7.3 and 7.4 Narrated Notes

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Chapter Seven – Part 2 : 

Chapter Seven – Part 2 7.3 – Sizes of Atoms and Ions 7.4 – Ionization Energy

Sizes of Atoms and Ions : 

Sizes of Atoms and Ions According to the quantum mechanical model, atoms and ions do not have sharply defined boundaries at which electron distribution becomes zero 7.3

Sizes of Atoms and Ions : 

Sizes of Atoms and Ions How is the bonding atomic radius different from a nonbonding atomic radius? For nonbonding atomic radius, it is the closest distance separating nonbonding atoms when they are involved in a collision Their electron clouds do not penetrate each other The bonding atomic radius is half the distance between the nuclei of two bonded atoms 7.3

Slide 4: 

7.3

Practice Exercise : 

Practice Exercise Using figure 7.6, predict which will be greater, the P – Br bond length in PBr3 or the As – Cl bond length in AsCl3 The P – Br bond in longer 7.3

Periodic Trends in Atomic Radii : 

Periodic Trends in Atomic Radii Within each column (group), atomic radius tends to increase from top to bottom As we go down a column, the outer electrons have a great probability of being farther from the nucleus, causing the atom to increase in size 7.3

Periodic Trends in Atomic Radii : 

Periodic Trends in Atomic Radii Within each row (period), atomic radius tend to decrease from left to right The increasing effective nuclear charge steadily draws the valence electrons closer to the nucleus, causing the atomic radius to decrease 7.3

Practice Exercise : 

Practice Exercise Arrange the following atoms in order of increasing atomic radius: Na, Be, Mg (Do not use figure 7.6) Be < Mg < Na 7.3

Periodic Trends in Ionic Radii : 

Periodic Trends in Ionic Radii The size of an ion depends on: its nuclear charge the number of electrons it possesses the orbitals in which the valence electrons reside 7.3

Periodic Trends in Ionic Radii : 

Periodic Trends in Ionic Radii Why are cations smaller than their parent atom? The formation of a cation vacates the most spatially extended occupied orbitals in an atom and also decreases the number of electron-electron repulsions 7.3

Periodic Trends in Ionic Radii : 

Periodic Trends in Ionic Radii Why are anions larger than their parent atom? When electrons are added to a neutral atom to form an anion, the increased electron-electron repulsions cause the electrons to spread out more in space 7.3

Slide 12: 

7.3

Explain the following trend … : 

Explain the following trend … For ions carrying the same charge, size increases as we go down a column in the periodic table. As the principal quantum number of the outermost occupied orbital of an ion increases, the radius of the ion increases 7.3

Practice Exercise : 

Practice Exercise Which of the following atoms and ions is largest: S-2, S, O-2 S-2 is the largest 7.3

Isoelectronic Series : 

Isoelectronic Series An isoelectronic series is a group of ions all containing the same number of electrons Give an example of a five element isoelectronic series. Do not use the one listed in the book. P-3, S-2, Cl-1, K+1, Ca+2 7.3

Isoelectronic Series : 

Isoelectronic Series If you arrange your isoelectronic series in order of increasing atomic number, explain why the ionic radius decreases. In the isoelectronic series, the number of electrons remains constant The nuclear charge increases as atomic number increases 7.3

Practice Exercise : 

Practice Exercise Which is the following ions is largest, Rb+1, Sr+2, or Y+3 Rb+1 is the largest ion in the series 7.3

Ionization Energy : 

Ionization Energy The ionization energy of an atom or ion is the minimum energy required to remove an electron from the ground state of the isolated gaseous atom or ion 7.4

Ionization Energy : 

Ionization Energy The first ionization energy, I1, is the energy needed to remove the first electron from a neutral atom The second ionization energy, I2, is the energy needed to remove the second electron from a neutral atom 7.4

Ionization Energy : 

Ionization Energy The greater the ionization energy, the more difficult it is to remove an electron 7.4

Variation in Successive Ionization Energies : 

Variation in Successive Ionization Energies Explain why for a given element, the ionization energies increase as successive electrons are removed With each successive removal, an electron is being pulled away from an increasingly more positive ion, requiring increasingly more energy 7.4

Ionization Energies : 

Ionization Energies Why is there a large increase in ionization energy as inner shell electrons are removed? Inner electrons shells are closer to the nucleus and experience a greater effective nuclear charge than outer electron shells 7.4

Ionization Energies : 

Ionization Energies What does this have to do with bonding between atoms? This is why the outer (valence) electrons are the ones involved in bonding The inner electrons are too tightly bound to the nucleus to be lost from the atom or even shared with another atom 7.4

Practice Exercise : 

Practice Exercise Which will have the greater third ionization energy, Ca or S? Ca will have the higher third ionization energy 7.4

Periodic Trends in First Ionization Energies : 

Periodic Trends in First Ionization Energies Within each row (period) of the table, I1, generally increases with increasing atomic number Within each column (group) of the table, the ionization energy generally decreases with increasing atomic number The representative elements show a larger range of values of I1 than do the transition-metal elements 7.4

Periodic Trends in First Ionization Energies : 

Periodic Trends in First Ionization Energies In general, smaller atoms have higher ionization energies 7.4

Ionization Energies : 

Ionization Energies The energy needed to remove an electron from the outermost occupied shell depends on both the effective nuclear charge average distance of the electron from the nucleus 7.4

Ionization Energies : 

Ionization Energies Either increasing the effective nuclear charge or decreasing the distance from the nucleus increases the attraction between the electrons and the nucleus 7.4

Slide 29: 

7.4

Explain the Periodic Trend : 

Explain the Periodic Trend Explain the period and group trends for ionization energy in terms of effective nuclear charge. Effective nuclear charge increases across a period, therefore, ionization energy increases across a period Effective nuclear charge decreases down a row, therefore, ionization energy decreases down a row 7.4

Practice Exercise : 

Practice Exercise Which has the lowest first ionization energy, B, Al, C or Si? Which has the highest first ionization energy? Al has the lowest first ionization energy C has the highest first ionization energy 7.4

Electron Configurations of Ions : 

Electron Configurations of Ions When electrons are removed from an atom to form a cation, they are always removed first from the occupied orbitals having the largest principal quantum number, n 7.4

Electron Configurations of Ions : 

Electron Configurations of Ions Explain how this is different from the order of adding electrons when constructing an electron configuration Examples, the 3d fills after the 4s but the 4s is vacated before the 3d 7.4

Electron Configurations of Ions : 

Electron Configurations of Ions When electrons are added to an atom to form an anion, they are added to the empty or partially filled orbitals having the lowest value of n. 7.4

Practice Exercise : 

Practice Exercise Write the electron configuration for Ga+3 [Ar]3d10 Cr+3 [Ar]3d3 Br-1 [Ar]3d104s24p6 = [Kr] 7.4