periodic table

• john newlands noticed that the properties of every 8th element were similar
• mendeleev placed elements in order of atomic mass and left gaps for undiscovered elements
• the reacitivity of alkali metals increase as you go down the group because the outer electrons are further from the nucleus so its easier to be lost in reactions
• transition elements often act as catalysts, mostly form coloured compounds and have high melting points and densities
• the halogens are found in group 7 of the periodic table
• the group number represents how many electrons are in the outer shell of the atom
• the period number represents how many shells an atom has