6.4 Molecular substances

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6.4 Molecular substances

Molecular substances

• characteristics of molecular compounds.
• bond within the molecules .
• structural formula en how to draw it.
• bond between the molecules

Molecular substances

• combination of a metal with a non-metal.
• do not conduct electricity because there are no charged particles, except for carbon.
•  
• 
  

H​2​​​​​O

C​12​​H​22​​O​11​​

Atomic bond

• non-metals can share electrons to form an atomic bond
• bond consists of two shared elctrons, an electron pair.
• Vb: H₂

Atomic bond

Atomic bond 

To make a drawing of a molecule the bond between the atoms is indicated by a dash, a structural formula. Each dash represents an electron pair.

Covalency

Covalency: the number of atomic bonds that an element can form. 

Atom	Covalency
H	1
F, Cl, Br, I	1
O, S	2
N, P	3
C, Si	4

Je moet aan de hand van de covalentie een kloppend molecuul kunnen tekenen.

Je moet adhv een getekend molecuul kunnen bepalen wat de covalentie van een atoom is.

Covalency of C is ...

1. 1
2. 2
3. 3
4. 4

Covalency of O is ...

1. 1
2. 2
3. 3
4. 4

Van der Waals bond

page 181 text book 

• attractive forces between molecules .
• strength depends on the mass of the molecules. 
• the stronger the Van der Waals bond , the higher the melting and boiling point.

Van der Waalsbond and boiling point

page 181 textbook

-Methane (112K) vs. ethane (185K): mass of ethane is higher, so VdW-bond is stronger and boiling point is higher.

- Ethane (185K) vs. butane (273K): mass of butane is higher, so VdW-bond is stronger and boiling point is higher.

Van der Waals bond and boiling point

page 181 text book

- Methylbutane (301K) vs. dimethylpropane (283K): 

mass is the same but boiling points are different 

• Methylbutane (301K) vs. dimethylpropane (283K): mass is the same but  boiling points are different.
• Hoe kan dat?
• Wat valt je op aan het verschil tussen methylbutaan en dimethylpropaan?

Try to explain the difference in boiling point between Methylbutane (301K) and dimethylpropane (283K):

branched molecules and linear molecules

• Methylbutane  is less branched than dimethylpropane.
• Branched have a smaller contact area so VdW bond is not a strong as in lineair molecules.
• So boiling point of methylbutane is higher  for this molecules is less branched. 

Hydrophilic and hydrophobic

Hydrophilic mixes with hydrophilic

Hydrophobic mixes with hydrophobic

Hydrophobic mixes poorly with hydrophylic

Strength of VdW bond depends on mass of the molecules.

1. yes
2. no

ion bond

1. is stronger than VdW bond
2. occurs in metals
3. is present when a salt is dissolved in water
4. is formed when protons are exchanged between atoms.

1 atomic bond is present in molecular substances.
2 VdW bond between molecular substances.

1. 1 correct, 2 incorrect
2. 1 incorrect, 2 correct
3. 1 and 2 correct
4. 1 and 2 incorrect

Hydrophilic substances mix well with water.

1. yes
2. no

boliling point of ethane (C2H6) is higher than boiling point of butane butaan (C4H10)

1. yes
2. no

metal bond is a very weak bond

1. yes
2. no

strength of VdW bond depends on mass of the molecules

1. yes
2. no

De covalentie van O is ...

1. 1
2. 2
3. 3
4. 4

De covalentie van C is ...

1. 1
2. 2
3. 3
4. 4

Molecular compound

Salt

Metal

atomic bond

metal bond

ions

free electrons

Van der Waals bond

ionic bond

metallic lattice

molecular lattice

ionic lattice

only non-metals

all decomposable substances

a solid salt consists of                                bonded by

in a regular lattice. 

In dissolving a salt these                         bonds  are broken down.

ions

ionbond

atoms

atomic bond 

strong

weak

molecules

H-bridge

VdWaals bond 

metals

metalbonds

types of bonds  

Two groups :

Bonds inside the molecules so between atoms :

- atomic bond

- metal bond

- ionic bond

 Bonds between molecules:

- Van der Waals bond in solid and liquid phase. 

par 6.4

read par 6.4 and do questions