Periodicity Flashcards
Dobereiner
Proposed a law of triads, stating that ‘nature contains triads of elements where the middle element has properties that are an average of the other two members of the triad when ordered by the atomic weight’ e.g. chlorine, bromine, iodine.
Newlands
First person to devise a Periodic Table of elements, arranged in order of relative atomic mass. Proposed law of octaves, stating that any given element will exhibit analogous behaviour to the eighth element following it in the table.
Mendeleev
Published a new periodic table 4 years after Newlands, also based on atomic masses. He arranged elements in columns, with similar properties, with gaps left if an element didn’t fit the repeating patterns. Made it possible to predict properties of elements.
Moseley
Determined atomic number for each element. Modified Mendeleev’s table to order according to number, not weight.
Seaborg
Discovered transuranic elements. Remodelled periodic table to have actinide series below lathanide at the bottom of the table
Arrangement of the periodic table
- By increasing atomic (proton) number
- In periods showing repeating trends in physical and chemical properties
- In groups, having similar physical and chemical properties
Periodicity
A regular periodic variation of properties of elements with atomic number and position in the Periodic Table. A repeating pattern across different periods
Atoms of elements in the same group have similar properties because….
They have similar outer shell electron configurations, resulting in similar properties
How do first ionisation energies change across a period?
They increase across a period, due to an increase in nuclear charge, and a decrease in atomic radii due to nuclear charge pulling electrons towards it
How do first ionisation energies change down a group?
They decrease, due to an increase in atomic radius an increase in electron shielding, outweighing the effect of increasing nuclear charge. This is all due to the addition of a new electron shell.
