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

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