§2.3 Using chemical formulas

• Scheikunde
• Middelbare school
• vwo
• Leerjaar 3

Planning for today

§2.3

Using chemical formulas

Remember the particle model?

 

Chemical Reactions...

Molecules are broken down and new molecules are formed.

A reaction can be written down as an equation or process:

molecules go in (reactants), different molecules come out (products).

 

The periodic table; the alphabet of chemistry

Het alfabet and the PT:

Alphabet	PT
Letter	Atom/Element
Word	Molecule
Sentence	Substance
Story	Materials

Atoms in a molecule are connected by atomic bonds (bonds between atoms)

d

Elements

Based on one kind of atom or molecules with one kind of atom (pure)

ggg

g

Compounds

Molecules containing more than one kind of atom.

There are seven elements which always form molecules with two of their atoms. These are the BrINClHOF substances 

(Br, I, N, Cl, H, O, and F) 

Molecules can be drawn but they can also be given a molecular formula.

Naming compounds - Nomenclature, systematic

1. First element of compound keeps its own name
2. Second element gets -ide at the end 
3. Greek numbering words are used to indicate how many of each element is in the formula

N2O = dinitrogen oxide                      CCl4  = carbon tetrachloride 

  

Greek:	number
mono-	1
di-	2
tri-	3
tetra-	4
penta-	5
hexa	6

hepta-	7
octa-	8

Name: index comes first

Formula: symbol comes first, followed by index

Never start a name with mono

Practise:

Give the name:

1. N2O5

2. P2I4

3. S2Cl2

Give the formula:

1. phosphorous trichloride

2. dinitrogen monoxide

3. diphosphorous pentaoxide

Index and coëfficient

Methane is made up of one Carbon atom and four Hydrogen atoms. Its formula will be:

CH4

The 4 in methane is called an Index

If you have 2 methane molecules, you write it down as:

2 CH4 (and not C2H8)

The 2 before methane is called the coefficient

Index and Coëfficient

The Index denotes how many atoms of one kind are WITHIN a molecule

C2H6

The coëfficient denotes how many molecules are present in a situation

2 HNO3 (Two Nitric acid molecules)

Some practice

What atoms are one water molecule made up from? What is its formula? Does it have an index or coëfficient?

 

What atoms are sugar molecules made up from? What would you write down if you had three sugar molecules?

What atoms are water molecules made up from?

2 Hydrogen atoms, 1 oxygen atom

its formula is H2O
 

What atoms are glucose molecules made up from?

6 Carbon atoms, 12 Hydrogen atoms and 6 Oxygen atoms

If you have three of those molecules you write down:

3 C₆H₁₂O₆

Much used substances

Water, Ammonia, Carbon dioxide, Ethanol, Methane,
Sulfur dioxide, Sufuric acid

The diatomic elements: Br I N Cl H O F

Just a few more things!

Molecules and atoms have mass

We weigh a certain amount, 

because

 the molecules and atoms we are made of weigh a certain amount!

an Atom's mass is indicated in the Periodic table!

One Helium atom

weighs 4,003 u

u stands for Units 

of mass

1 u is equal to 0,00000000000000000000000166 grams 

https:

Mass calculation

If water molecules consist of two hydrogen atoms and one oxygen atom they're mass is:

16,00 u + 2 x 1,008 u = 18,016 u

All the molecules which you have been looking at you will use quite regularly so you will need to know the names and formulas of most of them by heart.

Moleculen en atomen zijn onzichtbaar klein. Als je zuiver water (H2O), zuivere alcohol (C2H6O) en keukenzout (NaCl) met elkaar in een glas mengt, krijg je een heldere, kleurloze oplossing.

Hoeveel soorten atomen zitten er in dat glas?

1. 1
2. 3
3. 5
4. vele miljoenen

Moleculen en atomen zijn onzichtbaar klein. Als je een theelepel zuivere suiker oplost in een glas zuiver water, ontstaat een heldere suikeroplossing.

Hoeveel soorten moleculen zitten er in dat glas?

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

Verbinding

Element

H2

CH4

Cl2

HF

C6H12O6

Na

1. separation
2. phase transition
3. chemical reaction

1. separation
2. phase transition
3. chemical reaction

1. separation
2. phase transition
3. chemical reaction

1. separation
2. phase transition
3. chemical reaction