Atomic Structure and the Periodic Table

Ever wondered what makes up everything in the universe? Atoms are incredibly small particles that contain three main components. The nucleus sits at the centre, packed with positively charged protons $+1 charge, mass of 1$ and neutral neutrons (0 charge, mass of 1).

Whizzing around this nucleus are negatively charged electrons $-1 charge, virtually no mass at 1/1840$. Atoms stay neutral because they have equal numbers of protons and electrons - the positive and negative charges cancel each other out perfectly.

Here's something mind-blowing: most of an atom's mass is crammed into that tiny nucleus! The mass number equals protons plus neutrons, whilst the atomic number simply counts the protons. Isotopes are atoms of the same element with identical protons and electrons but different numbers of neutrons.

The periodic table has evolved from Mendeleev's version (arranged by atomic mass with clever gaps for unknown elements) to today's version organised by atomic number. Rows are called periods (showing energy shell numbers), whilst columns are groups (revealing outer shell electrons). The electronic configuration follows a simple pattern: first shell holds 2 electrons, second and third shells each hold 8.

Quick Tip: Remember that group number = outer electrons, and period number = number of energy shells!