Periodic Trends
• What is the radius of a circle?
• What would the atomic radius be?
2
l. Atomic Radius
A. The electron cloud surrounding a nucleus
is based on probability and does not have
a clearly defined edge
B. Defined by how closely an atom lies to a
neighboring atom
ll. Atomic Radius Across a
Period
A. Atomic radius generally decreases in size as you move
Why?
left to right across the period
1. Increasing positive charge in the nucleus pulls the
electrons of the same energy level in.
What is this force called?
• What happens to the radius as you go
down a column? Why?
• What keeps the additional protons from
drawing the electrons closer?
5
lll. Atomic Radius Down a Group
A. Atomic radius increases as you move down a
group
1. Orbital size increases as you move down a group with
increasing energy level
2. Larger orbitals means that outer electrons are farther
from the nucleus. This increased distance offsets the
greater pull of the increased nuclear charge.
3. As additional orbitals between the nucleus and the outer
electrons are occupied, the inner electrons shield the
outer electrons from the pull of the nucleus this is called
shielding.
Shielding
The inner electrons
shield the outer
electrons from feeling
the pull of the nucleus
Question Time
• How do you define the atomic radius since
the electron cloud does not have a clearly
defined edge?
• What happens to the atomic radius as you
move left to right? Why?
• What happens to atomic radius as you
move down a group? Why?
• What is shielding?
• An- prefix (Anarchy) vs Cat- prefix
• An = without
Cat = with
• Anodes are without what?
• Cathodes are with what?
10
lV. Cation and Anion
A. An ion is a positively or negatively
charged atom that gains or loses an
electron.
Cations are attracted to cathodes. What is the charge of a cation?
B. A cation loses electrons and produces a
positive charge
Anions are attracted to anodes. What is the charge of an anode?
C. An anion gains electrons and produces a
negative charge
Anion
18 electrons
16
protons
S2Sulfur Anion
Cation
10 electrons
12
protons
Mg2+
Magnesium Cation
• What happens to the atomic radius of
cations? Why?
13
V. Ionic Radius - Cations
A. Groups 1A, 2A, 3A, and other metals tend to lose
electrons and form cations.
B. When atoms lose electrons they become smaller
1. The electron lost will be a valence electron leaving a
completely empty outer orbital
2. Electrostatic repulsion between fewer number of
remaining electrons decreases, allowing them to be
pulled closer to the nucleus
These atoms lost electrons and became
smaller cations.
• What happens to the atomic radius of
anions? Why?
16
Vl. Ionic Radius - Anions
A. Group 5A, 6A, and 7A tend to gain
electrons and form anions
B. When atoms gain electrons and form
negatively charged ions, they become
larger.
1. The addition of an electron to an atom
increases the electrostatic repulsion between
the atom’s outer electrons forcing them
farther apart resulting in a larger radius.
These atoms gained electrons and
became larger anions
Question Time
• What is an ion?
• What is a cation and an anion?
• What happens to the size of the atom
when it becomes a cation? Why?
• What happens to the size of the atom
when it becomes an anion? Why?
End for today!
20
• What could ionization energy mean?
• How do atoms become ions?
• Which atoms are more likely to become
ions (by removing electrons)? Do they
have a high or low ionization energy?
21
Vll. Ionization Energy
A. The energy required to
remove an electron from
a gaseous atom
B. Indication of how
strongly an atom’s
nucleus holds onto its
valence electron
C. Groups 1A, 2A, and 3A
tend to have low
ionization energies
because they want to
lose electrons.
Vlll. Ionization Energy Trends –
Across a Period
A. Ionization energy increases as you move
left to right
1. Across a period electrons are added to the
same energy level (same distance away
from the nucleus), yet the nuclear charge is
increasing across a period increasing the
attraction to the electrons.
Why would ionization energy increase?
lX. Ionization Energy Trends –
Down a Group
A. Ionization energy decreases as you move
down a group
1. Down a group electrons are added to a
higher energy level (farther distance away
from the nucleus), making it easier to
remove an electron
What happens to the ionization energy as you go down
a column? Why?
• What does every atom want?
• What are the two exceptions?
26
X. Octet Rule
A. Sodium atom 1s22s22p63s1
B. Sodium ion 1s22s22p6 (Sodium atom lost 1
electron)
C. Neon 1s22s22p6
D. Sodium ion has the same electron configuration
as neon
E. Octet rule states that atoms gain, lose, or
share electrons to acquire a full set of eight
valence electrons (to be like a noble gas)
Xl. Electronegativity
A. Indicates an element’s ability to attract
electrons in a chemical bond
is there going to
B. fluorine (F)Where
is the
most electronegative
be a high amount of
element electronegativity? Why?
C. Cesium (Cs) and francium (Fr)are the
least electronegative
D. Noble gases do not tend to have an
electronegativity number since they tend
not to form compounds
Xll. Trends with Electronegativity
A. Electronegativity increases as you move
left-to-right across a period
1. As you go left to right, the nuclear charge
increases, more strongly attracting electrons
A. Electronegativity decreases as you move
down a group
1. Electrons get further away from the positive
nucleus
Question Time
• What is ionization energy?
• What is the trend in ionization energy as you move
left to right? Down a group?
• What is the octet rule? What elements do atoms
want to be like?
• What is electronegativity?
• What are the trends in electronegativity?
• What is the most electronegative element? What is
the least?
• Why do noble gases tend not to have an
electronegativity value?
• What is the difference between ionization energy
and electronegativity?