§3.3 Molecular Substances

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

Warm up question:

Practice:

1. Draw a sodium atom (with its protons, neutrons and electrons) and draw a sodium ion (Na⁺)

2. How many protons and electrons does a magnesium ion Mg²⁺ contain? 

3. How many protons, neutrons and electrons are present in a ³⁵Cl^- ion?

Answer Q 2

Magnesium has atomic number 12, so the number of protons is 12.

The charge is 2+ so it has (12-2) 10 elektronen (it has given away 2 electrons)

Answer Q 3

Cl has atomic number 17

Protons = 17

Mass number = 35

Neutrons = 18

Charge is -1 so there must be (17 + 1) 18 electrons

 

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

3.3. Molecular substances

• Molecular substances
• Van der Waals bonding
• Atomic bonding
• Structural formula

Molecular Substances

Made up of non-metals only

Structural formula: How atoms are linked together

ethanol (C2H6O)

H2S

N2

Van der Waals bonding

Forces between molecules in molecular substances

They get stronger with bigger and heavier molecules

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

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 

Homework (3 and 4):

Draw structural formulae for:

HCN

CO₂

C₂H₂

H₂

C₂H₂

O₂