3.1 The Periodic Table Flashcards
What was happening during the 19th century?
- chemists were finding new elements almost every year
- they were also trying to find patterns in the behaviour of the elements
What did John Dalton do?
- arranged elements in order of their masses which had been measured in various chemical reactions
- 1808 published a table of elements (in book ‘A New System of Chemical Philosophy’)
How did John Newlands build on Dalton’s ideas?
- 1864, ‘law of octaves’ (based on music-8 notes)
- he arranged them in order of their mass and noticed that every 8th element seemed similar
What was the problem with Newlands’ table of elements?
- he produced his table of octaves assuming all elements had been discovered (even though chemists were discovering new ones)
- he filled in his octaves even when elements weren’t similar so his table only worked up to about calcium
How did Dimitri Mendeleev solve the problem of odering elements?
- 1869, Russian chemist arranged the 50 discovered elements in a table in order of their atomic weights before arranging them so that their periodic (regularly occurring) properties could be seen…
- his breakthrough was that HE LEFT GAPS for undiscovered elements and used his table to predict their properties
- a few years later the new elements closely matched Mendeleev’s predictions and he was hailed the father of the modern periodic table
How do we now arrange our elements in the table? (from 20th century)
in order of their atomic (proton number)
when we found out more about the structure of an atom
What does the group number tell us?
the number of electrons in the outermost shell (highest occupied energy level) of an atom
What happens to the number of shells of elements as we go down a group?
the number of shells occupied by electrons increase and the atoms get bigger
What 2 effects can it have going down a group? And why does this happen?
1 larger atoms lose electrons more easily
2 larger atoms gain electrons less easily
this happens because the outer electrons are further away from the attractive force of the nucleus and the inner shells ‘shield’ the outer electrons from the positive charge in the nucleus
What happens to reactivity as you go down group 1 and why?
reactivity increases
atoms get bigger and the single electron in the outer shell gets further away from positive nucleus so it is more volatile and easy to lose
What happens to reactivity as you go down group 7 and why?
reactivity decreases
atoms get bigger and an electron added to outermost shell is less strongly attracted to positive nucleus so it is less easily attracted to outer shell
What are the properties of group 1 alkali metals?
- very reactive
- must be stored in oil (react with oxygen in air and water)
- reactivity increases going down group
- very low density compared to other metals
- very soft
- silvery/shiny surface which quickly goes dull when oxygen reacts forming metal oxide
Why are group 1 alkali metals so reactive?
- electronic structure
- one electron in their outermost shell gives them similar properties and very reactive as they need to lose one electron to have a stable electronic configuration
(- react with non-metals, losing single outer electron, form a metal ion carrying +1 charge and always form ionic compounds)
What are the melting and boiling points of group 1 alkali metals?
- melt and boil at relatively low temperatures for metals
- going down the group they get lower
What happens when we add a group 1 alkali metal to water?
- metal floats on water, moving around and fizzing
- fizzing happens because of hydrogen gas formation
(- potassium reacts so vigorously that the hydrogen catches fire)
0 reaction between an alkali metal and water also produces a METAL HYDROXIDE
