4.1.2.2 Development of the periodic table

Döbereiner

Döbereiners’s Triads- scientists began to see if they could put elements into some sort of order.

Element has similar properties often came in threes

John newlands

‘law​ ​of octaves’​ 

* Ordered​ ​his​ ​table​ ​in​ ​order​ ​of​ ​atomic mass


* Realised​ ​similar​ ​properties​ ​occurred every​ ​eighth​ ​element​ ​–​ ​​but​ ​broke​ ​down​ ​after calcium.

\

Why was Newland not taken seriously by other scientists?

By sticking exactly by order of atomic weight, sometimes elements were grouped together when they had differnt properties,

therefore Newlands law of Octaves was not taken seriously by other scientists

many new elements were still being discovered and did not fit in the table

Mitring Mendeleev

● Ordered​ ​his​ ​table​ ​in​ ​order​ ​of​ ​atomic mass,​ ​but​ ​not​ ​always​ ​strictly​ ​–​ ​i.e.​ ​in some​ ​places​ ​he​ ​changed​ ​the​ ​order based​ ​on​ ​atomic​ ​weights.

Which two things did Mendeleev do that had never done before

\
● Left​ ​gaps​ ​for​ ​elements​ ​that​ ​he thought​ an element was missing as there was undiscovered elements

* switched the order of specific elements, so they fit patterns of other elements in the same group

Why is it called the periodic table

​elements with similar​ ​properties​ ​occur​ ​at​ ​regular intervals.

Modern periodic table vs Mendeleev periodic table

Similarities:

* Elements with similar properties are placed in the same group
* Horizontal rows are called 'periods'

Differences

* Mendeleev's table left gaps for undiscovered elements
* more elements in the modern periodic table


* increasing order of ATOMIC MASS NUMBER vs. increasing order of ATOMIC NUMBER
* Noble Gases included in modern table
* In the modern table, transition metals have their own area
* Clear difference between metals and non-metals in the modern periodic table