a type of periodic table in which He is moved from the top of group 18 (noble gases) to the top of group 2 (alkaline earth metals). It also places the s-block elements on the right, so that the blocks are arranged in **f, d, p, s format**.

1. Advantages: Has symmetrical lengths corresponding to electron configuration (2,2,8,8,18,18).

2. Disadvantages: Destroys triads and places He with alkaline earths, which it is not similar to. Based on n+l rule. principle quantum number

n= 1, 2, 3...

1. Determines the **shell** the electron is in. The shell is the main component that determines the energy of the electron (higher n corresponds to higher energy), as well as nuclear distance (higher n means further from the nucleus).

2. The row that an element is placed on the periodic table tells how many shells there will be. Helium (n = 1), neon (n = 2), argon (n = 3), etc.

**Each shell with quantum number n has n subhells, n^2 orbitals and can hold up to 2n^2 electrons.**

i.e. n = 3 has 3 subshells (s, p, d). It contains 9 orbitals: 3s, 3px, 3py, 3pz, 3dxy, 3dxz, 3dyz, 3dz2, 3dx2-y2 magnetic quantum number, describes quantization of direction (or orientation) of angular momentum (tells you what **direction the electron is facing**.

Given a certain l, ml is an interval ranging from -l to +l, so it can be zero, a negative integer, or a positive integer.

1. Determines the orbital in which the electron lies.

2. Example: If n=3, and l=2, then what are the possible values of ml ? Answer: Since ml must range from -l to +l, then ml can be: -2, -1, 0, 1, or 2. 4th; electron spin quantum number

1. Unlike n, l, and ml, the electron spin quantum number ms does not depend on another quantum number. It **designates the direction of the electron spin** and may have a spin of +1/2, represented by ↑, or -1/2, represented by ↓. This means that when ms is positive the electron has an upward spin, which can be referred to as "spin up." When it is negative, the electron has a downward spin, so it is "spin down." (+1/2 h/2pi, and -1/2 h/2pi)

2. The significance of the electron spin quantum number is its determination of an atom's ability to generate a magnetic field or not. Besides the magnetism related to its motion and anticipated by the other quantum numbers, there is an intrinsic magnetism that is quantized. ;