Particles Study Guide

Atoms are incredibly tiny particles, far too small to be seen with the naked eye or even with a conventional light microscope. Their size is measured in nanometres (nm), where one nanometre is equivalent to one billionth of a metre (1 nm = 1 x 10⁻⁹ m). To put this into perspective, a human hair is about 100,000 nanometres thick! The typical diameter of an atom is approximately 0.1 nanometres. This means an atom is about 1 x 10⁻¹⁰ metres across. Different types of atoms will have slightly different sizes due to their electron shells and nuclear charge, but they all fall within this general order of magnitude.

Small molecules, which are made up of a few atoms chemically bonded together, are also extremely small. Their size is typically a few tenths of a nanometre, ranging from approximately 0.1 to 1 nanometre. For example, a water molecule (H₂O) or a carbon dioxide molecule (CO₂) would have a diameter within this range. Understanding the order of magnitude of these particles is crucial in chemistry, as it helps us comprehend why materials behave in certain ways and why advanced techniques like electron microscopy are needed to visualise individual atoms. It also highlights the vast scale difference between the macroscopic world we observe and the microscopic world of atoms and molecules.

Every atom is made up of even smaller particles called subatomic particles. The three main subatomic particles are protons, neutrons, and electrons. Each of these has a unique role in defining the properties of an atom and how it interacts with other atoms. Understanding their relative charges and approximate relative masses is fundamental to comprehending atomic structure and chemical reactions.

Protons are found in the central part of the atom, called the nucleus. They carry a positive electrical charge, which is assigned a relative value of +1. Their mass is significant, and they contribute substantially to the overall mass of an atom. For simplicity in calculations and comparisons, a proton is given an approximate relative mass of 1.

Neutrons are also located in the nucleus, alongside protons. As their name suggests, neutrons are electrically neutral, meaning they carry no charge. Their relative charge is 0. Like protons, neutrons also have a significant mass, approximately the same as that of a proton. Therefore, a neutron is also assigned an approximate relative mass of 1.

Electrons are much smaller and are found orbiting the nucleus in shells or energy levels. They carry a negative electrical charge, which is assigned a relative value of -1, balancing the positive charge of protons in a neutral atom. The most striking difference with electrons is their mass. Electrons are incredibly light compared to protons and neutrons. Their approximate relative mass is often considered to be negligible, or approximately 1/1836 (sometimes rounded to 1/2000 or simply 0 for many calculations) when compared to a proton or neutron. This effectively means that almost all of an atom's mass is concentrated in its nucleus. The number of protons determines the atomic number and the element, while the number of electrons orbiting the nucleus dictates an atom's chemical behaviour and its charge. The number of neutrons in the nucleus can vary, leading to isotopes of the same element.