■ Formation of cation and anion
► | An atom is neutral because it has an equal number of protons and electrons. | |
► | An ion formed when an atom donates or accepts one or more electrons. |
■ Formation of cation
► | ||
► | When an atom donates electrons, it becomes positively charged as there are more protons than electrons in it. | |
► | A positively charged ion or cation is obtained. | |
► | M → Mn+ + ne |
► | ||
► | When an atom accepts electrons, it becomes negatively charged as there are more electrons than protons in it. | |
► | A negatively charged ion or anion is obtained | |
► | A + ne → An- |
■ Formation of ionic bonds
► | Electrons are transferred from a metal to a non-metal. | |
► | The metal donates its valence electron(s) to attain the noble gas stability. Positive ions (cation) are formed. | |
► | The non-metal received the electron(s) to attain the noble gas stability. Negative ion (anion) are formed. | |
► | The positive and negative ions are held together by strong electrostatic forces of attraction. | |
► | This strong electrostatic forces of attraction between ions of opposite charges is known as ionic bond. | |
► | The animation below shows the formation of sodium chloride (NaCl), magnesium oxide (MgO), and sodium oxide (NaO2).
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■ This video contains information on the formation of ionic bonds.
Laboratory Activity 5.2.1: Preparation of Ionic Compounds |
■ Formulae of an ionic compound.
► | Metal atoms will release their valence electrons to achieve the stable electron arrangement as in the inert gases. | |
► | Non-metal atoms will accept electrons in order to achieve the stable electron arrangement of the inert gases. | |
► | For cations Mb+ and anions Xa-, the formula of an ionic compound formed between them is written as MaNb. | |
► | The total positive charge of the cation must be equal to the negative charge of the anion in an ionic compound. | |
► | Hence, the formula of an ionic compound formed between them can also be derived as follows : aMb+ + bXa- → MaNb |
✍ Worked-example 5.2(a)
Complete the following table to show the written ionic compound formulae.
Solution
Atom | Proton number | Electron arrangement | Ion formula | Atom | Proton number | Electron arrangement | Ion formula |
A | 3 | 2.1 | A+ | V | 9 | 2.7 | V- |
B | 11 | 2.8.1 | B+ | W | 8 | 2.6 | W2- |
C | 12 | 2.8.2 | C2+ | X | 17 | 2.8.7 | X- |
D | 20 | 2.8.8.2 | D2+ | Y | 9 | 2.7 | Y- |
E | 19 | 2.8.8.1 | E+ | Z | 17 | 2.8.7 | Z- |
⇲ For exercise(objective and subjective), download for free on Android OS. | ||
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