Bonding and Structure Flashcards
Define ionic bonding
Ionic bonding is the electrostatic attraction between positively and negatively charged ions.
when construction ionic dot cross diagrams what must be added to the products and why?
square brackets and charger to show that the charge is spread over each ion
Why are only the outer shells shown in dot cross diagrams?
Only the outer shells are shown because the inner shells are not used in bonding
explanation behind the structure of giant ionic lattices
Each ion attracts oppositely charged ions in all directions
what arrangement are giant ionic lattices
regular arrangement.
Why do ionic (lattice) compound have high melting/boiling points?
Large amounts of energy are required to overcome the strong electrostatic forces between oppositely charged ions.
What two factors increase the melting and boiling points of ionic (lattice) compounds?
- The charge of the ion, higher charge creates stronger electrostatic forces between ions and therefore higher melting and boiling points.
- Size of the ions, the smaller the size of the ions the closer they are to one another, the stronger the electrostatic forces, the higher the melting and boiling points.
what are most ionic compounds soluble in?
Polar solvents (water)
What 2 processes occur for solubility to take place in ionic substances?
- Solvent must break down the lattice.
- Solvent must surround and attract each ion
What factor effects solubility in ionic compunds?
Charge of ions, higher the charge the lower the solubility, highly charged ion’s electrostatic forces are too strong for the solvent to break up, leading to low solubility.
What states do ionic compounds conduct electricity?
Liquid an aqueous as the ions can then act as mobile charge carriers.
Define covalent bonding
Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
what occurs in double covalent bonding
Two pairs of electrons are shared between the bonding nuclei
what occurs in triple covalent bonding
Three pairs of electrons are shared between the bonding nuclei
Define dative/ coordinate bonding
Dative covalent bonding is a covalent bond in which the shared pair of electrons is supplied by one of the bonding atoms only.
Define average bond enthalpy
Average bond enthalpy is a measure os covalent bond strength.
Describe electronegativity
The attraction of a bonded atom for the pair of electrons in a covalent bond
How is electronegativity measured
Pauling scale
Electronegativity increases (periodic table)
Across the groups (left to right)
Up the period
Describe non polar bonds
The electron pair is evenly shared between the bonded atoms.
what must be the same for a non polar bond to occur
The bonded atoms must have the same electronegativity/ same element
Describe polar bonds
The electronegativity of the bonded atoms are not the same, the electron pair is therefore shared unequally between the bonded atoms
In a molecule what is the separation of opposite charges called
Dipole, resulting in a permanent dipole
What makes a polar molecule
Overall dipole
Why is CO2 not a permanent dipole
Both dipoles cancel each other out, (both horizontal with opposing directions)
What are intermolecular forces?
weak interactions between the dipoles of different molecules
Order the intermolecular forces in increasing bond strength
1.(London forces) Induced dipole-dipole
2. Permanent dipole-dipole interactions
3.Hydrogen bonding
Describe induced dipole-dipole (London forces)
Weak intermolecular forces that exist between all molecules.
Describe the formation of induced dipole-dipole moments
1) When electrons become unevenly distributed an instantaneous dipole will occur.
2) The instantaneous dipole then induces an instantaneous dipole in neighbouring molecules.
3) This produces a knock on effect inducing dipoles in further molecules.
4) Creating a weak interaction between the molecules.
What increases the strength on induced dipole-dipole (London) forces
Larger numbers of electrons creates a stronger dipole, inducing stronger interactive forces between the molecules.
Describe permanent dipole-dipole forces
The weak intermolecular forces between permanent dipoles in different molecules.
Describe the melting and boiling points of simple molecular lattices
Low melting and boiling points
Describe the solubility of simple molecular substances (non polar)
Soluble in non polar solvents, not soluble in polar solvents as the polar solvents intermolecular forces are too strong to break apart, not allowing them to weaken the intermolecular forces of the simple molecular lattice
Describe the solubility of (polar) simple molecular substances
May be soluble in polar solvents
What is the electrical conductivity of simple molecular substances
no conductivity as there are no mobile charge particles.
Define hydrogen bonding
Intermolecular bonding between electronegative (lone pair carrying) atoms ‘Oxygen, Fluorine, Nitrogen’ and Hydrogen. Between the lone pairs of one electronegative atom of one molecule to the hydrogen atom from another molecule.
Describe the melting and boiling points of water
High (compared to expected without hydrogen bonding).
Describe the density of water in liquid and solid state
Water is less dense in its solid state as hydrogen bonding forces the water molecules to form a tetrahedral structure occupying more volume, making the solid less dense than the liquid form.
