Explain the periodic table. What the rows and columns mean and when electronegativity increases and decreases?

Expert Answers
ncchemist eNotes educator| Certified Educator

The periodic table is a bit oddly shaped but it does make sense in terms of electronic configuration.  The horizontal rows are called periods and there are seven of them.  The vertical rows are called groups and there are 18 of them. 

Elements contained in the same group tend to have similar properties and these different groups have names.  Group 1 elements are called Earth metals and readily give up an electron to become plus 1 cations.  Group 2 elements are called alkaline Earth metals and readily become plus 2 cations.  On the other end of the table we have group 17 which are called the halogens.  They readily gain an electron to become minus 1 anions.  Group 18 are called the noble gases and are highly stable with extremely low reactivity.

The periods are arranged to make sense in terms of electron configurations.  Simply put, electrons are found in 4 basic types of orbitals: s, p, d, and f.  These orbitals inhabit different shells, or energy levels, about the nucleus.  Period 1 elements have only 1s electrons, hence there are only two.  Period 2 elements have the second shell electrons in the s and p orbitals and so on down the line.  The elements between groups 3 and 12 are called transition metals and they contain the d shell electrons.  Finally, the two outlying rows on the very bottom (often labelled the lanthanide and actinide series) contain the f orbitals.

There are various trends when one goes across a period (from left to right) or when one goes down a group (from top to bottom).  Atomic radius (size) decreases across a period and increases down a group.  Another trend is electronegativity which increases across a period and decreases down a group.  This makes fluorine (upper right corner) the most electronegative element on the periodic table.

urekasarangi | Student

The electronegativity generally increases as you go from left to right across the periodic table.let's see how it happens;the atoms of each element all have the same number of energy levels and the same number of shielding electrons.When the nuclear charge increases ,the attraction that the attom has for electrons in its outermost energy level also increases.Then the electronegativity increases.

Electronegativity decreases as you go down the periodic table.Down a group from one atom to another you are collecting one more energy level of electrons for each period.The increased shielding mostly balances the increased nuclear charge.So,when you go down the periodic table the electrons are getting away from the nucleus and better shielded from the nuclear charge and not attracted to the nucleus.

No values are given for gases as they do not bond to the other atom. 

urekasarangi | Student

In the periodic table you have 7periods to vertical and 14groups to horizontal . For the convieniency you can see that they have grouped as A and B,for example 1A,2A then up to 11 you find 3B,4B....but before 12A you find 2B,1B as group number 10 and 11 in the Transition metal series.If i name the groups from left to right;they are Alkali metals,Alkaline earth metals,group 3B-11 Transition metals,12A No common names,13A Halogens and 14A Noble gases.Apart from these you find  atomic number 113,114,115,116,117,118 as under revealation elements.At the bottom of the table you find two horizontal lines where atomic number 57-71 are called Lanthanides and 89-103 are called Actinides.

If you take an element it is surrounded by electrons,protons and neutrons.In every element protons are positively charged,neutrons are neutral and electrons are negatively charged sub atomic particals.Let's take' H',on top right corner you can see the atomic number( protons)as 1 and bottom of element the atomic mass weight range ( average of protons and neutrons combined) .These two measurements will appear in all the elements and the numbers may vary in the periodic table.

If we consider the eliments according to the properties,you will find the followings;

  • Other non metals-H,C,N,O,P,S,Se
  • Alkali metals-Li,na,K,Rb,Cs,Fr
  • Alkaline earth metals-Be,Mg,Ca,Sr,Ba,Ra
  • Transitional elements-atomic number 21-30 in groups and 4-7 in periods except atomic number 71-Lanthanides,103-Actinides
  • Poor metals-Al,Ga,In,Tl,Sn,Pb,Bi
  • Metaloids-B,Si,Ge,As,Sb,Te,Pr
  • HalogensF,Cl,Br,I,At

Noble gases He,Ne,Kr,Xe,Rn

one may find this more clear if you can colour these catogories using different colours in the table.Had to go for a long answer as i don't have the facility of drawing the  periodic table


dolphin28 | Student

Periodic table shows chemical elements. These elements are arranged on the basis of their electronic configuration and atomic number. Elements are organised in increasing atomic number. It has 18x7 grid.

Halogen and noble gases are kept together in a same group due to the same number of valency. There are four rectangular blocks. The f block is floated below and not included in the main table. Russian chemist Dmitri Mendeleev is generally credited with the invention of the periodic table. Today, the periodic table organizes 112 named elements and acknowledges several more unnamed ones.It has become one of the most useful tools in chemistry.  As a result, it provides a useful framework for analyzing chemical behavior.