Electron Configuration in Atoms

Atomic Structure

• The nucleus is the basic core of an atom, consisting of protons and neutrons.
• Protons are positively charged particles with a much greater mass than electrons.
• Neutrons have the same mass as protons but carry no electrical charge.
• Electrons are negatively charged particles that orbit the nucleus, with a mass of 1/1836 that of a proton or neutron.
• Atoms are electrically neutral, with an equal number of electrons and protons.
• The chemical properties of an atom are determined by the number of electrons it has.

Ions

• Ions are atoms that have gained or lost one or more electrons.
• Loss of an electron makes an atom electropositive, resulting in a positive ion.
• Gaining an electron makes an atom electronegative, resulting in a negative ion.

Crystal Structure

• Once a nucleus of a crystal forms, it provides a solid/liquid interface where crystallization can proceed.
• The nuclei which form will be crystal unit cells, typically face-centred cubic, body-centred cubic, or close-packed hexagonal.
• As the crystal grows, it tends to develop spikes and changes into a tree-like shape called a dendrite.
• The dendritic crystal grows until the spaces between the branches fill up, and eventually, the entire liquid solidifies.

Solubility

• A substance can be dissolved in a solvent to form a solution.
• The solubility of a substance can increase or decrease with temperature changes.
• Solubility curves can be used to determine the maximum amount of a substance that can be dissolved in a solvent at a given temperature.
• Substances that will not dissolve in a solvent are said to be insoluble.

Solid Solutions

• Most metals are completely and mutually soluble in the liquid state, but some remain in solution upon cooling and become solid solutions.
• There are two types of solid solutions: substitutional and interstitial solid solutions.
• Substitutional solid solutions occur when the atoms of the solvent and solute are approximately the same size and have similar electrochemical properties.
• The formation of a substitutional solid solution is also influenced by the valency of the metals involved.

Examples of Solid Solutions

• The copper-nickel alloy is a substitutional solid solution, where atoms of nickel replace atoms of copper in the lattice.
• The composition of a solid solution can change as the temperature changes, leading to the precipitation of one phase out of another.
• The final composition of an alloy can consist of crystals of different phases dispersed through a matrix.