
High-fired electrons which made them give off X-rays and he discovered that for every step increase in atomic number there was a step change in the energy of these X-rays
What did Moseley realise an atomic number was equal to?
To the number of positive charges in the nucleus of an atom, and the particle that carries this charge was discovered a few years later. So the atomic number must be the. Number of protons in a nucleus
The element in the modern periodic table are arranged in order of increasing atomic number,z, when this is done:
Elements in a row or period are in order of increasing atomic number
Elements with similar properties are in the same column or group
Non-metals are on the right of the table (the other elements are metals)
The iodine-tellurium pair reversal is explained
Turn to page 29 and look at the second paragraph
And the table
What did more X-ray analysis show?
That just seven elements between hydrogen (z=1) and uranium (z=92) were left to be discovered. These were all discovered between 1917 and 1945. Neptunium, the first element with an atomic number above 92 was discovered in 1940. Other such ‘transuranium’ elements continue to be discovered and can be placed all over the periodic table
What is electrons filling shells in an atom like?
Rather like filling a bus one seat at a time from the front
