Monday, October 24, 2011

Period Tables & Trends!

Today Mr. Doktor explained that many properties of the elements change in a predictable way as you move through the periodic table; what is otherwise known as periodic trends. There are seven important periodic trends:

REACTIVITY
Reactivity is the tendency of a substance to undergo chemical changes in a system. Metals and non-metals show different trends. The most reactive metal is Francium. The most reactive non-metal is Fluorine. Note that non-metals are located on the right side of the periodic table. As you move down the metals in the table, the reactivity increases. However, for non-metals, the reactivity increases as you move up. For the transition metals, reactivity increases as you move outwards (left and right).  




 
 

Mr. Doktor even demonstrated the reaction of sodium with water. Here's a video showing what happens when you mix alkali metals with water:







ION CHARGE
The ion charges of different elements depend on their group (column).







MELTING POINT
Melting point is the temperature at which a substance changes from a solid to a liquid form. Elements in the center of the periodic table have the highest melting point (Tungsten). Noble gases have the lowest melting points. Also, melting point increases (until the middle of the table) starting from left and moving right. Exceptions are Carbon, Silicon, and Boron.





 
ATOMIC RADIUS
Atoms get larger going down a group, and smaller moving left to right across each period. For example, Helium has the smallest atomic radius, while Francium has the largest atomic radius. Electrons with a larger principle quantum number are found in orbitals that extend farther away from the nucleus. This makes the atomic radius larger. As well, atoms that have more positive charge in their nuclei exert a stronger pull on the electrons in a given principal quantum level. In other words, atoms are made smaller when a stronger attractive force shrinks the electrons' orbitals.







IONIZATION ENERGY
An atom's ionization energy is the energy needed to remove one of its electrons. That is, the energy needed to completely remove an electron from an atom. Ionization energy increases going up and to the right. These trends are the exact opposite of the trends for atomic radius. This is because both an atom's size and its ionization energy depend on how strongly its electrons are attracted to the nucleus. All noble gases have high ionization energy. Helium has the highest ionization energy. Francium has the lowest ionization energy (it is easy to get rid of an electron).



 
ELECTRONEGATIVITY
An atom's electronegativity reflects its ability to attract electrons in a chemical bond; how much atoms want to gain electrons. It has the same trend as ionization energy. For example, Fluorine is the most electronegative element (an electronegativity of 4.0). Cesium and Francium both have electronegativities of 0.7. When two atoms form a chemical bond, the atom with the higher electronegativity would more strongly attract the bond's electrons. Electronegativity has the same trends as ionization energy.





DENSITY
Density is very similar to atomic mass. Although, we did not go into great detail with this periodic trend.

Here's a video to help with your understanding of period tables and trends:







Next class, electron dot diagrams!

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