Chapter 5 – Atoms & Bonding
Electron Shells

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Electrons aren’t the same
distance from the nucleus.
They are arranged in shells or
energy levels.
The electrons in the outer
shell are called valence
electrons
Each shell can hold only a
certain number of electrons.
Shells



First shell = 2 electrons
– “the sports car”
Second shell = 8
electrons – “the mini
van”
Third shell= 8 electrons
– “another mini van”
Valence Electrons & Bonding

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Valence e- = electrons in the outermost shell
responsible for bonding
The number of valence e- in an atom of an
element determines many traits of that element,
including the ways in which the atom can bond
with other atoms
The family # tells you the number of valence
electrons for each element in the family (A
groups only)
Lets practice!

According to the periodic table how many
valence electrons do the following atoms have:
Sodium (Na)
 Oxygen (O)


How do you know?
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It’s the same as the family #
Valence Electrons & Bonding

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Atoms are more stable (less likely to react) when
they have 8 valence electrons
Atoms can gain or lose electrons in order to
have 8 valence electrons
Chemical Bond – the force of attraction that
holds two atoms together
Valence Electrons & Bonding

Electron Dot Diagram – includes the symbol
for the element surrounded by dots…the dots
show the valence electrons
Chapter 5 – Atoms & Bonding

Section 3 - Covalent Bonds
Standards
 3.b – Students know that compounds are formed
by combining two or more different elements and
that compounds have properties that are different
from their constituent elements.
 7.c – Students know substances can be classified by
their properties, including their melting
temperature, density, hardness and thermal and
electrical conductivity
Electron Sharing




Atoms can share valence e- to fill the outer
shell.
Non-metals tend to make covalent bonds.
Covalent Bond – a chemical bond formed
when two atoms share electrons
Ex: H2O Cl2
Drawing covalent Bonds

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We can use electron dot diagrams to set up an
atom to have 8 valence electrons
Electrons can be shared in order to fulfill the
octet rule (8 valence electrons)
Draw an electron dot diagram for Oxygen in
black:
Draw 2 Hydrogen atoms electron dot
diagrams in red:
Circle the shared electrons for each atom:
How many Bonds?



Atoms can share more
than one pair of
electrons.
Double Bond – two
pairs of electrons
being shared between
two atoms
Triple Bond – three
pairs of electrons
being shared between
two atoms
Chapter 5 – Atoms & Bonding

Section 2 – Ionic Bonds
Standards
 3.b – Students know that compounds are formed
by combining two or more different elements and
that compounds have properties that are different
from their constituent elements.
 3.c – Students know that atoms and molecules form
solids by building up repeating patterns, such as the
crystal structure of NaCl or long-chain polymers
Ionic Bonding


Atoms can give and take valence electrons to fill
their outer shell.
When an atom loses or gains electrons, the
protons no longer balance out the electrons, and
the atom becomes positively or negatively
charged.
Ions

Ion – an atom or group of atoms that has become
electrically charged
When an atom loses an electron it has a positive charge
 When an atom gains an electron it has a negative charge

10 electrons
8 valence e-
Element
Ion
Element
Ion
Hydrogen
H+
Flouride
F-
Potassium
K+
Chloride
Cl -
Sodium
Na +
Bromide
Br -
Barium
Ba 2+
Iodide
I-
Calcium
Ca 2+
Bromide
Br -
Magnesium
Mg 2+
Oxide
O 2-
Aluminum
Al 3+
Sulfide
S 2-
Boron
B 3+
Nitride
N 3-
Lithium
Li +
Phosphide
P 3-
Ions
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Ionic Bond – the attraction between two
oppositely charged ions
Ionic bonds form as a result of the attraction
between positive and negative ions
Ionic Compound – compound that consists of
positive and negative ions
Properties of Ionic Compounds

The characteristic properties of ionic
compounds are:
Crystal Shape – orderly 3-D shape
 High Melting Point – ionic bonds are strong
 Electrical Conductivity – when dissolved in water,
ionic compounds conduct electricity

Chemical Formula & Names
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Chemical Formula – combination of symbols
that shows the ratio of elements in a compound

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Ex. MgCl2 or NaCl or K2S
When ionic compounds form, the ions come
together in a way that balances out the charges
on the ions
Subscript – tells you the ratio of elements in the
compound

Ex. MgCl2 - 1 Magnesium ion and 2 Chlorine ions
Naming Ionic Compounds
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The name of the positive ion goes first
Then the name of the negative ion
If the negative ion is an element, add the ending
–ide
If the negative ion is polyatomic, leave the name
the same
Mg2+ + O2-  MgO Magnesium Oxide
Na+ + CO32-  Na2CO3 Sodium Carbonate
Practice with Ionic Bonds
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Examples:

Na
+
+

Na

Mg
2+

Mg

Ca

Ca

Al

Cl
+
Cl
+
2+
3+
Al
+
+
 NaCl
Cl
Cl
–
–
O
O
 MgCl2
 CaO
O
+ O
+
NaCl
 MgCl
2–
+

2–

CaO

AlO

Al2O3
Ions

Polyatomic Ion – ions that are made of
more than one atom
 Poly
means ‘many’
 So polyatomic means ‘many atoms’
Element
Ion
Ammonium
NH4 +
Bicarbonate
HCO 3-
Nitrate
NO3 -
Carbonate
CO3 2-
Sulfate
SO4 2-
Phosphate
PO4 3-