Atoms, elements and compounds - Ions and ionic bonds (3)
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1.
Non-metals form negative ions (anions) by gaining one or more electrons. Explain how non-metals achieve this and give two examples of non-metals and the anions they form. Include a brief explanation of why non-metals tend to gain electrons.
Non-metals form negative ions (anions) by gaining one or more electrons. They do this because they have few electrons in their outermost shell and are closer to having a full outer shell, which is a stable configuration. By gaining electrons, they achieve a full outer shell and become negatively charged. For example, chlorine (Cl) readily gains one electron to form a chloride ion (Cl-), a -1 anion. Oxygen (O) gains two electrons to form an oxide ion (O2-), a -2 anion. The tendency of non-metals to gain electrons and form negative ions is a key characteristic of their chemical behaviour. The gain of electrons results in an increase in electron density around the atom, leading to a negative charge.
- Non-metals gain electrons to achieve a full outer shell.
- This results in a negative charge on the atom.
- The number of electrons gained determines the anion's charge.
- This process leads to a stable, filled electron configuration.
2.
Describe the process by which metals form positive ions (cations). Include in your answer a discussion of the electronic changes that occur and the charge of the resulting cation. Give two examples of metals and the cations they form.
Metals form positive ions (cations) by losing one or more electrons. The electrons are typically lost from the outermost shell (valence shell) which are loosely held. This process results in the metal atom having more protons than electrons, giving it a positive overall charge. The number of electrons lost determines the charge of the cation. For example, sodium (Na) readily loses one electron to form a sodium ion (Na+), a +1 cation. Magnesium (Mg) loses two electrons to form a magnesium ion (Mg2+), a +2 cation. The electronic changes involve the formation of a filled electron shell, which is a stable configuration. The tendency of metals to lose electrons and form positive ions is a key characteristic of their chemical behaviour.
- Metals lose electrons from their outermost shell.
- This results in a positive charge on the atom.
- The number of electrons lost determines the cation's charge.
- This process leads to a stable, filled electron configuration.
3.
Describe the properties of ionic compounds, focusing on their high melting points and boiling points. Explain why these properties are observed.
Ionic compounds, such as sodium chloride (NaCl), have significantly higher melting and boiling points compared to most covalent compounds. This is due to the strong electrostatic forces between the positively charged ions (cations) and the negatively charged ions (anions) in the ionic lattice.
Explanation:
- Strong Electrostatic Forces: The attraction between oppositely charged ions is a powerful force. These forces extend throughout the entire crystal lattice.
- Energy Required to Overcome Forces: To melt or boil an ionic compound, a large amount of energy is required to overcome these strong electrostatic forces and disrupt the ionic lattice.
- Large Number of Ions: Ionic compounds consist of a vast number of ions packed closely together in a regular arrangement. This contributes to the overall strength of the lattice.
The higher the charge on the ions and the smaller the ionic radii, the stronger the electrostatic forces and the higher the melting and boiling points will be. For example, magnesium oxide (MgO) has a higher melting point than sodium chloride (NaCl) because magnesium ion (Mg2+) has a higher charge and smaller radius than sodium ion (Na+).