3- The Periodic Table Flashcards
What was Newlands law of octaves? (1863)
What was the problems with his table?
Stated that similar properties are repeated every eighth element.
After calcium, they did not match well and he did not leave gaps for the unknown
What was Mendaleev’s table? (1869)
Why was it successful?
Elements arranged in increasing order of atomic weight, certain sets of properties recur periodically
He left gaps for unknown elements and predicted their properties. When he was proved right, scientists believed him
What do the 1)groups 2)periods mean in the modern periodic table?
1) same number of electrons in its outer shell
2) same number of shells
Why was Mendaleev’s table altered in the early 20th century?
Protons and electrons were discovered
What trends appear when we go down a group?
The distance between the outermost electrons and the nucleus increases
The number of occupied inner shells increases
1)In terms of metals 2)in terms of non metals, what is the correlation between going down a group and it’s reactivity?
1) The reactivity of metals increases as we go down the group (they loose electrons)
2) the reactivity of non-metals decreases as we go down the group (they gain electrons)
What are alkali metals?
Group 1 elements that react readily with air and water
What are the properties of alkali metals?
Soft solids at room temperature Low melting and boiling points (decreases going down the group) Low densities (Li, Na, K float on water) Going down the group, the reactivity increases
What happens when alkali metals react with certain things?
React with water to produce hydrogen gas and metal hydroxide
React with halogens to form white or colourless salts
When reacted, they lose their outer electron to form ionic compounds
Compounds of alkali metals dissolve in water forming colourless solutions
What are transition elements? And all their properties
Found between group 2 and 3, these metals have higher melting and boiling points than alkali metals (except mercury).
They are malleable, ductile and good conductors
Most are strong and dense - useful for building
Not very reactant at ordinary temperatures (with oxygen and water)
Compounds are brightly coloured
What are transition metals often used for?
Catalysts for chemical reactions
What are halogens?
Non metallic elements in group 7 - small molecules made up of pairs of atoms
What are the properties of halogens?
Low melting and boiling points (increase as we go down the group)
Their reactivity decreases going down the group
7 electrons in their outer shell
What happens when halogens react with certain things?
When reacting with metals, halogens form ionic compounds (halide ions have a 1- charge)
Bond covalently with non metals to form molecules
More reactive halogens displace less reactive halogens form an aqueous solution
What colours are each halogen at room temperature?
Fluoride - pale yellow (gas)
Chlorine - green (gas)
Bromine - red/brown (liquid)
Iodine - grey (solid)
