1 Electron Configurations and the Periodic Table Chapter 3 Section 2

2 Electron configuration – the arrangement of electrons in an atom The most important of these electrons are the valence electrons or outermost electrons. Electron Configurations

3 The number of valence electrons for all representative elements is determined by the number of the group in which the atom is found. Examples Hydrogen - Group IA or 1 –1 valence electron. Fluorine – Group VIIA or 17 – 7 valence electrons Valence Electrons

4 How many valence electrons do the following elements contain? A. Lithium B. Carbon C. Aluminum D. Sulfur E. Krypton NOW YOU TRY!

5 Valence electrons are important because they determine how atoms interact with each other to form compounds! So, who cares?

6 Arrangement of Electrons in Atoms according to the Quantum Mechanical Model Electrons in atoms are arranged as ENERGY LEVELS SUBLEVELSORBITALS

7 Energy Levels Think of the energy level as the relative distance from the nucleus. Currently, all electrons for known elements will occupy the first seven levels, but there is a possibility of infinite levels.Think of the energy level as the relative distance from the nucleus. Currently, all electrons for known elements will occupy the first seven levels, but there is a possibility of infinite levels

8 Sublevels AKA Subshells The sublevels are named s, p, d, and f and are listed in increasing energy.The sublevels are named s, p, d, and f and are listed in increasing energy. We specify both the energy level and sublevel when describing an electron, i.e. 1s, 2s, 2p.We specify both the energy level and sublevel when describing an electron, i.e. 1s, 2s, 2p.

9 Determining the number of sublevels The first energy level has 1 sublevel “1s”.The first energy level has 1 sublevel “1s”. The second energy level has 2 sublevels “2s and 2p”.The second energy level has 2 sublevels “2s and 2p”. How many sublevels exist on the 3 rd energy level?How many sublevels exist on the 3 rd energy level? What would they be called?What would they be called? 3 3s, 3p, & 3d

10 Orbitals Orbital – a specific region of a sublevel containing a maximum of 2 electrons. The p sublevel has 3 orbitals. They are called px, py, and pz. The p sublevel has 3 orbitals. They are called px, py, and pz. The s sublevel has 1 orbital. The d sublevel has 5 orbitals. The f sublevel has 7 orbitals.

11 Shapes of Orbitals Typical f orbital (flower) Typical s orbital (sphere) (peanut) (double peanut)

12 s sublevel d sublevel Number of orbitals Number of electrons p sublevel f sublevel 7 14 How many electrons can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital.

13 Aufbau Principle An electron occupies the lowest- energy orbital that can receive it. This guides how electron configurations are written.

14 Rules to Remember when Writing Electron Configurations 1.Obtain the number of total electrons from the periodic table. 2.Electrons occupy the lowest energy orbitals first. 3.Each energy level (n) only contains n sublevels. 4.The s sublevel holds 2 e-, the p 6 e-, the d 10 e-, and the f 14 e-. 5.Follow the filling pattern only moving once each sublevel is full.

15 Filling Pattern

16 Periodic Table Method Steps: Find the element for which you are writing the configuration. Starting with Hydrogen, write down the energy level and sublevel. Count the boxes in the sublevel and add it as a superscript. Continue moving through the sublevels until you reach your destination.

17 Electron Configurations 3d 7 Energy Level Sublevel Number of electrons in the sublevel 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 … etc.

18 Let’s Try It! Write the electron configuration for the following elements: H C N Br S

19 Let’s Try It! Write the electron configuration for the following elements: H1s 1 C1s 2 2s 2 2p 2 N1s 2 2s 2 2p 3 Br 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 S 1s 2 2s 2 2p 6 3s 2 3p 4

20 Noble Gas Notation A way of abbreviating long electron configurations Since we are only concerned about the outermost electrons, we can skip to places we know are completely full (noble gases), and then finish the configuration

21 Noble Gas Notation Step 1: Find the closest noble gas to the atom, WITHOUT GOING OVER the number of electrons in the atom. Write the noble gas in brackets [ ]. Step 2: Find where to resume by finding the next energy level (row in periodic table). Step 3: Resume the configuration starting with ns 2 where n is the next level

22 Noble Gas Notation Chlorine –Longhand is 1s 2 2s 2 2p 6 3s 2 3p 5 You can abbreviate the first 10 electrons with a noble gas, Neon. [Ne] replaces 1s 2 2s 2 2p 6 The next energy level after Neon is 3 So you start at level 3 on the diagonal rule (all levels start with s) and finish the configuration by adding 7 more electrons to bring the total to 17 [Ne] 3s 2 3p 5

23 Practice Noble Gas Notation Write the noble gas notation for each of the following atoms: Cl P O I

24 Practice Noble Gas Notation Write the noble gas notation for each of the following atoms: Cl[Ne]3s 2 3p 5 P[Ne]3s 2 3p 3 O[He]2s 2 2p 4 I[Kr]5s 2 4d 10 5p 5