Covalent bonding Flashcards
What is a covalent bond?
The strong electrostatic attraction between two nuclei and the shared pair of electrons between them.
What is a dative covalent bond?
When the pair of electrons shared by 2 atoms in a covalent bond comes from the same arom
what is the average bond enthalpy?
a measure of the strength of a covalent bond. The stronger the bond, the higher its value.
Why don’t covalently bonded molecules conduct electricity?
Because there’s no delocalised electrons available to carry a charge
Describe the solubility of covalent molecules
They tend to be more soluble in organic solvents than in water- some are hydrolysed
Why do covalent molecules have low boiling points?
Because the intermolecular forces between molecules are weak and don’t require a large amount of energy in order to be overcome
When does the intermolecular forces between covalent molecules increase?
when the molecules gain more electrons because then there’s a stronger force of attraction between the electrons and the nucleus
What is electronegativity?
A measure of how strongly atoms can attract shared electrons
the smaller the distance between the nucleus and the outer electrons, the ….
stronger the force of attraction between the shared electrons and the nucleus
the greater the distance between the nucleus and the outer electrons, the ….
weaker the force of attraction between the shared electrons and the nucleus
the greater the charge of the nucleus [the more protons it has] ….
the stronger the attraction between the nucleus and the shared electrons
is aluminium chloride a covalent molecule or an ionic compound?
An covalent molecule
Draw the covalent bonding shown in O2
Answer in book
Draw the covalent bonding shown in CO2
Answer in book
Draw the covalent bonding shown in HCl
Answer in book
Draw the covalent bonding shown in H2O
Answer in book
Draw the covalent bonding shown in NH4+
Answer in book
Draw the covalent bonding shown in CO
Answer in book
Draw the covalent bonding shown in H3O+
Answer in book
How many electrons does boron have on its outer shell after covalently bonding?
6
What is a lone pair of electrons?
2 electrons that aren’t used in bonding
What is phosphorus pentachloride?
Where the phosphorus atom has formed 5 covalent bonds so that it has a total of 10 electrons on its outer shell. This is because of phosphorus’ 3d subshell and as it uses all 5 of its outer electron to covalently bond, it end up with 10 electrons on its outer shell. This is called the expansion of the octet
Why can’t atoms in period 1 and 2 undergo the expansion of the octet?
Because these elements don’t have a d subshell
Why is aluminium chloride covalently bonded instead of ionically?
What is electron pair repulsion theory?
The idea that the shape of the molecule is determined by the electron pairs surrounding the central atom
What do solid lines tell you?
That bonds lie on the plane of the screen or page
What do solid wedges tell you?
That bonds are coming out of the plane of the page
What does a dotted wedge tell you?
That a bond is projecting back behind the plane of the page
What structure does beryllium chloride have?
A linear one., Or a straight line
When you have a central atom with with 3 pairs of bonding electrons around it what is this called?(as long as the central atom has no lone pairs of electrons)
Trigonal planar
What does planar mean?
Flat
What shape of molecule is formed when a central atom has 4 pairs of bonding electrons surrounding it?
A tetrahedral molecule e.g methane
What degrees are all the angles in tetrahedral molecules?
109.5 degrees
What shape is the central atom if it has 5 pairs of bonding electrons surrounding it?
Two of the bonding pairs move to opposite sides of the molecule. The other 3 bonding pairs take up a central position lying on the same plane and they spread themselves out as far as they can. This forms a shape called a trigonal bipyramidal
Describe the octahedral shape of a molecule
The central atom is surrounded by 6 bonding pairs
Do dative bond affect the shape of molecules?
No.because dative bonds act in the same way as covalent bonds
Do lone pairs repel more strongly than bonding pairs?
Yes. This extra repulsion decreases other bond angles by 2.5 degrees
What happens to the lone pair in the ammonium ion?
It forms a dative covalent bond, which has the same level of repulsions as a covalent bond
How many lone pairs does water have?
- It’s shape is based on the tetrahedron And is v shaped
How does a short bond affect the bond enthalpy?
The shorter the bond, the higher the bond enthalpy
What do lone pairs do to bonding pairs?
Push them closer together because bond pairs repel lone pairs more than they repel each other
If there’s 2 bonding pairs and no lone pairs, what shape will the molecule be?
Linear
If there’s 2 bonding pairs and no lone pairs, what will the bond angle be?
180 degrees
What is an example of a molecule with 2 bond pairs and no lone pairs?
BeCl2
If there’s 3 bonding pairs and no lone pairs, what shape will the molecule be?
Trigonal planar
If there’s 3 bonding pairs and no lone pairs, what will the bond angle be?
120 degrees
What is an example of a molecule with 3 bonding pairs and no lone pairs?
BF3
If there’s 4 bonding pairs and no lone pairs, what shape will the molecule be?
Tetrahedral
If there’s 4 bonding pairs and no lone pairs, what will the bond angle be?
109.5 degrees
What’s an example of a molecule with 4 bonding pairs and no lone pairs?
CH4
Is a tetrahedral 2D or 3D?
3D
If there’s 5 bonding pairs and no lone pairs, what shape will the molecule be?
Trigonal bipyramidal
If there’s 5 bonding pairs and no lone pairs, what will the bond angles be?
One will be 90 degrees and one will be 120 degrees
What is an example of a molecule with 5 bonding pairs and no lone pairs?
PCl5
If there’s 6 bonding pairs and no lone pairs, what shape will the molecule be?
An octahedral
If there’s 6 bonding pairs and no lone pairs, what will the bond angle be?
90 degrees
What is an example of a molecule with 6 bonding pairs and no lone pairs?
SF6
If there’s 3 bonding pairs and 1 lone pair, what shape will the molecule be?
Trigonal pyramidal
If there’s 3 bonding pairs and 1 lone pair, what will the bond angle be?
107 degrees
What’s an example of a molecule with 3 bonding pairs and one lone pair?
NH3
If there’s 2 bonding pairs and 2 lone pairs, what shape will the molecule be?
Bent
If there’s 2 bonding pairs and 2 lone pairs, what will the bond angle be?
104.5 degrees
What’s an example of a molecule with 2 bonding pairs and 2 lone pairs?
H2O
If there’s 3 bonding pairs and 2 lone pairs, what shape will the molecule be?
A distorted T
If there’s 3 bonding pairs and 2 lone pairs, what will the bond angle be?
87.5 degrees
What is an example of a molecule with 3 bonding pairs and 2 lone pairs?
ClF3
If there’s 4 bonding pairs and 1 lone pair, what shape will the molecule be?
Seesaw
If there’s 4 bonding pairs and 1 lone pair, what will the bond angles be?
87 degrees and 102 degrees
If there’s 5 bonding pairs and 1 lone pair, what shape will the molecule be?
Square pyramidal
What’s an example of a molecule with 4 bonding pairs and 1 lone pair?
SF4
If there’s 5 bonding pairs and 1 lone pair, what will the bond angles be?
90 degrees and 81.9 degrees
What’s an example of a molecule with 5 bonding pairs and 1 lone pair?
IF5
If there’s 4 bonding pairs and 2 lone pairs, what will the shape of the molecule be?
Square planar
If there’s 4 bonding pairs and 2 lone pairs, what will the bond angle be?
90 degrees
What’s an example of a molecule with 4 bonding pairs and 2 lone pairs?
XeF4
Why does graphite have a high melting point?
Because a lot of energy is required to overcome its strong covalent bonds
Why does graphite have a low density and why is it lightweight?
Because the layers are very far apart in comparison to the covalent bond lengths.
Is graphite soluble or insoluble?
Insoluble because of its strong covalent bonds
What shape is diamond ?
A tetrahedral
What does diamonds tightly packed arrangement allow it to do?
Conduct heat
What can diamond be cut into?
Gemstones
Is diamond soluble or insoluble?
Insoluble
Describe graphene
1 layer of graphite, 1 atom thick, hexagonal carbon rings
What can graphene be used in ?
Electronics
