Ionic bonding workbook PDF

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Ionic Bonding An ionic bond is an electrostatic attraction between oppositely charged ions. These ions are formed by the transfer of electrons from an electropositive element to an electronegative element. Ionic bonding occurs between metals and non-metals and involves the transfer of electrons from the metal atom to the non-metal atom and the formation of ions. Ionic Bonding - How to draw the dot and cross diagrams  Even though all electrons are identical, dots and crosses are used to distinguish between electrons originating from the donor atom and those from the acceptor atom.  Only outer shell electrons are shown. An atom of lithium is drawn as below. Complete the diagrams for sodium and potassium (donor atoms): Li

Na

K

An atom of fluorine is drawn as below. Complete the diagrams for chlorine and bromine (acceptor atoms):

F

Cl

Br

Example 1: sodium chloride Complete the following to show the outer shell electron structure:

Na

Cl

Sodium atom

Chlorine atom

Electron structure: 2,8,1

Electron structure: 2,8,7

Na+

Cl-

Sodium ion

Chloride ion

Electron structure: 2,8,0

Electron structure: 2,8,8

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The sodium atom loses an electron in forming an ion, so the protons outnumber the electrons by one, giving a charge of +1. The chlorine atom gains an electron to form an ion of charge –1 in which the electrons outnumber the protons by one. The empirical formula (the smallest ratio of ions) of sodium chloride is NaCl. Example 2: magnesium oxide

Mg

O

Magnesium atom Electron structure: 2,8,2

Oxygen atom Electron structure: 2,6

Mg2+

O2-

Magnesium ion Electron structure: ………

Oxide ion Electron structure: ………

To balance the charge, the ratio of Mg2+ : O2- = 1 : 1 Empirical formula = ………………

Example 3: potassium oxide

K

O

Potassium atom

Oxygen atom

Electron structure: 2,8,1

Electron structure: 2,6

K+

O2-

Oxide ion

Potassium ion

Electron structure: ………

Electron structure: ……… To balance the charge, the ratio of K+ : O2- = 2 : 1 Empirical formula = ……………… North Hertfordshire College

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Example 4: calcium bromide

Ca Calcium atom Electron structure: ………

Br Bromine atom Electron structure: ………

Ca2+

Br-

Calcium ion

Bromide ion

Electron structure: ………

Electron structure: ………

To balance the charge, the ratio of Ca2+ : Br- = …… : …… Empirical formula = ………………

Example 5: aluminium fluoride

Al Aluminium atom Electron structure: ………

F Fluorine atom Electron structure: ………

Al3+

Aluminium ion Electron structure: ………

F-

Fluoride ion Electron structure: ………

To balance the charge, the ratio of Al3+ : F- = …… : …… Empirical formula = ………………

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What happens when ionic bonds form?  

Positive and negative ions are strongly attracted to one another Vast numbers of ions are involved but the overall charge is neutral and therefore the molar ratio of cation : anion depends on the individual charges on these ions Na+ : Cl- = 1 : 1

Mg2+ : Cl- = 1 : 2

Na+ : O2- = 2 : 1

(Remember the Avogadro constant is 6.02 × 1023, so one mole of NaCl contains 6.02 × 1023 Na+ ions and 6.02 × 1023 Cl- ions.)



These ions form a giant crystalline lattice in which strong, multidirectional, electrostatic forces hold them in place. They take up a position in the crystal where the attractive forces between the nucleus of one ion and the electron cloud of another, balance the repulsive forces between neighbouring electron shells.

The unit cell This is the smallest building block or repeating unit that reveals the detailed ionic structure of the crystalline lattice. The unit cell of sodium chloride is based on a cubic structure and it takes into account that the ratio of Na+ : Cl- is 1:1

Sodium ion Chloride ion

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Properties of ionic substances High melting temperatures and boiling temperatures If a solid has a high melting temperature, much energy has to be supplied to break the bonds between the particles so the attractive forces must be very strong. Melting temperatures / K:

Na2O: 1548

MgO: 3125

Sodium and magnesium are in the same period of the periodic table. Give reasons for the considerable difference in the melting temperatures of their ionic oxides:

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Conduct an electric current when molten or in aqueous solution Substances that conduct an electric current must possess charged particles that are mobile. Ionic compounds qualify in two ways: 

If they are soluble in water, the ions in solution will move to the oppositely charged electrode when a potential difference is applied. An aqueous solution that behaves in this way is called an electrolyte.



Solid ionic substances do not conduct an electric current. If heated until they are molten, however, the ions become mobile and can do so.

Predict which compound, in each of the following pairs has the higher melting point. Explain your reasoning. a. NaF and MgF2

b. Na2O and MgO

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c. NaCl and AlCl3

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(This is an extension question you may need to do some extra research on this one)

With reference to the Periodic Table predict the formula of each of the following ionic compounds. a. caesium fluoride b. sodium nitride c. potassium oxide d. aluminium fluoride e. calcium oxide f.

magnesium sulphide

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