Bonding Flashcards
How should you draw a dot and cross diagram?
- Draw the electrons being transferred to the other atom with crosses and do the other atom in dots
- State which noble gases the ions formed have the same electron configuration as
- Draw square brackets around each ion with a plus or a negative charge on each one, e,g + , 2+ or 3+
Describe the properties of ionic compounds
-They have very high melting and boiling points because it takes a great deal of energy to overcome the strong forces of electrostatic attraction, this can only be achieved at high temperatures
-Soluble in polar substances such as water as when they dissolve in the water the water molecules surround the ions and can overcome the forces of electrostatic attraction
-If charge on each ion increases solubility often decreases
-Only dissolve when dissolved in water because when they are solid the ions are locked in place by electrostatic forces of attraction and cannot move through the structure and carry a charge
What is a covalent bond
A bond that forms between a pair of non metals, they share some of their outer electrons so they can have noble gas arrangements. A covalent bond is a shared pair of electrons
The pair of electrons is attracted to the nuclei of the atoms forming the bond. Atomic orbitals overlap from each of the the two atoms and share a new electron density
How do you draw a dot and cross diagram that represents a covalent bond?
Draw the two ions with overlapping circles with the element symbol in the middle of each. Draw the covalent bond in the circle that is formed in the overlap. If there is more than one covalent bond forming keep them on the lines of the circles.
What is a dative bond?
-When one atom provides both of the electrons to form a covalent bond
-The atom that accepts the electron pair is an atom that does not have a filled main outer shell of electrons, the atom is electron deficient
-The atom that donates the electrons has a pair of electrons that is not being used in a bond called a lone pair
-They are exactly the same as a normal covalent bond
_ Both of he shared electrons come from one bonding pair
How do we represent a dative covalent bond and how is this different to how a normal covalent bond is displayed?
An arrow that points towards the atom that accepts the electron pair is a dative bond however a normal covalent bond is displayed using an
What is electron pair repulsion theory?
The shape of a molecule is determined by the electron pairs that surround the central atom, only referring to the outer level. This is based on the fact that electron pairs will repel other electron pairs, and they will move as far apart as possible to minimise this repulsion
Describe the shape of a molecule when there is 2 pairs of electrons around the central atom?
The shape will be linear as the furthest apart that the two electrons can be is 180 degrees
Describe the shape of a molecule when there is 3 pairs of electrons around the central atom
They will be 120 degrees apart, the molecule is planar and is called a trigonal planar e.g boron triflouride
Describe the shape of a molecule when there are 4 pairs of electrons around the central atom
They form a tetrahedron shape , for example methane and ammonia. They are 109.5 degrees away from each other.
Describe the shape of a molecule when there are 5 pairs of electrons around the central atom
Trigonal bipyramid for example phosphorous pentachloride with 120 degree angles and 90 degres
Describe the shape of a molecule when there are 6 pairs of electrons around the central atom
Adopts a octahedral shape with bond angles of 90 degrees
What effect does lone pairs of electrons have on the shape of a molecule?
They repel more strongly than bonding pairs which decreases each bond angle by 2.5 degrees
What is the bond angle and shape of a molecule with 3 bonding pairs and one lone pair? GIve examples
107 degrees because 109.5 has taken away 2.5 degrees
Ammonia
These have a trigonal pyramidal shape
What is the bond angle and shape for a molecule with 2 bonding pairs and 2 lone pairs? Give an example
It has 4 charge clouds with two lone pairs so this decreases the angle by 2.5 degrees for each pair so it is 104.5 degrees. V shaped
Example is water
Describe why magnesium chloride has a high melting point
Giant ionic lattice structure with strong electrostatic forces of attraction between oppositley charged ions
Describe the bonding in magnesium
Attraction between MG 2 plus ions and delocalised electrons
3 bonds and 2 lone pairs?
T shape
2 lone pairs and 2 bonds
Bent o
How does the sharing of electrons in an atom hold the atom together?
The negative electron pairs in the outermost orbitals are electrostatically attracted to the positive nuclei of each atom pulling the atoms together
Describe how ammonia acting as a base is an example of dative covalent bonding
The forming of an ammonium ion, NH4 ,from ammonia and a hydrogen ion is an example of this because ammonia has a lone pair of electrons which occupy a full orbital in the central N atom. The hydrogen ion is formed when an electron is removed from a hydrogen atom, meaning this ion is just a singular proton with the remaining empty orbital. When the full orbital from the N atom and the empty orbital from the H ion come close enough these orbitals overlap, creating a new bonding orbital where electrons are shared, creating a co ordinate bond
Why do ionic bonds between atoms form a lattice
There are forces of replusion between the like charges of the ipns so they arrange themselves in order to be as far apart as possible to minimise replusion
How are instantaneous dipoles formed?
Electrons move very quickly and randomly across a whole molecule , meaning at any one time electrons may not be equally shared between the two atoms. These electrons have a negative charge so when there are more electrons on one certain side it will have a partial negative charge, and the other side will have a partial positive charge. This causes a dipole as electrons are unevenly distributed.
How can a molecule be induced to have a dipole?
If you line up a molecule with a dipole next to another molecule because electrons held in the neighbouring molecule will be either attracted to the slight positive charge on the end of the first molecule or be repelled by the slight negative charge on the first molecule
