Ionization Energy and Electronegativity
Atomic RadiusBelow is a chart showing the radius of neutral atoms in picometers (1 pm = 1 x 10-12 m) for the s and p block elements. The situation is a little more complicated for the d and f block elements.
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The volume occupied by an atom mostly depends on the electrons. The latest data on the size of a proton gives it as 0.84 femptometer (1 fm = 1 x 10-15 m). For the hydrogen atom with 1 proton and 1 electron, the radius is of the atom is 37 pm with the nucleus making up only 0.00084 pm of that.The atomic radius increases with each filled shell of electrons. For any column in the periodic table, the size increases down a column. So, for example: He The attraction between the positively charged protons and the negatively charged electrons causes a contraction, or a decrease in size as the number of protons increases. In any row, increasing the number of protons decreases the size of the atom even though the number of protons always equals the number of electrons. So, for example: Na > Mg > Al > Si > P > S > Cl > Ar
Ionization EnergyWhen atoms are ionized they lose an electron and become positively charged.
|Electron configuration||Ionization Reaction||Energy Required|
|Li Li+ + e-||520 kJ/mol|
|Be Be+ + e-||899 kJ/mol|
|B B+ + e-||800 kJ/mol|
|C C+ + e-||1090 kJ/mol|
|N N+ + e-||1400 kJ/mol|
|O O+ + e-||1310 kJ/mol|
|F F+ + e-||1680 kJ/mol|
|Ne Ne+ + e-||2080 kJ/mol|
Click here for a chart of ionization energies for elements H-Ar by orbitals.
Electron AffinityThe electron affinity is the heat released (negative energy term) when a free electron combines with a neutral atom to make a negatively charged ion. Below are the electron affinities for some halogen elements.
|F + e- F-||-328 kJ/mol|
|Cl + e- Cl-||-349 kJ/mol|
|Br + e- Br-||-324 kJ/mol|
|I + e- I-||-295 kJ/mol|
ElectronegativityElectronegativity is a property of atoms within molecules rather than free atoms. It measures the tendency of that atom to draw bonding electrons towards itself. In HF, the fluorine atom is much more electronegative than the hydrogen atom. The electrons in the H-F bond are not equally distributed between the atoms. The electron density is greater around the fluorine atom. In general, the electronegativity increases from left to right in any row of the periodic table and it increases from bottom to top in any column.
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|When the electronegativity difference between atoms is 0.5 or greater, we characterize the bond as polar. The H-F bond is polar but the C-H bond in CH4 is non-polar. We can represent the bond polarity of HF as a vector. The bond is covalent but there is excess electron density around F, giving it a partial negative charge, and a deficiency of electron density around H, giving it a partial positive charge.|