📝 Bonding

Task

🎧️ Listen to the recording and mind pronunciation of words.

Forces between molecules are called intermolecular forces. The forces between two molecules having permanent dipoles are called permanent dipole-dipole forces. Very weak forces of attraction between all atoms or molecules are called van der Waals’ forces. These forces increase with the increasing number of electrons (and protons) in the molecule and with increasing the number of contact points between the molecules. Hydrogen bonding is the strongest type of intermolecular force. For hydrogen bonding to occur between twomolecules we need:
a) one molecule having a hydrogen atom covalently bonded toF, O or N (the three most electronegative atoms) and
b) a second molecule having a F, O or N atom with an availablelone pair of electrons Ionic compounds are solids at room temperature and pressure.
This is because:
a) there are strong electrostatic forces (ionic bonds) holding the positive and negative ions together
b) the ions are regularly arranged in a lattice, with the oppositely charged ions close to each other. The higher the charge on the ions and the smaller they are, the stronger the attraction between them will be and the higher the melting and boiling points. Ionic compounds do not conduct electricity in the solid state. They conduct electricity when they are molten or dissolved.
A covalent bond is a pair of electrons shared between two atoms. Covalently bonded substances with a simple molecular structure fall into two groups.
a) Those that are insoluble in water. Most covalently bonded molecules are non-polar. Water molecules are not attracted to them, so they are insoluble. An example is iodine.
b) Those that are soluble in water. Small molecules that can form hydrogen bonds with water are generally soluble. An example is ethanol.
A co-ordinate bond (or dative covalent bond) is formed when one atom provides both the electrons needed for a covalent bond. For dative covalent bonding we need:
a) one atom having a lone pair of electrons; and
b) a second atom having an unfilled orbital to accept the lone pair.
A metallic bond is an attraction between cations and a sea of electrons. These bonds are formed when atoms lose electrons and the resulting electrons are attracted to all the resulting cations.
Since the electrons in a metal are delocalized, they are free to move throughout the crystal in a certain direction when a potential difference is applied, and metals can thus conduct electricity in the solid and the liquid state. Melting and boiling points of metals are relatively high.
All bonds are assumed to be covalent in principle: differences in electronegativity can be used to predict how much ionic or metallic character a covalent bond will have. Electronegativity is the relative ability of an atom to attract electrons in a covalent bond.
We can measure the strength of a bond by its bond energy. This is the energy needed to break one mole of a given bond in a gaseous molecule.

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