Particles Overview

We then looked at two covalent network solids with very different properties: graphite and diamond.

A model of diamond showing the 3D lattice - 4 covalent bonds per carbon atom.

A model of graphite showing 2D sheets - 3 covalent bonds per carbon
atom with valence electrons between the sheets

Our next task was to explore a couple of the characteristic physical properties of these allotropes of carbons: hardness; and electrical conductivity. The trick is to link these properties to the particles and/or bonds/forces within the substance.

Particles, Forces and Properties

We started looking at the relationship between particles, forces (bonds) and properties, using metallic and ionic solids as our context:

Particles - Introduction

In this topic, we are looking at pure substances. What are the particles that make up pure substances? What are the forces/bonds that hold them together (in the solid state)? How can I show this as a diagram?

Ions Overview

This link is to a blog which goes through the tests for ions:
http://level2ions.blogspot.co.nz/

CATIONS

This specific post is the one you want for the cation experiments we are doing in class at the moment:
http://level2ions.blogspot.co.nz/2014/09/colourless-cations.html

One key point to note is about Barium, The Flow Chart we are using says that Barium ions do not precipitate out with Hydroxide ions. If the concentration of either is high enough, it does go milky/cloudy. Therefore, it can be confused for Magnesium. If you suspect an ion is Magnesium, test a new sample with sulfuric acid. If it precipitates out, it is really Barium. If nothing happens, it is Magnesium.

ANIONS

If you have any issues distinguishing between the colours of the precipitates, the following Flow Chart is sometimes easier to use. For example, it there is a coloured cation, it is tough to tell exactly what colour the precipitate is.

Coloured Ions

The first (preliminary) test we do on unknown ionic solutions is to see if it has a colour. Some ions have characteristic colours, so we can infer one of the ions present in a coloured solution. We do need to confirm this "hunch" with chemical reactions, but it is a great starting point.

Writing Formulae and Balancing Equations

We started by being reminded of how to write the formulae for ionic compounds and molecules:

Next, we did these simple experiments and used these to practice making observations and to balance chemical equations:

Bonding

Why do atoms bond together? They are already electrically-neutral, so why do some become ions?

With this brief (and quick) overview of bonding, we were given this challenge: