Chemistry - The Periodic Table (Group properties and Transition elements)

The Periodic Table is arranged in order of increasing atomic number ($Z$). Periods represent the number of electron shells, while Groups represent the number of valence electrons.

Group 1 (Alkali Metals): These are soft metals with low densities. Reactivity increases down the group because the outer electron is further from the nucleus, experiencing less attraction and thus is easier to lose ($M \rightarrow M^+ + e^-$).

Group 7 (Halogens): These are non-metals that exist as diatomic molecules (e.g., $F_2$, $Cl_2$). Reactivity decreases down the group as it becomes harder to attract an incoming electron into the shell further from the nucleus.

Displacement Reactions: A more reactive halogen will displace a less reactive halogen from its halide solution. For example, $Cl_2$ will displace $Br^-$ from $KBr$.

Group 0 (Noble Gases): These are monatomic gases with a full outer shell of electrons ($8$ electrons, except $He$ which has $2$). They are chemically inert/unreactive.

Transition Elements: Metals located in the center of the table. Characteristics include: high melting points, high density, formation of colored compounds (e.g., $Cu^{2+}$ is blue), and use as catalysts (e.g., $Fe$ in the Haber process).

Variable Oxidation States: Unlike Group 1 metals which only form $+1$ ions, transition metals can form multiple ions, such as $Fe^{2+}$ and $Fe^{3+}$.