Ions & formation of Ionic compounds A ‘type of’ chemical reaction you need to master… IONS: an atom or molecule with a net electric charge due to the loss or gain of one or more electrons, eg Mg2+

Unlike charges attract Side point: Electrostatic Forces Unlike charges attract Like charges repel…

Atom has extra electrons I.e. wants to get rid of them Fe2+ or Fe3+ +ve CATION Atom has extra electrons I.e. wants to get rid of them NH4+ Ca2+ metals (Mg) lose electrons ---> cations sodium hydrogen Na+ H+

-ve F- CO32- ANION Atom needs electrons i.e. wants to grab them OH- SO42- nonmetals (F) gain electrons ---> anions chlorine O2- oxygen Cl-

CATION +ve How to remember? Cation has a t

Review State the number of protons, neutrons, and electrons in each of these ions. 39 K+ 16O -2 41Ca +2 19 8 20 #p+ ______ ______ _______ #no ______ ______ _______ #e- ______ ______ _______

Naming ions & ionic compounds Names of cations are the same as the names of the elements. Na+ = sodium ion Names of anions = Name of element but ending with “-ide”

Learning Check Complete the names of the following ions. Ba2+ Al3+ K+ _________ __________ _________ N3 O2 F _________ __________ _________ P3 S2 Cl

Solution Ba2+ Al3+ K+ barium aluminum potassium N3 O2 F nitride oxide fluoride P3 S2 Cl phosphide sulfide chloride

When an atom loses or gains electrons it becomes Ion.

Ions combine together to form a compound so that there is no excess charge

Ionic bonding (metal + non-metal) Look! Group 7 element Look! Group 1 element Very strong forces of attraction between positive and negative ions = ionic bond

Mg + O = MgO Metal gas Metal oxide 2Mg + O2 2MgO Heat Mg2+ O2- Ions ?

Mg (2,8,2) → Mg2+ (2,8) magnesium ion Electron arrangement for Mg (2,8,2) Mg has two valence electrons. (Valence electrons are… Atoms are stable when their outer shell is full An atom may lose or gain 1,2 or 3 electrons to form an ion. An ion is an atom or compound that has lost or gained electrons Mg (2,8,2) → Mg2+ (2,8) magnesium ion Mg 2 electrons get ‘lost’ in a Chemical reaction to another substance! Compare with O (2,6) → O2- (2,8) Oxygen ion Here O ‘gains’ 2 electrons in a Chemical reaction to another substance!

The formula is Al2O3 Aluminium Oxide Aluminium Oxygen To work out the number of ions of each element we need to balance the number of electrons being given and taken. 2 x 3= 6 electrons from the aluminium and 3 x 2 = 6 electrons to the oxygen 2- 3+ 2- 3+ 2- The formula is Al2O3 Aluminium Oxide

Polyatomic ions are made up of more than one element OH- = hydroxide ion NO3- = nitrate ion NH4+ = ammonium ion CO32- = carbonate ion SO42- = sulfate ion PO43- = phosphate ion HCO3- = hydrogen carbonate ion Fiddly naming rule – learn in senior Chemistry! Since transition metals and poor metals can form ions of more than one charge, the name of the cation has to include the charge:

Examples of Ionic Compounds with Two Elements Formula Ions Name cation anion NaCl Na+ Cl- sodium chloride K2S K+ S2- potassium sulfide MgO Mg2+ O2- magnesium oxide CaI2 Ca2+ I- calcium iodide Al2O3 Al3+ O2- aluminum oxide

Learning Check Write the names of the following compounds. 1) CaO ___________ 2) KBr ___________ 3) Al2O3 ___________ 4) MgCl2 ___________

Solution Write the names of the following compounds: 1) CaO calcium oxide 2) KBr potassium bromide 3) Al2O3 aluminum oxide 4) MgCl2 magnesium chloride

http://science. nayland. school http://science.nayland.school.nz/graemeb/yr11%20work/atomic_structure/practice_on_writing_formulae_of.htm

Learning Check Select the correct name for each. A. Fe2S3 1) iron sulfide 2) iron(II) sulfide 3) iron(III) sulfide B. CuO 1) copper oxide 2) copper(I) oxide 3) copper(II) oxide

Solution Select the correct name for each. A. Fe2S3 3) iron (III) sulfide Fe3+ S2- B. CuO 3) copper (II) oxide Cu2+ O2-

One Last Learning Check Write the nuclear symbol form for the following atoms or ions: A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 46 e- ___________