Lesson 21 Notes
Examining and Grouping
Elements
chemicool.com © 2005
|
Group
|
|
|
|
|
I
|
II
|
|
III
|
IV
|
V
|
VI
|
VII
|
VIII
|
|
|
1
|
|
|
|
|
|
2
|
|
|
|
|
|
|
|
|
|
|
|
3
|
|
|
|
|
|
|
|
|
|
|
|
4
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
6
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
7
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Legend
|
|
|
Solid
|
|
Liquid
|
|
Gas
|
|
Synthetic
|
|
|
Alkali
metals
|
|
Alkali
earth metals
|
|
Transition
metals
|
|
Rare
earth metals
|
|
|
Other
metals
|
|
Noble
gases
|
|
Halogens
|
|
Other
nonmetals
|
|
|
The
periodic table is a widely used classification system that can help predict the
physical and chemical properties of elements and that the properties of some
elements, such as helium, were predicted before the elements were discovered. In
the periodic table, the horizontal rows are called periods and the
vertical columns are called groups.
The roman numerals correspond to the number of electrons in the outer
shell of the elements contained within the group (with the exception of group 0
elements, which have complete outer shells).
The
pattern of the table is most easily followed for the first 20 elements. The sequence is then complicated by a block
of elements called the transition elements.
The
following general patterns can be observed in the periodic table:
-
Metals are on the left side of the table; nonmetals are on the right.
-
The most reactive metals are at the bottom of group 1. These metals have larger atoms, and they
more easily lose electrons in the outer shells, making them more reactive.
-
The most reactive nonmetals have the smallest atoms. All nonmetals (excluding the noble gases)
have incomplete outer shells; therefore, they readily accept electrons.
-
Elements within a group combine with particular elements in similar
ratios. For example: group 1 elements,
the alkali metals always form chlorides in the ration of 1:1.
-
Group number is related to valence – a measure of the number of atoms
that an element can combine with (for example: hydrogen has a valency of 1 and oxygen has a valency
of 2, which accounts for the formula of water H2O). In groups
I – IV, the valance number is 8 minus the number of the group. Example: group V elements hav
a valence of 3 ( 8-5).
Isotope – the sum of the neutrons
and protons in the element’s nucleus.
Reactivity – the readiness or
quickness with which one element reacts with others.
-
Not all metals are magnetic.
-
Not all elements are solids.
-
More than 100 elements exist.
-
The symbols of the elements are internationally standardized, but the
names of the elements change depending on the language spoken.