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Lecture 16

CHMA10H3 Lecture Notes - Lecture 16: Electron Affinity, Electronegativity, Ion

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Marco Zimmer

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CHMA10- Lecture 16 (Feb. 15th)
Periodic Trends
Ionization Energy
Ionization Energy- amount of energy required to remove a ground state electron from a
gaseous atom
First ionization energy increases across a period
First ionization energy decreases down a group
Electron Affinity
Electron affinity- energy released when an atom gains an electron in the gaseous state
A measure of extent to which an atom can accept an extra electron
Either positive or negative depending on the element: a negative electron
affinity means that the electron is forced to “stick” and resulting anion will
spontaneously release the gained electron
Trends in electron affinity (similar to ionization energy)
1. Within a group, there is not much change
2. Within a period, there is a general increase
Three notable exceptions in EA trends include the following:
1. Group 2A (why? Added orbitals)
2. Group 5A (why? Electron-electron repulsion)
3. Group 8A (why? They’re already stable)
Highest EA values in any period occur for the halogens
How do elements stick together?
Elements stick together by forming chemical bonds
Sometimes, two elements can make more than on bond with each other (double or
triple bonds)
Why do elements form bonds?
o Energy can be stored in chemical bonds
o Elements by themselves are less stable when they are not chemically
bonded to other elements
What makes an atom chemical reactive?
Atoms that have incomplete valence shells are considered reactive atoms
Atoms may gain or lose electron or share electrons to other atoms
Types of chemical bonds
1. Ionic bonds- formed between ions; there is no electron sharing
2. Covalent bonds- formed between elements via sharing of electron
Electronegativity and the Periodic Table
Electronegativity- power of an element to attract electrons to itself when it is a part of a
Electronegativity generally increases from across a period
Electronegativity generally decreases down a group
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