PERIODIC TRENDS
Atomic Radius

The bond lengths and atomic radii for selected substances are provided in the
table below.
Substance
Bond Length (Å)
Atom
Atomic Radius (Å)
F2 (F–F)
1.4119
F
0.70595
Cl2 (Cl–Cl)
1.9878
Cl
0.99390
Br2 (Br–Br)
2.2811
Br
I2 (I–I)
1.3332
Na2 (Na–Na)
3.0789
Na
1.5395
Si2 (Si–Si)
2.246
Si
1.123
P2 (P–P)
1.8931
P
S2 (S–S)

I
S
0.94460
According to the table above, atomic radius is defined as __________ the distance
between the _______________ of identical atoms that are _______________
together.
1. Calculate the atomic radius of bromine and phosphorus.
2. Calculate the bond length of iodine (I2) and sulfur (S2).

What’s the trend?

Trend explanation:
o Period Trend

What happens to the size of the outer shell as you move left to
right across a period? Remember, electrons are filling the
sublevels within the same energy level…

What happens to the number of protons in the nucleus as you move
left to right across a period?

So if the nucleus is getting _______________ and the outer shell is
not getting _______________, what will happen to the radius as
you go across the period?
o Group Trend

What happens to the size of the outer shell as you move down a
group?

So if the outer shell is getting _______________, what will happen
as you go down the group?
Ionic Radius

An ion is simply defined as a _______________ particle.
o A positively charged ion forms from _______________ electrons, so as
the remaining electrons draw closer to nucleus because the number of
protons was not affected, the radius _______________.
o Metals tend to form _____ charged ions called _______________.
Neutral atom
__________
o A negatively charged ion forms from _______________ electrons. This
causes the electron cloud to expand, which causes the radius to
_______________.
o Nonmetals tend to form _____ charged ions called _______________.
Neutral atom

__________
What’s the trend?
o Same as _______________ _______________, but now with charged
particles instead of neutral atoms.
Electronegativity

Measure an atom’s ability in a chemical compound to __________ electrons.

Trend explanation:
o Group trend:

Fluorine has __________ valence electrons, which means it is only
_____ electron away from being as stable as a Noble Gas. It is
desperate for that electron, so it has a _______________ attraction
for electrons. Therefore, it has a __________ electronegativity.

Lithium has _____ valence electron, which means it is also only
_____ electron away from being as stable as a Noble Gas. It is
desperate to __________ its outer electron, so it has a
_______________ attraction for electrons. Therefore, it has a
__________ electronegativity.
o Period trend:

We’ve already established that fluorine has a high
electronegativity, but there’s another reason for this: Its valence
shell is only n = 2, so it is rather __________ to the nucleus. The
stronger nuclear pull also helps fluorine have a high
electronegativity.

Astatine has __________ valence electrons, so it is also desperate
for that last electron to fill its shell, but since its valence shell is n
= 6, the pull of the nucleus on electrons is weaker than fluorine’s.
Therefore, it has a __________ electronegativity.

What’s the trend?

Fluorine has the _______________ electronegativity - assigned _____ by Linus
Pauling’s relative electronegativity scale. The values of other element
electronegativities have been calculated in relation to Fluorine’s. Cesium and
francium share the _______________ electronegativity at _____.
Electron Affinity

The _______________ change that occurs when an electron is _______________
from a neutral atom

Most atoms _______________ energy when they acquire an electron, so most
affinities are negative.

Trend explanation:
o Period trend:

As the p–orbital is filling, the element tends to want electrons more
(to fill their outer shells), so electron affinity gets __________
_______________ to the right.
o Group trend:

As you go down a group, the pull of the nucleus on electrons gets
_______________, so electron affinity gets __________
_______________ down a group.

What’s the trend?
Ionization Energy

Ionization: Any process that results in the formation of an __________.

Ionization Energy: The energy required to _______________ one electron from a
neutral atom.

Trend explanation:
o Period trend:

As you go across a period, the nucleus _______________ in
strength, making it _______________ to remove electrons from
the atoms. Therefore, ionization energy _______________.
o Group trend:

As you go down a group, the electrons are getting
_______________ from the nucleus, making it _______________
for the electron to be removed. Therefore, ionization energy
_______________.

What’s the trend?
Metallic and Nonmetallic Character

Metal, nonmetal and metalloid characteristics were discussed in chapter 1.

What’s the trend?

Metals are on _______________ side of the “_____-_____” line, nonmetals are
on _______________ side of the “_____-_____” line

Metalloids surround the “_______________” line – only _____ of them!
Reactivity

Reactivity depends on the number of _______________ electrons the element
has.
o It also depends on the reactivity of the other _______________, so this is
a general reactivity trend.

We will discuss metals and nonmetals separately.

Metals:
o The _______________ valence electrons they have, the
_______________ reactive they are.
o Trend explanation:

Group Trend:

Electrons are not held as strongly as the atomic radius
increases, so it’s _______________ to remove electrons
further down the group. Reactivity _______________.

Period Trend:

Electrons are held more tightly as the nuclear charge
increases, so it’s _______________ to remove electrons
across a period. Reactivity _______________.

What’s the trend?

Nonmetals:
o The _______________ valence electrons they have, the
_______________ reactive they are.

Trend explanation:
o Group Trend:

p-sublevels that are close to the nucleus can be filled up
_______________ because the nucleus has a _______________
pull on free electrons. Reactivity _______________.
o Period Trend:

As the _____-sublevel is being filled up, the elements tend to want
the electrons more because they’re getting closer to being
_______________. Reactivity _______________.

What’s the trend?