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Electron Configuration. Electron Configuration: “ The ground-state distribution of electrons among the orbitals of a gaseous atom “. Two Rules Guide the Assignment of Electrons to Orbitals: At ground state the electrons fill the lowest energy orbitals available

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  1. Electron Configuration Electron Configuration: “ The ground-state distribution of electrons among the orbitals of a gaseous atom “ • Two Rules Guide the Assignment of Electrons to Orbitals: • At ground state the electrons fill the lowest energy orbitals available • No orbital can have more than two electrons • The true basis of the periodic table lies in the electron sublevels as • they are arranged in the table • Specific sublevels are filled in different regions of the table by group designation Groups Highest Occupied Energy Sublevel 1A (1) & 2A (2) s - orbitals 3A (13) to 8A (18) p - orbitals 3B to 8B (3 to 12) d - orbitals lanthanide and actinide series f - orbitals continue……. MC 8.1 Electrons in Atoms, Periodic Table

  2. p block s block d block f block 3 Electron Configuration & The Periodic Table Specific sublevels are filled in different regions of the periodic table by group designation continue…….

  3. Electron Configuration (cont) • Filling Orbitals In Order of Increasing Energy: • Follow the path described by the arrows starting in the upper left corner • Notice that the 4s sublevel fills before the 3d sublevel according to this method 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s continue…….

  4. Number Electronic Element of Electrons Configuration Electron Configuration (cont) • What are the Electron Configuration for Elements in the Periodic Table? Hydrogen 1 1s1 Helium 2 1s2 = [He] Lithium 3 1s2 2s1 Berylium 4 1s2 2s2 Boron 5 1s2 2s2 2p1 Carbon 6 1s2 2s2 2p2 Nitrogen 7 1s2 2s2 2p3 Oxygen 8 1s2 2s2 2p4 Fluorine 9 1s2 2s2 2p5 Neon 10 1s2 2s2 2p6 = [Ne] Helium Core Neon Core continue…….

  5. Number Electronic Element of Electrons Configuration Electron Configuration (cont) Electronic Configurations for 3rd Period Elements Sodium 11 1s2 2s2 2p6 3s1 Magnesium 12 [Ne] 3s2 Aluminum 13 [Ne] 3s2 3p1 Silicon 14 [Ne] 3s2 3p2 Phosphorus 15 [Ne] 3s2 3p3 Sulfur 16 [Ne] 3s2 3p4 Chlorine 17 [Ne] 3s2 3p5 Argon 18 [Ne] 3s2 3p6 = [Ar] or [Ne] 3s1 Neon Core Argon Core continue…….

  6. Number Electronic Element of Electrons Configuration Electron Configuration (cont) • Electronic Configurations for 4th Period Elements • Fill the 4s orbital before the 3d orbitals Potassium 19 [Ar] 4s1 Calcium 20 [Ar] 4s2 Scandium 21 [Ar] 4s2 3d1 Titanium 22 [Ar] 4s2 3d2 Vanadium 23 [Ar] 4s2 3d3 Zinc 30 [Ar] 4s2 3d10 Gallium 31 [Ar] 4s2 3d10 4p1 Germanium 32 [Ar] 4s2 3d10 4p2 Bromine 35 [Ar] 4s2 3d10 4p5 continue…….

  7. Electronic Valence Element Configuration Electron(s) Electronic Valence Element Configuration Electron(s) Valence Electrons • Valence Electrons: “ The total number of s and p electrons in the highest occupied energy level “ Sodium 1s2 2s2 2p6 3s1 3s1 • The 3rd level is the highest occupied energy level • The 3s1 electron is the one and only valence electron Oxygen 1s2 2s2 2p4 2s2 2p4 • The 2ND level is the highest occupied energy level. • The 2s2 2p4 electrons are the valence electrons (6 total) continue……. MC 8.1 Electrons in Atoms, Periodic Table

  8. Electronic Valence Element Configuration Electron Valence Electrons (cont) • Group Trends: “ Down any group the type and number of • valence electrons is the same “ Example: Group 1A Elements Lithium [He] 2s12s1 Sodium [Ne] 3s1 3s1 Potassium [Ar]4s1 4s1 Rubidium [Kr] 5s1 5s1 Cesium [Xe] 6s1 6s1 Common Designation ns1 All Group 1A Elements Have One Valence Electron in an s - orbital continue…….

  9. Electronic Valence Element Configuration Electrons Valence Electrons (cont) • Group Trends: “ Down any group the type and number of • valence electrons is the same “ Example: Group 6A Elements Oxygen [He] 2s2 2p4 2s2 2p4 Sulfur [Ne] 3s2 3p4 3s2 3p4 Selenium [Ar] 4s2 3d10 4p4 4s2 4p4 Tellurium [Kr] 5s2 4d10 5p4 5s2 5p4 Common Designation ns2 np4 All Group 6A Elements Have Six Valence Electrons in s and p - orbitals continue…….

  10. Valence Electrons (cont) • Another way to show valence electrons is to use Lewis Symbols • Lewis Symbols: “ The element displayed with an electron dot • symbol to show the valence electrons “ Group E.C. No V. e- Lewis Symbol 3A ns2np1 3 . . B . 4A ns2np2 4 . . C . . 5A ns2np3 5 . . N : . 6A ns2np4 6 . : O : . 7A ns2np5 7 . : F : . . 8A ns2np6 8 . . : Ne : . . 1A ns1 1 Li . 2A ns2 2 . Be. E.C. = Electron Configuration No V. e-= Number of Valence Electrons continue……. MC 8.1 Electrons in Atoms, Periodic Table

  11. Na (g) Na + (g) + e - Trends in the Periodic Table • Ionization Energy: “ The energy required to remove an electron • from a gaseous atom of an element “ Example: Change in Electronic Configuration The Sodium Ion (+) Now Has the Electronic Configuration Of Neon continue…….

  12. Trends in the Periodic Table (cont) • How Does the Ionization Energy Change Relative to the Position • Of Elements in the Periodic Table? • There are three peaks: He, Ne & Ar (Group 8A elements) • The Ionization Energy is Highest for the Noble Gases The low points occur for Li, Na and K (Group 1A elements) • The Ionization Energy is Lowest for the Alkali Metals continue…….

  13. Trends in the Periodic Table (cont) Across a Period (Red Line) Period 2 Period 1 Period 3 • In general, ionization energy increases with increasing • atomic number across a period • This is a general trend - There are exceptions (Be > B, N > O, Mg > Al, P > S) continue…….

  14. Trends in the Periodic Table (cont) • Down a Group (Blue Lines): • Ionization energy decreases going down a group (blue lines) • Li > Na > K • Be > Mg > Ca • He > Ne > Ar continue……. MC 8.1 Electrons in Atoms, Periodic Table

  15. Trends in the Periodic Table (cont) • Ionization Energy decreases going down a group • Li > Na > K ( > Rb > Cs) • Be > Mg > Ca • He > Ne > Ar • Down a Group (Blue Lines) - cont: Explaination: • The higher the principal energy level in which the ns1 electron • is located the farther it is from the nucleus • The farther the electron is from the positively charged nucleus • the more easily it is removed Reactivity: “ The tendency for an element to react with other elements to form compounds “ • The reactivity is highest for Cesium and lowest for lithium • Reactivity Order: Cs > Rb > K > Na > Li continue……. MC 8.1 Electrons in Atoms, Periodic Table

  16. Trends in the Periodic Table (cont) • Isoelectronic: “ Elements and ions of elements are isoelectronic when they have the same electronic configuration “ Example: Isoelectronic Configurations Ne = 1s2 2s22p6 Na = 1s2 2s22p6 3s1 Na+= 1s2 2s22p6 Mg = 1s2 2s22p6 3s2 Mg2+= 1s2 2s22p6 Sodium ion (+) is isoelectronic with Neon Magnesium ion (2+) is isoelectronic with sodium ion (+) and neon The Chemical Properties of Many Elements Can Be Explained in Terms of Their Atoms Becoming Isoelectronic with a Noble Gas Atom continue……. MC 8.1 Electrons in Atoms, Periodic Table

  17. Ca (g) Ca+ (g) + e- Ca+ (g) Ca2+ (g) + e- Trends in the Periodic Table (cont) • Group 2A Elements: ns2 Alkaline Earths (Be, Mg, Ca, Sr, Ba, Ra), First Ionization Step Second Ionization Step Electronic Configuration: Calcium 2+ ion is isoelectronic with Argon Ca2+= 1s2 2s22p6 3s23p6 = [Ar] Group 2A Elements Always Form Compounds In Which the Element is in the Plus 2 State (Isoelectronic With a Noble Gas Electronic Configuration) continue……. MC 8.1 Electrons in Atoms, Periodic Table

  18. Trends in the Periodic Table (cont) • The Halogens have 7 valence electrons (ns2p5 ) • The easiest way for the halogens to reach a noble gas • electronic configuration is by gaining an electron • Group 7A Elements: ns2p5 Halogens (F, Cl, Br, I) F + e- F- Cl + e- Cl- Electronic Configuration: F- = 1s2 2s22p6 = [Ne] Fluoride ion (-) is isoelectronic with Neon Chloride ion (-) is isoelectronic with Argon Cl- = 1s2 2s22p6 3s23p6 = [Ar] • The tendency to gain an electron is greatest for small atoms • The added electron will be closer to the nucleus • Reactivity Order: F > Cl > Br > I continue……. MC 8.1 Electrons in Atoms, Periodic Table

  19. Trends in the Periodic Table (cont) • Group 8A Elements: ns2p6 Noble Gases (He, Ne, Ar, Kr, Xe, Rn) The noble gases have 8 valence electrons (ns2p6 ) • In chemistry the word noble means: “ A reluctance to react “ • The low reactivity is attributed to the fact that the • valence shell is completely filled • This configuration represents a “ minimization of energy “ • arrangement of electrons that is very stable • Evidence for low reactivity of Noble Gases: • High ionization energies (the highest in the period) • Low tendency to gain an electron • The noble gases all appear in nature by themselves, • they are not combined with other elements continue……. MC 8.1 Electrons in Atoms, Periodic Table

  20. Trends in the Periodic Table (cont) • Hydrogen: A Unique Element 1s1 Shown Over Group 1A & 7A • Hydrogen is neither an alkali metal nor a halogen • However, hydrogen does show reactions that are • similar to both alkali metals and halogens Alkali Metal Reaction: . . . Cl : . . . . Na : Cl : . . Na . + Hydrogen Reaction: . . . Cl : . . . . H : Cl : . . H . + continue……. MC 8.1 Electrons in Atoms, Periodic Table

  21. H . + e- H : - or H -called hydride H . + Na . Na : H Trends in the Periodic Table (cont) Hydrogen: A Unique Element 1s1 Shown Over Group 1A & 7A Hydrogen can also gain an electron to form an ion with a 1- charge Electronic Configuration: Hydride ion has the same electronic configuration as helium H -= 1s2 = [He] Hydrogen reaction with sodium: continue……. MC 8.1 Electrons in Atoms, Periodic Table

  22. Trends in the Periodic Table (cont) • Atomic Size: • Moving down a group size increases • Moving across a period (row) size decreases continue……. MC 8.1 Electrons in Atoms, Periodic Table

  23. Trends in the Periodic Table (cont) • Atomic Size: • Moving down a group size increases • Moving across a period (row) size decreases There are two influences that give the observed trends in size: • First Influence • Electrons in higher principal energy levels are farther from the nucleus and experience less interaction with the positive charge of the nucleus than electrons in lower principal energy levels • Atomic size increase as the highest occupied • energy level increases • Second Influence • As valence electrons increase, the number of protons in the nucleus also increases. The valence electrons are held closer to the nucleus as the nuclear charge increases. End…….. MC 8.1 Electrons in Atoms, Periodic Table

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