Chapter 5 Electrons in Atoms

Electrons Electrons have a negative charge. The maximum number of electrons that can fit in the FIRST energy level is TWO. The maximum number of electrons that can fit in the OUTER energy levels is EIGHT.

Octet Rule All atoms crave their outer energy level to be filled (with 8 electrons)—this known as the octet rule. is Hydrogen & Helium are the exception—they only need TWO electrons. Their first energy level IS their outer energy level, so they only need TWO to be “ filled. ” Atoms will gain, lose, share electrons in order to fulfill this rule. Once an atom has their outer energy level filled, the atom becomes unreactive. Atoms with filled energy levels are more stable (less reactive) than those atoms with half-filled energy levels.

Charges Protons = + Charge Electrons = - Charge Ions = atom with any charge (+ or -) O -2 8p & 10e H +1 1p & 0e F -1 9p & 10e Ba +2 56p & 54e Al +3 13p & 10e

4 Quantum Numbers 1- Energy Level 2- Sublevel 3- Oribital 4- Spin We will go over each one….

1 st Quantum Number An electron can occupy only specific energy levels. The greatest number of electrons possible in any one energy level is represented by the following formula: 2 n 2 “ n ” = number of energy levels (1,2,3…). The number of energy levels (n) is also known as the principal (first) quantum number (n). The period number (energy level) on the periodic table designates the principal quantum number. For example: Energy Level 1: Max. # Electrons: 2(1) 2 = 2 Energy Level 2: Max. # Electrons: 2(2) 2 = 8 Energy Level 3: Max. # Electrons: 2(3) 2 = 18

2 nd Quantum Number Energy Sublevels (second quantum number): An energy level is actually made of many energy states that are also closely grouped together. These states are called sublevels (l). The number of sublevels (l) for each energy level equals the value of the principal quantum number of that level. (For example: Level one will have 1 sublevel, Level 2 will have 2 sublevels, Level 3 will have 3 sublevels…)

Sublevels SublevelName# of Orbitals Max. Electrons Sublevels Present 1 st s12s 2 nd p36s, p 3 rd d510s, p, d 4thf714s, p, d, f

3 rd Quantum Number The third quantum number is represented by (m). It gives information about the orientation in space of an orbital.

4 th Quantum Number ♦ The fourth quantum number, (s), is the spin quantum number. Spin is either clockwise or counterclockwise. Designated +1/2 or -1/2 charge

Summary Energy Level Sublevels Present Max. Electrons in Sublevels Total2n 2 1s222 2s, p2, 688 3s, p, d2, 6, s, p, d, f 2, 6, 10, 14 32

Summary Quantum Number MeaningSymbol 1 st (principal) Energy leveln 2 nd Sublevell 3 rd Orbitalm 4thspins

Electron Configuration Five rules, or principles, define how an atom ’ s electrons are arranged in the atom ’ s orbitals.  aufbau principle  Pauli exclusion principle  Hund ’ s rule  Bohr ’ s model of the atom  Rutherford ’ s nuclear model

Electron Configuration The pathway into which electrons are arranged in atoms is through a process called electron configuration. Aufbau principle- electrons enter the lowest energy first. This causes difficulties because of the overlap of orbitals of different energies. Pauli Exclusion Principle- at most 2 electrons per orbital with opposite spins According to Bohr ’ s model of the atom, the lowest allowable energy state of an atom is known as the ground state.

Electron Configuration Rutherford is most famous for his Gold Foil experiment which proved that the electrons are located outside the nucleus and are floating around in a random and constant motion. Hund ’ s Rule- When electrons occupy orbitals of equal energy they don ’ t pair up until they have to. This means we fill each orbital with ONE electron and then if need be, pair them up.

Filling order Lowest energy fill first. The energy levels overlap The orbitals do not fill up order of energy level (1, 2, 3…). We will draw arrows to represent electrons.

Arrow Diagram

Electron Configuration Notation and Orbital Diagrams Orbital diagrams- This includes a box for each atom ’ s orbitals. Each box is labeled with the corresponding principle quantum number. Three different types of orbital boxes. EmptyHalf filled Full

Step-by-Step for Oxygen 1s 2s2p 1s 2s2p 1s2 2s2 2p4 Oxygen 1s2 2s2 2p4

Fill from the bottom up following the arrows 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s 7p 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 56 electrons

Write these electron configurations & orbital notations Titanium Helium Strontium Iron Sodium Chlorine Radium Hydrogen Selenium Vanadium Lithium Terbium Xenon Mercury

Lewis Dot Diagrams The Lewis dot diagram is used to draw outer electrons around the symbol of the element. The main concern will be the electrons in the outer energy level only. Because the Lewis Dot diagram is only concerned with outer energy level electrons, the maximum number of dots drawn is EIGHT.

Procedure for Drawing Lewis Dot Diagrams 1- Write the electron configuration of the element. 2- From the configuration, find all the electrons in the outer energy level. They will have the largest principal quantum number (1s2, 2s2, 3s2, 4s2). 3- Let the symbol represent the nucleus. 4- Each “ side ” of the symbol represents an orbital (top, bottom, left, right). Draw dots on the appropriate sides to represent the electrons in that orbital.

Lewis Dot Diagram Draw the Lewis Dot Diagram for the following elements: Potassium Beryllium Gallium Carbon Arsenic Sulfur Fluorine Argon