Compounds and Their Structure

A compound is a substance formed when two or more elements are chemically bonded together.
Compounds have different properties from the elements that make them up.
Covalent bonds hold together atoms in compounds like water (H2O) and carbon dioxide (CO2).
Compounds with covalent bonds may form simple molecules or giant structures.
Complex ionic compounds, such as sodium chloride (NaCl), have a lattice structure formed by ionically-bonded atoms.

Formation and Breakdown of Compounds

Compounds are formed when atoms share or transfer electrons to get a full outer energy level, in what’s known as a chemical reaction.
Energy is either absorbed or released during the formation of compounds.
The breaking down of a compound into its constituent elements requires a certain amount of energy called the activation energy.
Chemical changes during the formation and breakdown of compounds often involve colour changes, gas production, or transformation into a new substance.

In a lab setting, physical properties such as melting point, boiling point, density, hardness, and conductivity can help to identify a compound.
Chemical tests can also identify compounds. A flame test, for example, could identify metal ions in a compound.
Spectroscopy, such as mass spectrometry or infrared spectroscopy, can provide detailed analysis of a compound’s composition.
Titration is another method used for analysis and identification, allowing for precise measurements of reaction quantities.

Several chemical reactions involve compounds, such as combination, decomposition, displacement, and redox reactions.
Compounds act as reactants and products in a balanced chemical equation, which represents a chemical reaction.
The principle of conservation of mass applies to these reactions, meaning the total mass of products equals the total mass of reactants.
Rate of reaction is the speed at which reactants are converted to products in a chemical reaction, which can be influenced by temperature, concentration, surface area, and catalysts.

There are periodic trends seen in compounds, grounded in the periodic table.
These trends relate to element reactivity, atomic size, ionization energy, electron affinity, and electronegativity.
These periodic properties affect the type of bonding and resultant compound properties.
For example, the reactivity of elements in the same group typically increases down the group, affecting the compound types formed.