§6.4 Molecular Substances

• Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 3

 

The atomic number = p⁺

The mass number =

p⁺ + n⁰

In a neutral atom: 

p⁺ = e^-

Remember this?

Atomic structure:

Ions vs. atoms:

Metals like to lose one or more electrons

Non metals like to take in one or more electrons

Example: 

Metal: Li --> Li+ + 1e-

Non Metal: F + 1e- --> F-

Text

Metals (at the micro-level)

• Metals are elements (so not compounds, not molecules)
• They consist of positively charged metal atoms (called ions) with free electrons moving between between them. 
• Strong attraction (metallic bonding)
• Electricity and heat conductivity of the metal 

lattice follows from these free flowing electrons. 

Salts

Solids salts are composed of metal and non-metal

ions. 

An ion is an atom with a charge. 

Ions form when an atom is losing or gaining electrons 

(and the number of p⁺ is not equal to the number of e^-)

Examples: 

Kitchen salt consists of Na+ and Cl- ions

Lime stone consists of  Ca2+ CO32-(carbonate) ions

d

d

Metals

• Solid at room temperature (except Hg)
• Positively charged atoms (ions) surrounded by moving electrons
• Metallic bonding
• Metallic lattice
• Conduct electricity in their solid AND liquid state.

Salts

• Salts are solids at room temperature
• Consist of positive metal ions and negative non-metal ions
• Ionic bonding
• Ionic lattice
• Conduct electricity in the liquid state (and in solution)

Comparison between metals and salts

§6.4 Molecular substances

• Molecular substances
• Van der Waals bonding and hydrogen bonding
• Atomic (covalent) bonding
• Structural formula

Molecular Substances

* Made up of non-metals only

Structural formula: How atoms are linked together

ethanol (C2H6O)

H2S

N2

Attractive forces between
Molecular substances

• van der Waals forces
  => result in van der Waals bonding => the greater the molecular mass and the contact area (surface) the stronger the van der Waals bonding(VdW-bonding).
  
  
• possible Hydrogen-bonding
   (hydrophilic)

Van der Waals bonding
and 

hydrogen bonding

Forces between molecules in molecular substances

They determine physical properties like phase transitions (melting point, boiling point etc.)

Molecular substances

* Covalent bond or atomic bond

* Covalency or covalence

* Hydrophylic and hydrophobic (NH- and/or OH-groups!)

* emulsifier

hydrophilic and hydrophobic 

The OH-  or NH-group group can form an extra bond with the OH- group in water molecules: hydrogen bond. These substances mix well with water, hydrophilic. 

Substances with no OH-group, (halo)alkanes and alkenes do not mix with water, hydrophobic. 

hydrophilic and hydrophobic 

Some molecules have

a hydrophobic tail (e.g.                  ) and a hydrophilic head (OH-group) 

This is 

an emulsifier

C​8​​H​17​​

Covalent Bonding - share electrons

Covalency:

How many bonds an atom can form

The picture shows 1 bond (consisting of 2 electrons, 1 from each atom)

Covalency and structural formula

Type of atom	Covalency
H	1
F, Cl, Br, I	1
O, S	2
N, P	3
C	4

Practice (in class)

Use the table on the previous slide to draw a structural formula for: 

• ethanol (C₂H₅OH)
• H₂S
• N₂