CH105 Part II: Inorganic Chemistry

transcript

Part II: Inorganic Chemistry

The optimist sees the glass half full.

The pessimist sees the glass half empty.

The chemist see the glass completely full,

half in the liquid state and half in the vapor state.

A proton and a neutron are walking down the street.

The proton says, "Wait, I dropped an electron help

me look for it.”

The neutron says "Are you sure?"

The proton replies ……

What is the most important rule in chemistry?

Never lick the spoon!

What did the scientist say when he found 2 isotopes of helium?

Did you hear Oxygen went on a date with potassium?

It went OK

IUPAC Nomenclature of elements

With atomic number above 100

• Digit Name Abbreviation

• 0 nil n

• 1 un u

• 2 bi b

• 3 tri t

• 4 quad q

• 5 pent p

• 6 hex h

• 7 sept s

• 8 oct o

• 9 enn e

Ununquadiu

118Ununoctium

Money has recently been discovered to be a

not-yet-identified super heavy element.The proposed name is: Un-obtainium.

Factors Affecting Atomic Orbital Energies

• The energies of atomic orbitals are affected by

– nuclear charge (Z) and

– shielding by other electrons

• Higher nuclear charge increases nucleus-electron

interactions and lowers sublevel energy

• Shielding by other electrons reduces the full nuclear

charge to an effective nuclear charge (Zeff).Zeff is the nuclear charge an electron actually experiences. True Love !!

• Orbital shape also affects sublevel energy.

Shielding

The energy order of orbitals for a given

quantum number depends on shielding

effects (σ), effective nuclear charge (Z*)

& penetration of orbitals

Z* = Z - σ(inner electrons !!!)

How to determine or estimate the Z*?

P. S. There may be other ways of calculating these as given in the literature. Please stick

to this procedure as far as this course is concerned.

1. All e-’s in higher principal shell contribute 0 to σ

2. Each e- in the same principal shell contribute 0.35 to σ

{If the electron resides in s or p orbital}

3. Electrons in (n-1) shell: each contribute 0.85 to σ

4. Electrons in deeper shell: each contribute 1.00 to σ

Calculate the Z* for the 2p electron:

Fluorine (Z = 9) 1s2 2s2 2p5

Z* = Z – σ

P. S.: There may be other ways of calculating these as given in the literature. Please stick

to this procedure as far as this course is concerned.

Screening constant for one of the outer electron (2p):

6 six (2s2 2p4 two 2s e- and four 2p e-) = 6 X 0.35 = 2.10

2 (1s2 two) 1s e- = 2 X 0.85 = 1.70

σ = 1.70 + 2.10 = 3.80 and Z* = 9 - 3.80 = 5.20

1. All e-’s in higher principal shell contribute 0 to σ

2. Each e- in the same principal shell contribute 0.35 to σ

3. All inner shells in (n-1) and lower contributes 1.00

How to determine or estimate the Z*?

{If the electron resides in d or f orbital}

P. S. There may be other ways of calculating these as given in the literature. Please

stick to this procedure as far as this course is concerned.

Z* increases very slowly down a group for the

“valence electron”.

Example of Valence configuration as ‘ns1’

n Z Z*

H 1 1 1.0

Li 2 3 1.3

Na 3 11 2.5

K 4 19 2.2

Rb 5 37 2.2

Cs 6 55 2.2

H He Li Be Be C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Z* is effective nuclear charge

A neutron walks into a bar. He asks the bartender, "How much for a beer?"

The bartender offers him a warm smile and says, "For you, no charge".

Z* increases rapidly along a periodFor example, take period two

Li Be B C N O F Ne

3 4 5 6 7 8 9 10

1.3 1.9 2.4 3.1 3.8 4.5 5.1 5.8

2s1 2s2 2p1 2p2 2p3 2p4 2p5 2p6

Z* is effective nuclear charge

Penetration of Orbitals

Orbital shape causes electrons in some orbitals to “penetrate” close to the nucleus. Penetration increases nuclear attraction and decreases shielding

bability

Penetration of Orbitals

The penetration potential of an orbital

varies as: ns > np > nd > nf

The energy of the orbitals for a given n

varies as: ns < np < nd < nf

The penetration of 2s electron through the inner core is greater than

that of a 2p electron because the latter vanishes at the nucleus.

Therefore, the 2s electrons are less shielded than the 2p electrons.

penetration of 2s e- is greater than 2p

penetration increases nuclear attraction and decreases shielding

The electrons present in f are much less influenced by

the nucleus as compared to d, those present in d much

less influenced as compared to p, than s, etc.

Influence of nucleus on electrons

Two electrons (2e-) present in the same d-orbital repel

each other more strongly than do two electrons in the

same s-orbital.

It is essential to consider all contributions to the energy

of a configuration, and just not one-electron orbital

energies.

(Hostel Room Mates)

Order of filling of orbitalsPenetration and shielding have enabled atomic orbitals to be

arranged in rough order of increasing energy.

How do you fill electrons ?

Depicting orbital occupancy

for the first 10 elements.

Two electrons (2e-) present in the same d-orbital repel

each other more strongly than do two electrons in the

same s-orbital.

Therefore, occupation of orbitals of higher energy can result

in a reduction in the repulsion between electrons (for eg.,

4s), otherwise the repulsion will be more if the lower-energy

3d orbitals were occupied.

It is essential to consider all contributions to the energy of

a configuration, and just not one-electron orbital energies.

How do you fill electrons? Justification of 4s first over 3d

Experimental data show that d-block elements are

of the form 3dn4s2, with 4s orbital fully occupied.

Sc (at. No. 21) is [Ar]3d14s2

This order is followed in most cases

- but not always! (some exceptions)

Z = 24 Cr [Ar] 3d54s1; not [Ar] 3d44s2

Z = 29 Cu [Ar] 3d104s1; not [Ar] 3d94s2

Two atomic configurations do not follow the

sequence of filling of orbitals

As atomic number increases, energy of 3d orbitals

decreases relative to both 4s and 4p

At z = 29, energy of 3d becomes much lower than 4s

Hence order of filling 3d < 4s < 4p

Filling & removal in Transition elements

• Transition series: filling order: 4s, 3d

• removal order (cation formation): 4s, 3d (not 3d, 4s)

e.g. Ti [Ar] 3d2 4s2

• Ti2+ [Ar] 3d2 (not [Ar] 4s2) Why?

Ti2+ [Ar] 3d2 4s0 (not [Ar]3d04s2) Why?

• When 2 electrons are removed, regardless of where they

come from, all atomic orbitals contract (Z* increases because of

net ionic charge and reduced shielding)

• Contraction has a small effect on 4s orbital which owes its

low energy to its deep penetration

• Contraction in d orbital causes a considerable decrease in

energy – this decrease is evidently enough to lower the energy of

3d well below 4s in the ion that results from this.

“A lion runs the fastest when he is hungry.”

“In life go straight and turn right.”

r decreasesr

Metallic RadiusMetallic radii of 5d- block elements are expected to

be larger than that of the 4d-elements, but found

that these are not larger. Of course these are

larger than 3d- block elements.

Lanthanide Contraction

f-orbitals have poor shielding properties;

low penetrating power.

So Zeff (Z*) increases (more significantly) from left to

right (for 5d) across the period leading to more compact

atoms.

Ionisation Energy (IE)

The minimum energy needed to remove an electron from a

gas phase atom

Depends on:

(a) Size, IE decreases as the size of the atom increases

(b) Nuclear Charge (NC), IE increases with increase in NC

(c) The type of electron Shielding effect

Reasons:

(1) Average distance of 2s electron is greater than that of 1s

(2) Penetration effect

(3) Electronic configuration

1st IE: H = 1312 KJ mol-1 Li = 520 KJ mol -1

On moving across a period

1. the atomic size decreases

2. nuclear charge increases

Thus IE increases along a period

Ionisation Energy (IE)

I would like to apologize for not adding more

jokes... but I only update them.... periodically!

Electron affinity (EA)

The amount of energy associated with the

gain of electrons

The greater the energy released in the process of

taking up the extra electron, greater is the EA

The EA of an atom measures the tightness with

which it binds an additional electron to itself.

Electron affinity (EA)On moving across a period: As the size decreases, the

force of attraction by the nucleus increases. Consequently, the

atom has a greater tendency to attract added electron, i.e.,

EA increases

Generally the EA’s of metals are low while those of non-

metals are high

Halogens have high EA. This is due to their strong tendency

to change their configuration to ns2np6

On moving down a group,

the atomic size increases and therefore, the effective

nuclear attraction decreases and thus electron affinity

decreases

The process can be exo or endothermic

Electronegativitymeasure of the tendency of an element to attract

electrons to itself (from its neighbour)

On moving down the group• Z increases but Z* almost remains constant

• number of shells (n) increases

• atomic radius increases

• force of attraction between added electron and

nucleus decreases

Therefore EN decreases down the group

Electronegativity

On moving across a period left to right

• Z and Z* increases

• number of shells remains constant atomic

radius decreases

• force of attraction between added electron

and nucleus increases

Hence EN increases along a period

Trends in three atomic properties.

Hardness and Softness[Chemical but not mechanical]

An important concept of compounds formed

Rich people's dines with richer ones !!

High IE, smaller size, low polarizability -- makes Harder

Low IE, larger size, high polarizability -- makes softer

Chemical Hardness or Softness of an atom can be correlated

with ionization energy (IE), electron affinity (EA), size and

polarizability. If the IE > EA, the EA can be ignored.

The lighter atoms of a group are chemically harder

The heavier atoms of a group are chemically softer

Happiness is state of mind !!

SCN- can bind through either S or N depending upon

the HSAB nature of the metal ion. For e.g., Si or Pt

Trends are exhibited,

By keeping the metal same and changing the anion/ligand

By keeping the anion/ligand same and changing the metal

S will prefer Pt due to Soft … Soft type interactions, since

‘S’ is soft Lewis base & ‘Pt’ is soft Lewis Acid

N will prefer Si due to Hard … Hard type interactions, since

‘N’ is hard Lewis base, & ‘Si’ is hard Lewis Acid.

Oxidation States[In atomic state they are all zero].

Alkali atoms show +1 & alkaline earth shows +2

More electronegative atoms tend to form anions and

lesser electronegative atoms tend to form cations

when combined with others

Tendency of an atom to form ions with different oxidation states

(negative or positive) would depend on solvation or hydration

or ligation and lattice formation energies of the corresponding

ions. Compare this with the IE.

Why did the noble gas cry?

Because all his friends Ar- gon.

Bonding (Interaction) types:

Covalent, Non-covalent, Ionic

Non-covalent interactions are WEAK Interactions

between (atoms, molecules, compounds)

Atoms Molecules Supramolecules Materials/Solids

Hydrogen bonding interactions

Ion –molecular interactions

Vander Waal’s interactions

What do you call a tooth in a glass of water?

A one molar solution.

The name's Bond. Ionic Bond. Taken, not shared

Van der Waal’s Interactions

Three types of Van der Waal’s interactions:

a) Dipole – Dipole Interactions

b) Dipole – Induced Dipole Interactions

c) Induced Dipole – Induced Dipole

Transient Dipole – Transient Dipole

(London Dipersion Forces)

What do dipoles say in passing?

"Have you got a moment?”

Coordination numbers

Number of neighbours in interaction with the

central ion

-- Can be primary (closely interacting and/or

bonding)

-- Can be secondary (distant than the primary but

interacting – mostly no bonding)

-- All this affects the reactivity, conductivity,

electronic and magnetic properties

Coordination GeometryThe way the nearest neighbours are arranged in space,

a variety of geometries emerge:

(Main group, Transition and Lanthanides)

Linear (2) Trigonal (3)

Tetrahedral (4) Square planar (4)

Trigonal bipyramidal (5) Square pyramid (5)

Octahedral (6) Pentagonal bipyramid (7)

Singly capped octahedron (7)

Doubly capped octahedron (8)

Capped pentagonal bipyramid (9)

Decahedron (10)

Dodecahedron (12)

Linear (2)

Trigonal plane (3)

Square planar (4)

Tetrahedral (4)

Number Geometry Polyhedron

If I could rearrange the periodic table, I'd put Uranium and Iodine together.

Square pyramid (5)

Trigonal bipyramid (5)

NumberGeometry Polyhedron

Coordination No. 5

Did you hear oxygen and magnesium got together?

Triagonal prism

Octahedral (6)

Coordination No. 6

Singly capped

octahedron (7)

Pentagonal

bipyramidal (7)

NumberGeometry Polyhedron

Coordination No. 7

Doubly capped

octahedral (8)

Heptagonal dipyramid Tricapped triagonal prism

Coordn. No. 8 (only for information, not for the exam)

Pentagonal Prism Bicapped square Prism

Octadecahedron Hendecahedron

Icosahedrons Cuboctahedrons

Hexagonal prism Hexagonal antiprism

CH105 Part II: Inorganic Chemistry

Documents