Chemical bonding Flashcards
Why are ionic bonds so stable?
Because the reactant molecules have filled their valance shells in order to Create the bond so they are unreactive.
What is an ionic bond?
This is when ions are created by transferring electrons until the valance shell is full.
What holds the ions together in crystals?
Forces of electrostatic attraction between oppositely charged ions.
What is lattice energy?
A measure of the strength of the electrostatic forces in an ionic crystal.
What ions don’t have a noble gas structure?
The D block elements.
What creates the forces of repulsion found in an ionic crystal?
The ions with the same charge
The forces between the inner shells of electrons and between positively charged nucleus
What determines the distance between the atoms in a bond?
The balance of the repulsive and attractive forces.
What is covalent bonding?
Covalent bonding exists between atoms when electrons are shared in pairs. In general the number of electrons involved is such to allow a noble gas structure to be built up around each atom.
Describe the spin on the electrons involved in a single covalent bond.
They spin in opposite directions.
Where do the attractive forces come from in a covalent bond?
That produced between the two positive nuclei and the negative charge cloud of the shared electron pair.
Describe an electron density map for a covalent bond.
The bulk of it surrounds the two positive nuclei with only a little density in the internuclear region.
Where do the repulsive forces come from in a covalent bond?
Between the inner shells of electrons in each atom.
Describe an electron density map for an ionic compound.
The cloud is spherical around the nucleus of the ions with an area between the ions where there are no electrons.
What is dative/co-ordinate bonding?
When both the electrons that form a covalent bond come originate from one of the atoms.
How is a dative bond indicated in a structural formula?
It is drawn as an arrow which points to the atom receiving the two electrons.
Give two examples of co-ordinate bonding.
Th reaction between ammonia and Boron-triflouride to produce NH₃BF₃
The production of ammonium from a hydrogen ion and ammonia.
What do spectroscopic studies of the vaporised alkali halides show and what does this imply?
They show that the internuclear distance in these molecule is less than the in the corresponding ionic solid. Implying stronger bonding than in the crystal and this can only happen if there is a higher concentration of electrons between the nuclei, implying a distortion of the electron cloud of one or both ions from their usual spherical distribution.
What does polarisation(distortion) of an ion represent?
The transition from ionic bonding to covalent bonding .
What does the polarisation of the negative ion increase with?
With increasing ionic radius.
What are the factors that might affect the distortion of the electron charge clouds around a negative ion?
A small cation is more effective than a large one as it can get closer to the anion.
The larger the charge on the cation, the more effective it is.
The larger the negative ion is, the more easily distorted it is as the electrons are further away from the nucleus so are attracted less strongly.
An anion with a larger charge will be more readily distorted as there is increased mutual repulsions between electrons and a greater quantity of negative charge to be transferred.
Why aren’t the bonding electrons equally shared between atoms in a covalent bond?
Because the attraction of the nuclei or the bonding electrons will be different.
Define electronegativity.
The ability of an atom to draw attract a pair of bonding electrons in a covalent bond to itself.
Describe the trends of increasing electronegativity.
Electron negativity increases across a period and up a group.
What are the electronegative elements in order of electronegativity?
Fluorine
Nitrogen
Oxygen
Chlorine.
