Ions are charged particlescharged particle: A particle that carries an electric charge. which are formed when atoms [atom: All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. ], or groups of atoms, lose or gain electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ]. For the examination, you need to know which ions are produced by acids, and which are produced by alkalis. You will also need to know the ionic equation for neutralisationneutralisation: Neutralisation is the reaction between an acid and a base to form a salt plus water..
State symbols are used in symbol equations:
- (s) means solid
- (l) means liquid (not the same as dissolved in water - see below)
- (g) means gas
- (aq) means aqueous (dissolved in water)
When acids dissolve in water they produce aqueous hydrogen ions, H+(aq). For example, looking at hydrochloric acid:
HCl(aq) → H+(aq) + Cl–(aq)
When alkalis dissolve in water they produce aqueous hydroxide ions, OH–(aq). For example, looking at sodium hydroxide:
NaOH(aq) → Na+(aq) + OH–(aq)
Ammonia is slightly different. This is the equation for ammonia in solution:
NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq)
Be careful to write OH– and not Oh– or oh–.
When the H+(aq) ions from an acid react with the OH–(aq) ions from an alkali, a neutralisation reaction occurs to form water. This is the equation for the reaction:
H+(aq) + OH–(aq) → H2O(l)
For example, hydrochloric acid and sodium hydroxide solution react together to form water and sodium chloride solution. The acid contains H+ ions and Cl– ions, and the alkali contains Na+ ions and OH– ions. The H+ ions and OH– ions produce the water, and the Na+ ions and Cl– ions produce the sodium chloride, NaCl(aq).
Back to Acid, bases and salts index
Ions are electrically charged particles formed when atoms [atom: All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. ] lose or gain electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ]. They have the same electronic structures as noble gases.
Metal atoms form positive ions, while non-metal atoms form negative ions. The strong electrostatic [electrostatic: An electrostatic force is generated by differences in electric charge (ie positive and negative) between two particles. It can also refer to electricity at rest. ] forces of attraction between oppositely charged ions are called ionic bonds.
Ionic compounds [ionic compound: An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron): The ions swap electrons to achieve a full outer shell. ] have high melting and boiling points.
What is an ion?
Ions are electrically charged particles formed when atoms lose or gain electrons [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ]. This loss or gain leaves a complete highest energy level, so the electronic structure of an ion is the same as that of a noble gas - such as a helium, neon or argon.
Metal atoms and non-metal atoms go in opposite directions when they ionise:
- Metal atoms lose the electron, or electrons, in their highest energy level and become positively charged ions
- Non-metal atoms gain an electron, or electrons, from another atom to become negatively charged ions
How many charges?
There is a quick way to work out what the charge on an ion should be:
- The number of charges on an ion formed by a metal is equal to the group number of the metal
- The number of charges on an ion formed by a non-metal is equal to the group number minus eight
- Hydrogen forms H+ ions
|Group 1||Group 2||Group 3||Group 4||Group 5||Group 6||Group 7||Group 0|
|Charge||1+||2+||3+||Note 1||3-||2-||1-||Note 2|
|Symbol of ion||Na+||Mg2+||Al3+||Note 1||N3-||O2-||Cl-||Note 2|
Note 1: carbon and silicon in Group 4 usually form covalent bonds [covalent bond: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. ] by sharing electrons.
Note 2: the elements in Group 0 do not react with other elements to form ions.
Positively charged sodium and aluminium ions
Negatively charged oxide and chloride ions
Back to Ionic compounds and analysis index