C1 : Development of the Periodic Table Flashcards
What is the big block of elements between group 2 and 3
The transition elements
Why is it called the periodic table
The word periodic means occurring at regular intervals
In the periodic table, elements with the same properties occur at the same intervals
(in groups)
Why do all the elements in the same group react similarly
They have the same number of electrons in their outer energy shells
Dobereiner
Dobereiner noticed that elements with similar properties often occurred in threes he called these triads. e.g. potassium, lithium and sodium which all react rapidly with water
From this scientists wondered if elements could be arranged into some type of logical order
What did John Newlands discover
He arranged elements in increasing atomic weight and saw that every eighth element reacts a different way
He called this the law of octaves
What were some problems with John Newlands system
By sticking to exact order of atomic weight
sometimes elements were grouped together when they had totally different properties
Meaning Newlands law of octaves was taken differently by other scientists
Dmitri Mendeleev
Mendeleev developed the first modern periodic table
How did Mendeleev develop the table
. Arranged the elements in order of increasing atomic weight
What 2 things did Mendeleev do that other scientists hadn’t
He would switch the order of elements so they fitted the patters of other elements in the same group
He left gaps for where he thought an element was missing
He was so confident his table was correct that he predicted the properties of the undiscovered elements based on other elements in the same group
The elements were discovered several years later and matched Mendeleev’s predictions
Because of that other scientists accepted Mendeleev’s table
What are some differences to the modern day table and Mendeleev’s table
.In the modern table, elements are arranged in atomic number (number of protons)
Mendeleev discovered his table when protons weren’t yet discovered so he ordered elements by atomic weight (This is wrong as elements can appear in the wrong order due to isotopes)
. The modern table has group 0 : the noble gases
These had not been fully discovered when Mendeleev published his table
