8. ELECTRON NEGATIVITY Flashcards
1
Q
- How would you describe electronegativity?
A
- it is the power of an atom in a molecule to attract a bonding pair of electrons towards itself
- it determines how shared electrons are distributed
- A measure of the tendency of an atom to attract a bonding pair of electrons
2
Q
- How and where in the periodic table does the electronegativity increase?
A
- the electronegativity increases down the up the group
- it increases across the period (from left to right)
- metals have lower electronegativites
- non metals have higher electronegativities
3
Q
- What is the electronegativity of the following elements?
3.1: Hydrogen
3.2: Carbon
3.3: Nitrogen
3.4: Oxygen
3.5: Fluorine
3.6: Chlorine
3.7: Bromine
3.8: Iodine
A
3.1: 2.1
3.2: 2.5
3.3: 3.0
3.4: 3.5
3.5: 4.0
3.6: 3.0
3.7: 2.8
3.8: 2.5
4
Q
- What is the result of the electronegativity when two atoms that have a non-polar bond to one another?
A
- the atoms pull at the shared electrons with the same strength
- the electronegativity is zero
5
Q
- What is the result of the electronegativity when two atoms have a polar bond to one another?
A
- the atoms pull at the shared electrons with a greater strength
- each connected atom pulls with a different strength
- the electronegativity is greater than zero
6
Q
- What do all polar bonds have?
A
- they have a degree of ionic character
- the percentage of ionic character is related to the strength of the electronegativity between the atoms
- the percentage ionic character and the electronegativity difference are proportional
(when one increases, so does the other) - is worked out by this graph:
7
Q
- What is the percentage of ionic character between two atoms bonded together by a pure non-polar covalent bond?
A
- the electronegativity difference between the two atoms is zero
- the percentage of the ionic character is zero
- the percentage of covalent character is 100%
8
Q
- What happens if the electronegativity difference between two atoms is 1.7?
A
- the two atoms are polar covalently bonded together
- they have a 50% ionic character
- they have a 50% covalent character
9
Q
- What does the curve on this graph indicate?
A
- it indicates that all polar covalent bonds always have some degree of ionic and covalent character
- they can never be 100% ionic
10
Q
- What is the percentage of ionic character in HCL?
A
- H has an electronegativity of 2.1
- Cl has an electronegativity of 3.0
- ▵Electronegativity= 3.0-2.1
= 0.9 - it has a 15% ionic character
- it has an 85% covalent character
11
Q
- How would you write partial negative and partial positive charges?
A
- δ +
- δ -
12
Q
- Why do partial charges arise?
A
- all the polar covalent bonds have some degree of ionic character
13
Q
- Which element is always partially negatively charged (δ-)?
A
- the one with the greater electronegativity
14
Q
- Do polar bonds result in polar molecules?
A
- no, polar bonds can result in non-polar molecules
15
Q
- How do the arrows (linear geometry) signify the polarity of the CO2 molecule?
A
- O has a higher electronegativity than C
- that is why the arrow points from C to O
- it points from an element of lower electronegativity to an element of higher electronegativity
- the magnitudes of the arrows are equal in value
- they face in the opposite direction of one another
- this means that they cancel each other out
- the CO2 molecule does not have an overall polarity
- it is non polar
16
Q
- How do the arrows (linear geometry) signify the polarity of the H2O molecule?
A
- the O has a higher electronegativity than the H
- the arrows points from H towards O
- the arrows are of equal magnitude
- they do not point in opposite directions
- when added together
- they cannot cancel each other out
- the molecule has an finite (nonzero) net dipole
- it is a polar molecule
17
Q
- How do the arrows (linear geometry) signify the polarity of the HCCl3 molecule?
A
- Cl is more electronegative than C
- the three bond dipoles (arrows) point downwards towards the Cl atoms
- between C and H, C is more electronegative
- the bond dipole (arrow) points down towards the C atom
- all the bond dipoles (arrows) point downwards
- they will not be able to cancel each other out
- the molecule is polar
18
Q
- How do the arrows (linear geometry) signify the polarity of the CCl4 molecule?
A
- Cl is more electronegative than C
- we have 4 bond dipoles (arrows) of equal magnitude
- they are acting in opposing directions
- when we add these bond dipoles (arrows) together
- they cancel out
- the bond is non-polar
19
Q
- What does each polar molecule have?
A
- a dipole moment
20
Q
- What will a higher dipole moment result in?
A
- a more polar molecule
21
Q
- What is a dipole moment?
A
- it is a measure of polarity
- it is important for deciding what solvent to use to dissolve a substance
22
Q
- What kind of solvents do polar and non-polar substances dissolve in?
A
- polar substances dissolve in polar solvents
- non-polar substances dissolve in non-polar solvents
- this is why water and oil do not mix
23
Q
- What is necessary to know in order to predict whether a molecule will be polar or non polar?
A
- we need to know its three dimensional geometry
- this is seen after drawing the Lewis Structures
24
Q
- What do Lewis Structures represent?
A
- they represent how the valence electrons of the central atom are distributed as bonds and lone pairs
25
Q
- Read through the summary.
Does everything make sense?
A
- yes
