AGHS CHE222 2021

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Ionic Compounds - Melting Point

on April 06, 2021

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We need to use the structure and bonding of ionic compounds to justify their very high melting points.

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Molecular Formulae

When non-metals combine with other non-metals (or semi-metals), they form molecules . The bonding between the atoms is a covalent bond , where the electrons are shared to fill both atoms' valence shell. The names of molecules are a little different to those of ionic compounds. There are some prefixes to remember so you know how many of each atom will be in the molecule. Sometimes, they have names like "water" or "ammonia" that tell us nothing at all about their composition (the atoms inside them). These are the ones we need to learn off by heart...sorry!

Solutions and Precipitation

Whether something will dissolve or not is generally determined by some solubility rules. We are provided these rules for our internal assessment, and have to justify our conclusions by linking to these solubility rules: When we mix two solutions and a solid forms (it goes cloudy, usually), we call this precipitation . It is because a combination of two of the ions (a cation and an anion) is insoluble . By looking at the solubility rules, we can infer what the precipitate is.

Mole Calculations

MOLAR MASS Before we can use the mole in any calculations, we need to know about molar mass . We met this earlier, looking at the mass of atoms. It is usually called relative atomic mass in that context. When we use these values off the Periodic Table of Elements for a molecule or compound, we call it relative molar mass . We add up the relative atomic mass of every atom in the compound/molecule to find the relative molar mass. CALCULATIONS Once we have a balanced equation for a chemical reaction, and know the mass of one of the reactants (or products), we can find the mass of everything else in that reaction/equation. We are using our mole ratios and manipulating this equation: SOURCE: https://iteachly.com/wp-content/uploads/2019/01/4-1-Chemistry-Formula-Triangles-Lab.pdf

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Ionic Compounds - Melting Point

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