lesson 01: the structure of the atom 01 …...chemistry 11, atoms and the periodic table, unit 07 1...
TRANSCRIPT
Chemistry 11, Atoms and the Periodic Table, Unit 07 1
Lesson 01: The Structure of the Atom
01 Introduction
All physical objects in the universe are composed of matter and all matter is composed of elements and all elements are composed of atoms. But what are atoms composed of?
Matter
Chemistry 11, Atoms and the Periodic Table, Unit 07 2
02 Modern Basic Structure of the Atom Atoms are made up of three types of sub atomic particles…
electrons: negatively charged particles which orbit the nucleus
protons: positively charged particles which are located in the nucleus
neutrons: particles with no charge located in the nucleus
An Atom of the Element Carbon
Chemistry 11, Atoms and the Periodic Table, Unit 07 3
Atoms are not all the same, since any two atoms of…
one particular element will always be identical since both would have the same number of sub atomic particles
different elements will always be different since both would have differing numbers of sub atomic particles
Two Atoms, Two Elements
Hydrogen Atom Helium Atom
Chemistry 11, Atoms and the Periodic Table, Unit 07 4
03 Atomic Number, Atomic Mass, Ions and Isotopes The way in which all known elements are displayed is using the periodic table of elements…
For a neutral atom, there are three pieces of information are usually displayed on the periodic table…
element symbol
atomic number is the number of protons or electrons there are in the nucleus
atomic mass is the number of neutrons added to the number of protons
Chemistry 11, Atoms and the Periodic Table, Unit 07 5
Atoms of the same element will always have the same number of…
electrons
protons
neutrons
Two Atoms of Hydrogen
H Atom H Atom
1 proton
1 electron 1 proton
1 electron
Example 01
How many electrons, protons and neutrons are in a neutral atom of C?
carbon carbonatomic number protons electrons 6
carbon carbon carbon
carbon carbon carbon
carbon
atomic mass protons neutrons
neutrons atomic mass protons
neutrons 12 6 6
Chemistry 11, Atoms and the Periodic Table, Unit 07 6
Example 02
How many electrons, protons and neutrons are in a neutral atom of Fe?
iron
iron ironatomic number protons electrons 26
iron iron iron
iron iron iron
iron
atomic mass protons neutrons
neutrons atomic mass protons
neutrons 56 32 06
Atoms of the same element…
having different numbers of electrons but having the same number of protons and neutrons
are called ions
Three Forms of the Element Hydrogen
H Ion H Atom H
Ion
1 proton 1 proton
1 electron 1 proton
2 electrons
positively charged hydrogen ion
neutral hydrogen atom
negatively charged hydrogen ion
Chemistry 11, Atoms and the Periodic Table, Unit 07 7
Example 03
How many electrons, protons and neutrons are in the ion
2Fe ?
iron
iron
atomic number protons
atomic number electr
26
2ns 4o 26 2
iron iron iron
iron iron iron
iron
atomic mass protons neutrons
neutrons atomic mass protons
neutrons 56 32 06
Atoms of the same element…
having the same number of electrons and protons, but differing by the number of neutrons
are called isotopes…
Three Isotopes of Hydrogen
Hydrogen Deuterium Tritium
1 proton 1 electron
1 proton 1 neutron 1 electron
1 proton 2 neutrons 1 electron
most common isotope
less common isotope
less common isotope
Chemistry 11, Atoms and the Periodic Table, Unit 07 8
04 Modern Detailed Structure of the Atom
Electron Arrangement Electrons are arranged around a nucleus in shells…
In most cases (not all)…
a shell will have subshells, and
a subshell will have its own orbitals
Chemistry 11, Atoms and the Periodic Table, Unit 07 9
Quantum Numbers Quantum numbers determine the location and number of electrons in a particular shell… There are four quantum numbers…
Location and Number of Electrons
Name Symbol Meaning Values
principle quantum number
n energy level 1, 2, 3…
angular momentum quantum number
l shape 0, 1, 2, 3...
s, p, d, f...
magnetic quantum number
lm orientation
s: 1 orbital
p: 3 orbitals
d: 5 orbitals
f: 7 orbitals
spin quantum number sm electron spin
1+
2 or
1-2
Chemistry 11, Atoms and the Periodic Table, Unit 07 10
Orbital Shapes
Since a maximum of two electrons can exist in any atomic orbital the following results…
Number of Electrons Per Shell and Sub-Shell
Shell Sub-Shell(s) Maximum
Electrons Per Sub-Shell
Total Number of Electrons
1 s 2 2
2 s, p 2, 6 8
3 s, p, d 2, 6, 10 18
4 s, p, d, f 2, 6, 10, 14 32
Chemistry 11, Atoms and the Periodic Table, Unit 07 11
Electron Configurations How do we write the exact distribution for all electrons within a particular atom? This depends on two factors…
how many electrons an atom has, and...
how many electrons each shell and sub-shell can accommodate
The Aufbau Principle is used to determine the electron configuration of an atom. According to the principle, electrons fill orbitals…
lowest energy levels first, followed by
higher levels next
Chemistry 11, Atoms and the Periodic Table, Unit 07 12
To determine the electron distribution, a useful diagram is commonly used…
Orbital Filling Order for Multi-Electron Atoms
Chemistry 11, Atoms and the Periodic Table, Unit 07 13
It is also useful to realize that the periodic table of the elements has been constructed with electron configuration in mind…
Orbital Filling and the Periodic Table
Knowing this, it is now possible to generate electron configurations for atoms of any element...
Chemistry 11, Atoms and the Periodic Table, Unit 07 14
Example 04
Determine the electron configuration for the following atoms…
Atomic Number
Element Structure
1 Hydrogen 11s
2 Helium 21s
3 Lithium 122s1s
4 Beryllium 222s1s
5 Boron 2 2 11s 2s 2p
6 Carbon 2 2 21s 2s 2p
7 Nitrogen 2 2 31s 2s 2p
8 Oxygen 2 2 41s 2s 2p
9 Fluorine 2 2 51s 2s 2p
10 Neon 2 2 61s 2s 2p
Chemistry 11, Atoms and the Periodic Table, Unit 07 15
Electron Configurations and Core Notation Displaying electron configurations for elements following a noble gas is done using core notation. Core notation is a way of displaying electron configurations in a kind of short form.
core electrons are referred to as those electrons nearest noble gas having an atomic number less than that which is being considered
outer electrons are those outside the core
Chemistry 11, Atoms and the Periodic Table, Unit 07 16
Example 05
Determine the electron configuration using core notation for the following…
Atomic Number
Element Structure
10 Neon 2 2 61s 2s 2p
Neon
(core notation) [Ne]
11 Sodium 2 2 6 11s 2s 2p 3s
Sodium (core notation)
1[Ne]3s
12 Magnesium 2 2 6 21s 2s 2p 3s
Magnesium
(core notation) 2[Ne]3s
13 Aluminum 2 2 6 2 11s 2s 2p 3s 3p
Aluminum (core notation)
2 1Ne 3s 3p
14 Silicon 2 2 6 2 21s 2s 2p 3s 3p
Silicon (core notation)
2 2Ne 3s 3p
Chemistry 11, Atoms and the Periodic Table, Unit 07 17
Electron Configurations and Ions Displaying electron configurations for ions is straightforward. All the needs to be done is…
determine the number of electrons in the atom that forms the ion, and then
add an electron for each negative change
remove an electron for each positive charge
Example 06
Determine the electron configuration for Br using core notation.
first determine the total number of electrons in bromine and then make sure to add an extra electron due to the presence of one negative charge
bromineatomic number electrons 35 61 3
determine the nearest noble gas
argon
place electrons in the core and remainder outside the core
2 10 5Ar 4s 3d 4p
Chemistry 11, Atoms and the Periodic Table, Unit 07 18
There are two exceptions to the configurations of elements up to krypton. These two exceptions are due to the fact that there is greater stability in having either…
a filled sub-shell
exactly half filled sub-shell
Electron Configuration Exceptions
Incorrect Correct
Chromium 2 4Ar 4s 3d 1 5Ar 4s 3d
Copper 2 9Ar 4s 3d 1 10Ar 4s 3d
Chemistry 11, Atoms and the Periodic Table, Unit 07 19
Valence Electrons – Accessible or Reactable Electrons Valence electrons are all accessible electrons or all electrons in outer shells even if the outer shell is completely closed (filled). Core electrons are inaccessible electrons or electrons of the nearest noble gas.
Accessible / Valence and Inaccessible / Core Electrons
element core electrons valence electrons
lithium He 12s
inaccessible accessible
Valence electrons are important in determining how the atom reacts chemically with other atoms…
complete shell: atoms with a complete or closed shell of valence electrons tend to be chemically inert
over-filled shell: atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions
under-filled shell atoms with one or two valence electrons fewer than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions
Chemistry 11, Atoms and the Periodic Table, Unit 07 20
Example 07
Determine the number of valence electrons in the following atoms...
Ato
mic
Num
ber
Ele
me
nt
Str
uctu
re
Vale
nce
Ele
ctr
ons
1 Hydrogen 11s 1
2 Helium 21s 2
3 Lithium 1He 2s 1
4 Beryllium 2He 2s 2
5 Boron 2 1He 2s 2p 3
6 Carbon 2 2He 2s 2p 4
7 Nitrogen 2 3He 2s 2p 5
8 Oxygen 2 4He 2s 2p 6
9 Fluorine 2 5He 2s 2p 7
10 Neon 2 6He 2s 2p 8
Chemistry 11, Atoms and the Periodic Table, Unit 07 21
Lesson 02: The Periodic Table
01 Introduction to the Periodic Table
The periodic table of the chemical elements is a method of displaying the chemical elements. The invention of the periodic table is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev intended the table to illustrate recurring (periodic), trends in the properties of the elements…
Mendeleev's 1871 periodic table
Chemistry 11, Atoms and the Periodic Table, Unit 07 22
Today, the periodic table is now common within chemistry, providing an extremely useful way to classify, systematize and compare all the many different chemicals and their behaviours. The current periodic table, as of January 2008 contains 117 elements.
Modern Periodic Table
Chemistry 11, Atoms and the Periodic Table, Unit 07 23
02 Arrangement of Elements
Groups, Families or Columns A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements.
Groups are numbered numerically 1 to 18 from the left to right. Some of these groups have been given trivial names, such as…
alkali metals (group 1)
alkaline earth metals (group 2)
pnictogens (group 15)
chalcogens (group 16)
halogens (group 17)
noble gases (group 18)
transition metals (group 3 through group 12)
Chemistry 11, Atoms and the Periodic Table, Unit 07 24
However, other groups, are referred to simply by their group numbers, since they display fewer similarities and/or vertical trends.
Periods or Rows A period is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are regions where horizontal trends are more significant than vertical trends.
Chemistry 11, Atoms and the Periodic Table, Unit 07 25
Blocks Because of the importance of the outermost electron shell, the different regions of the periodic table are sometimes referred to as blocks, named according to the sub-shell in which the last electron resides…
s-block
p-block
d-block
f-block
Periodic Table Blocks
Chemistry 11, Atoms and the Periodic Table, Unit 07 26
03 Trends in the Periodic Table
Atomic Radius
As an atom's atomic number increases, more protons are added to the nucleus, while more electrons are stacked in the shells and sub shells around the atom. The trends are…
left to right (radius decreases): electrons become more tightly held to the nucleus because they are not being added to new energy levels
up to down (radius increases): electrons become more loosely held to the nucleus because they are being added to new energy levels
Chemistry 11, Atoms and the Periodic Table, Unit 07 27
Electronegativity
Electronegativity is the desire of an atom to take another atom's electrons. The trends are…
left to right (electronegativity increases): greater desire to fill missing valence shell electrons
up to down (electronegativity decreases): greater radius, increased shielding effect
Chemistry 11, Atoms and the Periodic Table, Unit 07 28
Ionization Energy
The ionization energy is the energy required to remove an outermost electron. The trends are…
left to right (ionization energy increases): greater desire to fill missing valence shell electrons
up to down (ionization energy decreases): greater radius, increased shielding effect
Chemistry 11, Atoms and the Periodic Table, Unit 07 29
Note Regarding the Shielding Effect The shielding effect describes the attraction between an electron and the nucleus in any atom with more than one electron shell. Shielding effect can be defined as a reduction in the effective nuclear charge on electrons due to a difference in attractive forces of between outer electrons on the nucleus.
Shielding Effect
Chemistry 11, Atoms and the Periodic Table, Unit 07 30
Lesson 03: Chemical Bonding
01 Introduction
Chemical reactions involve…
making bonds, and
breaking bonds
Chemical Reactions are a Result of Chemical Bonding
Before we can understand how a chemical reaction takes place, it
is essential that we know…
what bonds are, and
how they form
Once we have discussed these two topics we also need to
discuss…
what makes bond strong or weak, and
the implications of both
Chemistry 11, Atoms and the Periodic Table, Unit 07 31
02 Review
There are three terms you need to be aware of and careful not to
confuse…
valence electrons
core electrons
valence
Valence Electrons and Core Electrons
Valence electrons are those electrons in the outermost shell of an
atom. Core electrons are all electrons inside the outermost shell of
an atom.
Valence and Core Electrons Example: Carbon Atom
Valence Electrons Core Electrons
4 2
Valence electrons are important in determining two things…
IF an atom will react with other atoms, AND
HOW an atom will react with other atoms
Chemistry 11, Atoms and the Periodic Table, Unit 07 32
Atoms can have a…
completely filled outer shell: tend to be chemically inert and
thus unreactive
Completely Filled Outer Shell: Helium:
He
over filled outer shell: one or two valence electrons more
than a complete shell are highly reactive because the extra
electrons are easily removed to form positive ions
Over Filled Outer Shell: Lithium:
1He 2s
Chemistry 11, Atoms and the Periodic Table, Unit 07 33
under filled outer shell: one or two valence electrons less
than a complete shell are also highly reactive because of a
tendency to gain the missing electrons and form negative
ions or to share electrons and form covalent bonds
Under Filled Outer Shell: Fluorine
2 5He 2s 2p
Chemistry 11, Atoms and the Periodic Table, Unit 07 34
Valence
Valence, on the other hand, is the number of electrons gained or
lost to make the outermost shell of an atom stable.
Filling or emptying the outermost shell results in increased
stability.
Atoms bond to form compounds so as to fill their outer shells and
thus increase their stability.
Note
Never assume, however, that the valence of a given atom is simply
determined by the number of electrons present in the outermost
shell, or its valence electrons. In reality it is much more
complicated. Instead, just memorize valence values as column
numbers on the periodic table.
Chemistry 11, Atoms and the Periodic Table, Unit 07 35
Valence Electrons and Valence
Here is a table showing the differences between…
valence electrons, and
valence
Ato
mic
Num
ber
Ele
men
t
Str
uct
ure
Val
ence
Ele
ctro
ns
Val
ence
1 Hydrogen 11s 1 1
2 Helium 21s 2 0
3 Lithium 1He 2s 1 1
4 Beryllium 2He 2s 2 2
5 Boron 2 1He 2s 2p 3 3
6 Carbon 2 2He 2s 2p 4 4
7 Nitrogen 2 3He 2s 2p 5 3
8 Oxygen 2 4He 2s 2p 6 2
9 Fluorine 2 5He 2s 2p 7 1
10 Neon 2 6He 2s 2p 8 0
11 Sodium 1Ne 3s
1 1
Chemistry 11, Atoms and the Periodic Table, Unit 07 36
12 Magnesium 2Ne 3s
2 2
03 What is a Bond?
A chemical bond is the process…
responsible for the attractive interactions between atoms and
molecules
which confers stability to all chemical compounds
There are two main types of chemical bonds or forces...
intramolecular forces: strong bonding forces
intermolecular forces: weak bonding forces
These two types are commonly subdivided more-or-less as
follows...
Chemistry 11, Atoms and the Periodic Table, Unit 07 37
04 Intramolecular Forces
There are three main types of intramolecular forces…
metallic bonds
covalent bonds
ionic bonds
Metallic Bonding
Metallic bonding is the type of bonding found in metallic
elements.
This is the electrostatic force of attraction between positively
charged ions and delocalised outer electrons.
Chemistry 11, Atoms and the Periodic Table, Unit 07 38
Pure (Non-Polar) Covalent Bonding
Atoms in a covalent bond are held together by electrostatic forces
of attraction between positively charged nuclei and negatively
charged equally shared electrons.
When two atoms are bonded by a covalent bond and have…
the SAME electronegativity the electrons will be equally
shared between nuclei
For example, diatomic molecules such as…
nitrogen gas or 2N
oxygen gas or 2O
hydrogen gas or 2H
Chemistry 11, Atoms and the Periodic Table, Unit 07 39
Polar Covalent Bonding
In most covalent compounds the bonding is polar covalent. This
type of covalent bond exhibits an unequal sharing of electrons.
When two atoms are bonded by a covalent bond and have…
DIFFERENT electronegativities the electrons will not be
equally shared between nuclei
In this case, the end result is one atom having a slight negative
charge and the other a slight positive charge.
Chemistry 11, Atoms and the Periodic Table, Unit 07 40
Ionic Bonding
Ionic bonding is the electrostatic force of attraction between
positively and negatively charged ions.
The formation of ions is a result of a transfer of electron(s)
between atoms with a…
LARGE DIFFERENCE in electronegativities
Ionic bonding results from metals combining with non-metals. For
example, sodium combining with chlorine forms sodium chloride.
Chemistry 11, Atoms and the Periodic Table, Unit 07 41
Bonding Spectrum
Covalent, polar covalent and ionic bonding can be considered as
forming a continuous bonding spectrum…
as the difference in electronegativity increases
the bonds become more polar (then finally ionic)
Chemistry 11, Atoms and the Periodic Table, Unit 07 42
Electronegativity and Bond Type
Relative Strengths of Intramolecular Forces
Chemistry 11, Atoms and the Periodic Table, Unit 07 43
05 Intermolecular Forces
Chemistry 11, Atoms and the Periodic Table, Unit 07 44
Polarity is an important concept in understanding intermolecular
forces.
Molecules will either be…
polar, or
non-polar
Polarity is a situation that arises when a molecule develops a…
slight positive end due to fewer negative charges or more
positive charges
slight negative end due to more negative charges or less
positive charges
To determine whether a molecule is polar or not depends on
symmetry…
Polar VS Non-Polar
Polar Non-Polar
unequal sharing
of electrons between bonded
atoms
equal or unequal sharing
of electrons between bonded
atoms
asymmetrical
arrangement of bonded atoms
symmetrical
arrangement of bonded atoms
Polar Example Non-Polar Example
hydrogen fluoride, HF boron tri-fluoride, 3BF
Chemistry 11, Atoms and the Periodic Table, Unit 07 45
There are five main types of intermolecular forces…
permanent dipole - permanent dipole
permanent dipole - induced dipole
instantaneous dipole - induced dipole
ion dipole
ion - induced dipole
Permanent Dipole – Permanent Dipole Force
Chemistry 11, Atoms and the Periodic Table, Unit 07 46
This type of attraction take place when two or more neutral
permanently polar covalent molecules orient themselves so that
their positive and negative ends are close to each other.
One very important and unique case of the permanent dipole -
permanent dipole attraction is known as hydrogen bonding.
A hydrogen bond is a type of attractive intermolecular force that
exists between…
a hydrogen atom on one molecule, and
an electronegative atom such as nitrogen, oxygen or fluorine
on another molecule
A hydrogen bond results when the partial positive charge on the
hydrogen is attracted to a lone pair of electrons on another atom
which bears a partial negative charge.
Chemistry 11, Atoms and the Periodic Table, Unit 07 47
The most common, and perhaps simplest, example of a hydrogen
bond is found between water molecules…
Permanent Dipole – Induced Dipole Force
Chemistry 11, Atoms and the Periodic Table, Unit 07 48
This type of attraction takes place due to the interaction between a
permanent dipole and a non-polar molecule.
Instantaneous Dipole - Induced Dipole Force
Chemistry 11, Atoms and the Periodic Table, Unit 07 49
This type of attraction is also known as…
London forces, or
London dispersion forces, or
dispersion forces
It is a relatively weak forces of attraction that exists between…
all substances, but
are of particular importance with nonpolar covalent
molecules and noble gases
In this process…
electron distribution in individual molecules suddenly
becomes asymmetrical (or distorted)
the newly formed dipoles now become attracted to one
another
Chemistry 11, Atoms and the Periodic Table, Unit 07 50
The ease with which the electron cloud of an atom can be distorted
to become asymmetrical is called the molecule’s polarizability.
The greater the number of electrons an atom has, the farther they
will be from the nucleus, and the greater the chance for them to
shift positions within the molecule.
This means that larger nonpolar molecules tend to have stronger
London dispersion forces.
Ion - Dipole Forces and Ion - Induced Dipole Forces
Chemistry 11, Atoms and the Periodic Table, Unit 07 51
An ion - dipole force consists of interactions between…
an ion, and
a polar molecule
They align so that the positive and negative forces are next to one
another, allowing for maximum attraction.
An ion - induced dipole force consists of interactions between…
Chemistry 11, Atoms and the Periodic Table, Unit 07 52
an ion, and
a non-polar molecule
Like a dipole-induced dipole force, the charge of the ion causes a
distortion of the electron cloud on the non-polar molecule.
Relative Strengths of Intermolecular Forces
Chemistry 11, Atoms and the Periodic Table, Unit 07 53
06 Structures Caused by Bonding
Chemistry 11, Atoms and the Periodic Table, Unit 07 54
Metallic Structure
A metallic structure consists of a giant lattice of positively charged
ions and delocalised outer electrons.
Covalent Molecular Structure
A covalent molecular structure consists of discrete molecules held
together by weak intermolecular forces, and hydrogen bonds.
Network Covalent Structure
Chemistry 11, Atoms and the Periodic Table, Unit 07 55
A network covalent solid is a chemical compound in which the
atoms are bonded by covalent bonds in a continuous network. In a
network solid there are no individual molecules and the entire
crystal may be considered a macromolecule.
Ionic Structure
An ionic structure consists of a giant lattice of oppositely charged
ions.
Chemistry 11, Atoms and the Periodic Table, Unit 07 56
Monatomic Structure
A monatomic structure consists of discrete atoms held together by
intermolecular forces, such as the Noble gases.
Chemistry 11, Atoms and the Periodic Table, Unit 07 57
07 Why Make a Bond?
In nature we find that…
Noble gases: are never found bonded to other atoms,
whereas
most other elements: are only found bonded to other
elements
The reason for this is due to electron configurations…
Noble gases: the valence shell is completely full, it cannot
accept another electron into the shell
most other elements: the valence shell is not completely full,
it can accept another electron into the shell
In essence, all atoms with unfilled valence shells…
react with other atoms to form bonds, in an attempt
to achieve a closed shell electron configuration
Example 01: Lithium Fluoride
For example, when a lithium atom and a fluorine atom meet,
lithium can achieve a noble gas configuration by donating an
electron to fluorine...
Chemistry 11, Atoms and the Periodic Table, Unit 07 58
Example 02: Diatomic Fluorine
You may have asked yourself why two fluorine atoms don't come
together to perform the following reaction...
Even though the reaction may appear to be favourable because of
the production of a closed shell species, there is a better way to
achieve a Noble gas configuration… by sharing electrons.
See the next part of this lesson…
Chemistry 11, Atoms and the Periodic Table, Unit 07 59
08 Lewis Structures and Covalent Bonding
A covalent bond represents a shared electron pair between
atoms…
Methane Covalent Bond
Before we can determine how an atom bonds covalently with
other atoms we need a simple method for displaying valence
electrons…
Chemistry 11, Atoms and the Periodic Table, Unit 07 60
Lewis Structures Basics
Since only valence electrons are involved in bonding, all other
electrons can be ignored when it comes to determining the number
of covalent bonds between atoms. The way involves drawing
Lewis Structures.
Lewis structures are drawn using the following steps…
determine the number of valence electrons
draw one dot next to the symbol for the atom for each
valence electron
place two electrons (max) on each of the four sides of the
atomic symbol since atoms strive to achieve a full octet of
electrons
Lewis Structures for First 18 Elements
Lewis structures allow us to simplify complex multi-electron
diagrams.
Chemistry 11, Atoms and the Periodic Table, Unit 07 61
Lewis Structures and Covalent Bonding (Atoms)
Lewis structures are going to display two features…
bonding (pair) electrons: drawn using a line between the two
atoms
non-bonding electrons: drawn using dots to represent each
non-bonding electron
Example 03
Take for instance the bonding that takes place between hydrogen
and bromine…
Once bonding has completed, both atoms have completely filled
outer shells…
hydrogen has two electrons
bromine has eight electrons
Chemistry 11, Atoms and the Periodic Table, Unit 07 62
Example 04
The deadly gas carbon monoxide provides an interesting example
of how to correctly draw Lewis structures…
Since carbon has four electrons and oxygen has six…
using a single bond: if only one bond were to be formed
between carbon and oxygen, carbon would have five
electrons and oxygen 7
using a double bond: if two bonds were to be formed
between carbon and oxygen, carbon would have six
electrons and oxygen 8
using a triple bond: if three bonds were to be formed
between carbon and oxygen, carbon would have eight
electrons and oxygen 8
Such multiple bonds must be employed to explain the bonding in
many molecules. However, only single, double, and triple bonds
are commonly encountered.
Chemistry 11, Atoms and the Periodic Table, Unit 07 63
Lewis Structures and Covalent Bonding (Ions)
For more complex molecules and molecular ions, it becomes
important to keep an accurate count of the number of electrons in
the molecule.
Example 05
For example, let us make a Lewis structure for 2NO .
We have…
5 electrons from nitrogen
12 from the oxygens
1 extra electron due to the negative charge
Therefore, 2NO has a total of 18 electrons and we should draw
the following Lewis structure…
If we had tried to draw the above structure without taking the
charge of the ion into account, we could not have produced a full
octet around at least one atom.
Chemistry 11, Atoms and the Periodic Table, Unit 07 64
Example 05
If the 2NO ion had been positively charged, as in 2NO , we
would count the electrons as follows…
5 from nitrogen
12 from oxygens
-1 one due to the charge
Therefore 2NO has 16 electrons and we should draw the
following structure...
Chemistry 11, Atoms and the Periodic Table, Unit 07 65
Lesson 04: Properties of Major Chemical Families
Nobel Gases
Atomic
Number
Element Electrons /
Shell
Reactivity MP / BP
2 helium 2
low
low
10 neon 2, 8
18 argon 2, 8, 8
36 krypton 2, 8, 18, 8
54 xenon 2, 8, 18, 18,
8
86 radon 2, 8, 18, 32,
18, 8 high
Tendency: stable.
The noble gases are a group of chemical elements with very
similar properties: under standard conditions, they are all odorless,
colorless, monatomic gases, with very low chemical reactivity.
The six noble gases that occur naturally are helium (He), neon
(Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive
radon (Rn).
The properties of the noble gases can be well explained by modern
theories of atomic structure: their outer shell of valence electrons
is considered to be full, giving them little tendency to participate
in chemical reactions.
Like other groups, the members of this family show patterns in its
electron configuration, especially the outermost shells resulting in
trends in chemical behavior...
Chemistry 11, Atoms and the Periodic Table, Unit 07 66
The noble gases have full valence electron shells. Valence
electrons are the outermost electrons of an atom and are normally
the only electrons that participate in chemical bonding. Atoms
with full valence electron shells are extremely stable and therefore
do not tend to form chemical bonds and have little tendency to
gain or lose electrons.
Chemistry 11, Atoms and the Periodic Table, Unit 07 67
Alkali Metals
Atomic
Number
Element Electrons /
Shell
Reactivity MP / BP
1 hydrogen 1 low high
3 lithium 2, 1
11 sodium 2, 8, 1
19 potassium 2, 8, 8, 1
37 rubidium 2, 8, 18, 8, 1
55 cesium 2, 8, 18, 18,
8, 1
87 francium 2, 8, 18, 32,
18, 8, 1 high low
Tendency: give up 1 electron.
The alkali metals include lithium (Li), sodium (Na), potassium
(K), rubidium (Rb), cesium (Cs) and francium (Fr). Hydrogen (H),
although a member, very rarely exhibits behaviour comparable to
the alkali metals. This group lies in the s-block of the periodic
table, which means that all its elements have their outermost
electron in an s-orbital.
Like other groups, the members of this family show patterns in its
electronic configuration, especially the outermost shells, resulting
in trends in chemical behaviour...
The alkali metals are all highly reactive and are never found in
elemental forms in nature. Because of this, they are usually stored
in mineral oil or kerosene.
Chemistry 11, Atoms and the Periodic Table, Unit 07 68
Chemically, all of the alkali metals react aggressively with the
halogens to form ionic salts. They all react with water to form
strongly alkaline hydroxides. The vigor of reaction increases down
the group. All of the atoms of alkali metals have one electron in
their valence shells, hence their only way for achieving the
equivalent of filled outermost electron shells is to give up one
electron to an element with high electronegativity, and hence to
become singly charged cations.
Chemistry 11, Atoms and the Periodic Table, Unit 07 69
Alkaline Earth Metals
Atomic
Number
Element Electrons /
Shell
Reactivity MP / BP
4 Beryllium 2, 2 low high
12 Magnesium 2, 8, 2
20 Calcium 2, 8, 8, 2
38 Strontium 2, 8, 18, 8, 2
56 Barium 2, 8, 18, 18,
8, 2
88 Radium 2, 8, 18, 32,
18, 8, 2 high low
Tendency: give up 2 electrons.
The alkaline earth metals contain beryllium (Be), magnesium
(Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
The group lies in the s-block of the periodic table.
This specific group in the periodic table owes its name to their
oxides that give basic solutions. These oxides melt at such high
temperature that they remain solids in fires.
Like other groups, the members of this family show patterns in its
electron configuration, especially the outermost shells resulting in
trends in chemical behavior...
All the alkaline earth metals have two electrons in their valence
shell, so the energetically preferred state of achieving a filled
electron shell is to lose two electrons to form doubly charged
positive ions.
Chemistry 11, Atoms and the Periodic Table, Unit 07 70
The alkaline earth metals have much higher melting points and
boiling points compared to the alkali metals. The alkali metals are
also softer and are more lightweight whereas the alkaline earth
metals are much harder and denser.
The second valence electron is very important when it comes to
comparing chemical properties of the alkaline earth and the alkali
metals. The second valence electron is in the same “sublevel” as
the first valence electron. This means that the elements of the
alkali earth metals group contain a smaller atomic radius and
much higher ionization energy than the alkali metals group. Even
though the alkali earth metals group contains much higher
ionization energy, they still form an ionic compound with 2+
cations. Beryllium, however, behaves differently. This is because
in order to remove two electrons from this particular atom, it
requires significantly more energy. It never forms Be2+ and its
bonds are polar covalent.
Chemistry 11, Atoms and the Periodic Table, Unit 07 71
Halogens
The halogens or halogen elements are a series of nonmetal
elements comprising fluorine (F), chlorine (Cl), bromine (Br),
iodine (I), and astatine (At).
Like other groups, the candidates of this family show patterns in
its electron configuration, especially the outermost shells resulting
in trends in chemical behavior...
Atomic
Number
Element Electrons /
Shell
Reactivity MP / BP
9 fluorine 2, 7 high low
17 chlorine 2, 8, 7
35 bromine 2, 8, 18, 7
53 iodine 2, 8, 18, 18,
7
85 astatine 2, 8, 18, 32,
18, 7 low high
Tendency: gain 1 electron.
Halogens are highly reactive, and as such can be harmful or lethal
to biological organisms in sufficient quantities. This high
reactivity is due to the atoms being highly electronegative due to
their high effective nuclear charge. They can gain an electron by
reacting with atoms of other elements. Fluorine is one of the most
reactive elements in existence, attacking otherwise inert materials
such as glass, and forming compounds with the heavier noble
gases. It is a corrosive and highly toxic gas. The reactivity of
fluorine is such that if used or stored in laboratory glassware, it
Chemistry 11, Atoms and the Periodic Table, Unit 07 72
can react with glass in the presence of small amounts of water to
form silicon tetrafluoride. Thus fluorine must be handled with
substances such as Teflon (which is itself an organofluorine
compound), extremely dry glass, or metals such as copper or steel
which form a protective layer of fluoride on their surface.
The high reactivity of fluorine means that once it does react with
something, it bonds with it so strongly that the resulting molecule
is very inert and non-reactive to anything else. For example,
Teflon is fluorine bonded with carbon.
Both chlorine and bromine are used as disinfectants for drinking
water, swimming pools, fresh wounds, spas, dishes, and surfaces.
They kill bacteria and other potentially harmful microorganisms
through a process known as sterilization. Their reactivity is also
put to use in bleaching. Sodium hypochlorite, which is produced
from chlorine, is the active ingredient of most fabric bleaches and
chlorine-derived bleaches are used in the production of some
paper products. Chlorine also reacts with sodium to create sodium
chloride, which is another name for table salt.