Download Periodic Trends

Periodic Trends
Chapter 6 Section 3
pp.163-169
What is a trend?
1. The general direction in which
something tends to move.
2. A general tendency or inclination. See
Synonyms at tendency.
Things to remember…
Nuclear charge

Positively charged nucleus pulls electrons
towards it
Atomic radius is measured in picometers

1 x 10^-12 meters = 1 pm
Ions


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An atom or bonded group of atoms that has a
positive or negative charge
Occurs when an atom gains or loses an electron
Electrons are charged so you are gaining or losing
a negative charge
Affects the overall charge of the atom
Electrostatic repulsion

Remember like charges repel each
other…electrons in orbitals repel/push each other
away
Energy is needed to overcome the
attraction between the positive protons and
negative electrons


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Ionization energy (IE) is the energy required to
remove an electron from a gaseous atom
(kJ/mol)
IE indicates how strongly a nucleus can hold
onto its valence eHigh IE= strong hold on e-; less likely to make
positive ions
Low IE= atom can lose valence e- easily; likely
to make positive ions
More about ionization energy…
After removing the 1st e- it is still possible
to remove additional electrons
Second ionization energy:

The IE needed to remove a second electron
from a +1 ion
Third ionization energy:

The IE needed to remove a third electron from
a +2 ion
Electro negativity
Characteristic of an element that indicates
the relative ability of its atoms to attract
electrons in a chemical bond
Units: Paulings
Values are less than 3.98 or less
Leave out noble gases (they really don’t
react)
Atomic Radius
Electron cloud


Spherical surface in which there is a 90%
probability of finding an eNot physical
Atomic size is defined by how closely an
atom lies to its neighboring atom

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Each atom has different properties so there
are going to be different sizes…
Different sizes in different blocks…
Atomic Radius of a Metal
Metals

Atomic radius
half the distance between adjacent nuclei in a
crystal of that element
Atomic Radius of a Nonmetal
Usually occur as molecules
Atomic radius:


Half the distance between nuclei of identical
atoms that are chemically bonded together
Diatomic molecules
Hydrogen
Bromine
Iodine
Oxygen
Ionic Radius
Losing/gaining electrons affects size of an atom
Gain an electron atom becomes negative atom
becomes larger

Electrostatic repulsion between atom’s outer electrons
increase
Forces outer electrons to move further apart
Makes radius bigger
Lose an electron atom becomes positive atom
becomes smaller

Electron lost is valence electron
Can lead to completely empty orbital=smaller radius

Electrostatic repulsion between atoms decrease so they
can be pulled closer to nucleus
Periodic Trend Scramble
Break up into your first group

Find everyone with the same type of card…all
kings together, all queens together, etc….
Listen for instructions
Atomic Radius: Trends in Periods
DECREASE in atomic radii left-to-right
Increasing positive charge in the nucleus
Principle energy level (n) remains the same
throughout the period

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Each successive element the atomic # Increase
Add proton and electron
Electron gets added to same Prin. E level (n)
No additional electrons come across valence
electrons and nucleus
Val. E- are not shielded from increased nuclear charge
Therefore the increased nuclear charge brings the outermost
electrons closer to the nucleus …which means…
Smaller atomic radii going   
Atomic Radius: Trends within
Groups
INCREASE as you move down a group
Nuclear charge increases
What happens to your principle energy level as you
move down a group?

Therefore…Electrons added to higher principle energy levels
Although nuclear charge increased, other factors in play
to overpower increased nuclear charge...

Outermost orbital increases in size
Electrons are farther from the nucleus b/c of bigger orbital
More resistant to higher nuclear charge b/c of increased distance

Principle energy level increased
Puts more orbital with electrons between the nucleus and the
outermost electrons
These electrons in between shield the outermost electrons from the
pull of the nucleus
Solve…
Which has the largest radius?
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Magnesium (Mg)
Silicon (Si)
Sulfur (S)
Sodium (Na)
Which has the smallest radius?
And the answer is…
Largest: Na (sodium)
Smallest: S (sulfur)
Ionic Radius: Trends in Period
What type of ions do you think will be formed on the
left side of the table?

Smaller positive ions
What type of ions do you think will be formed on the
right side of the table?

Larger negative ions
General Rule:

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Left-to-right across a period, the size of positive ions
gradually decreases
Around 5A and 6A, the size of much larger negative ions
gradually decreases
Ionic Radius: Trends in Group
What happens to the principle energy level
as we move down a group?

Increases
Ion’s outer electrons are in a higher
principle level

This means an increase in ionic size
Ionic radii increases as we move down a
group for both positive and negative ions
Ionization Energy
What type of IE does group 1A have? High or
low?
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Low IE
Likely to form + ions
What type of IE does group 8A have?
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High IE
Unlikely to form ions
From left to right, the IE to remove successive
electrons always increases

Does not happen smoothly…requires large jump of
energy
IE continued….
Trends in periods:
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First IE generally increases as you move leftto-right
The nuclear charge increases with each
successive element…
What does this have to do valence electrons?
Increase the nuclear charge=stronger hold on
valence electrons
IE continued…
Trends within groups…
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First IE generally decrease as you move
down a group
What happens to the size of an atom as you
move down a group?
Increases
This cause decrease in IE
Valence electrons are farther from the nucleus
Easier to remove
Octet Rule
What is the electron configuration for sodium?
What is the new configuration when a sodium
atom becomes a +1 sodium atom?
What noble gas does this configuration look
like?
OCTET RULE:
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Atoms tend to gain, lose, or share electrons in an
order to acquire a full set of valence electrons
First period elements are en exception to the rule
This rule helps to determine what kind of ions will
form
Food for thought….
Do atoms on the right side of the periodic table
tend to gain or lose electrons?

Gain electrons
What type of ions are they likely to form?
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Negative ions
Do atoms on the left side of the periodic table
tend to gain or lose electrons?

lose e-
What type of ions do they form?

Positive ions
Electronegativity (EN)
Fluorine is the most electronegative
element

Value: 3.98
Cesium and Francium are the least
electronegative

Values: 0.79 and 0.7
Atom with greater electronegativity attracts
electrons in a chemical bond the strongest
Electronegativity (EN)
Trends in periods and groups:
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EN decreases as you move down a group
Increases as you move left to right on table
Where are the lowest electronegatives
found?
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Lower left side of the periodic table
Where are the highest electronegatives
found?
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Upper right side of the periodic table
Affinity
What are some things you have
an affinity for?
Electron Affinity
The energy change that occurs when an
electron is acquired by a neutral atom
Measure in kJ/mol
Many atoms release energy when they gain an
electron
A + e-  A- + energy
A + e- + energy  A

Some atoms need energy to be “forced” to gain an
electron
Produces unstable ions that lose electron quickly