Physical Science 9
Chapter 18:
Properties of Atoms and the
Periodic Table
Section 18.3:
The Periodic Table
The Periodic Table
--The first successful periodic table was!
designed by the Russian chemist Dimitri!
Mendeleev in the late 1800’s.!
--At the time there were about 50 known!
elements.!
--Mendeleev arranged the elements on his!
periodic table in order of increasing atomic!
mass and in groups based upon their properties.!
--He had to put a few elements out of order of!
their atomic mass so that they were in a group!
of elements with similar properties.!
--Mendeleev realized from his table that there!
must be elements that had not yet been!
discovered.!
--He left gaps in his table for some of these!
elements and used the properties of other!
elements in the same family to predict the!
properties of the unknown elements.!
--He called these elements ekasilicon (germanium)!
and ekaaluminum (gallium!
--His predictions proved to be very accurate:!
Predicted Properties
Actual Properties of
of Ekasilicon (Es)
Germanium (Ge)
Atomic mass = 72
Atomic mass = 72.61
High melting point
M.P. = 938oC!
Density = 5.5 g/cm3
Density = 5.323 g/cm3
Dark gray metal
Gray metal
Density of EsO2
Density of GeO2
= 4.7 g/cm3
= 4.23 g/cm3
Table 4, page 555!
Atomic Number
--In 1913, the English scientist Henry Moseley!
realized that the properties of elements were !
better viewed as periodic properties of their!
atomic number.!
--This is the basis for the modern periodic!
table and is called the Periodic Law.!
--The Periodic Law says that the properties of!
the elements are periodic functions of their!
atomic numbers.!
The Modern Periodic Table
--The elements on the present day periodic!
table are arranged in order of increasing!
atomic number and arranged into groups!
based upon their chemical properties.!
--A column of elements on the periodic table!
is called a group or family.!
--Elements in the same family have similar!
properties. !
--Groups are numbered 1-18 on modern periodic!
tables; some older periodic tables have the!
groups numbered with Roman numerals.!
--A row of elements is called a period; there !
are seven periods on the periodic table.!
--The properties of the elements repeat in!
each period; each period starts with an active!
metal and ends with a noble gas.!
Periodic Table of the Elements!
Other Things to Know
--You should be able to find the following on the!
periodic table:!
1. metals, nonmetals, and metalloids!
2. families of elements (alkali metals,!
!
!alkaline earth metals, halogens,!
!
!noble gases, oxygen family, etc.)!
3. transition metals!
4. lanthanide series and actinide series!
!
!(rare earth elements).!
Electron-Dot Models
--Atoms of different elements are!
represented with electron dot models,!
which show the number of electrons in the!
outer-most energy level of the atom; called!
the valence electrons.!
--The number of valence electrons can be!
found from the group number of the element!
on the periodic table (main group elements only.)!
The dots are placed around the atomic symbol!
in a pattern:!
.
.
.. x ..
..
!
!
!!
!
! !
!!
--Electron dot models for elements 1-20:!
He!
H!
Li!
Be!
Na! Mg!
K!
Ca!
B!
C!
N!
O!
F!
Ne!
Al!
Si!
P!
S!
Cl!
Ar!
--Electron dot models for elements 1-20:!
He!
H!
Li!
Be!
Na! Mg!
K!
Ca!
B!
C!
N!
O!
F!
Ne!
Al!
Si!
P!
S!
Cl!
Ar!