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Atoms, ions, molecules y macromolecules
Master of Crystallography and Crystallization – 2013T02 – Mathematical, Physical and Chemical basis of
Crystallography
Elements, Atoms and IonsThe Chemical elements, their names and symbols,
are collected on the PERIODIC TABLE
Dmitri Mendeleev (1834 - 1907)
Atoms of Cooper on a surface of silicium.
• An Atom is the smallest particle of an element mantaining
all chemical properties of the element itself.
Distance = 1.8 nanometers (1.8 x 10-9 m)
COMPOSITIONOf the ATOM
The atom is mainly empty space
• Protons (p+)– electric charge +– mass = 1.672623 x 10-24 g– relative mass = 1.007 units of atomic mass (amu)
may be rounded to 1
• Electrons (e-)– electric charge -– relative mass = 0.0005 amu
may be rounded to 0
• Neutrons (no)– without electric charge – mass = 1.009 amu may be rounded to 1– Has a spin momentum of 1/2
Atomic Number, Z13
Al
26.981
Atomic Number
Atomic Symbol
AVERAGE Atomic Mass
Mass Number, A• # protons + # neutrons
• An atom of boron may have A = 5 p + 5 n = 10 amu
• The Atomic Mass is the AVERAGE of the atomic masses.
A
Z
10
5B
Isotopes
• An element (same Z) different mass number (A)
• Boron-10 (10B) has 5 p y 5 n
• Boron-11 (11B) has 5 p y 6 n 10B
11B
0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
IONS
• IONS are atoms or groups of atoms charged positive
o negatively.
– Removing an electron of one atom produces a CATION
with positive charge.
– adding an electron to an atom produces an ANION with
negative charge.
Mg --> Mg2+ + 2 e- F + e- --> F-
Depending on the type of atoms joining:
• Metal – Non metal: one gives and other accepts
electrons (cations and anions)
• Non metal – Non metal: both accept electrons,
share electrons
• Metal – Metal: both give electrons
Ionic Bond• The Ionic compound is formed by reacting one metal
with a non metal.
• The atomos of the metal lose electrons (producing a cation) whic are accepted by the non metal (producingan anion).
• The ions of different charge attract electricalyeachother, ordering itselves to form and ionic network.The Ionic compounds are not made of molecules.
• The bond results of the natural force of atraction stablished among ions with oposite charges.
• That forces of attraction keep them united, forming a compound of ionic type.
Ionic Bond between Cl and Na: formation of the ions Cl- and Na+
IonicNetworks
NaCl CsCl
The compounds joint by ionic bonds when are periodicaly ordered usually form crystals.
Metallic Bond
• The metalic substances are made of atomos of the same metallicelement (low electronegativity).
• The atoms of the metallic element may lose some electrons,producing one cation or “metallic rest”.
• Producing at the same time a Cloud or sea of electrons: set offree electrons, delocalized, which do not belong to any particularatoms.
• The cations repel each other, but are attacted by the sea ofelectrons existing among them. This is the way to form a metallicnetwork: metalic sustances neither are formed by discretemolecules.
The model of the cloud of electrons represents the metal as a set of cations occupaying the fixed positions of the network, being the free electrons moving easily, without being confinated/attached to any especific cation.
Fe
Covalent BondCovalent compounds originates by Sharing Electrons
among non metallic atoms.
Electrons highly localized.
This type of bonds is stablished among a group of special atoms, called the non metallic elements.
Their atoms have simmilar forces of electricalattraction, for that reason share valence electrons
when participate in one bond of such type.
Covalent Bond and Molecules
• Atoms bonded by covalent bonds form individualparticles maned molecules.
• So, a molecule is any stable set of two or moreatoms bonded covalently, but many may havehundreds or thousands of bonded atoms.
• Covalent bonding allowsthe formation of molecules of elements(H2, O2, N2), whencambinating atomos of the same element, and molecules of compounds (H2O, CH4, when combining atomsof diferent elements.
There Exist molecules, or are really giant structures?
• Covalent Networks
• Covalent Molecules (Small - Macromolecules)
Diamond: tetraedra of carbon atoms
Grafite: layers of carbon atoms
The union between atoms sharing
electrons is very strong, very dificult
to break. The shared electrons are highly
localized.
Topological Characterization of Bonds
maxima, minima and saddle points critical points
x, y,z Electron density, : derivable function
r r
x, r
y, r
z
r c 0
Gradient zero: neccesary condition for maximum,
minimum or saddle point
H r
2
x2
2
x y
2
xz
2
y x
2
y2
2
yz
2
z x
2
z y
2
z 2
Range (): number of non zero eigenvalues
Signature (): N. positive - N. negative eigenvalues
mathematical nature
(, )
denomination
(Bader´s theory)
maximum (3, -3) tridimensional atractor
second order saddle point (3, -1) bond critical point
first order saddle point (3, 1) ring critical point
minimum (3, 3) cage critical point
Alows to derive the nature of the bond from the electron density
Type of interaction and bond multiplicity
From the density at the bond critical point, b
Bond Anisotropy
Bond Elipticity,
1
2
2
1
2
1
1
012
1
n
2
22.012
1
n
character of the threemembered rings
High elipticity
Nuclea + Bonds
Nuclear Positions
accesible theoretically and experimentally
ACCESIBLE FROM
X-RAY DIFFRACCION
Uncertainty Sources in the Fourier map
Uncertainty on the
Identification
Single Peaks
Uncertainty on the existence
of a chemical bond
Pairs of Peaks
Entropy associated to the
Atomic Nature S(A )
Entropy associated to the
connectivity S(C)
Total Entropy associated to a Fourier map
S ( F ) = S ( A ) + S ( C )
V & E d: R3 x R3 R
COMPOSITION CONSTITUTION
CONFIGURATION
AND
CONFORMATION
TOPOLOGICAL SPACE
(adimensional space)
TOPOLOGICAL
MOLECULAR STRUCTURE
or MOLECULAR GRAPH
EUCLIDEAN METRIC SPACE
(3-D Space)
GEOMETRICAL
MOLECULAR STRUCTURE
M = (V, E, d)
EMPIRICAL FORMULA
C16O3
O
O
OG = (V, E)
Algebraic
Representatio
n
Diagramatic
Representation
Topological
Interpretation of
Fourier Maps
Structural
Refinement
II
I
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III
Access toMolecularProperties
Electron Density:
(r) = ... ({r,s})*({r,s})dVdS
Spatial coordinates Wavefunction of many electrons
Hohenberg&Kohn (1964):
1) The electron density defines univocally the electronic fundamental state of
atoms, molecules and crystals.
2) The electron density provides a minimum of the energy functional.
E[] = G[] + ENe [] + Eee[] + Exc []
kinetic energy electron- electron energy
electron-nuclear energy change and correlation energy
Five characteristics of the atomic and molecular
interactions :
(rb), 2 (rb), g (rb), v (rb), E (rb)
Ee(r) = g (r) + v (r)
Atomic and molecular interactions characterized in terms
of bond critical points(acording to Bader, Bianchi, Espinosa, Macchi, Tsirelson y otros)
covalent and covalent-polar bonds
Vb << 0
gb << Vb
Eb << 0
Dative bonds
Vb < 0
gb Vb
Eb < 0
Metallic bonds
Vb < 0
gb Vb
Eb < 0
Ionic bonds
Vb < 0
gb Vb
Eb 0
vdW and H-bonds
Vb < 0
gb Vb
Eb 0
‘Shared’ Interactions
ρb > 0.5 eÅ-3, 2 ρ<0
‘Closed-shell’ Interactions
ρb < 0.5 eÅ-3, 2 ρ>0
Increase of gb, Vb, Eb
Sources of Electron densities:
1) Experiments of X-ray diffraction:
2) Theoretical :Calculation
- Four Circles Diffractometers
- Diffractometers equipped with area detectors (imaging plate or
CCD)
-non-empiric Hartree-Fock and methods based on
theTheory of the Density Functional
Dynamic electron density analysis:
Space of Nuclear ConfigurationsEquivalence Relation, E
Same Characteristic set of CP
Molecular Structure
B = 0.2 Å2
B = 0.0 Å2
C C
Topological Peculiarities of the conventional Fourier maps
Shared Interactions
ρb > 0.5 eÅ-3, 2 ρ<0
Closed-shell Interactions
ρb < 0.5 eÅ-3, 2 ρ>0
Deensity at the bond Critical Point, b
- non-covalent: 0.3 e/Å3 b 0.6 e/Å3
- Ionic or hightly polar covalent: 0.6 e/Å3 b 0.9 e/Å3
- Covalent Bonds
0.9 e/Å3 b 3.0 e/Å3
- simple: b < 2.0 e/Å3
- double: b ~ 2.0 e/Å3
- triple : b ~ 2.5 e/Å3
Bond paths
electron density
ridges created by
the gradient lines,
which go through
the bond CP and
connect some
nuclei
NaCl: ρ(r) field with bond paths and bond CP
Bond CP
Electron Density Modeling
Atomic Coordinates
Thermal displacement parameters
Electron Density parameters
Fmodel(q) = F [ {x,y,x}n, {Uij, Cijk, Dijkl }n, { P, κ }n ]
Σ w q [F experim (q) - F model (q)]2 minimum
Least Square fit
Properties which can be derived from electron density
Electrostatic potential
Electron diffraction
Quadrupole
electric moments
Optical measurements
Inner-crystal electric
field
Electric field gradient
NMR, NQR, Mössbauer
spectroscopy
Diamagnetic
susceptibility
Magnetic
measurements
Dipole electric atomic
and molecular
moments
Electrostatic atomic
and molecular
interaction energy
DFT
Kinetic electron
energy
Electron
density
Clasification of the Chemical Compounds
• They may be clasified into two large groups:
• 1.- Organic Compounds and
• 2.- Inorganic Compounds.
Inorganic Compounds
• Are those formed by any of elements differentof Carbon, including carbon in some specialcases (CO2 y el CO).
• Water (H2O), the table salt(NaCl), thesaltpeter/nitre (NaNO3) or the sodiumbicarbonate (NaHCO3) are some examples ofinorganic compounds.
Organic Compounds• Contain carbon as main element. • Besides contain elements as hydrogen, oxygen,
nitrogen and, less frecuently, phosphorus and sulphur.
• CHONPS• Except CO2 and CO
• Sucrose, is an example of Organic Molecule, acarbohydrate un this particular case.
• Other organic compounds important to life are, thefates, the vitamins and the nucleic acids, including DNAand RNA.
Macromolecules in nature
• Are large molecules and, besides, of highestructural complexity.
• Macromolecules may be clasified, atending to theirorigen, in Natural and Synthetic.
• Biomolecules, which are the molecules constituents of the living organisms, are mainly made of the following elements: carbon, hydrogen, oxygen, and nitrogen.
The main biomolecules are: Carbohydrates, Lipids, Proteins and Nucleic
Acids.
Chemical elements on the living organisms
H, C, O, y N constitute thr 96.5% weight of a living organism
Carbohydrates.
• Play energetic and estructural functions.
• Are made by the union of basic units calledmonosacarids.
• Acording to the number of basic units they contain, may be clasified as:
• Monosacarids: basic unit.
• Oligosacarids : between 2 and 10 monosacarids.
• Polisacarids : more than 10.
Lipids.
• Are organic macromolecules containing carbon, hydrogen and oxygen,
• Functions: energetics and estructurals.
• One of most particular characteristics of the lipidsis their insolubility in water.
• Examples:
• Colesterol,
• Saturated and insaturated fats and
• hormones as testosterone.
Proteins.• Are the most abundant macromolécules.
• Have various functions:
• Antibodies, participating in the defense of the organism;
• Enzimes which acelerate the speed of the chemicalreactions of the cells;
• Estructurals, by forming part of different tissues as the skin, nails and hears;
• Hormonal, regulation of growing, levels of sugar in blood, etc.
• It is important to point out that, normaly, proteins DO NOTact as a source of energy.
Nucleic Acids.• These macromolecules are especialy important to the living
organisms, because thay store and transport the geneticmessage.
• There exist two types of Nucleic Acids:
desoxirribonucleic acid (DNA) and the ribonucleic (RNA).
ADN is the most important nucleic acid. It contains allgenetic information to determine the color of your eyes,whether your hair is straight or curl, and even the pattern ofyour fingerprints.
• ARN, is formed from the DNA and transports the information toallow cells syntesize all their proteins.
• Both DNA and RNA are formed by basic units called nucleotids.
- Are the most abundant biologicmacromolecules.
- Are present in all cell and everywhere withinthe cell.
- There exist thousans of different types andsizes of proteins.
- Exhibit an amasing number and diversity offunctions.
Proteins.
Each organism may biuld proteins using a base of 20 defferent aminoacids
Enzimes poisons
Hormones colagen (skin, bones)
Antibodies receptors
Transporters hemoglobin
Proteins of milk
Queratine (horns, scales, hairs, wool, nails)
•an amino group (-NH2)
•a carboxilo group (-COOH)
•an atomo of H
•a characteristic group R (lateral chain)
Basic estructural Units of proteins
a- aminoacids
connected carbon aatom
POLAR
NON POLAR
The difference among then is based in size, electric charge, hydrofobicity
aliphatic
aromatic
chargedpositively
negatively
• Proteins of all living organisms are build by20 aminoacids covalentely bonded indifferent combinations and sequences.
• Due to that each of these aminoacids havediferent lateral chains, with different chemicalproperties, this group of 20 molecules may beconsidered as the ALFABET to WRITE thelanguage of the proteins.
• Thanks to this variety the cells may produceproteins with Physical and functionalpropierties fully different
Aminoacids with aliphatic lateral chains
Glicina(Gly, G)
Alanina(Ala, A)
Valina(Val, V)
Leucina(Leu, L)
Isoleucina(Ile, I)
Prolina(Pro, P)
Glicina(Gly, G)
Alanina(Ala, A)
Valina(Val, V)
Leucina(Leu, L)
Isoleucina(Ile, I)
Prolina(Pro, P)
Fenilalanina(Phe, F)
Tirosina(Tyr, Y)
Triptofano(Trp, W)
Aminoacids whith aromatic lateral chains
Sulphur containing lateral chains
Cisteína(Cys, C)
Metionina(Met, M)
SH
Aminoacids with positively charged (+) lateral chains
Lisina(Lys, K)
Arginina(Arg, R)
Histidina(His, H)
pKa=10.8 pKa=12.5 pKa=6.0
Aminoacids with negatively charged (-) latetral chains
Glutamato(Glu, E)
Aspartato(Asp, D)
Such subunits linked by AMIDE BOND orPEPTIDIC BOND provide the structure ofproteins
The skeleton of the whole protein is made by repetition of the N-Ca-C.This unit propagates bonded by peptidic bonds
Bonded to the polipeptidic skeleton we find, hydrogens of the aminogroup, oxygens of the carbonil group and hydrogens and the lateralchains of the alpha carbons.
Proteins are macromolecules which maycontain from 400 to 25,000 residues
MW between5,000 y 700,000
Ser Gly
Tyr
Ala
Leu
The aminoacid sequence of a protein are geneticallydetermined :
The nucleotids sequence of DNA codifies a
Complementary sequence of nucleotids on the RNA
Which determines the aminoacids sequence of the protein
Espacial structure function
mutationsgenetic alterations
Electric dipole Trans position
CHARACTERISTICS OF THE PEPTIDIC BOND
Double bond character
These 6 atoms are on the same plane
Sheets
a Helix
a Helix (left)
Gráfico de Ramachandran
CONFORMATION OF PROTEINS
hierarchic structure
Sequence of aminoacids of thepeptidic skeletonand S-S
Array / distribution / ordering of the skeletonand lateral chains of the
protein in space
Describes the tridimensional order of the
protein
* La Naturaleza del Enlace Químico. L. Pauling, (1939) ¡A clasic!
* Atomo. I. Asimov, (1992). Ed. Plaza-Janés ¡On the way to become a clasic!
* Física Cuántica: Atomos, Moléculas, Sólidos, Núcleos y Partículas.
R. Eisberg, (1992, 16ª re-impresión 2002). Ed. Limusa
* Construyendo con Átomos y Moléculas. Indigo, (2006). Ed. Eudeba
* Enlaces Químicos. A.L. Companion, (2008). Ed. Reverté.
* Electrones, Neutrinos y Quarks. F.J. Indurain, (2001). Ed. Crítica (Collection Drakontos)
* Partículas Elementales. G.T. Hooft, (2008). Ed. Crítica (Collection Drakontos)
* An Introduction to the Electronic Structure of Atoms and Molecules. R.F.W. Bader, (1970).
* Atoms in Molecules. A Quantum Theory.
R.F.W. Bader, (1994). Ed. Oxford University Press.
* Density-Functional Theory of Atoms and Molecules.
R.G. Parr & Y. Weitao, (1994). Ed. Oxford University Press
* Bonding and Structure of Molecules and Solids.
D.G. Pettifor, (1995). Ed. Oxford University Press
* Physics of Atoms and Molecules.
B.H. Bransden & C.J. Joachain, (2003, 2ª edición) Ed. Prentice Hall.
* The Chemist's Guide to Valence Bond Theory.
S.S. Shaik & P.C. Hiberty, (2007). Ed. Wiley-Interscience
* The Quantum Theory of Atoms in Molecules.
C.F. Matta & R.J. Boyd, (2007). Ed. Wiley-
VCH
* The Chemical Bond: A Fundamental Quantum-Mechanical Picture.
T. Shida, (2008, 2ª edition corrected). Ed. Springer
On the Chemical Bond (antecedents-history):
http://platea.pntic.mec.es/~jrodri5/web_enlaces_quimicos/antecedentes.htm
On molecular structures. Links to various “books” electronics and pages on several aspects of chemical bond(formulas, characteristics, figures, geometries, etc..)http://www.uhu.es/quimiorg/estructuraweb.html
Atoms, ions, molecules y macromolecules
Master of Crystallography and Crystallization – 2013T01 – Mathematical, Physical and Chemical basis of
Crystallography
END