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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 of Ekasilicon (Es)
Actual Properties of 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 = 4.7 g/cm3
Density of GeO2 = 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:!
H! He!
Li! Be! B! C! N! O! F! Ne!
Na!
K!
Mg!
Ca!
Al! Si! P! S! Cl! Ar!
--Electron dot models for elements 1-20:!
H! He!
Li! Be! B! C! N! O! F! Ne!
Na!
K!
Mg!
Ca!
Al! Si! P! S! Cl! Ar!
