Chemistry 11
Unit 9 Chemical Bonding #1
Name:____________________________
Block:_________
Electrostatic Forces
An electrostatic force is a forces existing as a result of the
between 2
All
particles.
is based on the experimentally-derived relationships
of electrostatics:
•
•
Like charges repel (+ + or - -)
•
The
between two charged particles,
the
•
the attractive force
The greater the
on two particles, the
of attraction (or repulsion) between them
Electron Shells REVISITED!
The periodic table shows that patterns in the properties of elements are linked to
What links atomic number and the properties of elements?
As
increases by one, the number of
also increases by one.
This means that the elements in the periodic table are also arranged in order of the number of
electrons.
What is periodicity?
The Russian chemist Dmitry Mendeleev observed that when the
elements are arranged in order of atomic mass, there are
The modern periodic table can be used to analyse trends in properties such as
across periods and down groups. (draw this on your diagram above)
.
What is atomic radius?
The atomic radius of an element is difficult to precisely define because of the uncertainty over the
. Several definitions are used.
One definition is half the shortest
distance found in
the structure of the element.
For non-metallic elements, the
is
often used as the atomic radius. This is half the internuclear distance
between two identical atoms in a single
For
.
adjacent atoms (e.g. in a covalent crystal of a non-metallic
element), the
is used as a value for atomic
radius. This is half the shortest internuclear distance between two similar non-bonded atoms.
For metallic elements, the
is often used as the atomic radius. This
is half the shortest internuclear distance between two adjacent atoms in a metallic bond.
Assignment #1A - Lab Activity: Atomic Radius Trends
1. On graph paper, construct a grid
using the data listed in table 1.
2. Plot the atomic number (x-axis)
of each element against the
atomic radius (y-axis) of the
same element.
3. Label each point on your graph
with the atomic symbol for the
element.
4. Can you observe a periodic
trend? If so, describe the trend
shown by your graph.
Trends in atomic radius in period 3
The atomic radius of the elements across period 3
.
This might seem counter-intuitive, because as the numbers of
, the
radius might be expected to also increase.
However, more than 99% of the atom is empty space – the nucleus
and electrons themselves occupy a tiny volume of the atom.
WHY? Increase in proton number
The
in the nucleus of the atoms
increases across period 3.
This increase in the number of protons increases the
The nucleus has
and so the atomic radius
of the atoms.
attraction for the electrons, pulling them in
across the period.
What is shielding? (follow with the animation and complete notes here. Use the diagrams to help
explain shielding)
Explaining atomic radius in period 3
Proton number
across period 3, but shielding remains
approximately constant.
This causes an increase in
leading to a
,
attraction between the nucleus and the outermost
electrons.
This pulls these electrons
to the nucleus and results in a
radius.
How are electrons arranged?
Electrons are arranged in
around an atom’s nucleus.
(also called
-principle quantum number n1).
Each shell has a maximum number of
Electrons will fill the shells
that it can hold.
the nucleus first.
Electrons within each PERIOD
The first shell can only hold a maximum of
electrons,
so
only includes the
elements hydrogen and helium.
What is special about the outer shell of
helium?
Elements in
have a
all
first shell.
What happens to electrons in the second
shell in period 2?
What is special about the outer shell of
neon?
Elements in period 3 have complete first
and second shells.
What happens to electrons in the third
shell in period 3?
What is special about the outer shell
of argon?
Electron trends in the periodic table
Trends down a group:


Trends across a period:


Valence Electrons Revisited
Draw the valence electrons on the following atoms: (hint…they all need another energy level)
Valence electrons are:


Valence electrons are considered
electrons
ASSIGNMENT #1B: answer the Hebden questions on a separate page.
Hebden pg. 165 #40-41
pg.167 #45-47
4. Arrange the following atoms in order of decreasing atomic radius:
Na
Al
P
Cl
Mg
5. Which is the largest atom in Group IV?
6. Which is the smallest atom in Groups VII?
7. Which is the smallest atom in period 5?
8. For each of the following pairs, which of the two species is larger?
a. N-3 or F-
b. Mg+2 or Ca+2
c. Fe+2 or Fe+3
9. For each of the following pairs, which of the two species is smaller?
a. K+ or Li+
b. Au+ or Au+3
c. P-3 or N-3
10. Order the following groups from largest to smallest radii
a. Ar, Cl-, K+, S-2
c. Na, Mg, Ar, P
b. C, Al, F, Si
d. I-, Ba+2, Cs+, Xe
11. Which species of each pair has the larger radius?
a. Mg or Mg+2
c. O or O-2
b. K+ or Cl-
d. P-3 or S-2
12. What are valence electrons used for by an element?
13. Which elements listed above want to lose electrons?
14. Which elements above want to gain electrons?
15. Determine the element’s number of valence electrons (# of electrons in the “outermost” shell).
Example: Carbon has 4 valence electrons, carbon__4__
a.
b.
c.
fluorine _____
lithium _____
phosphorus _____
d.
e.
f.
zinc _____
calcium _____
carbon _____
g.
h.
nitrogen _____
iodine _____