Intermolecular Bonding

Question 1

Intermolecular (definition)

Answer 1

The force of attraction between a molecule and a neighboring molecule

The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together. These intermolecular attractions are, however, strong enough to control physical properties, such as boiling and melting points, vapor pressures, and viscosities.)
(strong intramolecular attraction, weak intermolecular attraction)

1. Van der waal
2. dipole-dipole
3. hydrogen bonds

Question 2

Van der Waals Forces (definition)

trends and properties (2)

Answer 2

Van der waal forces are attractions between an instantaneous dipole (양.음 서로 마주하고 있는 상태), and an induced dipole.
The strength of dispersion forces tends to increase with increased molecular weight.
This is because larger atoms have larger electron clouds that are easier to polarize.
Weak intermolecular forces are weak then the melting/boiling point is going to be low.

Question 3

dipole-dipole forces

Answer 3

molecules that have permanent dipoles are attracted to each other. The positive end of one is attracted to the negative end of the other, and vice versa. These forces are only important when the molecules are close to each other.

The higher the molecular weight/ the more polar the molecules are ,
The dipole-dipole forces are stronger;

ex) CH3F, HBr

Question 4

hydrogen bonding

Answer 4

The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. These interactions are called hydrogen bonds.
-> NH3, CH3OH are exceptionally high.

Question 5

Trends in boiling points of hallogens

Answer 5

The boiling point “increases” down the hallogen group because of the van der waals forces. The size of the molecules increases down the group. This increase in size means an increase in the strength of the van der waals forces. (F

Question 6

Trends in boiling points of Hydrogen Halides

Answer 6

The intermolecular forces between molecules of HCl, HBr and HI are dipole-dipole forces. The HI has the highest ‘melting’ point among them as the molecular mass is the greatest. The boiling point of HBr is less than that of HI as it has lower molecular mass, however is higher than that of HCl hence its boiling point is higher.
HF is an exception i.e. has the highest melting point because of the stronger force of attraction between HF molecules resulting from hydrogen bonds acting between the HF molecules. Weaker dipole-dipole interactions act between the molecules of HCl, HBr and HI. So HF has a higher boiling point than the other molecules in this series.

Question 7

Trends in electronegativity of Halogens

Answer 7

The number of valence electrons in an atom increases down the group due to the increase in energy levels at progressively lower levels. The electrons are progressively further from the nucleus; therefore, the nucleus and the electrons are not as attracted to each other as shielding effects increase. Electronegativity therefore decreases down the group.
(F>Cl>Br>I>At)

Question 8

Trends in oxidising ability of halogens

Answer 8

*oxidising agent is reduced during a redox reaction
during reduction the oxidation number decrease
reduction is gain of electrons

When a halogen acts as oxidising agent in solution, it will end up as a halide ions
The oxidising ability decreases down the halogen group as: the atomic radius increases/valence electrons are more shielded + There is less attraction between electron and positive nucleus

Question 9

When disproportionation reaction occurs + ex

Answer 9

when the same reactant is oxidised and reduced

2H2O2 > 2H2O + O2
Cu2O + H2SO4 > Cu + CuSO4 + 2H2O
3HNO3 > HNO3 + 2 NO + H2O

Question 10

displacement reaction

Answer 10

The reactivity of the halogens decreases down the group. This can be shown by looking at displacement reactions. (F>Cl>Br>I>At)

그래서 예를들어
potassium bromide 에 chloride 나 bromine water 넣으면 반응 없고 (no reaction), potassium iodide에 bromine 이나 chloride 넣으면 brown.

Question 11

testing for halide ions - silver nitrate/

Answer 11

1. silver nitrate; The precipitates are insoluble(turned into solid) silver halides - silver chloride(white), silver bromide(cream) or silver iodide(yellow).
2. dilute ammonia; The precipitates formed with silver (AgCl, AgBr, and AgI) are either soluble or insoluble in ammonia.
3. solubility of chlorides