The Electronic structure of an atom

Bohr’s model of an Atom Electrons located in circular orbits around an atom When an electron absorbs or emits energy it moves from 1 orbit to the next The greater the energy the farther from the nucleus

Energy level: a specific amount of energy which an electron in an atom can possess

When an electron is hit with energy it can jump to another energy level

As an electron in a higher energy level gives off energy (light) it drops down to a lower level

Quantum: The energy difference between two particular energy levels Orbital: the actual region of space occupied by an electron at a specific energy level

Energy levels are designated by a quantum number called “n – the principal quantum number” Level n=1 has just the 1s orbital

Shape representation for a 1s orbital - 2 electrons can occupy the 1s orbital. - Start in energy level n = 1.

The n=2 level has 4 orbitals, a 2s (same shape but larger than a 1s) and three 2p orbitals n = 1 n = 2 n = 3 n = 4 1s 2s 3s 4s 2p 3p 4p 3d 4d 4f Energy Level Diagram for Hydrogen

p orbitals 3 orbitals in total. 2 electrons can occupy each orbital. All 3 orbitals can be in one orbital level (n level). Start in energy level n = 2.

N=3 level has one 3s, three 3p orbitals and five 3d orbitals. Each level “n” has n 2 orbitals n = 1 n = 2 n = 3 n = 4 1s 2s 3s 4s 2p 3p 4p 3d 4d 4f Energy Level Diagram for Hydrogen

d orbitals 2 electrons per orbital. Total of 5 orbitals. Total of 10 electrons. Start at energy level n = 3.

The five 3d orbitals

Level n = 4 has a 4s, three 4p orbitals, five 4d orbitals and seven 4f orbitals n = 1 n = 2 n = 3 n = 4 1s 2s 3s 4s 2p 3p 4p 3d 4d 4f Energy Level Diagram for Hydrogen

f orbitals: 2 electrons per orbital. Total of 7 orbitals. Total of 14 electrons. Start at energy level n = 4.

The 4f orbitals

Energy level diagram for polyelectron atoms. #’s = n. Letters = type orbitals. Dashed lines = orbitals = 2 electrons per dashed lines.

Shell: the set of all orbitals having the same n value. 3 rd shell has 3s, 3p, and 3d Subshell: a set of orbitals of the same type 5 3d orbitals in the 3 rd shell

Look at the diagram on p153 For a given value of “n”, n different types of orbitals are possible. For n = 1: only the s- orbital is possible. For n = 2: the s – and p- orbitals are possible. For n = 3: the s-, p-, and d- orbitals are possible. For n = 4: the s-, p-, d-, and f- orbitals are possible

An s- subshell consists of 1 s- orbital. A p – subshell consists of 3 p- orbitals. A d- subshell consists of 5 d- orbitals. An f- subshell consists of 7 f- orbitals.

s subshell = 2 electrons p subshell = 6 electrons d subshell = 10 electrons f subshell = 14 electrons

Electron configuration Rules: –Add to orbitals having lowest energy first –Max of 2 electrons per orbital

Electron configuration