The Shapes of Simple Molecules + Ions Flashcards
1
Q
Draw the shape of a linear molecule.
A
- X—A—X
2
Q
State the bond angle for a linear molecule.
A
- 180°
3
Q
Draw the shape for a trigonal planar molecule.
A
- central A
- 3 X coming off central A
4
Q
State the bond angle of a trigonal planar molecule.
A
- 120°
5
Q
Draw the shape of a non-linear molecule.
A
- X—A—X
- 2 lone pairs on A
6
Q
State the bond angle of a non-linear molecule.
A
- 104.5°
7
Q
Draw the shape of a pyramidal molecule.
A
- central A
- 3 X coming off A
- 1 lone pair on A
8
Q
State the bond angle in a pyramidal molecule.
A
- 107°
9
Q
Draw the shape of a tetrahedral molecule.
A
- central A
- 4 X coming off A
10
Q
State the bond angle of a tetrahedral molecule.
A
- 109.5°
11
Q
Draw the shape for a trigonal bipyramidal molecule.
A
- central A
- 5 X coming off A
12
Q
State the bond angles in a trigonal bipyramidal molecule.
A
- 90°
- 120°
13
Q
Draw the shape of an octahedral molecule.
A
- central A
- 6 X coming off A
14
Q
State the bond angle in an octahedral molecule.
A
- 90°
15
Q
Describe the shape of trigonal planar molecule.
A
- has 3 bond pairs + 0 lone pairs
- pairs of e-s repel as far apart as possible + repel equally bc is symmetrical
16
Q
Describe the shape of tetrahedral molecule.
A
- has 4 bond pairs + 0 lone pairs
- pairs of e- repel as far apart as possible + repel equally bc is symmetrical
17
Q
Describe the shape of pyramidal molecule.
A
- has 3 bond pairs + 1 lone pair
- pairs of e- repel as far apart as possible
- lone pairs of e-s repel > bond pairs of e-s
18
Q
Describe the shape of a non-linear molecule.
A
- has 2 bond pairs + 1 lone pair
- pair of e-s repel as far apart as possible
- lone pair of e-s repel > bond pair of e-s
19
Q
Describe the shape of an octahedral molecule.
A
- has 6 bond pairs + 0 lone pairs
- pairs of e-s repel as far apart as possible + repel equally bc is symmetrical
20
Q
Define the term electronegativity.
A
- ability of an atom to attract pair of e-s in a covalent bond towards itself
21
Q
What factors affect the electronegativity of an element?
A
- nuclear charge
- atomic radius
- e- shielding
22
Q
How does nuclear charge affect the electronegativity of an element?
A
- inc in NO° of protons = inc in nuclear attraction between protons + outer shell e-s = inc electronegativity
23
Q
How does atomic radius affect the electronegativity of an element?
A
- as atomic radius inc, attraction between nucleus + outer shell e-s dec, dec electronegativity
24
Q
How does e- shielding affect the electronegativity of an element?
A
- as e- shielding inc, outer e-s are less attracted to nucleus bc e-s experience more repulsion, dec electronegativity
25
How does electronegativity change down a group + explain why?
- electronegativity dec bc although nuclear charge inc, e- shielding + atomic radius inc = overall dec in attraction between nucleus + outer shell e-s
26
How does electronegativity change across a period + explain why?
- electronegativity inc, bc nuclear charge inc + atomic radius slightly dec (as nuclear attraction for bonding pair of e-s slightly inc) as well as e- shielding remaining relatively constant
27
What are polar molecules?
- molecules w a polar covalent bond due to 2 atoms having diff electronegativities
- e-s are drawn towards more electronegative atom so gain a partial neg. charge (δ-) whereas less electronegative atom gains a partial pos. charge (δ+)
28
What is a dipole moment?
- measure of how polar a bond is
- arrow points to partially neg. end of dipole
29
Why so some molecules have polar bonds but aren’t overall polar?
- bc polar bonds cancel each other out usually bc molecule is symmetrical
30
What are intramolecular forces?
- forces (usually covalent bonds) within a molecule
31
What are intermolecular forces?
- forces between molecules
32
What are the 3 types of intermolecular forces?
- London forces (induced dipole-dipole forces)
- permanent dipole-permanent dipole forces
- hydrogen bonding (type of permanent dipole-dipole force)
33
What are London forces (induced dipole-dipole forces)?
- greater NO° of e-s = stronger London forces bc have more temporary dipoles
34
Describe the relative strength of induced dipoles + permanent dipoles.
- permanent dipoles are stronger than induced dipoles so require more energy to overcome these intermolecular forces = higher b.p.
35
What is hydrogen bonding?
- strongest form of intermolecular bonding + is a type of permanent dipole-permanent dipole bonding
- when H is covalently bonded to an O, N or F, it can form a H bond w a lone pair from an O, N or F in another molecule
36
What are the properties of water?
- high melting + boiling points
- high surface tension
- higher density liquid state (water) than solid state (ice)
37
Describe the high melting + boiling points of water.
- water has strong H bonds between molecules which hold molecules tightly together
- so lots of energy is required to break these intermolecular forces = high melting/boiling points
38
Describe the high surface tension of water.
- strong H bonds between molecules pull water molecules at surface inwards = tightly packed layer = high surface tension
39
Describe why ice is less dense than water.
- bc in ice, water molecules are arranged in a rigid lattice + H bonds have relatively long bond lengths
- so water molecules are slightly further apart than in liquid form
- so ice has a lower density than water
40
Describe the effects of intermolecular forces in iodine.
- iodine has a uniform arrangement of molecules in a crystal lattice, held together by weak London forces (intermolecular)
- purple vapour is observed when iodine sublimes
41
Describe the solubility of molecular substances due to intermolecular forces.
- non-polar substances mostly dissolve in non-polar solvents bc form London forces
- polar substances mostly dissolve in polar solvents bc form H bonds or dipole-dipole interactions
42
Describe the conductivity of molecular substances due to intermolecular forces.
- covalent substances can’t conduct electricity bc don’t have any freely moving charged particles
- some polar covalent molecules, under certain conditions, can ionise + conduct electricity
- some giant covalent structures can conduct electricity bc has delocalised e-s
