Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 78

 Atoms are made up of a central, dense region containing neutrons and protons surrounded by electrons in outer shells with different energies.

 Protons and neutrons have the same relative masses as each other whereas electrons are almost 2000 times lighter. Protons have a positive charge, electrons have a negative charge and neutrons are neutral. Isotopes of an element have the same number of protons (Z) but different numbers of neutrons and therefore different mass number (A).

 There are three main types of radioactive decay namely alpha-, beta- and gamma-.

 Electrons are arranged in orbitals according to their energies in the outer shells, or energy levels of the atom.

 The ground state electronic configuration of an atom can be defined by using the Aufbau principle, the Pauli exclusion principle, and Hund's rule.

 Each successive element has one more proton in the nucleus and one more electron in its outer shell. The different areas of the periodic table (s block, p block etc) are characterised by the type of orbitals in the outer shells being filled by electrons.