Number that specifies the properties of the atomic orbitals Tells us the distance from the nucleus and the shape of the orbital Main level or shell These are the Bohr energy levels n = 1, n = 2, n = 3 As n increases, the distance from the nucleus increases Each main level is divided into sublevels Four types of sublevels s p d f Each sublevel is made of orbitals Every orbital can hold 2 electrons s – 1 orbital – 2 electrons p – 3 orbitals – 6 electrons d – 5 orbitals – 10 electrons f – 7 orbitals – 14 electrons One spherical shaped orbital Three dumbbell shaped One dumbbell in each axis Main Level Sublevels Number of Sublevels Electrons in sublevels Total Electrons in Main Level 1 s 1 2 2 2 s p 1 3 2 6 8 3 s p d 1 3 5 2 6 10 4 s p d f 1 3 5 7 2 6 10 14 18 32 Arrangement of electrons in an atom Aufbau Principle – electrons fill into an atom starting with the lowest energy levels Way which the electrons rotate on their axis Pauli Exclusion Principle – in order for two electrons to occupy the same orbital, they must have opposite spin Hund’s Rule – electrons occupy orbitals singly first before doubling up Write the configuration for each of the below C S Br Na Cl Kr Electrons in the last main energy level These are the electrons farthest out on the atom These will interact with other atoms These are the electrons involved in chemical reactions There are a maximum of 8 valence electrons Write configuration and count electrons in last main energy level Examples: Find valence electrons for C Na P Fe Ar Atoms will give up, accept, or share electrons in order to achieve a filled valence shell (8 valence electrons) Metals become more reactive (more metallic in character) as you go down a group Most metallic elements bottom left corner of the periodic table Least metallic, top right corner Energy required to remove the most loosely held electron from an atom The greater the ionization energy, the more strongly the atom holds onto its electrons M + energy → M+ + e Ionization energy increases as moving across a period Ionization energy decreases as moving down a group Half of the distance between two adjacent nuclei Radius decreases across a period (atoms hold the electrons tightly in) Radius increases down a group