Atomic Structure and
Chemical Bonds
Why do atoms combine?
Chapter 6 Section 1
Atomic Structure
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The center of every atom is a nucleus that
contains protons and neutrons
The electron cloud- the area of space
surrounding the nucleus where the
electrons are found
We cannot calculate the exact position of
any one electron, but we can predict
where they are likely to be
Element Structure
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The number of protons and electrons is
always the same for a neutral atom of an
element
Example: A neutral atom of Helium has 2
protons and 2 electrons
Electron Arrangement
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All electrons are found somewhere in the
electron cloud, however some are closer
to the nucleus than others
Energy levels are different areas for an
electron in an atom, each level represents
a different amount of energy
The farther the energy level is from the
nucleus the more electrons it can hold
Energy Steps
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Electrons in the level closest to the
nucleus have the lowest amount of energy
and are said to be in energy level one
Electrons farthest from the nucleus have
the highest amount of energy and the
easiest to remove
Removing electrons that are closer to the
nucleus take more energy than removing
electrons farther from the nucleus
Energy Steps
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Energy
Energy
Energy
Energy
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level
level
level
level
1—holds
2—holds
3—holds
4—holds
2 electrons
8 electrons
18 electrons
32 electrons
A formula for to find how many electrons each
energy level can hold is
2n² where n is the number of the energy
level
Periodic Table and Energy Levels
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You can use the periodic table to find the
number of electrons, by using the atomic
number, which is the same as the number
of protons
Electron Configurations
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You can see in the periodic table that the
number of electrons in a neutral atom of the
element increases by one from left to right
across a period
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If you look at period one it contains Hydrogen and
Helium. Energy level one can hold up to 2 electrons,
so Helium fills the first energy level, which means that
it is a stable atom.
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Stable atoms do not like to combine with other atoms
Each period ends with a stable element or a full
configuration
Here is a thought!
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What does the electron energy level
diagram look like for bromine and
calcium?
What happens to the outer electrons when
these two elements combine to form
calcium bromide?
Calcium
Bromine
Element Families
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Last chapter we learned a lot about each
element family.
Look at the outer energy levels, notice that the
energy levels for noble gases are completely
filled, this is why they are the most stable
elements.
The alkali metals, which we already learned are
the most reactive only have one electron in their
outer shell, which makes them very reactive.
Electron Dot Diagrams
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An electron dot diagram is the symbol for the
element surrounded by as many dots as there
are electrons in its outer energy level.
We only use the outer energy electrons because
they are the only electrons that determine how
the element reacts.
What forms when atoms are joined by a
chemical bond?
What is this good for
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We use the electron dot diagram to decide
how elements bond and where the
chemical bond will form.
Atoms always bond with other atoms in a
way so their outer energy level is full.