Matter Trends and Chemical Bonding Expectations: B2.2, B Periodic Trends and Atomic Properties

Learning Goals By the end of this class I will… Describe and explain periodic trends related to: – Atomic radii – Ionic radii – Ionization Energy – Electron Affinity

Last Class Reviewed ways in which the periodic table is organized Reviewed periodic table groups/families Conducted an investigation in which we determined that the atomic radii – Increases as you go down a group – Decreases as you go across a period

Atomic Radius Atomic Radius: Distance from the nucleus of an atom to the valence electrons Measured in picometers (pm) * 1 pm = 1 x m, m Atomic radii increases as you go down a group – why?

Atomic Radius Atomic Radius: Distance from the nucleus of an atom to the valence electrons Measured in picometers (pm) * 1 pm = 1 x m, m Atomic radii increases as you go down a group – another energy level added as you go down a group

Atomic Radius Atomic Radii decreases as you go across a period – Why?

Atomic Radius Atomic Radii decreases as you go across a period – A result of the increasing positive charge of the nucleus – increased attraction pulls the electrons closer to the nucleus resulting in a smaller atomic radius

Atomic Radius TLDR: Atomic radius increases down a group decreases across a period

Ionic Radius Recall: Ions are formed when an atom gains or loses an electron Ionic radius describes the size of an ion Ionic radius can be larger or smaller than the atom’s atomic radius – Cations = bigger or smaller? – Anions = bigger or smaller?

Ionic Radius Recall: Ions are formed when an atom gains or loses an electron Ionic radius describes the size of an ion Ionic radius can be larger or smaller than the atom’s atomic radius – Cations = smaller than their neutral atoms – Anions = bigger than their neutral atoms

Ionization Energy and Electron Affinity Valence electrons are held to the atom by their attractive forces – Removing electrons requires energy – Gaining electrons releases energy

Ionization Energy Ionization energy (IE): the amount of energy required to remove a single valence electron from an atom/ion – General equation: X (g) + energy → X + (g) + e – Based on what you know about atomic size – What do you predict the trend for IE is as you… – Go down a group? Why? – Go across a period? Why?

Ionization Energy Decreases as you go down a group – less energy required – attraction between the electron and the nucleus decreases as atomic radius increases Increases as you go across a period – more energy required – as atomic radius decreases, the pull on the outermost electrons increases

Electron Affinity Electron Affinity (EA): the amount of energy released when an atom gains an electron – General equation: X (g) + e – → X – (g) + energy – The higher the EA, the easier it is to add an electron to an atom Based on what you know about atomic size – What do you predict the trend for EA is as you… – Go down a group? Why? – Go across a period? Why?

Electron Affinity Decreases as you go down a group – less energy released – Decreased attraction between nucleus and valence shell Increases as you go across a period – more energy released – Greater attraction forces by the nucleus to draw in an electron

Periodic Trends

Homework Page 41 #2-6