Catalyst
1. Open up the Bohr’s Model educanon video for today’s
class. Complete the questions associated with the video.
2. Put your laptop at 45 degrees and place your eyes on me
so I know when you’re finished.
End
Review - Important Point #1
• The atom is mostly empty space. This is why
most of the alpha particles went through
• The majority of the atom does not have
anything in it.
Review - Important Point #2
• The atom has very small, but very dense
nucleus.
• Alpha particles that bounced back were coming
into contact with nucleus.
• Alpha particles were deflected back because
nucleus is positive.
Review - Nuclear Model
Lecture 1.7 – Bohr, Electronegativity,
and Atomic Radius
Today’s Learning Targets
• 1.6 – I can explain the development of atomic theory
incorporating the contributions of Dalton, Thomson,
Rutherford, and Bohr.
• 1.7 – I can define electronegativity and explain how it
relates to the charge of the nucleus and the electron.
Furthermore, I can explain how this trend changes as
you move throughout the Periodic Table.
• 1.8 – I can define atomic/ionic radius and explain how
it relates to the charge of the nucleus and the electron.
Furthermore, I can explain how this trend changes as
you move throughout the Periodic Table.
Niels Bohr
• Refined Rutherford’s
model of the atom
with his discovery in
1913.
What Bohr Knew
• Shooting electricity through the hydrogen
excited electrons.
• Color produced only for specific values
• Problem – If electrons were free to roam, then
we should get all sorts of colors
Bohr’s Solution
• Electrons are not free to roam in the electron
cloud, electrons are restricted to orbits or
energy levels.
The Modern Model
Dalton’s atom
electron
Thompson’s electrons
neutron
Rutherford’s space
and nucleus
proton
Bohr’s energy levels
SUMMARIZE
What’s More Attractive?
Magnets!
How do they work?
I. Nuclear Attraction
• The negatively charged electrons are
attracted towards the positively charged
nucleus.
• The more the electron “feels” the nucleus.
The tighter it is held
II. Electronegativity
• Electronegativity is the measure of the ability of an
atom to attract electrons.
III. How does the size of the atom relate to the
positive and negative charges in an atom?
What do the
arrows
represent?
How does the
thickness of the
arrows relate to
nuclear attraction?
IV. Why are the atoms getting bigger?
a
• As you move from the smallest atom
to the largest atom, how does the
distance between the valence
electrons and the nucleus change?
• As you move from the smallest atom
to the largest atom, how does the
attractive force between the valence
electrons and the nucleus change?
• What direction does this go on the
periodic table?
Electronegativity Trends
• As you go down a group, the electronegativity of
an element decreases.
• As you go across a period, the electronegativity of
an element increases.
Why Electronegativity Decreases Down a Group
• As you go down a group more orbits are added.
• Electron Shielding – Valence electrons become
shielded from the positively charged nucleus as
you add more orbits.
• Electroneg. decreases because there is a
decreased ability of the nucleus to attract
electrons because of larger distance.
Why Electronegativity Increases Across a Period
• As you move across a period you add more
protons and electrons within the same orbit.
• The larger amount of protons in the nucleus and
electrons in orbit show an increased attraction.
• This leads to increased electronegativity as you
move within a period.
Class Example
• Order the elements from smallest to largest
electronegativity: oxygen, beryllium, lithium,
Table Talk
• Order the elements from largest to smallest
electronegativity: chlorine, bromine, fluorine
Stop and Jot
• Order the elements from smallest to largest
electronegativity: silicon, aluminum, sulfur
SUMMARIZE
Master Chef - White Board Races
White Board Relay Race Problems
1. Which has a larger electronegativity: chlorine or
silicon?
2. Which has a smaller electronegativity
magnesium or calcium?
3. Put the following elements in order from smallest
electronegativity to largest: B, F, N, O.
4. Put the following elements in order from smallest
electronegativity to largest: N, As, Bi, P .
5. Why does bromine do a worse job of attracting
electrons than fluorine?
Atomic Radius
• Atomic Radius – The distance from the center of
the nucleus to the outermost edge of the
electron cloud
Outer edge of
electron cloud
Nucleus
Atomic Radius Trends
• Atomic radius increases as you go down a group on
the Periodic Table.
• Atomic radius decreases as you go across a period on
the Periodic Table
Why Atomic Radius Increases Down a
Group
• As you add more electron shells to an element, the
element becomes “bulkier”.
• This means that as you go down a group, more orbits
are added, so the radius becomes bigger.
Why Atomic Radius Decreases Across a
Period
• As you move across a period, more protons are
added to the nucleus.
• Also, more electrons are added within the same
orbit.
• This means there is a larger positive and negative
charge, which results in a higher attraction and a
decrease in the radius.
SUMMARIZE
Master Chef - White Board Races
Whiteboard Questions (T/F)
1. Atomic radius is the distance from the center
of the nucleus to the first electron orbit.
2. Atomic radius increases across a period and
down a group.
3. Atomic radius decreases down a group
because you are adding more electron orbits.
4. Atomic radius decreases across a period
because there are less electrons in the same
orbit.
Whiteboard Questions (cont)
5. Order the following from largest to smallest
atomic radius: Ca, Se, Ni
6. Order the following from largest to smallest
atomic radius: O, Po, S
7. Order the following from smallest to largest
atomic radius: Cs, F, Ga
Exit Ticket
1. Define atomic radius
2. Define electronegativity.
3. Order from largest to smallest
electronegativity: Ca, Se, Ni
4. Order from smallest to largest atomic radius:
O, Po, S
Rate Yourself
• Based on the exit ticket and your current level
of understanding, rate yourself 1 – 4 on LT 1.6
- 1.8
Closing Time
• Practice 1.7 – Electronegativity and Atomic
Radius
• UNIT 1 EXAM coming up soon!