Ugrás a tartalomhoz Lépj a menübe
 


02 Kémiai kötések

2014.04.09

 

Chemical Bondings
 
 
First class” bondings: strong
          Metallic
          Covalent
          Ionic
Intermolecular forces: weaker
Metallic bonding
Electronegativity: a measure of how strongly an atom attracts electrons in a bond
Metal atoms can lose their outer electrons – electronegativity is low
Metallic lattice: metal ions and delocalised electrons
Metallic bond: electric attraction between ions and delocalised electrons
Good conductors of electricity and heat - Delocalised electrons can move easily
High density, high melting point -ions (and free electrons) are packed closely together, a lot of bonds in a space
Malleable and ductile - Ion layers can slide over each other easily
 
Covalent bonding
Atoms need full outer shells
H atom: 1 electron is needed
Solution: sharing
Covalent bonding: atoms are bonded by shared pair(s) of electrons
Molecular orbital: the space where an electron can be found in 90% of probability in a molecule
Simple bond: is located between the atoms - Sigma (σ) bond
Double bonds: second pair of electrons (π –bond) is located over and below the σ-bond – it is weaker
Triple bonds: 1 σ-bond and 2 π –bonds
Properties
Bond energy: the measure of bond strength in a chemical bond (kJ/mole)
Bond length: the average distance between the centres of the nuclei of two bonded atoms in a molecule
Bond angle: the angle formed between two bonds surrounding an atom in a molecule
Dative bonding
Bonding pair came from the same atom
Shape of molecules
          Depends on the number of electron
          pairs surrounding the central atom
          Electron pairs repel each other
           Lone pair needs more place than bonding pair
Shapes: Linear, Trigonal planar, Tetrahedral, Pyramidal, V-shaped
            
Bond polarity
Bond between similar atoms: electronegativity is the same – nonpolar bond
Bond between different atoms: electronegativity is different – polar bond
Polarity of molecules
It depends on the polarity of bonds and the shape of the molecule
          H – H:
     nonpolar bond and molecule
          H – Cl:
     polar bond, dipole molecule
          H2O:
     polar bonds, dipole molecule
          CH4:
     polar bonds and nonpolar molecule
Ionic bonding
Two ways to get full outer shell:
          To lose electron(s): make cation (+ charge), group 1-3
          To gain electron(s): make anion (- charge), group 5-7
Ionization energy: the energy required to remove electron(s) from 1 mole of gaseous atoms or ions
          in a group decreases (distance of electrons increases - attraction decreases)
          in a period increases (charge of the nucleus increases - attraction increases)
          Electron affinity
          Energy is required or released to gain electron(s) in 1 mole of gaseous atoms or ions
Changing of atom radius
          Losing electrons: atom radius decreases
          Gaining electrons: atom radius increases
          Ionic compounds
Are formed by metals and non-metals
Ionic lattice: anions and cations, neighbours have opposite charge
Ionic bonds: the electrostatic forces of attraction between oppositely charged ions
Lattice energy: is required to break down the lattice to ions
Intermolecular forces
Van der Waals’ forces
          The weakest intermolecular force
          Electron cloud is not symmetric
          Temporary dipoles induce a dipole in their neighbours
          Larger the molecule – stronger the VdW forces
          E. g. iodine, hydrogen, sulphur
Dipole-dipole forces
          Dipole molecules: electrostatic attraction between partially + and – parts
          Larger the attraction – higher the melting and boiling point
Hydrogen bonding
          H-O-H
          A partially + H atom
          A strongly negative O atom with lone electron pairs and high electronegativity
H-bonding: attraction between the partially positive H atom and the lone pair of the O (or F, N) atom
          Importance in Nature
Water melting point and boiling point is quite high: evaporation needs a lot of energy - thermoregulation
Water density: the highest at 4 oC
Density of ice is lower than density of water:
          Living creatures can survive, they are protected in winter
          Rivers can flow in winter too
          Ocean currents can work all over the world
 

 

Lattice types

Atomic lattice

Ionic lattice

Metallic lattice

Molecular lattice

Particles

Atoms

Ions

Metal ions and delocalised electrons

Molecules (or noble gas atoms)

Type of attraction

Covalent bonding

Ionic bonding

Metallic bonding

Intermolecular forces (Van der Waals, dipol-dipol, Hydrogen bonding)

Strength of attraction

Strong

Strong

Strong (usually)

Weak

Hardness

Hard

Hard

Hard (usually)

Soft

Melting point

High

High

High (usually)

Low

Can conduct electricity?

No (insulator)

No (insulator)

Yes (conductor)

No (insulator)

Can conduct heat?

No (insulator)

No (insulator)

Yes (conductor)

No (insulator)

Solubility

Insoluble

In polar solvents

Physically no (some react with water, e. g. Na)

In polar or nonpolar solvents

Types, examples, specialities

Diamond, quartz

Salts (NaCl, KF)

Cubic body centered (Fe, Cr), Cubic face centered (Al, Ag, Cu, Ag), hexagonal (Zn, Mg)

H2O, HCl, I2