Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry > Intermolecular Forces > Flashcards

Intermolecular Forces Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

Electronegativity

A

The ability of an atom to attract a BONDING PAIR of electrons in a covalent bond towards ITSELF.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Factor affecting electronegativity 1

A

SIZE OF THE POSITIVE CHARGE ON THE NUCLEUS:

  • moving left to right across a period, the number of PROTONS in the nucleus INCREASES.
  • This increased positive charge, increases the ATTRACTION between the NUCLEUS and the pair of electrons in the covalent bond.
  • Therefore, elements on the right of the periodic table are more electronegative than those on the left.

( The two electrons in the first shell of an atom CANCEL OUT the effect of TWO PROTONS in each element)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Factor affecting electronegativity 2

A

ATOMIC RADIUS:
- The SMALLER the atomic radius , the CLOSER the bonding electrons will be to the nucleus of an atom.

  • As we move from left to right across a period, the atomic radius DECREASES.
  • Therefore elements on the right of the periodic table are more electronegative than those on the left.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Factor affecting electronegativity 3

A

THE NUMBER OF INNER SHELLS:

  • Electrons in the inner shell SHIELD electrons in the outer shell from the positive charge of the nucleus.
  • Therefore , the greater number of inner shells, the LOWER the electronegativity.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Covalent bonds between two IDENTICAL atoms

A
  • The NUCLEUS of each atom attracts the bonding pair of electrons to the EXACT SAME extent.
  • The bonding pair will be SHARED EQUALLY between the two atoms and will be found on average HALF WAY between the two nuclei.
  • The bond between two identical atoms is NON-POLAR and 100% covalent.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Covalent bonds between two DIFFERENT ATOMS

A
  • The more ELECTRONEGATIVE atom will cause its nucleus to attract the bonding pair of electrons MORE STRONGLY than the other atoms nucleus.
  • The bonding pair will NOT BE SHARED EQUALLY between the atoms and will on average found CLOSER to the more electronegative atom.
  • The bond between two different atoms is said to be POLAR
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Representing Polar covalent bonds

A
  • Write DELTA + and a DELTA - to show the charges.
  • Delta means slight and this is because the electron pair has only SHIFTED towards the more electronegative atom.
  • The DELTA - always goes on the MORE ELECTRONEGATIVE atom.
  • Alternatively , we use a CROSSED ARROW pointing towards the MORE ELECTRONEGATIVE element.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Polar covalent bonds

A

A separation of OPPOSITE CHARGES.

The separation of opposite charges ACROSS A BOND is called a DIPOLE.

If the difference in charge across the polar covalent bond does not change, it is called a PERMANENT DIPOLE.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Polar molecule

A

When a PERMANENT DIPOLE exists over an UNSYMMETRICAL MOLECULE.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Non-polar molecule

A
  • The molecule is SYMMETRICAL.
  • The PERMANENT DIPOLES in the bonds CANCEL OUT with each other
  • This is because they OPPOSE each other EQUALLY due to the SYMMETRY of the molecule.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The polar nature of WATER

A
  • Both O-H bonds have a PERMANENT DIPOLE.
  • The molecule is UNSYMMETRICAL with a bond angle of 104.5 degrees and NON- LINEAR shape.
  • The dipoles act in different directions and do NOT oppose each other equally and cancel each other out.
  • Overall the OXYGEN end has a DELTA - charge and the HYDROGEN end of the molecule has a DELTA + charge.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

The non-polar molecule CARBON DIOXIDE

A
  • Both C=O bonds have a PERMANENT DIPOLE.
  • The molecule is SYMMETRICAL with a bond angle of 180 degrees and a LINEAR shape.
  • The dipoles act in opposite directions and exactly oppose each other.
  • The overall dipole over the molecule is ZERO because the dipoles CANCEL OUT.
  • Therefore, a carbon dioxide molecule has NO OVERALL POLARITY.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

The Pauling scale of Electronegativity

A

The scale compares the electronegativity of atoms of different elements.

NON-METALS:
- nitrogen
- oxygen
- fluorine
- chlorine
Are the MOST electronegative atoms.

GROUP 1 METALS:
The LEAST electronegative atoms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Type of bonding and electronegativity

A

The DIFFERENCE in electronegativity between two atoms indicates the type of BONDING.

PURE COVALENT:
Non-polar bond due to identical atoms bonded together with NO difference in electronegativity.
Electronegativity difference is 0

POLAR COVALENT:
SMALL difference in electronegativity due to NON-IDENTICAL atoms bonded together.

Therefore, PARTIAL charges exist on atoms.
Electronegativity is between 0 and 1.80.

IONIC:
LARGE differences in electronegativity and so ions with FULL charges form.

Electronegativity difference is ABOVE 1.80

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

INTERmolecular forces

A
  • WEAK interactions BETWEEN the dipoles of different molecules.
  • Occur because molecules are attracted to each other.
  • Determine the PHYSICAL properties of molecules.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

INTRAmolecular forces

A
  • STRONG interactions that occur WITHIN molecules.
  • Refer to either COVALENT or IONIC bonds
  • Determine the CHEMICAL REACTIVITY of molecules.
17
Q

Simple molecular substances

A
  • Consist of relatively SMALL molecules and each molecule has a FIXED number of atoms.

LOW boiling point ~ takes very little energy to break intermolecular forces.

  • HEATING a simple molecular substance causes the molecules to move faster.
  • At a certain temperature, the intermolecular forces break and this allows the molecules to move away from each other.
18
Q

Induced dipole-dipole interactions

A

Also referred to as LONDON or DISPERSION forces.

ATOM 1 ~
- electrons are randomly moving from place to place and are not evenly spread out.
- For a fraction of a second , more electrons are on the RIGHT hand side of the atom.
- Forms an INSTANTANEOUS DIPOLE ~ right hand side has a delta negative charge and the left hand side has a delta positive charge.

ATOM 2 ~
- Because the right hand side of atom 1 has a delta negative charge, it will REPEL the electrons in atom 2.
- This causes the electrons in atom 2 to move towards the right hand side.
- Forms an INDUCED DIPOLE as it was caused by the dipole in atom 1.

Induced dipoles form in further neighbouring molecules.

ALL of these dipoles now experience a force of attraction known as LONDON forces.

  • Typically 0.001 the strength of a covalent bond.
19
Q

Properties of LONDON forces

A
  • Weakest IMF and easily broken
  • Caused by RANDOM electron movement.
  • Every single atom or molecule will experience London forces even if they experience other IMF as well.
  • The STRENGTH depends on the number of ELECTRONS.
    This means atoms with a GREATER number of electrons have a HIGHER BP as they experience strong London forces.
20
Q

PERMANENT dipole-dipole interactions

A

When two molecules that have a PERMANENT DIPOLE get near enough then their permanent dipoles can lead to an ATTRACTION.

H-F —— H-F ——- H-F—— H-F—–H-F ——–

  • POLAR molecules like H-F have permanent dipoles.
  • The delta negative charge on the fluorine atom is attracted to the delta positive charge on the hydrogen atom on the neighbouring molecule.
  • This results in a WEAK permanent dipole-dipole force.
  • This force is typically 0.01 the strength of a covalent bond.
21
Q

The TWO types of intermolecular forces

A

VAN DER WAALS FORCES:
Dipole-dipole interactions & induced dipole-dipole interactions.

HYDROGEN BONDING

22
Q

PERMANENT dipole-INDUCED forces

A

When a PERMANENT DIPOLE in a molecule induces a dipole in another molecule.

EXAMPLE:
H-F —– F-F

  • The delta negative charge on the F atom of H-F repels the electrons in F2 , moving the electrons in F2 to the right side of the atom.
  • This makes the right side delta negative and the left side delta positive.
  • The permanent dipole in HF has induced a dipole in F2 and results in a weak permanent dipole-induced force.
  • Typically 0.01 the strength of a covalent bond.
23
Q

Hydrogen bonding

A
  • The strongest type of intermolecular force
  • Around one tenth the strength of a covalent bond
  • They are a specialised type of permanent dipole-dipole force.
24
Q

TWO conditions for hydrogen bonds to form

A
  • A hydrogen atom must be bonded to a STRONGLY ELECTRONEGATIVE element.
  • The electronegative atom must have at least one LONE PAIR of electrons.

This means the only elements that can from hydrogen bonds are:

  • NITROGEN
  • OXYGEN
  • FLUORINE
25
Q

The formation of a hydrogen bond in HYDROGEN FLUORIDE

A
  • The hydrogen atom is highly electron deficient d+, due to being covalently bonded to the highly electronegative fluorine atom d-
  • The Hd+ is attracted to the LONE PAIR of electrons on the fluorine atom in a neighbouring molecule.
  • This attraction is known as a hydrogen bond and is indicated using a HASHED LINE.
  • The hydrogen atom is found along the straight line drawn between the two fluorine atoms - LINEAR SHAPE.
26
Q

Properties of water : DENSITY

A
  • In its LIQUID form, the water molecules are moving RANDOMLY , sometimes close together, other times further apart.
  • This means as a liquid , hydrogen bonds are constantly being FORMED and BROKEN.
  • In its solid form, ICE, the water molecules arrange themselves into an ordered structure , stabilised by hydrogen bonds.
  • This means the water molecules are further apart.
  • Therefore, the solid form of water, is LESS DENSE than the liquid form.
  • This means that ice can float on the surface of water.
27
Q

Properties of water : BOILING POINT

A
  • HIGHER THAN EXPECTED temperatures are required .
  • This is because EXTRA ENERGY is required to overcome the strength of the hydrogen bonds , IN ADDITION to the permanent dipole-dipole and induced dipole-dipole forces.
  • This means water has a RELATIVELY high melting and boiling point.
28
Q

Properties of water : SURFACE TENSION

A
  • The presence of hydrogen bonding gives water a HIGHER THAN EXPECTED surface tension.
  • This means water ha a RELATIVELY high surface tension.
29
Q

Properties of water : VISCOSITY

A
  • Liquid water flows LESS easy than expected.
  • This means water has a RELATIVELY HIGH viscosity.
30
Q

The structure of ice

A
  • Forms an OPEN TETRAHEDRAL LATTICE structure of water molecules.
  • Each water molecule forms FOUR HYDRGEN BONDS due to having TWO lone pairs and TWO hydrogen atoms.
31
Q

How to figure out if a molecule is POLAR or NON-POLAR

A

Identify the CHARGES on each element:

  • If the elements are different , there will be a difference in electronegativity.
  • The more electronegative element (further left) will have a delta negative charge, whilst the other element has a delta positive charge.
  • The bonds have a PERMANENT DIPOLE

Is the molecule SYMMETRICAL or NOT :
- Are the charges evenly distributed
- Draw the molecule and identify the shape and bond angle.

POLAR:
- Unsymmetrical
- The dipoles act in different directions and DO NOT not oppose each other equally and cancel out.
- The molecule has an OVERALL DIPOLE.

NON-POLAR:
-Symmetrical
- The permanent dipoles in the bonds oppose each other equally and CANCEL OUT.

Chemistry (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions