Periodic Table History

Our modern-day periodic table would not be what it is if it weren't for the contributions made by a few scientists in the 1800's.

The first one was William Odling.

William Odling
    

Odling seperated the 52 discovered elements into 13 groups based on their physical and chemical properties.

But new discoveries were being made and from 1863-1866, John Newlands stated that if hydrogen had a mass of 1, then every 8th element had common properties, which was named "the Law of Octaves".

John Newlands

But this was not the end of the periodic table. Our modern periodic table is based on the work of Dmitri Mendeleev, who arranged the elements by their masses and properties.  He found that properties of elements recur periodically. So he split his table into periods and groups (or families).  He made very accurate predictions on the undiscovered elements, which is why he left gaps in his table.

Dmitri Mendeleev


In the modern periodic table as shown below, the elements are arranged by atomic number, not by atomic mass as it was before.

Modern Periodic Table
You can see that the table is split up into the following sections:
1) Alkali metals
2) Alkaline earth metals
3) Lanthanoids
4) Actinoids
5) Noble gases
6) Other non-metals and
7) Poor metals

As you will notice, hydrogen is in its in group. This is because hydrogen behaves unlike any other element, although it has characteristics of groups 1 and 17.


There are other ways of displaying the periodic table, like this:

Circular Periodic Table


If you click here, you'll find some more useful information on the background of the periodic table.


Periodic Trends

Periodic Trends for Electronegativity

Electronegativity is a chemical property that attempts to describe the attraction between a bonding electron and an atom.
  • The electronegativity of the elements within a period increases from left to right. When the valence shell of an atom is less than half full, it requires less energy to lose an electron than gain one and thus, it is easier to lose an electron. Conversely, when the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate one.
  • Down a group, the electronegativity decreases from element to element. This is because the atomic number increases down a group and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius.
  • Important exceptions of the above rules include the noble gases and transition metals. The noble gases possess a complete valence shell and do not usually attract electrons. The transition metals possess a more complicated chemistry that does not generally follow any trends
                                           Electronegativity Trend IK.png

Periodic Trends for Ionization Energy

Ionization Energy is the amount of energy required to remove an electron from a neutral atom in its gaseous phase. 

  • The ionization energy of the elements within a period generally increases from left to right. This is due to valence shell stability.
  • The ionization energy of the elements within a group generally decreases from top to bottom. This is due to electron shielding.
  • The noble gases possess very high ionization energies because of their full valence shell as indicated in the graph. Note that Helium has the highest ionization energy of all the elements.
                               
                          Ionization Energy Trend IK.png

Periodic Trends for Electron Affinity

Electron affinity describes the ability of an atom to accept an electron.

  • Electron affinity increases from left to right within a period. This is caused by the decrease in atomic radius.
  • Electron affinity decreases from top to bottom within a group. This is caused by the increase in atomic radius.
Electron Affinity Trend IK.png

Periodic Trends for Atomic Radius

For atoms, one-half the distance between the nuclei of two atoms is called the atomic radius.

  • Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are being added to the same shell. But at the same time, protons are being added to the nucleus, making it more positively charged. The effect of increasing proton number is greater than that of the increasing electron number therefore there is a greater nuclear attraction. This means the nucleus attracts the electrons more strongly and therefore, the shell is pulled closer to the nucleus. The outermost electrons are held closer towards the nucleus of the atom. As a result, the atomic radius decreases.
  • Going down a group, it can be seen that atomic radius increases. The outermost electrons occupy higher levels due to the higher quantum number (n). As a result, the outermost electrons are further away from the nucleus as the ‘n’ increases. Electron shielding prevents these outer electrons from being attracted by the nucleus, thus they are loosely held and the atomic radius is large.
  • Atomic radius decreases from left to right within a period. This is caused by the increase in protons and electrons across a period. One proton has a greater effect than one electron and thus a lot of electrons will get pulled towards the nucleus and thus a smaller radius.
  • Atomic radius increases from top to bottom within a group. This is caused by electron shielding.
                                   Atomic Radius Trend IK.png

Periodic Trends for Melting Point

Generally, the stronger the bonds between the atoms of an element, the higher the energy requirement in breaking that bond.
  • Metals generally possess a high melting point.
  • Most non-metals possess low melting points.
  • The non-metal carbon possesses the highest boiling point of all the elements. The semi-metal boron also possesses a high melting point.
Melting Point Trend IK.png

Periodic Trends for Metallic Character

The ease of losing an electron is a measure of an element's metallic character.
  • Metallic characteristics decrease from left to right across a period. Metallic characteristics increase down a group. Electron shielding causes the atomic radius to increase thus the outer eletrons ionizes more readily than electrons in smaller atoms.
  • Metallic character relates to the ability to lose electrons, and nonmetallic character relates to the ability to gain electrons.
Metallic Character Trend IK.png
 
Overall, these charts can be simpled into this picture:

Here is a video found on YouTuBe about the periodic trends:




Outside Links

Problems

The following series of problems will review your general understanding of the aforementioned material.
1.) Based on the periodic trends for ionization energy, which do you except to have the highest ionization energy? 
  1. A.) Fluorine (F)
  2. B.) Nitrogen (N)
  3. C.) Helium (He)
2.) Nitrogen has a larger atomic radius than Oxygen. 
  1. A.) True 
  2. B.) False
3.) Which do you expect to have more metallic character, Lead (Pb) or Tin (Sn)?   
4.) Which element do you expect to have the higher melting point: chlorine (Cl) or bromine (Br)? 
5.) Which element do you expect to be more electronegative, sulfur (S) or selenium (Se)?
6) Why is the electronegativity value of most noble gases equal to zero?
7) Arrange the following atoms according to decreasing effective nuclear charge experienced by their valence electrons: S, Mg, Al, Si
8) Rewrite the following list in order of decreasing electron affinity: Fluorine (F), Phosphorous (P), Sulfur (S), Boron (B).
9) An atom with an atomic radius smaller than that of Sulfur (S) is __________.
  1. A.) Oxygen (O)
  2. B.) Chlorine (Cl)
  3. C.) Calcium (Ca)
  4. D.) Lithium (Li)
  5. E.) None of the above
10) A nonmetal will have a smaller ionic radius when compared to a metal of the same period.
  1. A.) True B.) False
11) Which one of the following has the lowest first ionization energy?
perio.PNG
  1. A. Element A
  2. B. Element B
  3. C. Element C
  4. D. Element D

Solutions

1. Answer: C.) Helium (He)

Explanation: Helium (He) has the highest ionization energy because, like other noble gases, Helium's valence shell is full. Because of this, Helium is stable and does not readily lose or gain electrons.

2. Answer: A.) True

Explanation: According to periodic trends, atomic radius increases from right to left on the periodic table. Therefore, we would expect Nitrogen to be larger than Oxygen.

3. Answer: Lead (Pb)

Explanation: Lead and Tin share the same column. According to periodic trends, metallic character increases as you go down a column. Lead is underneath Tin therefore we would expect Lead to possess more metallic character.

4. Answer: Bromine (Br)

Explanation: According to periodic trends, in non-metals, melting point increases down a column. Since chlorine and bromine share the same column, we would expect bromine to possess the higher melting point.

5. Answer: Sulfur (S)

Explanation: Note that sulfur and selenium share the same column. Periodic trends tell us that electronegativity increases up a column. This indicates that sulfur is more electronegative than selenium.

6. Answer: Most noble gases have full valence shells.

Explanation: Because of their full valence electron shell, the noble gases are extremely stable and do not readily lose or gain electrons.

7. Answer: S > Si > Al > Mg. 
Explanation: The electrons above a closed shell are shielded by the closed shell. S has 6 electrons above a closed shell, so each one feels the pull of 6 prontons in the nucleus.

8. Answer: Fluorine (F)>Sulfur (S)>Phosphorous (P)>Boron (B)

Explanation: According to periodic trends, the electron affinity generally increases from left to right and from bottom to top.

9. Answer: C.)  Oxygen (O)

Explanation: Periodic trends indicate that atomic radius increases up a group and from left to right across a period. Therefore, oxygen is expect to have a smaller atomic radius than of sulfur.

10. Answer: B.) False

Explanation: The reasoning behind this lies in understanding that a metal usually loses an electron in becoming an ion while a non-metal gains an electron. This results in a smaller ionic radius for the metal ion and a larger ionic radius for the non-metal ion.
11. Element D
Explanation: Element A, B and D have the same number of elentrons in the inner shell, but element D has the least number of eletrons in the outer shell which requires the lowest ionization energy.

Electronic Structure of the Atom

Electronic Configuration is the arrangement of electrons and atoms.It can help us to understand the periodic table of elements.

Orbital:It is the actual region of space occupied by an electron in a particular energy level.
There are 4 letters which are s,p,d,f refer to the 4 different kinds of orbitals.Look at the picture, each circle represents one orbitals.













An s-type subshell consists of ONE s-orbital
A p-type subshell consists of THREE p-orbitals
A d-type subshell consists of FIVE d-orbitals
An f-type subshell consists of SEVEN f-orbitals.

















How to write electronic configurations for neutral atoms?
Aufbau principle told us we should always start with the lowest energy level.
First, you should know how many electrons you have. Next, start at the lowest energy level(1s) and keep adding until you have no left.


How to write electron configurations for IONS?
1.For a negative ion:Add the electron(s) which equal(s) to the charge to the last subshell if it is unfilled.
2.For a positive ion:You should do neutral configuration first, remove the electrons which is in the most out shell.

Orbital Box Notation
Orbital Box Notation is the way shown in the orbital diagram below

Spectroscopic notation (more commonly used, but the "long way")
this is the was it is written under the electron configuration below on the right.
Core Notation
It is a short way to show the electron configuration by using core and the outer elements.You can write out just the ones since the last noble gas.

For example, find carbon in the periodic table, then go backwards till you find the noble gas.For C, the noble gas is He.So the core notation of carbon is [He]2s²2p².
C: 1s²2s²2p²
For C, box notation is also easy for you!
Here is a picture can make you easier to understand the relationship between the periodic table and Electronic Configuration.


BUT NOTICE!!!!



Predicting the Number of Valence Electrons
Valence electrons: Outermost electrons of an atom (in highest energy level). These determine the chemical properties of an element.
Valence Electrons are all the electrons in an atom EXCEPT those in the core, or in the filled d- or f- subshells.











Example.

O 1s²2s²2p6
core notation:[He]2s²2p6
So the Valence Electrons of O is 8.

YOU UNDERSTAND?
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