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What’s something that ionic, covalent, and metallic bonding all have in common? One answer to this is the fact that they can all form lattice structures. Because each lattice has a structure and bonding of different types, this causes them to have different physical properties, such as differences in solubility, melting point, and conductivity, which can all be explained by their varying chemical structures.
A lattice is a three-dimensional arrangement of ions or atoms in a crystal.
You may remember from our articles on Bonding that Ionic Bonding occurs via the transfer of electrons from metals to non-metals. This causes metals to become charged by losing electrons, forming positively charged ions (cations). Non-metals, on the other hand, become negatively charged by gaining electrons. Ionic bonding, therefore, involves strong electrostatic forces forming between oppositely charged ions in a lattice structure.
These compounds can be arranged in giant ionic lattices called ionic crystals. They are referred to as “giant” as they are made up of large numbers of the same ions arranged in a repeating pattern.
An example of a giant ionic lattice is sodium chloride, NaCl. In the lattice of sodium chloride, the Na+ ions and Cl- ions are all attracted to each other in opposite directions. The ions are packed together in a cubic shape with the negative ions being larger in size than the positive ions.
Diagram of a giant ionic lattice of NaCl. StudySmarter Originals
Another example of a giant ionic lattice is Magnesium Oxide, MgO. Similar to the lattice of NaCl, Mg2+ ions and O2- ions are attracted to each other in its lattice. And also similar to the lattice of NaCl, they are packed together in a cubic lattice. Negative ions of Oxygen are larger than the positive ions of Magnesium.
Lattice structure of magnesium oxide, MgO | Embibe
Another important type of bonding is Covalent Bonding. Covalent bonding takes place between non-metals only.
Covalent bonding is the strong electrostatic attraction between two positive nuclei and the shared pair of electrons between them.
There are two types of structures that can contain covalent bonding: giant covalent structures and simple covalent structures. The difference between them is that the electrostatic attraction holding giant structures together is stronger than the electrostatic attraction holding simple structures.
Some examples of simple molecular lattices would be iodine, buckminsterfullerene (C60), and ice.
Buckminsterfullerene (C60) is an allotrope of carbon, which means its molecules only consist of carbon atoms. There are total 60 carbon atoms in buckminsterfullerene (C60) which are arranged in 20 hexagonal rings, and 12 pentagonal rings. These rings form a spherical structure.
Diagram representing buckminsterfullerene (C60). Studysmarter Originals
When water freezes, the H2O molecules arrange themselves in a crystal lattice structure. Did you know that water expands when it freezes? That is because the water molecules get more space between them when arranged in a crystal structure than in liquid state. The red circles are oxygen atoms, and the yellow circles are hydrogen atoms.
H2O molecules in ice arranged in a crystal structure | Azimuth
Iodine is another simple molecule with its molecules arranged in a crystal lattice. Iodine molecules arrange themselved in a face-centric-cubic lattice. A face centric cubic lattice is a cube of molecules with other molecules on the centre of the faces of the cube.
Iodine lattice structure | favpng
Lattice of iodine can be a little hard to visualize even with an image. Look at the lattice from above - you'll see that molecules on the right and left side of the cube are aligned in the same way, while those in the middle are aligned the other way.
Examples of giant molecular lattices are graphite, diamond, and silicon (IV) oxide.
Shapes of the giant molecular lattices. StudySmarter Originals
Graphite is an allotrope of Carbon i.e., it is completely made up of carbon atoms. Graphite is a giant covalent structure because millions of carbon atoms can exist in a single molecule of graphite. Carbon atoms are arranged in hexagonal rings, and several rings are joined together to form a layer. Graphite consists of several of these layers stacked on top of each other.
Structure of Graphite | Quizlet
The bonds shared by carbon atoms in a layer are strong covalent bonds. Each carbon atom makes 3 single covalent bonds with 3 other carbon atoms. There are weak intermolecular forces between layers (shown by dotted lines in the figure). Graphite is a unique material with some very interesting properties and uses, which you can read more about here.
Diamond is yet another allotrope of carbon, and a giant covalent structure. Diamond and graphite both are made completely of carbon, but have completely different properties. This is because of the difference in the lattice structure of the two compounds. In diamond, carbon atoms are arranged in a tetrahedral structure. Each carbon atom makes 4 single covalent bonds with 4 other carbon atoms.
Carbon atoms arranged in tetrahedral geometry in diamond | Tutormyself
This tetrahedral geometry makes diamond the hardest material in the world! You can read more about diamond here.
Another example of a giant covalent structure is silicon (IV) oxide, also known as silica. Silica is the major constituent of sand. The chemical formula of silica is SiO2. Like diamond, atoms in silica are also arranged in a tetrahedral geometry.
Tetrahedral arrangement of atoms in Silicon Dioxide |Mathsmadeeasy
Due to the tetrahedral structure, silicon (IV) oxide is very hard. Silica is also used in the formation of glass.
When atoms of metals are closely packed together, they create a regular shape which we call a giant metallic lattice.
Within this lattice, there are free electrons in the outer shell of the metal atoms. These free electrons are also known as ‘delocalised’ electrons and they are free to drift around the structure allowing positive ions to form. This causes metallic bonding to occur.
Metallic bonding is the strong electrostatic attraction between the delocalised electrons and the positive metal ions.
An example of a metallic lattice is calcium, and its ions have a 2+ charge. Copper forms a face-centred-cubic (FCC) lattice. In an FCC lattice, there is an atom at each vertex of the cube, and there is an atom at the centre of each face of the cube. Metals form giant metallic structures as they consist of millions of atoms.
Face centred cubic (FCC) lattice of copper | John A. Dutton e-Education Institute
Giant ionic lattices have very high melting and boiling points because of the strong attraction holding the ions together.
They conduct electricity but only when they are dissolved or molten. When ionic lattices are in a solid state, their ions are fixed in position and cannot move so electricity is not conducted.
Giant ionic lattices are soluble in water and polar solvents, however, they are insoluble in non-polar solvents. Polar solvents have atoms that have a large difference in electronegativity. Non-polar solvents contain atoms with a relatively small difference in electronegativity.
Simple covalent lattices have low melting and boiling points because they have weak intermolecular forces between the molecules. Therefore, only a small amount of energy is required to break the lattice.
They do not conduct electricity in any of the states – solid, liquid, or gas as there are no ions or delocalised electrons to move around the structure and carry a charge.
Simple covalent lattices are more soluble in non-polar solvents and are insoluble in water.
Giant covalent lattices have high melting and boiling points as a large amount of energy is required to break the strong bonds between the molecules.
Most of these compounds cannot conduct electricity because there are no free electrons available to carry a charge. However, graphite can conduct electricity because it has delocalised electrons.
These types of lattices are insoluble in water as they don’t contain any ions.
Giant metallic lattices have moderately high melting and boiling points because of the strong metallic bonding.
These lattices can conduct electricity when solid or liquid as free electrons are available in both states and can drift around the structure carrying an electric charge.
They are insoluble in water due to the metallic bonds being very strong. However, they can be soluble in only liquid metals.
A lattice is a three-dimensional arrangement of ions or atoms in a crystal.
Lattice structures can be used for additive manufacturing.
- Giant ionic lattices
- Covalent lattices
- Metallic lattices
An example is sodium chloride, NaCl. The ions in this structure are packed in a cubic shape.
1. Draw a square
2. Draw an identical square offset from the first one.
3. Next, join the squares together to make a cube.
4. Then, divide the cubes into 8 smaller cubes.
5. Draw three lines through the centre of the cube, from the centre of each face to the centre of the opposite face.
6. Add the ions, but remember the negative ions (Cl-) will be larger in size than the positive ions.
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