Structure of the Atom
Your phone, your desk, even you - everything is made of atoms, and these microscopic particles have a surprisingly organised structure. Each atom contains three main parts: protons (positive charge), neutrons (no charge), and electrons (negative charge).
The atomic number tells you how many protons an atom has, which also equals the number of electrons in a neutral atom. Take carbon - it has 6 protons and 6 electrons. The mass number is trickier; it's the total of protons plus neutrons, so carbon's mass number is 12.
Electrons don't just float randomly around - they're organised in shells like layers of an onion. The first shell holds a maximum of 2 electrons, then every shell after that can hold up to 8. This arrangement determines how elements behave and where they sit on the periodic table.
Quick Tip: The number of electron shells equals the period number, and the number of outer electrons equals the group number on the periodic table!
Isotopes are atoms of the same element with different numbers of neutrons. Chlorine, for example, comes in two main forms - one with 18 neutrons and another with 20. To find the average atomic mass, you multiply each isotope's mass by its percentage abundance, then add them together.
The periodic table we use today is arranged by atomic number, not mass like Mendeleev's original version. Mendeleev was brilliant though - he left gaps for undiscovered elements and his predictions were spot on!
From John Dalton's simple particle idea in 1803 to Rutherford's nuclear model and Chadwick's neutron discovery, our understanding of atoms has evolved dramatically. Each scientist built on previous work, giving us the atomic model that explains chemistry today.
