Atoms

• The idea of an atom started as early as the 5th century B.C. when Democritus expressed his belief that matter is made up of smaller, indivisible particles he called ‘atomos,’ meaning indivisible.
• atoms are made up of even smaller particles we now know as subatomic particles. These particles include protons, neutrons, and electrons.
• Electrons are negatively charged
• Neutrons are electrically neutral
• Protons are positively charged
• In the modern periodic table, an atomic number is usually written on the upper left side corner of each element block
• If the number of neutrons is added to the atomic number, it becomes the mass number (no. of protons + no. of neutrons).
• electron configuration is the distribution of electrons among the various orbitals in an atom, molecule, or ion.