Sublevels in Each Energy Level

Transcription

1 Sublevels in Each Energy Level Principal energy level (n) Possible subshells 1 1s 2 2s, 2p 3 3s, 3p, 3d 4 4s, 4p, 4d, 4f

2 Orbitals Orbital - a specific region of a sublevel containing a maximum of two electrons Orbitals are named by their sublevel and principal energy level 1s, 2s, 3s, 2p, etc. Each type of orbital has a characteristic shape s is spherically symmetrical p has a shape much like a dumbbell

3 Orbital Shapes s is spherically symmetrical

4 Orbital Shapes Each p has a shape much like a dumbbell, differing in the direction extending into space

5 Orbital Shapes There are five different d shapes. The f orbitals have seven different shapes, too complicated and therefore seldom shown.

6 Electron Arrangement and the Periodic Table Electron Spin Electron Configuration -the arrangement of electrons in atomic orbitals Aufbau Principle -or building up principle helps determine the electron configuration Electrons fill the lowest-energy orbital that is available first Remember s<p<d<f in energy When the orbital contains two electrons, the electrons are said to be paired

7 Subshell Number of orbitals s 1 p 3 d 5 f 7 How many electrons can be in the 4d subshell? 10 Electron Arrangement and the Periodic Table

8 Rules for Writing Electron Configurations Obtain the total number of electrons in the atom from the atomic number Every electron has a place to stay Electrons in atoms occupy the lowest energy orbitals that are available 1s first Each principal energy level, n contains only n sublevels Each sublevel is composed of orbitals No more than 2 electrons in any orbital Maximum number of electrons in any principal energy level is 2(n) 2

9 Electron Distribution This table lists the number of electrons in each shell for the first 20 elements Note that 3 rd shell stops filling at 8 electrons even though if could hold more

10 Electron Distribution

11 Writing Electron Configurations H Hydrogen has only 1 electron It is in the lowest energy level & lowest orbital Indicate number of electrons with a superscript 1s 1 Li Lithium has 3 electrons First two have configuration of helium 1s 2 3 rd is in the orbital of lowest energy in n=2 1s 2 2s 1

12 Electron Arrangement and the Periodic Table Shorthand Electron Configurations Uses noble gas symbols to represent the inner shell and the outer shell or valance shell is written after Aluminum- full electron configuration is: 1s 2 2s 2 2p 6 3s 2 3p 1 What noble gas configuration is this? Neon Configuration is written: [Ne]3s 2 3p 1

13 Remember: How many subshells are in each principal energy level? There are n subshells in the n principal energy level. How many orbitals are in each subshell? s has 1, p has 3, d has 5, and f has 7 How many electrons fit in each orbital? 2 Hence: s can have 2, p 6, d 10 and f 14 electrons

14 Remember: How many electrons is subshells? There are n subshells in the n principal energy level. s up to 2, p up to 6, d up to 10, f up to 14 electrons Therefore: for n=1: s subshell - up to 2 electrons for n=2: s and p subshells - up to 8 electrons for n=3: s, p, and d subshells - up to 18 electrons for n=4: s, p, d and f subshell, up to 32 electrons

15 Classification of Elements According to the Type of Subshells Being Filled Electron Arrangement and the Periodic Table

16 The Octet Rule [eight in Latin of Greek - octo, οκτώ ocho] The noble gases are extremely stable Called inert as they don t readily bond to other elements The stability is due to a full complement of valence electrons in the outermost s and p sublevels: 2 electrons in the 1s of helium the s and p subshells full in the outermost shell of the other noble gases (eight electrons)

17 Octet of Electrons The Octet Rule Elements in families other than the noble gases are more reactive Strive to achieve a more stable electron configuration Change the number of electrons in the atom to result in full s and p sublevels Stable electron configuration is called the noble gas configuration

18 The Octet Rule The Octet Rule Octet Rule - elements usually react in such a way as to attain the electron configuration of the noble gas closest to them in the periodic table Elements on the right side of the table move right to the next noble gas Elements on the left side move backwards to the noble gas of the previous row Atoms will gain, lose or share electrons in chemical reactions to attain this more stable energy state

19 Ion Formation and the Octet Rule The Octet Rule Metallic elements tend to form positively charged ions called cations Metals tend to lose all their valence electrons to obtain a configuration of the noble gas Na Sodium atom 11e -, 1 valence e - [Ne]3s 1 Na + + e - Sodium ion 10e - [Ne]

20 Cation Formation Na Sodium atom 11e -, 1 valence e - [Ne]3s 1 Na + + e - Sodium ion 10e - [Ne] Energy required to remove an electron from an isolated atom, to form a cation is called the ionization energy

21 Ion Formation and the Octet Rule The Octet Rule All atoms of a group lose the same number of electrons Resulting ion has the same number of electrons as the nearest (previous) noble gas atom Al Aluminum atom 13e -, 3 valence e - [Ne]3s 2 3p 1 Al e - Aluminum ion 10e - [Ne] Formation of a cation, positively charged species with a missing electron(s)

22 Using the Octet Rule The Octet Rule The octet rule is very helpful in predicting the charges of ions in the representative elements Transition metals still tend to lose electrons to become cations but predicting the charge is not as easy Transition metals often form more than one stable ion Iron forming Fe 2+ and Fe 3+ is a common example

23 Examples Using the Octet Rule The Octet Rule Give the charge of the most probable ion resulting from these elements Ca Sr S P Which of the following pairs of atoms and ions are isoelectronic? Cl -, Ar Na +, Ne Mg 2+, Na + O 2-, F -

24 Calculating Subatomic Particles Composition of the Atom K S Mg in Ions How many protons, neutrons and electrons are in the following ions?

25 Trends in the Periodic Table Many atomic properties correlate with electronic structure and so also with their position in the periodic table atomic size ion size ionization energy electron affinity

26 Atomic Size Trends in the Periodic Table The size of an element increases moving down from top to bottom of a group The valence shell is higher in energy and farther from the nucleus traveling down the group The size of an element decreases from left to right across a period The increase in magnitude of positive charge in nucleus pulls the electrons closer to the nucleus

27 Variation in Size of Atoms Trends in the Periodic Table

28 Cation Size Trends in the Periodic Table Cations are smaller than their parent atom More protons than electrons creates an increased nuclear charge Extra protons pulls the remaining electrons closer to the nucleus Ions with multiple positive charges are even smaller than the corresponding monopositive ions Which would be smaller, Fe 2+ or Fe 3+? Fe 3+ When a cation is formed isoelectronic with a noble gas the valence shell is lost decreasing the diameter of the ion relative to the parent atom

29 Anion Size Trends in the Periodic Table Anions are larger than their parent atom. Anions have more electrons than protons Excess negative charge reduces the pull of the nucleus on each individual electron Ions with multiple negative charges are even larger than the corresponding monopositive ions

30 Relative Size of Select Ions and Their Parent Atoms Trends in the Periodic Table

31 Ionization Energy Trends in the Periodic Table Ionization energy - The energy required to remove an electron from an isolated atom The magnitude of ionization energy correlates with the strength of the attractive force between the nucleus and the outermost electron The lower the ionization energy, the easier it is to form a cation ionization energy + Na Na + + e -

32 Ionization Energy of Select Elements Trends in the Periodic Table Ionization decreases down a family as the outermost electrons are farther from the nucleus Ionization increases across a period because the outermost electrons are more tightly held Why would the noble gases be so unreactive?

33 Electron Affinity Trends in the Periodic Table Electron Affinity - The energy released when a single electron is added to an isolated atom Electron affinity gives information about the ease of anion formation Large electron affinity indicates an atom becomes more stable as it forms an anion Br + e - Br - + energy Formation of an anion, negatively charged species with an extra electron

34 Periodic Trends in Electron Trends in the Periodic Table Affinity Electron affinity generally decreases down a group Electron affinity generally increases across a period

35 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Structure and Properties of Ionic and Covalent Compounds Denniston Topping Caret 6 th Edition

36 3.1 Chemical Bonding Chemical bond - the force of attraction between any two atoms in a compound This attractive force overcomes the repulsion of the positively charged nuclei of the two atoms participating in the bond Interactions involving valence electrons are responsible for the chemical bond

37 Lewis Symbols Lewis symbol (Lewis structure) - a way to represent atoms using the element symbol and valence electrons as dots As only valence electrons participate in bonding, this makes it much easier to work with the octet rule The number of dots used corresponds directly to the number of valence electrons located in the outermost shell of the atoms of the element

38 Lewis Symbols Each side of the symbol represents an atomic orbital, which may hold up to two electrons Using Lewis symbols Place one dot on each side until there are four dots around the symbol Now add a second dot to each side in turn The number of valence electrons limits the number of dots placed Each unpaired dot (unpaired electron of the valence shell) is available to form a chemical bond