Flashcards in C4b Deck (7):
What are isotopes?
-different forms of the same element, which have the same number of protons, but a different number of neutrons
-same atomic number but different mass numbers
-different atomic number means different element altogether
What are the rows on the periodic table called and what do they tell us?
-each new period represents another full shell of electrons
-the period an element belongs to corresponds with the number of shells of electrons it has
What are the columns on the periodic table called and what do they tell us?
-the group an element belongs to corresponds to the number of electrons in its outer shell
-group 8's outer shells are full
What did Dobereiner do?
-put elements into groups of three (triads) based on chemical properties
-middle element in a triad had a relative atomic mass that was the average of the other two
What did Newlands do?
-noticed that every eighth element had similar properties and so listed some known elements in rows of seven
-these sets of eight were called Newlands' Octaves
-the pattern broke on the third row
-he left no gaps so is work was criticised because:
*his groups contained elements that didn't have similar properties
*he mixed up non-metals and metals
*no gaps left for undiscovered elements
What did Dmitri Mendeleev do?
-around around 50 known elements in a Table of Elements with gaps
-put elements in order of atomic number like Newlands
-he found he had to leave gaps in order to keep elements with similar properties in the same vertical groups
-gaps predicted properties of the undiscovered elements
-when they were found they fitted the pattern