Date:
Topic/Objective:
Valence Electrons and Reactivity
Essential Question: How do atoms interact with each other?
Questions:
How do atoms join together?
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Chemical Bond – an interaction that holds atoms or ions together.
Molecule – a group of atoms that are held together by chemical bonds.
What happens to atoms during chemical changes?
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Atoms are NOT created or destroyed
Atoms are rearranged to make new substances with different properties.
Chemical bonds have to be formed or broken
A Model Atom – What do different atom models show?
The Electron Cloud Model - Shows how electrons are found in a region around the
nucleus called the electron cloud.
The Bohr Model – Shows the number of electrons on different energy levels around
the nucleus.
Molecular Model – Shows different atoms as spheres bonded together to form a
chemical compound called a molecule.
What are Valence Electrons?
Bohr Models show atoms’ electrons
organized into energy levels.
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1st energy level can hold up to
2 electrons
2nd energy level can hold up to
8 electrons
Atoms can have up to 7 energy
levels
Outermost energy level – The
energy level shown furthest
from the nucleus in a Bohr
Model
Valence Electrons – Electrons on the outermost energy level of an atom.
How does the periodic table show the number of valence electrons?
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Elements in the same group, or vertical column, have the same # of
valence electrons.
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Use the group # on the periodic table to find the # of valence electrons
for groups 1, 2, and 13-18
*There is no simple rule to find the # of valence electrons in groups 3-12
*Group #1, the Alkali Metals, are the most reactive group of elements
because they only have 1 valence electron to lose to form a chemical bond.
*Group #18, the Nobel or Inert Gases, have full outermost energy levels,
therefore are unreactive and do not tend to form chemical bonds.
 He – 2 valence electrons
 Ne, Ar, Kr, Xe, Rn – 8 valence electrons
*Group #17, the Halogens, are very reactive non-metals because they only
need to gain 1 electron to have a complete set of 8 valence electrons.
Why do atoms form bonds? Eight is Great!
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Atoms tend to form bonds if its outermost energy level is not full.
*8 Valence electrons = Full outer energy level
Atoms that have fewer than 8 valence electrons, with the exception of Helium,
do not have a full outermost energy level.
These atoms gain, lose or share valence electrons to form chemical bonds.
Metals tend to lose electrons
Non-Metals tend to gain or share electrons
When atoms form bonds, their outermost energy levels may be filled.
Ions – charged particles that form when a neutral atom gains or loses an electron in
a chemical bond.
Summary: