The International School of Panama

General Chemistry

Periodicity Notes

To understand how the periodic table was created and how it can be used allows you to predict:

 “the properties of elements even if you never saw them”.

To be able to understand and predict their properties it was necessary to organize them.

The modern periodic table is similar to Mendeleev’s periodic table, but with a difference proposed by Henry Moseley to solve some discrepancies between some elements (Ar and K , I and Te). If they are put in order of increasing atomic mass their properties do not match with those of the elements in the same column. In the modern periodic table the elements are in order of increasing atomic number instead of  mass.

PERIODIC LAW: “The properties of the elements repeat periodically when they are arranged in increasing order by their atomic numbers.”

http://www.uky.edu/Projects/Chemcomics/

Metals are at the left (blue)

Non-metals at the right, except for H (turquoise)

Metalloids are between metals and non-metals and they have properties of both.

Properties of metals and nonmentals.

It is divided into horizontal rows called periods and vertical columns called groups. Groups are also called families. Why? Because the elements in a group share properties like the members of a family.

http://www.britannica.com/nobel/cap/periodicb.html

There are seven periods, numbered 1 to 7

There are 18 groups named in two ways:

1)    Our book way: 1A to 8A for the representative elements or main group and 1B to 8B for the transition elements.

2)    Modern way: 1 to 18 in order

Groups or families of metals:

·        Alkali metals (1 / IA), most reactive metals (block s)

·        Alkaline earth metals (2 / IIA), very reactive metals (block s)

·        Transition elements (3 to 12 / IB to VIIIB) which are divided into

·        Transition metals (block d)

·        Inner transition metals (block f) divided into

·        Lanthanoids (Actinide series)

·        Actinoids (Lanthanide series)

Groups or families of nonmetals (all of them in block p):

·        Boron Group (13 / IIIA)

·        Carbon Group (14 / IVA)

·        Nitrogen Group (15 / VA)

·        Oxygen Group (16 / VIA)

·        Halogen (17 / VIIA) Most reactive nonmetals

·        Noble Gases (18 / VIII or 0) unreactive nonmetals.

The following site gives you instantaneously the properties of each of the elements in the PT.

http://www.iscifistory.com/scifaku/elements/periodichaiku.asp

He (Z = 2): 1s²

H (Z = 1): 1s¹

Li (Z = 3): 1s² 2s¹

Na (Z = 11): 1s² 2s² 2p⁶3s¹

K (Z = 19): 1s² 2s² 2p⁶3s²3p⁶4s¹

Rb (Z = 37): 1s² 2s² 2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹

What do these elements have in common?

They all have one single electron in the outermost energy level.

They have the same amount of valence electrons.

This relationship occurs in all groups of the periodic tables (with some exceptions)

The elements in the same group have the same outer configuration.

That is why the electron dot structure for representative elements in the same column have the same number of dots and the only difference is the symbol:

Diagram taken from the power point presentation of Omega Garces, Dr. Fred, Chemistry 100, Miramar College at:

http://www.miramar.sdccd.cc.ca.us/faculty/fgarces/ChemComon/Tutorial/Lewis/LewisTutorial.pdf

Very important: Why do you think that the elements in the same group of the periodic table have similar chemical properties?

The elements in the same group have similar chemical properties, because they have the same number of valence electrons.

The noble gases have their outermost s and p orbitals complete. All noble gases have 8 valence electrons except for He which has 2 because the first level of energy can contain only 2 electrons, but the level is complete.

Therefore the noble gases are the happy family!

They have their outer level complete. That is why the noble gases are very unreactive. They don't want to give away or gain electrons because they have all the electrons they need.

All the other elements in the periodic table tend to give away or gain electrons in order to have their outer level complete. Atoms that loose or gain electrons become ions (particles with a charge). If they give away electrons they become positive ions (cations) and if they gain electrons they become negative ions (anions).  For example, the alkali metals, tend to give away the single electron they have in the outer level to acquire a noble gas configuration; but the amount of protons remains the same and therefore they become 1+ ions. Alkaline earth metals tend to give away two electrons and become 2+ ions. On the other hand, elements like the halogens which have 7 valence electrons, tend to gain one electron to complete the outer level. These elements become 1- ions. The elements in the oxygen group, with 6 valence electrons tend to gain 2 electrons and become 2- ions.

Other important facts:

For the representative elements (groups 1,2 and 13 to 18) the number of valence electrons tells you in which group they are and the level of energy of the valence electrons tells you in which period they are.

Properties related to the position Periodic Table and Periodic Trends

Metallic properties:

•1) Increase from top to bottom and from right to left.

 Most reactive metals: Cs & Fr

•So the activity of the alkali metals increases from top to bottom. However the activity of the halogens (non metals of group 17) increases from bottom to top.  

•The most reactive nonmetal is F

Atomic Radius

Theatomic radius gives a measure of the size of the atom. The atomic size is defined by how closely an atom lies to a neighboring atom.  Form metals it is defined as half the distance between adjacent nuclei in a crystal of the element. For elements that commonly occur as molecules, such as many nonmetals, it is defined as half the distance between nuclei of identical atoms that are chemically bonded together.

 Relative atomic size of representative elements:

 http://ull.chemistry.uakron.edu/genobc/Chapter_03/

 The atomic radii decrease from left to right  and from bottom to top in the PT.  

1. The atomic radii decrease from left to right in the PT. Why?

 Because, as we move from left to right through a period of the PT, the nuclear charge increases attracting more the electrons that are added to the same energy level.

2. The atomic radii increase from top to bottom. Why?

Because as we move down a group the electrons are added to higher energy levels (electrons have the same outermost but with higher principal quantum number), so they are less attracted by the nucleus. Besides that, as there are more inner electrons, there is more shielding effect, which also reduces the attraction of the outer electrons by the nucleus.

First Ionization Energy

 Is the energy necessary to remove an electron from a neutral gaseous atom.

 The smaller the atom, the more attracted the outer electron is by the nucleus therefore more energy is required to remove it.

                     http://ull.chemistry.uakron.edu/genobc/Chapter_03/   

Taking into account that the atom becomes smaller from bottom to top and form left to right in the PT, especially for the representative elements, the IE increases from bottom to top and from left to right.