Quantum Model & Configurations

Transcription

1 Quantum Model & Configurations

2 Bohr s Energy Levels: Bohr was able to tell us the electrons are found in layers around the nucleus based on the following: Each element gives off a unique emission spectrum after it absorbs energy. Each emission is a partial spectrum that shows bands of visible light with distinct wavelengths Bohr proposed that each band of light in the spectrum represented an energy change for the electrons in the space surrounding the nucleus.

3 Bohr s Energy Levels: Bohr was able to construct the planetary model of the atom based on the following: Using Planck s energy equation and constant we can determine the electrons can only experience certain energy changes In other words, electrons jump back and forth, between energy levels in the cloud From these observations and calculations we end up with electrons rotating around the nucleus like the planets around the sun.

4 Bohr s Energy Levels: In summary, Bohr was able to prove that electrons exist in layers and that the electrons move from one energy level to the next by absorbing or releasing energy. The electrons can only jump in whole level increments.

5 Bohr s Energy Levels: The energy level where an electron is found in its non-excited state is called its ground state The higher energy level that the electron exists in once it has absorbed energy is called its excited state Light is given off by an atom when the electron returns to the ground state from the excited state

6 So how do we know where the electrons go? Electrons in an atom are arranged by: Energy Levels Sublevels Orbitals We will explore how this system and the atomic number can tell us where the electrons belong in the cloud.

7 Energy Levels If you look at the periodic table you will see there are 7 rows that correspond to the seven ground state energy levels. The row on the table where the element is found tells us how many layers/energy levels are in the electron cloud of that element s atoms.

8 Capacities of Energy Levels Here is a quick formula to determine the # of electrons that each energy level can hold # e- in an EL = 2(EL#) 2

9 From Energy levels to Orbitals Before we can go to the next level (sublevels) we need to look at what ideas proposed by: Heisenberg: determined that it is not possible to know an electron s location and speed/direction simultaneously the uncertainty principle Schrödinger: Though we can t know the exact location of an electron in the cloud, there are areas where you are more likely to find them they are referred to as orbitals

10 Sublevels = Types of Orbitals According to Schrödinger, there are four types of orbitals: s, p, d & f Each sublevel contains a different # of orbitals s has 1 orbital p has 3 orbitals d has 5 orbitals f has 7 orbitals Each orbital can hold 2 electrons To determine the number of electrons each sublevel can hold multiply the # orbitals by 2 In order of lowest to highest energy they fill up s, p, d, f.

11 The s sublevel/orbital The s orbitals are spherical in shape whose center is the nucleus. Every energy level contains one s-orbital s-orbitals from higher energy levels encapsulate the lower energy level s-orbitals

12 The p sublevel/orbital The p orbitals align themselves with the x, y and z axis with a node or area of zero probability at the origin (aka the nucleus) There are 3 p orbitals in the p sublevel P x (along the x axis) P y (along the y axis) P z (along the z axis)

13 The p orbitals

14 The d sublevel/orbitals The d sublevel has 5 orbitals that typically fall between the x/y, x/z and y/z axis The d sublevel can hold 10 electrons in its 5 orbitals

15 The f sublevel/orbitals The f orbitals are the next highest energy There are 7 orbitals that can hold 14 e- in this sublevel orientations are here These shapes are very complex and thus require high energy

16 How many electrons can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital. s sublevel p sublevel d sublevel f sublevel Number of orbitals Total # of electrons in each sublevel

17 Filling Order of Sublevels Use the Diagonal Rule to help you determine the order in which electrons are placed in each sublevel. The Aufbau principle states electrons must fill the lowest available energy orbital first.

18 s s 2p s 3p 3d Diagonal Rule s 4p 4d 4f Steps: s 5p 5d 5f 5g? s 6p 6d 6f 6g? 6h? 1. Write the energy levels top to bottom. 2. Write the orbitals in s, p, d, f order. Write the same number of orbitals as the energy level. 3. Draw diagonal lines from the top right to the bottom left. 4. To get the correct order, follow the arrows! s 7p 7d 7f 7g? 7h? 7i? After 7p, we are past the current periodic table so we can stop.

19 Why are d and f orbitals always in lower energy levels? d and f orbitals require LARGE amounts of energy It s better to skip a d or f sublevel that requires a large amount of energy for a lower energy s or p from a higher energy level This is the reason for the diagonal rule! BE SURE TO FOLLOW THE ARROWS IN ORDER!

20 Electron Configurations A list of all the electrons in an atom (or ion) Must go in order (Aufbau principle) 2 electrons per orbital, maximum We need electron configurations so that we can determine the number of electrons in the outermost energy level. These are called valence electrons The number of valence electrons determines how many and what this atom (or ion) can bond to in order to make a molecule 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.

21 Electron Configurations 2p 4 Energy Level Number of electrons in the sublevel 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.

22 Orbital Diagrams Graphical representation of an electron configuration One arrow represents one electron Shows spin and which orbital within a sublevel Same rules as before (Aufbau principle, d 4 and d 9 exceptions, two electrons in each orbital, etc. etc.)

23 Orbital Diagrams One additional rule: Hund s Rule In orbitals of EQUAL ENERGY (p, d, and f), place one electron in each orbital before making any pairs All single electrons must spin the same way I nickname this rule the Monopoly Rule In Monopoly, you have to build houses EVENLY. You can not put 2 houses on a property until all the properties has at least 1 house.

24 Lithium Group 1A Atomic number = 3 1s 2 2s 1 ---> 3 total electrons 3s 2s 3p 2p 1s

25 Carbon 3s 2s 1s 3p 2p Group 4A Atomic number = 6 1s 2 2s 2 2p 2 ---> 6 total electrons Here we see for the first time HUND S RULE. When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible.

26 Lanthanide Element Configurations 4f orbitals used for Ce - Lu and 5f for Th - Lr

27 The Shape of the Periodic Table The PT is shaped the way it is because there are four major regions that are placed relative to one another. We call these regions Blocks but they actually help us determine the type of orbital the element s electrons are in especially their valence electrons.

28 Orbitals and the Periodic Table Orbitals grouped in s, p, d, and f orbitals (sharp, proximal, diffuse, and fundamental) s orbitals d orbitals p orbitals f orbitals

29 Why only 8 valence e-? If you look at the 4 th EL you will see that there are 18 elements in the period. BUT there are only 8 valence electrons. WHY? Because the elements in groups 3 12 are in the lower, 3 rd EL. Therefore there are only 8 electrons on the highest energy level EL 4.

30 Valence & Core Electrons Valence electrons are the electrons in the highest energy level (those farthest from the nucleus). Core electrons are all other electrons that are not found on the highest energy level. Valence electrons are the only electrons that take part in reactions. Thus the # valence electrons will determine the properties of the element. Every Group has a distinct # of valence electrons.

31 Lewis Dot Notation This is a way to show the number of electrons in the highest energy levels without having to draw the full Bohr Model of the atom

32 To Make a Lewis Dot Write the element symbol from the Periodic Table. Determine the # of Valence Electrons by looking at the group #. Show the electrons with X around the symbol in the 12, 3, 6 & 9 positions. P

33 Valence Electrons by Groups Group 1 1 e- Group 2 2 e- Group e- (refer to s/p/d/f blocks) Group 13 3 e- Group 14 4 e- Group 15 5 e- Group 16 6 e- Group 17 7 e- Group 18 8 e-