# 10.1 Intermolecular forces  (Page 9/17)

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Define the following and give an example of each:

(a) dispersion force

(b) dipole-dipole attraction

(c) hydrogen bond

(a) Dispersion forces occur as an atom develops a temporary dipole moment when its electrons are distributed asymmetrically about the nucleus. This structure is more prevalent in large atoms such as argon or radon. A second atom can then be distorted by the appearance of the dipole in the first atom. The electrons of the second atom are attracted toward the positive end of the first atom, which sets up a dipole in the second atom. The net result is rapidly fluctuating, temporary dipoles that attract one another (example: Ar). (b) A dipole-dipole attraction is a force that results from an electrostatic attraction of the positive end of one polar molecule for the negative end of another polar molecule (example: ICI molecules attract one another by dipole-dipole interaction). (c) Hydrogen bonds form whenever a hydrogen atom is bonded to one of the more electronegative atoms, such as a fluorine, oxygen, or nitrogen atom. The electrostatic attraction between the partially positive hydrogen atom in one molecule and the partially negative atom in another molecule gives rise to a strong dipole-dipole interaction called a hydrogen bond (example: $\text{HF}\text{⋯}\text{HF}\right).$

The types of intermolecular forces in a substance are identical whether it is a solid, a liquid, or a gas. Why then does a substance change phase from a gas to a liquid or to a solid?

Why do the boiling points of the noble gases increase in the order He<Ne<Ar<Kr<Xe?

The London forces typically increase as the number of electrons increase.

Neon and HF have approximately the same molecular masses.

(a) Explain why the boiling points of Neon and HF differ.

(b) Compare the change in the boiling points of Ne, Ar, Kr, and Xe with the change of the boiling points of HF, HCl, HBr, and HI, and explain the difference between the changes with increasing atomic or molecular mass.

Arrange each of the following sets of compounds in order of increasing boiling point temperature:

(a) HCl, H 2 O, SiH 4

(b) F 2 , Cl 2 , Br 2

(c) CH 4 , C 2 H 6 , C 3 H 8

(d) O 2 , NO, N 2

(a) SiH 4 <HCl<H 2 O; (b) F 2 <Cl 2 <Br 2 ; (c) CH 4 <C 2 H 6 <C 3 H 8 ; (d) N 2 <O 2 <NO

The molecular mass of butanol, C 4 H 9 OH, is 74.14; that of ethylene glycol, CH 2 (OH)CH 2 OH, is 62.08, yet their boiling points are 117.2 °C and 174 °C, respectively. Explain the reason for the difference.

On the basis of intermolecular attractions, explain the differences in the boiling points of n –butane (−1 °C) and chloroethane (12 °C), which have similar molar masses.

Only rather small dipole-dipole interactions from C-H bonds are available to hold n -butane in the liquid state. Chloroethane, however, has rather large dipole interactions because of the Cl-C bond; the interaction is therefore stronger, leading to a higher boiling point.

On the basis of dipole moments and/or hydrogen bonding, explain in a qualitative way the differences in the boiling points of acetone (56.2 °C) and 1-propanol (97.4 °C), which have similar molar masses.

The melting point of H 2 O( s ) is 0 °C. Would you expect the melting point of H 2 S( s ) to be −85 °C, 0 °C, or 185 °C? Explain your answer.

−85 °C. Water has stronger hydrogen bonds so it melts at a higher temperature.

Silane (SiH 4 ), phosphine (PH 3 ), and hydrogen sulfide (H 2 S) melt at −185 °C, −133 °C, and −85 °C, respectively. What does this suggest about the polar character and intermolecular attractions of the three compounds?

Explain why a hydrogen bond between two water molecules is weaker than a hydrogen bond between two hydrogen fluoride molecules.

The hydrogen bond between two hydrogen fluoride molecules is stronger than that between two water molecules because the electronegativity of F is greater than that of O. Consequently, the partial negative charge on F is greater than that on O. The hydrogen bond between the partially positive H and the larger partially negative F will be stronger than that formed between H and O.

Under certain conditions, molecules of acetic acid, CH 3 COOH, form “dimers,” pairs of acetic acid molecules held together by strong intermolecular attractions:

Draw a dimer of acetic acid, showing how two CH 3 COOH molecules are held together, and stating the type of IMF that is responsible.

Proteins are chains of amino acids that can form in a variety of arrangements, one of which is a helix. What kind of IMF is responsible for holding the protein strand in this shape? On the protein image, show the locations of the IMFs that hold the protein together:

H-bonding is the principle IMF holding the DNA strands together. The H-bonding is between the $\text{N}-\text{H}$ and $\text{C}=\text{O}.$

The density of liquid NH 3 is 0.64 g/mL; the density of gaseous NH 3 at STP is 0.0007 g/mL. Explain the difference between the densities of these two phases.

Identify the intermolecular forces present in the following solids:

(a) CH 3 CH 2 OH

(b) CH 3 CH 2 CH 3

(c) CH 3 CH 2 Cl

(a) hydrogen bonding and dispersion forces; (b) dispersion forces; (c) dipole-dipole attraction and dispersion forces

Why does carbonic acid don't react with metals
Why does carbonic acid don't react with metal
Some metals will react depending on their Standard Electrode Potential. Carbonic acid is a very weak acid (i.e. a low hydrogen ion concentration) so the rate of reaction is very low.
Paul
sample of carbon-12 has a mass of 6.00g. How many atoms of carbon-12 are in the sample
a sample of carbon-12 has a mass of 6.00g. How many atoms of carbon-12 are in the sample
an object of weight 10N immersed in a liquid displaces a quantity of d liquid.if d liquid displaced weights 6N.determine d up thrust of the object
how human discover earth is not flat
We don't fall off. If set off in any direction in a straight line and keep going. You'll end up back where you started.
earth is spherical
Unique
Also, every other planet is spherical as that is the most energy efficient shape. gravity pulls equally on all areas. Sphere.
what is an ion
an atom that loses or gains an electron. Atoms normally have the same number of protons and electrons, therefore there is no charge as each + cancels out each -. When an atom loses an electron, it has more protons that electrons. Therefore the ion is called positive.
When an atom gains electrons it has more of them than protons. Therefore the ion is negative. You cannot change the number of protons as this results in a different element.
Gaining or losing electrons is based around the octet rule. 8 electrons in the outer shell is the most stable electron configuration (for the first three rows in the periodic table. After that it gets confusing so don't worry) So all atoms want to achieve this configuration.
Wat is chemical bonding
how to determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon4
what is a catalyst
A substance that speeds up the rate of a given reaction but does not react with any reactants
Brandon
something that speeds up a chemical reaction without being used up itself. It lowers the activation energy
something that speed up a chemical reaction without its self been used
Zainab
Faraday's first law of electrolysis state that...
the mass of a substance librated during electrolysis is directly proportional to the quantity of electricity passing through the electrolyte
Zainab
nice
Owolabi
greeaat
Abdul
another question
Owolabi
ys
Abdul
good
olanrewaju
gud one pls write it mathematically
Lekan
How can ionic bonds dissociate in aqueous solution
Because of the polarity of both ionic compounds and water the ionic compound will dissolve as "like dissolves like", and the molecule forms bonds with the water.
Claud
are all aqueous solutions water contained?
blossom
No, but a lot are.
Claud
it dissociate when d metal is combined wit oxygen
Lekan
I wanna understand more about isomers
Isomers are essentially the same molecules of one particular substance, except with different bonding points along the molecule. if you want a better example, look up xylene, p-xylene, and m-xylene. isomers are more for organic chemistry
Aaron
what is catenation
The property of carbon to form long chain with other atom!
Lareb
hydrocarbons can be classified as..1.Aliphatic compounds 2.cyclic compounds.under aliphatic compounds there are two types saturated hydrocarbons(alkanes) and unsaturated hydrocarbons(alkenes and alkynes).
thanks but i have also heard of aromatic hydrocarbons
emmanuel
so am kinda confused
emmanuel
how
Emmanuel
hydrocarbons are classified into 2 namely: aliphatic compound and aromatic compound
Mgbachi
aliphatic compound and aromatic compound
Mgbachi
hello i have big problems in understanding organic chemistry
what are the main types of hydrocarbon
emmanuel
I'm not exactly sure what you mean by 'main types' but I think you should be talking about aliphatic and cyclic hydrocarbons
blossom
What's the difference?
Claud
what is the difference between atomic theory and modern atomic theory
Yakubu
Or are you referring to the types being alkane, alkene and alkyne? alkane - hydrocarbon molecule with only single bonds alkene - hydrocarbon molecule with at least 1 double bond alkyne - hydrocarbon with at least 1 triple bond. alkane least reactive, alkene in the middle alkynes most reactive
I think that is what he is talking about
IBRAHIM