Writing chemical formulae

Writing chemical formulae

Compounds made up of ions are called ionic compounds. When they are named the metal ion goes first and the non metal ion comes last.

To write the chemical formula from the name go through these steps.

(1)Write down the ions from the table (you are always given this)

(2)successively add postive and negative ions till the total charges balance

(3)Write the chemical formula. Aluminium oxide has been done for you. 

(4)in the case of copper nitrate where two nitrate ions are needed to balance charge we need to put the nitrate ions in brackets e.g.  Cu(NO3)2.

Homework

Enter the date in your book and write the chemical formula for these these compounds.

 

(1) sodium oxide

(2) calcium hydroxide

(3) potassium carbonate

(4) zinc chloride

(5) magnesium nitrate

(6) aluminium carbonate 

 

So much for atoms what about ions?

So much for atoms what about ions?

When we started this topic the big question was " what happens when atoms react"?

When we started this topic the big question was ” what happens when atoms react”? We know enough now to answer this. Here is a review of the main points so far.

  • Elements with same number of outer electrons are arranged in columns on the Periodic Table called groups. Elements with the same number of electrons in their outer shell tend to have similar physical and chemical properties.
  • Finally atoms gain lose or share electrons to achieve a full outer shell like the inert gases.Now lets have a look at what happens when sodium and chlorine atoms react. 

Sodium burns fiercely in an atmosphere of chlorine.

The product is a white solid, sodium chloride or ordinary table salt.

This compound is harmless.What has happened to the sodium and chlorine atoms?

Sodium burns fiercely in an atmosphere of chlorine.

The product is a white solid, sodium chloride or ordinary table salt.

This compound is harmless.

What has happened to the sodium and chlorine atoms?

Can you spot the deliberate mistake in the diagram?

The sodium atom has lost an electron to become a positively charged ion.

The chlorine atom has gained an electron to become a negatively charged chloride ion.

Watch sodium burning violently in chlorine here. 

Sodium and chlorine reacting to form an ionic compound sodium chloride

What happens when sodium and chlorine atoms react?

Sodium has one electron in its outer shell. Chlorine has seven electrons in its outer shell. When they react sodium loses an electron to become a sodium ion with a charge of +1. Chlorine atoms accept an electron to become chloride ions with a charge of -1. After reacting the sodium and chloride ions have a full outer shell of electrons. A full outer shell of electrons is a stable arrangement. The inert gasses in group 18 of the periodic table all have a full outer shell and characteristically are very unreactive (they don’t easily combine with other elements). The new substance sodium chloride is made up of ions. Compounds that have ions bonded together are called ionic. The ions are held together by powerful electrostatic forces. Ionic compounds typically have high melting and boiling points as a consequence.

Homework… how much of this do you understand?

Watch the video especially the bit that deals with the changes to sodium and chlorine atoms when they react with each other. Magnesium has two electrons in its outer shell and it burns in chlorine gas like sodium.
Draw sodium and chlorine atoms and show how ions are produced when they react.
What are the charges of the ions?
what is the formula of magnesium chloride?

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