🧪 1(c) At

Notes

•[Atomic Structure] Atom → The smallest part of an element that can still participate in a chemical reaction. Molecule → Two or more atoms chemically joined together. Structure of an atom • The nucleus, at the center, contains protons and neutrons. • Electrons move around the nucleus in energy levels (shells). • Proton → charge +1, mass 1 • Neutron → charge 0, mass 1 • Electron → charge –1, mass almost 0 Atomic number (proton number) → the number of protons in an atom. Mass number → the total number of protons and neutrons. Number of neutrons = mass number – atomic number. Isotopes → atoms of the same element with the same number of protons but different neutrons. Relative atomic mass (Ar) → the weighted average mass of an element’s isotopes compared with 1/12 of carbon-12. How to calculate Ar: Ar = [(isotope mass × % abundance) + (other isotope mass × % abundance)] ÷ total abundance •[The Periodic Table] Arrangement: • Elements are ordered by atomic number. • Groups (vertical columns) → number of electrons in the outer shell. • Periods (horizontal rows) → number of energy levels (shells). Example: Sodium (Na) → atomic numbe...