CHEM 1300 Lecture Notes - Lecture 7: Negative Number, Intermolecular Force, Catabolism
26 Jun 2018
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Lecture 7 – Radii, Ionization Energy (creating a cation) , Electron Affinity (creating an anion)
Atomic Radii
●Multiple methods to figure out the radius
●Kinds of bonds are shown differently in visual diagrams
oWedge bond: coming out of the page
oHatch bond: going behind the lattice
●Various kinds of bonds exit between elements resulting in different radii calculations:
oMetallic Radii
▪½ of the distance (r) between bonds of metal atoms
oCovalent Radii
▪Electrons are shared and it makes the radii slightly smaller
▪½ distance (r) between 2 covalently bonded atoms
oIonic Radii
▪One radii will shrink relative to the other because of the exchange of e- resulting
in one larger ion and one smaller ion
oVander Wal Radii
▪Noble gases such as helium are difficult to measure in terms of radii
▪The method is cooling the gas down to the point of it being in a frozen state,
allowing a more precise reading on the better-defined spaces between the
molecules to determine the radii
oAtomic Radii
▪The estimated radii of an atom calculated
▪Determined by number of protons, orbital level in the atom and other factors
that influence the size of an atom individually
Radii Trends – in decreasing importance
Trend 1 (MOST IMPORTANT, will out-rule Zeff***)
●An increase in n (orbital level) will increase size of atom and radius
●A higher energy resulting from a larger atom decreases stability
oSubshells are also further from nucleus creating a screening effect on the valence
electrons further adding to the instability of the atom
oSmaller Zeff
Trend 2
●Remember coulomb’s law: E=Kq1q2/r
●When you move across the periodic table from left to right the energy of the proton (Zeff)
becomes stronger and will pull more tightly onto its electrons
oThis is to maintain some sort of stability by the nucleus as the diameter of the atom
grows as it adds on electrons
find more resources at oneclass.com
find more resources at oneclass.com
oAtom does not grow significantly as it fills its d orbital, the Zeff becomes stronger as the
protons increase – see next rule
Trend 3
●The radius will change very little during the d block:
oDealing mostly with the transition and inner transition metals
oAtoms are simply filling an orbital which hardly effects the general size of the atom and
the Zeff only has a slight impact on the size of the atom’s radius
Trend 4
●Fully filled and half-filled orbitals are more stable than partially filled orbitals
oThis can be represented using Hund’s rule about electron repulsions
oWhen electrons are paired they have less energy and are more stable
oUnpaired (lone) electrons are unstable and want to fill their subshells
▪This translates into atoms with unpaired electrons, as in the partially filled
states, repulsing each other and making the atom slightly larger than if the
atom had a half filled or fully filled subshells that were more stable
Ionization Energy – Creating a Cation
●The amount of energy (IN JOULES) required to pull away an electron from its subshell creating a
positive cation with a charge of +1 for the 1st Ionization Energy (IE) level (+2 for the 2nd etc.)
●Element must be in gaseous state
oIntermolecular forces prevent looking at atoms in their solid state
oEnergy is required to ionize an atom into a cation
▪1st IE: X(g) → X+ (g) + e-
▪2nd IE: X+(g) → X2+ (g) + e-
▪3rd IE: X2+(g) → X3+ (g) + e-
▪Etc….
oTo find total energy required we add up the IE from each level to the 1s orbital
●Use the periodic table to find trends and predict the ionization energies relative to each other
●Metallic nature to form a cation, non-metals form anions
oIt is much easier for a metal to donate an electron
oEach successive IE becomes increasingly larger and more difficult to pull away an
electron, therefore it would take an extremely large amount of energy to make a non-
metal a stable cation
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 7 radii, ionization energy (creating a cation) , electron affinity (creating an anion) Multiple methods to figure out the radius. Kinds of bonds are shown differently in visual diagrams: wedge bond: coming out of the page, hatch bond: going behind the lattice. An increase in n (orbital level) will increase size of atom and radius. A higher energy resulting from a larger atom decreases stability: subshells are also further from nucleus creating a screening effect on the valence electrons further adding to the instability of the atom, smaller zeff. The amount of energy (in joules) required to pull away an electron from its subshell creating a positive cation with a charge of +1 for the 1st ionization energy (ie) level (+2 for the 2nd etc. ) Use the periodic table to find trends and predict the ionization energies relative to each other. Moving left to right: the zeff increases, increasing the ie.
