1
Q
What are isotopes?
A
- 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
2
Q
What are the rows on the periodic table called and what do they tell us?
A
- periods
- 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
3
Q
What are the columns on the periodic table called and what do they tell us?
A
- groups
- the group an element belongs to corresponds to the number of electrons in its outer shell
- group 8’s outer shells are full
4
Q
What did Dobereiner do?
A
- 1828
- 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
5
Q
What did Newlands do?
A
- 1864
- 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
6
Q
What did Dmitri Mendeleev do?
A
- 1869
- 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
7
Q
Why did Mendeleev’s table make more sense discoveries on atomic structure were made?
A
- each element has an atomic number one more than the previous element
- the pattern of the periodic table matched the way electrons are arranged in atoms
