Ion Definition Gcse Chemistry Coursework

Neutralisation reactions

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

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)

Acids

When acids dissolve in water they produce aqueous hydrogen ions, H+(aq). For example, looking at hydrochloric acid:

HCl(aq) → H+(aq) + Cl(aq)

Alkalis

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.

Neutralisation reaction

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 1Group 2Group 3Group 4Group 5Group 6Group 7Group 0
Example elementNaMgAlCNOClHe
Charge1+2+3+Note 13-2-1-Note 2
Symbol of ionNa+Mg2+Al3+Note 1N3-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

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