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Flashcards in C4b Deck (7)
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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