Define the following terms as applied to solid state chemistry

Here are the solutions to the questions: 2. (b) Define the following terms as applied to solid state chemistry (i) Unit cell: The smallest repeating unit* in a crystal lattice that, when repeated in three dimensions, generates the entire crystal structure. It represents the fundamental building block of a crystal. (i) Coordination number: The number of nearest neighbor atoms or ions* that surround a central atom or ion in a crystal lattice. (ii) Give an example of a metal with a close packed structure. Copper (Cu)* (Other examples include Magnesium (Mg), Zinc (Zn), Silver (Ag), Gold (Au)). 2. (c) The table below shows the electronegativity of some elements | Element | H | Li | B | C | O | F | | :--------------- | :---- | :---- | :---- | :---- | :---- | :---- | | Electronegativity | 2.1 | 1.0 | 2.0 | 2.5 | 3.5 | 4.0 | (i) What do you understand by the term electronegativity? Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons towards itself in a chemical bond. (ii) Give the formula of an ionic compound formed by two elements on the table. An ionic compound typically forms between a metal and a non-metal with a large difference in electronegativity. Lithium (Li) is a metal (EN = 1.0) and Fluorine (F) is a non-metal (EN = 4.0). The difference is 4.0 - 1.0 = 3.0, indicating a highly ionic bond. Formula: LiF (iii) Suggest the formula of a molecule that has the least polar bond. The least polar bond will be formed between two elements with the smallest difference in electronegativity. Comparing the elements: H (2.1) and B (2.0) have a difference of 2.1 - 2.0 = 0.1. H (2.1) and C (2.5) have a difference of 2.5 - 2.1 = 0.4. O (3.5) and F (4.0) have a difference of 4.0 - 3.5 = 0.5. The smallest difference is between Hydrogen (H) and Boron (B). Formula: BH_3 (Borane) (iv) The boiling points of three molecules are given in the table below | Molecule | Boiling point/K | | :----------------- | :-------------- | | F_2 | 85 | | CH_3F | 194 | | HF | 293 | Explanation of the trend (assuming this is the implied question): The boiling points increase due to the strength of intermolecular forces: F_2 is a nonpolar molecule, so it only experiences weak London Dispersion Forces*. CH_3F is a polar molecule, experiencing London Dispersion Forces and stronger dipole-dipole forces*. HF is a highly polar molecule that can form hydrogen bonds* (due to H being directly bonded to the highly electronegative F atom), which are the strongest type of intermolecular force among these molecules, leading to the highest boiling point.