chemistry一問

Period number of an element=number of occupied electron shells in an atom of the element

e.g. oxygen is in the 2nd period
the electronic arrangement is 2,6 (there are two numbers here)
so, the number of occupied electron shells is two(姐係有兩個electron shells有野)

sulfur is in the 3rd period
the electronic arrangement is 2,8,6 (there are three numbers here)
so, the number of occupied electron shells is 3(姐係有三個electron shells有野)

Group number of an element
=number of outermost shell electrons in an atom of the element

e.g. oxygen is in the 6th group (6 is group number)
the electronic arrangement is 2,6 (the last number is 6. the outermost shell has 6 electrons)

sodium is in the 1st group
the electron arrangement is 2,8,1 (the last number is 1. the outermost shell has 1 electron)

2)Elements within the same group of the Periodic Table have the same number of outermost shell electrons in their atoms,therefore they have similar chemical properties.However,there is a gradual change in reactivity down a group.

e.g. fluorine, chlorine, bromine, iodine are in the same group (group7, halogens)
all have 7 electrons on the outermost shell
they have similar chemical properties. (same no. of electrons on the outermost shell will result this)
but, their reactivity will decrese down the group (reactivity: fluorine>chlorine>bromine>iodine)
in the alkali metal / alkaline earth metal groups, the reacitivity will increase down the group (Li<Na<K) (Be<Mg<Ca)

3)Chemical properties of an unfamiliar element can be predicted from its position in the Periodic Table.
你可以預測一個你唔識GE element GE chemical property, 只要知佢GE位置就得
e.g. the element under iodine will have similar chemical property of iodine, but less reacitive than iodine.

the element under potassium will catch fire when it touches water, but the reaction is more vigorous