Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net

Erwin Schrödinger (1926) Quantum mechanics – electrons can only exist in specified energy states Electron cloud model – orbital: region around the nucleus where e - are likely to be found

Erwin Schrödinger (1926) Electron Cloud Model (orbital) dots represent probability of finding an e - not actual electrons

Why Are Electrons location Important  Their arrangement around the nucleus determines an atom’s chemical ability

Quantum Numbers  Def: Where electrons are located in an atom  There are four quantum numbers, each describing a different aspect of the orbiting electron.

First Quantum Number The Principle Quantum Number  Describes the distance from the nucleus.  Referred to as energy levels. 3rd energy level 2nd energy level

Second Quantum Number aka sublevels  Describes the shape of the atom  There are four shapes, based on the movement of the electrons S P D F Too weird to show

Third Quantum Number  Orbitals  Describes the number of electrons each sublevel can hold

 s orbital can hold 2 electrons  Orbital: a space that can be occupied by 0, 1, or 2 electrons.  P orbital can hold 6 electrons  d orbital can hold 10 electrons  f orbital can hold 14 electrons

Fourth Quantum Number  Symbol =  describes the spin of the electron  They can either spin clockwise or counterclockwise.  No two electrons can have the same set of all four quantum numbers electrons must spin in opposite directions! Ms

spdfspdf spdspd spsp 2 221s1 Number of electrons per main energy level (2n 2 ) Number of Electrons per sublevel Number of orbitals per sublevel Sublevels in main energy level (n sublevels) Energy Level (n) Energy Levels, Sublevels, Electrons

Feeling overwhelmed? Read Section 4-2!

Electron Configuration of Sodium For example, here is the ground- state configuration of sodium: Na Sodium Atom 1s2 2s2 2p6 3s1

2 types of electron notation 1. Long hand 2. Short hand

Purpose of electron notation Find valence electrons valence electron – electrons located in outer energy level

S 16e - Valence Electrons Core Electrons 1s 2 2s 2 2p 6 3s 2 3p 4 B. Notation Longhand Configuration

C. Periodic Patterns Period # – energy level A/B Group # – equals the total # of valence e - Column within sublevel block – # of e - in sublevel

Energy of Orbitals

s-block1st Period 1s 1 1st column of s-block C. Periodic Patterns Example - Hydrogen

Shorthand Configurations (1) Start with the last element on the previous row in brackets [ ]. (2) Find the difference in numbers of electron. (3) Add the remaining electrons by starting at the s orbital of the row that the element is in. Na = [Ne]3S 1

Fill in Shorthand Configurations 

1 A neutral atom has electron configuration 1s22s22p63s23p2. What element is this? A carbon B nitrogen C silicon Dgermanium EI don't know how to answer this.

2 A neutral atom has an electron configuration of 1s22s22p63s23p2. What is its atomic number? A 5 B 11 C 14 D 20 E I don't know how to answer this.

3 A neutral atom has an electron configuration of 1s22s22p6. If a neutral atom holds one additional electron, what is the ground state configuration? A 1s22s22p63s1 B 1s22s22p7 C 1s22s32p6 D none of the given answers E I don't know how to answer this.

4 What is the electron configuration for Li which has three electrons? A 1s3 B 1s12s2 C 1s22s1 D 1s21p1  E I don't know how to answer this.

Stability When the elements were studied it was notices that some of them do not react in certain situations in which others do. These elements were labeled "stable" because they did not change easily. When these stable elements were grouped together, it was noticed that periodically, there were patterns in the occurrence of stable elements. Today we recognize that this difference in stability is due to electron configurations.

Stability When the elements were studied it was notices that some of them do not react in certain situations in which others do. These elements were labeled "stable" because they did not change easily. When these stable elements were grouped together, it was noticed that periodically, there were patterns in the occurrence of stable elements. Today we recognize that this difference in stability is due to electron configurations.

1 A 2A 8A A 4A 5A 6A 7A B 3B 4B 5B 6B 7B 1B 2B } Group Numbers There are two methods for labeling the groups, the older method shown in black on the top and the newer method shown in blue on the bottom.

Stability Elements of varying stability fall into one of 3 categories. The most stable atoms have completely full energy levels.

Stability Next in order of stability are elements with full sublevels.

Stability Finally, the elements with half full sublevels are also stable, but not as stable as elements with fully energy levels or sublevels.