Trends+in+physical+properties

= **Physical properties ** = toc As was earlier stated, there are certain trends in the physical properties of the elements in the periodic table which can be seen as you go down a group or across a period of the periodic table. First of all we have to look at some of the physical properties that atoms of an element can have.

Na ---> Na + + e -
 * //Ionization energy //** is the minimum amount of energy required to remove one mole of electrons from one mole of gaseous atoms, to from one mole of the gaseous ions. For example the amount of energy required to ionize 1 mol of Na atoms is its ionization energy.

//(the values of the ionization energies and the electronegativity for each element is given on page 8 of the databooklet) //
 * //Electronegativity //** is a measure of how strongly an atom attracts the electron pair when it is covalently bonded to another atom. For example, the electronegativity of lets say oxygen is a measure of how strongly the oxygen attracts the shared electron pair when it is covalently bonded to another oxygen atom in O 2.

//**Atomic radius**//, as its name suggests, is the radius of the an atom. It is the distance of the nucleus of the atom from the outermost shell. However as the valence electrons are constantly moving around the nucleus, it isn’t easy to measure the distance between the nucleus and the outer shell. Thus what is done, is to measure the distance between the nuclei of two covalently bonded molecules; the atomic radius is half this distance. 

**//Ionic radius//** is the radius of the ion and it is different from the atomic radius. That means that the radius of the Fluorine atom (F 2 ) is different from the radius of the fluorine ion (F - ).
 * When an atom forms an anion  (negative ion) its <span style="color: #008000; font-family: Tahoma,sans-serif; font-size: 14pt;">radius increases <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">. This is because the atom has gained an extra electron to from an anion and an extra electron means that the repulsion between the outer shell electrons is going to be more, so they move further apart form each other causing the radius to increase.

<span style="font-family: Tahoma,sans-serif; font-size: 19px;">(you can find the values of the atomic radii and the ionic radii of elements on page 9 of the databooklet)
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">When an atom forms a cation (positive ion) its radius decreases . This is because the atom has lost one or more electrons to form a positive ion and the reduction in the number of valence electrons means that the repulsion is lesser, thus the radius decreases.

=**<span style="color: #ab14d7; font-family: Tahoma,sans-serif; font-size: 14pt;">The variation in these physical properties down a group **= <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">If you go down group 1, 7 or any other group, there will be a certain trend in the physical properties of the elements which are going to be discussed below.

//<span style="font-family: Tahoma,sans-serif;">Trend in atomic radii (plural of radius) //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As you go down a group the number of electron shell increases. For example as you go down group 7, form F to Cl to Br, each atom has one more electron shell than the previous one. Thus you would expect the atomic radii to increase down the group. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Similarly, the ionic radius would also increase down the group as the number of electron shells increases. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

//<span style="font-family: Tahoma,sans-serif;">Trend in ionization energy //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">We said that the ionization energy in the energy is the energy required to convert one mole of atoms to one mole of electrons. Depending on how strongly the outershell electrons are from the nucleus, the ionization energy varies. Typically if you go down a group, the ionization energy decreases. This is because as you go down the group, the outershell electrons are further away from the nucleus and thus there is lesser attraction forces between the nucleus and the outershell electrons. Thus lesser energy is required to ionize the atom. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

//<span style="font-family: Tahoma,sans-serif;">Trend in electronegativity //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As you go down a group, the valence electrons are further and further away from the nucleus. Thus the attraction of the nucleus for the valence electrons decreases. As a result electronegativity decreases down the group. This is because the nucleus would attract an electron pair less strongly due to the lower attraction of the nucleus for the far away electrons. <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">(Note: the above trends are true for going down any group of the periodic table) // =** //<span style="font-family: Tahoma,sans-serif;">The variation in these physical properties across period 3 // **= <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Now that we have talked about the trends in physical properties down the group, we can also talk about the trend in physical properties across a period. We are specifically going to look at the trend in physical properties as you go across period 3.

//<span style="font-family: Tahoma,sans-serif;">Trend in atomic radii (plural of radius) (as you go across period 3) //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As you move across period 3, form Na to Ar (argon), the number of electron shells remain constant (all elements in period 3 have 3 electron shells). What changes is the number of valence electrons and the number of protons in the nucleus. Since the number of electron shells is constant while the number of protons is increasing, it means that the valence electron become more strongly attracted to the nucleus, across the period; thus the electrons are pulled closer to the nucleus, leading to a decrease in the atomic radius. //<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Thus, as you move across period 3, the atomic radius decreases. //

//<span style="font-family: Tahoma,sans-serif;">Trend in ionization energy (as you go across period 3) //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As you go across the period, the number of protons increases while the number of electron shells remains constant. As a result, the //ionization energy increases as you go across the period.//

//<span style="font-family: Tahoma,sans-serif;">Trend in electronegativity (as you go across period 3) //
<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As you go across the period, as stated earlier, the proton attracts the outershell electrons more closely. //Thus the electronegativity of elements increases as you go across the period.// <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

<span style="color: #2600ff; font-family: Arial,Helvetica,sans-serif; font-size: 11pt;">By the end of this lesson you should be able to:
 * <span style="color: #2600ff; font-family: Arial,Helvetica,sans-serif; font-size: 15px; line-height: 22px;">Define the terms //ionization energy// and //electronegativity//
 * <span style="color: #2600ff; font-family: Arial,Helvetica,sans-serif; font-size: 15px; line-height: 22px;">Describe the trends in atomic/ionic radii, first ionization energy down groups 1 and 7 and across period 3.


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