Chemistry bonding and structure - part 3

  • Created by: I.m
  • Created on: 02-12-12 15:56
In a covalent bond, what is the shared pair of electrons attracted to?
lent bond the shared pair of electrons is attracted to the nucleus of each of the atoms in the bond.
1 of 36
Is a covalent bond polar or non-polar?
A covalent bond can be polar or non-polar.
2 of 36
What does a covalent bond being polar or non-polar depend on?
A covalent bond can be non-polar or polar depending on how evenly the electrons are distributed between the atoms.
3 of 36
What does this distribution of electrons depend on?
This distribution depends on the electronegativity of the atoms present.
4 of 36
What is electronegativity?
Electronegativity is the ability of an atom to attract the electron pair(s) in a covalent bond.
5 of 36
What does the electronegativity of an element depend on?
The electronegativity of an element depends on its position in the periodic table.
6 of 36
What is the most electronegative element?
Fluorine is the most electronegative element.
7 of 36
In non-polar bonds, do bonded atoms have the same or different electronegativity?
In non-polar bonds bonded atoms are the same and have the same electronegativity.
8 of 36
How are bonding electrons distributed in a non-polar bond?
Bonding electrons in a non-polar covalent bond are evenly distributed.
9 of 36
Give two examples of molecules that have a non-polar covalent bond.
H₂ and Cl₂.
10 of 36
In polar bonds, do bonded atoms have the same or different electronegativities?
In polar bonds bonded atoms have different electronegativities.
11 of 36
How are electrons attracted in a polar bond and what does this result in?
The atom with the greater electronegativity will attract the bonding electrons more strongly than the other atom, therefore electrons in a polar bond are unevenly distributed leading to a small charge separation within the covalent bond.
12 of 36
What is the small charge separation with a covalent bond called?
This small charge separation is called a permanent dipole. (permanent dipole - uneven distribution of electrons).
13 of 36
What kind of charge does the more/less electronegative atoms have?
The more electronegative atom has a small negative charge (S-). The less electronegative charge has a small positive charge (S+).
14 of 36
What does S- and S+ mean?
S- is delta minus and means the element is slightly but not fully negative. S+ is delta plus and means the element is slightly but not fully positive.
15 of 36
Does a molecule need to have non-polar bonds to be a non-polar molecules overall?
No. It is possible for a molecules to contain polar bonds but to be a non-polar molecule overall.
16 of 36
How do you work out if a molecule has a polar or non-polar bond?
It is important to consider whether the molecule is symmetrical or non-symmetrical.
17 of 36
How do you known if a molecule is symmetrical or non-symmetrical?
Symmetrical = no lone pairs on central atom. Non-symmetrical = lone pairs on central atom.
18 of 36
How do you know if a molecule is non-polar?
If a molecules is symmetrical (no lone pairs), the dipoles of any bonds will cancel and the molecules will be non-polar.
19 of 36
How do you know if a molecule is polar?
A molecule will be polar if it contains polar bonds and has a non-symmetrical shape (has lone pairs).
20 of 36
Explain how a molecule can have polar bonds but be a non-polar molecule overall?
Use CO₂ as an example. Each C=O bond is polar (C=S+ and O=S-) but CO₂ molecule is non-polar because CO₂ molecule is symmetrical (no lone pairs) so dipoles act in opposite directions and cancel out.
21 of 36
What can electronegativity be used to predict?
Can be used to predict the ionic or covalent character of the bond.Greater the EN difference between bonding atoms,greater the ionic character of the bond.Smaller the EN difference between the bonding atoms,greater the covalent character of the bond.
22 of 36
What are intermolecular forces?
molecular forces are the forces of attraction that occur between small covalent molecules.
23 of 36
Are the intermolecular forces of attraction between covalent molecules strong or weak and how does this affect the melting and boiling points?
These intermolecular forces of attraction between covalent molecules are weak and they do not require very much energy to break. Therefore many covalent compounds have low melting and boiling points and are generally liquids and gases at room temp.
24 of 36
Are intermolecular forces stronger or weaker than covalent bonds?
Intermolecular forces are much weaker than covalent bonds that hold atoms together within a molecule (and are also much weaker than ionic bonds).
25 of 36
Can covalent bonds be broken when being melted or boiled
No as this would take to too much energy and is only true for compounds with a giant covalent structure.
26 of 36
What are the three types of intermolecular forces?
Van der Waals’ forces (or induced dipole – instantaneous dipole), permanent dipole-dipole and hydrogen bonds.
27 of 36
What kind of molecules do Van der Waals’ forces exist between?
Van deer Waals’ forces exist between all molecules, whether polar or non-polar.
28 of 36
What is the evidence for Van der Waals’ forces existing between all molecules?
Evidence for the existence of these weak forces of attraction is that even noble gases which exist as single atoms and don’t form covalent bonds can be liquefied if the temperature is low enough.
29 of 36
How are Van der Waals’ forces made?
Movement of the electron cloud produces an instantaneous dipole as there is an uneven distribution of electrons. This instantaneous dipole induces (creates) a dipole in a neighbouring atom causing the atoms to be attracted to each other.
30 of 36
Are Van der Waals’ forces a weak or strong intermolecular force?
The effect of instantaneous dipole is short lived and Van der Waals’ forces are, as a result, the weakest of the intermolecular forces.
31 of 36
How do Van der Waals’ forces increase in strength?
Van der Waals’ forces increase in strength with increasing number of electrons.
32 of 36
Explain the increase in boiling and melting points of elements down a group in terms of Van der Waals’ forces?
There are VDW forces between all molecules. As you go down a group, the number of electrons increases so more electrons are randomly distributed. This means that there are larger induced dipoles. Strength of VDW’s increases, requiring more energy to
33 of 36
How are permanent dipole-dipole forces formed?
Polar molecules have permanent dipoles meaning that 1 atom/group will have partially poscharge while other will be partially negcharged.Permanent dipole in 1 molecule will attract permanent dipole in neighbour molecule resulting in weak per d-d force
34 of 36
Do molecules that contain permanent dipole-dipole bonds have a higher or lower melting point than non-polar molecules? Explain your reason
Permanent dipole-dipole interactions between molecules results in molecules packing together in a more ordered arrangement. This leads to high melting and boiling points than for non-polar molecules of similar size.
35 of 36
Explain why an atom may have a non-polar bond?
No electronegativity difference between atoms. Electrons distributed evenly between atoms. Non-polar covalent bond.
36 of 36

Other cards in this set

Card 2

Front

Is a covalent bond polar or non-polar?

Back

A covalent bond can be polar or non-polar.

Card 3

Front

What does a covalent bond being polar or non-polar depend on?

Back

Preview of the front of card 3

Card 4

Front

What does this distribution of electrons depend on?

Back

Preview of the front of card 4

Card 5

Front

What is electronegativity?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Bonding & shapes resources »