Matter Trends and Chemical Bonding Expectations: B2.2, B3.3 1.7 Periodic Trends and Atomic Properties
Jan 19, 2016
Matter Trends and Chemical Bonding
Expectations: B2.2, B3.3
1.7 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 10-12 m, 0.000000000001m
• 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 10-12 m, 0.000000000001m
• 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