# Lecture 2611/04/05. 1) Write the spdf notation for Cl. 2) Which element is larger: Si or Ar?

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Lecture 2611/04/05

1) Write the spdf notation for Cl. 2) Which element is larger: Si or Ar?

Trends in Ionization Energy IE increases across a period because Z* increases. Metals lose electrons more easily than nonmetals.

Trends in Ionization Energy IE decreases down a group Size increases  easier to lose an electron

Electron Affinity Electron affinity is the energy involved when an atom gains an electron to form an anion. A(g) + e- ---> A - (g) E.A. = ∆E

Electron Affinity of Oxygen ∆E is exothermic [He]      O atom EA = - 141 kJ + electron O [He]       - ion

Electron Affinity of Nitrogen ∆E is zero for N - due to electron-electron repulsions. EA = 0 kJ [He]     Natom  [He]    N - ion  + electron

Trends in Electron Affinity Electron affinity becomes more negative across a period Electron affinity becomes less negative down a group (except for some elements going from n=2 to n=3).

Fill in the table On ChEM ElementAtomic radius (pm) 90 120 140 180

Compare the elements Na, Mg, and P. a) Which has the largest atomic radius? b) Which has the most negative electron affinity? c) Place the elements in the order of increasing ionization energy.

A = [Ar]4s 2 B = [Ar]3d 10 4s 2 4p 5 a) Is element A a metal, metalloid, or nonmetal? b) Is element B a metal, metalloid, or nonmetal? c) Which element is expected to have a larger ionization energy? d) Which element has a smaller atomic radius?

Valence Electrons Electrons in the outermost shell Determines the chemical properties of atoms Reactions involve loss, gain, or rearrangement of electrons Core Electrons Electrons in the inner shells Not involved in chemical reactions

Main group elements: Valence electrons = s and p electrons in outermost shell Valence electrons are equal to the group number Transition elements: Valence electrons = ns and (n-1)d electrons Valence electrons are equal to the group number Valence electrons

Valence Electrons B 1s 2 2s 2 2p 1 Core = [He], valence = 2s 2 2p 1 Br [Ar] 3d 10 4s 2 4p 5 Core = [Ar] 3d 10, valence = 4s 2 4p 5

Example Write the spdf, noble gas, and electron orbital notation for carbon. Which are the valence electrons? Which are the core electrons?

Lewis Electron Dot Symbols Represents valence shell electrons Arrange electrons in pairs around the atom Maximum of eight electrons Octet rule

Example Write the Lewis Dot Symbols for: Nitrogen Phosphorous

Bonds 1. Atoms achieve noble gas configuration 1. Quest for complete octet 2. Products tend to have a lower chemical potential than the reactants 3. The bond that forms has the lowest potential energy (greatest stability)

Bonding Quest for complete octet Covalent bonds: Molecular compounds Sharing of valence electrons Cl 2

Ionic bond Ionic compounds Valence electrons are transferred from one atom to another Metal + non-metal NaCl Bonding

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