Download Chemistry can be defined as the study of the composition, structure

Scientific Principles (Chemistry, Biochemistry and Genetics).
Textbooks
•
“Science in Nursing and Health Care”, Mark Foss.
•
“Science in nursing”, Laurie Cree.
•
“Chemistry for the Health Sciences” Sackman, Lehman.
•
“General Chemistry”, Ebbing, Gammon.
•
“Fundamentals of general, organic, and biological chemistry” John McMurry.
Introduction to Chemistry (6 hours) – Dr. Scully

States of Matter.

Atoms, ions, elements, molecules, compounds, mixtures, chemical reactions.

The atom and its structure – definitions, composition, electronically neutral
atom, electronic shell, AMU, molecules.

Chemical symbols and formulae.

Basic introduction to the periodic table (chemical elements of the body,
importance of these elements and their function).

Basic principles of ionic and covalent bonding; cations, anions and covalent
compounds.

Hydrogen ions, acids and bases. The pH scale, buffers and indicators.
 Solutions, solution concentration, and its significance in nursing.
Organic chemistry (3hours) Dr. McGlacken
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Relevance of Chemistry to Nursing
 Your body is made of chemicals – keeps us alive.
 We breathe in oxygen and nitrogen to be used in different processes. Kreb's cycle
which is a series of enzyme-catalysed chemical reactions of central importance in
all living cells that use oxygen as part of cellular respiration.
 NSAIDs (nonsteroidal anti inflammatory drugs) for pain relief.
 Antibiotics for infections e.g. penicillin
 Cisplatin – cancer treatment.
 Blood work is analyzed in a lab using various chemical tests. We hyperventilate
because our body's pH is off and breathing in CO2 (like breathing in a paper bag)
helps stabilise the pH in our blood.
 Red blood cells contain haemoglobin which binds to oxygen and transports to
around the body. Anaemia is defined as a qualitative or quantitative deficiency of
hemoglobin.
 Oral rehydration therapy - effective treatment for dehydration – consists of a
solution of electrolytes, especially sodium and potassium administered orally.
 Learning chemistry allows you to understand chemistry Language for its
application in medicine
Chemistry can be defined as the study of the composition, structure and properties
of matter and the reactions that matter undergoes.
Physical Chemistry is concerned with structure of matter, energy changes.
Analytical Chemistry is concerned with the identification, separation and
quantitative determination of the composition of different substances.
Organic Chemistry deals with the synthesis and reactions of the compounds of
carbon.
Inorganic Chemistry is concerned with the chemistry of elements other than carbon
and their compounds.
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What is Matter?
Matter is the general term for the material things around us. It can defined as whatever
occupies space and can be perceived by our senses.
There are two ways of classifying matter – by its physical status (solid, liquid or gas)
or by its chemical status (element, compound or mixture).
Physical Classification of Matter:
A solid is a form of matter which is rigid and has a definite shape and volume.
A liquid is a form of matter which flows and has no fixed shape but has a definite
volume.
A gas is a form of matter which flows and has no fixed shape or volume.
Example: Water can exist as a solid, liquid or a gas. It exists as a solid in the form of
ice; as a liquid as liquid water; as a gas as steam (gaseous water).
Chemical Classification of Matter:
A substance is a kind of matter that cannot be separated into other kinds of matter by
any physical process.
While a mixture is a kind of matter that that can be separated by physical means.
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All matter is composed of indivisible (cannot be
decomposed further) atoms. An atom is an extremely
small particle of matter that retains its identity during
chemical reactions.
Basic diagram of an atom.
An element is a type of matter composed of only one kind of atom.
Today 111 elements are known and these are listed in the periodic table. Examples of
elements would be sodium, oxygen, chloride, iodine, gold, silver…
Basic diagram of an element, which is composed of only one kind of atom. These
atoms are not chemically bonded together.
A compound is a type of matter composed of two or more elements chemically
combined in fixed proportions. Examples of compounds are sodium chloride (the
element sodium and the element chloride are chemically bound together. This is
commonly known as salt).
Basic diagram of a compound composed of two ore more elements chemically bound
together.
Example: Both sodium and chlorine are elements. Therefore, sodium is only
composed of sodium atoms, and chlorine is only composed of chlorine atoms. Both of
these elements can chemically combine together in fixed proportions to form a
compound. This compound is called sodium chloride (salt). This compound is a
substance which cannot be separated by physical means.
A mixture is a material that can be separated by physical means into two or more
substances. Example: salt in water which can separated by distillation – boiling off the
water.
Mixtures can be classified into two types:
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A homogenous mixture (solution) is a mixture that is uniform in its properties
throughout the samples. Cannot be easily separated. Example: Air is a gaseous
mixture of nitrogen and oxygen, which are physically combined but not chemically.
A heterogeneous mixture is mixture that consists of physically distinct parts, each
with different properties. Can be easily separated. Example: a mixture of salt and
sugar stirred together. If you looked closely you would see the separate crystals of
sugar and salt.
Chemical Symbols and formulae:
It is convenient to use symbols for the atoms of the different elements. An atomic
symbol is a one or two letter notation used to represent an atom corresponding to a
particular element. Typically the atomic symbol consists of the first letter in capitals
from the name of the element, sometimes with an additional letter from the name in
lower case.
Examples: Chlorine has the atomic symbol of Cl.
Oxygen has the atomic symbol of O.
Hydrogen has the atomic symbol of H.
Sodium has the atomic symbol of Na (from its latin name).
Z
Name
Symbol protons neutrons electrons
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorous
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
2
4
5
6
6
7
8
10
10
12
12
14
14
16
1
2
3
4
5
6
7
8
9
10
11
12
1
14
15
16
17
18
19
Sulphur
Chlorine
Argon
Potassium
S
Cl
Ar
K
16
17
18
19
16
18
22
20
16
17
18
19
5
Molecules:
Some atoms do not normally naturally occur singly but as molecules. A molecule may
consist of two or more identical atoms such as oxygen (O2 – contains two atoms of
atoms chemically bonded together). Gases often like to exist as two atoms chemically
bonded together. i.e. N2 (nitrogen gas), H2 (hydrogen gas). A molecular formula gives
the exact number of atoms of an element in a molecule.
Example: H2O is the molecular formula of water (contains two atoms of hydrogen
and one atom of oxygen chemically bonded together)., CO2 is the molecular formula
for carbon dioxide (contains one atom of carbon and two atoms of oxygen), NaCl is
the molecular formula for sodium chloride, in which it contains one atom of sodium
and one atom of chlorine.
The molecules in a substance are so small that if a glass of water was enlarged to the
size of the earth, the water molecules would be about the size of a golf ball.
Chemical reactions:
Molecules or elements can undergo a chemical reaction to produce a new type of
compound:

2H2 + O2 = 2H2O
Two molecules of hydrogen gas (2 X H2) and one molecule of oxygen gas (O2)
gives two molecules of water (H2O).

Na + Cl2 = NaCl
One molecule of the element sodium (Na) and one molecule of chlorine gas
(Cl2) gives one molecule of sodium chloride (NaCl – salt).
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The Structure of the Atom:
Remember that an atom is an extremely small particle of matter that retains its
identity during chemical reactions. An atom consists of protons, electrons and
neutrons.
A proton is a particle that has a mass of approx. 1 amu (atomic mass unit) and is
positively charged.
An electron is a tiny particle which has a mass of approx. 0 amu and is negatively
charged.
A neutron is a particle that has a mass of 1 amu and is neutrally charged.
The protons and neutrons exist in the atom’s central core which is called a nucleus.
This is positively charged due to the protons.
The electrons exist around the atom’s central core of the nucleus in a region called the
electron cloud. Since electrons are negatively charged they balance the positively
charged protons in the nucleus, so that the overall charge of the atom is neutral.
Basic diagram of the atom.
Particle
Mass (amu)
Charge
Proton
~1.0
+1.0
Neutron
~1.0
Electron
~0
0
-1.0
Location in Atom
Nucleus
Nucleus
Electron cloud
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The electrons exist in areas within the electron cloud in regions known as electronic
shells. These electronic shells can only contain a certain number of electrons.
Electronic Shell
No. of Electrons
1
2
2
8
3
8
Therefore the first electronic shell can only contain two electrons.
The second electronic shell can only contain 8 electrons….
The Atomic Number (Z) of an element is the total number of protons or electrons in
the nucleus of an atom. Due to the fact that the overall charge of the atom is neutral
then the number of protons is equal to the number of electrons.
The Mass Number (M) of an element is the total number of protons plus neutrons in
the nucleus of an atom. (Note: the mass number is bigger than the atomic number).
The difference between the mass number and the atomic number is equal to the
number of neutrons in the nucleus.
Therefore each element has its own atomic number and mass number which is
represented as the mass number in subscript and the atomic number in superscript.
The atomic symbol, atomic number and mass number of the elements are listed in the
periodic table.
Mass Number = no. of neutrons + protons/electrons.
Atomic number = no. of electrons/protons.
Mass number – Atomic number = no. of neutrons.
Example: Oxygen is represented as 16O. The atomic number is 8. The mass number is
16. From the atomic number, oxygen has 8 electrons. It also tells us that oxygen has 8
protons. From the mass number, it has 16 neutrons and protons. Since we know it has
8 protons (from the atomic number), we know that oxygen has 8 neutrons.
Overall, oxygen has 8 protons (8 positive charges), 8 electrons (8 negative charges)
and 8 neutrons (neutral)… so overall charge of oxygen atom is neutral.
Carbon is written as 12C. Therefore, carbon has 6 protons, 6 electrons and 6 neutrons.
8
How to Draw an Atom:
Hydrogen is written as 1H. Therefore, hydrogen has 1 proton, 1 electron and 0
neutrons. It has 2 electrons in its valence (outer shell).
Carbon is written as 6C. Therefore, carbon has 6 protons (p+), 6 electrons (e-) and 6
neutrons (n).
There are two electrons in the first electronic shell, and the remaining four electrons
go into the second electronic shell. This is the outer most shell which is known as the
valence shell.
Oxygen is written as 8O. Therefore, oxygen has 8 protons, 8 electrons and 8 neutrons.
It has 6 electrons in its valence (outer shell).
9
Fluorine is written as 9F. Therefore, fluorine has 9 protons, 9 electrons and 10
neutrons. It has 7 electrons in its valence (outer shell).
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Isotopes
Some elements which have the same atomic number may differ in the number of
neutrons in the nucleus (i.e. their mass number).
These atoms which have identical atomic numbers but different mass numbers are
known as isotopes of the same element. In other words the nuclei have the same
number of protons but different numbers of neutrons.
Isotopes of the same element have the same chemical properties. The atomic weight
of carbon (C) is actually 12.011. This is because there are traces of heavier carbon
atoms found naturally 13C, 14C. These are termed isotopes of carbon as they have the
same atomic number (6) but differ in their mass number (differ in the number of
neutrons in the nucleas).
Isotope
12
6C
13
6C
14
6C
Abundance
98.89%
1.1%
trace
Periodic table:
In 1869 a Russian chemist Dmitri Mendeleev developed the first version of the
periodic table. The modern version, which all chemists use today, arranges the
elements by atomic number. Each entry lists the atomic number, atomic symbol and
atomic weight of an element.
The basic structure of the periodic table is its division into rows and columns, or
periods and groups.
A period consists of the elements in any one horizontal row of the periodic table.
Each time the outermost electron shell is filled and a further electron is then added a
new period is begun.
The first period of elements only consists of hydrogen (H) and helium (He).
The second period has 8 elements, beginning with lithium (Li) and ending with neon
(Ne).
The third period starts with sodium (Na) and ends with argon (Ar).
A group consists of the elements in any one column of the periodic table.
All the elements in a group have the same number of electrons in their outermost shell
(valence shell).
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Elements of the same group have similar chemical properties. Example: the elements
in the Group I are called the Alkali metals and are all metals (with the exception of
hydrogen which is a gas).
Group II = alkaline earth metals.
Group 17 = halogens.
Group 18 = Noble gases.
Group Name
no.
Valence Properties
electrons
Element
example
I
Alkali
metals
1
Metals (except for H Na
which is a gas);
Highly reactive
II
alkaline
earth
metals
2
Similar to alkali metals – Mg
not as reactive.
17
halogens
7
Variable
physical Br
properties - range from
solid (I2) to liquid (Br2) to
gaseous (F2 and Cl2);
Particularly reactive with
alkali metals.
18
Noble
gases
8 (full)
Non reactive due to full Xe
valence shell; Gases.
12
Metals, non-metals:
The elements of the periodic table are divided by a heavy staircase line into metals on
the left and nonmetals on the right. A metal is a substance or mixture that has a
characteristic luster, or shine and is generally a good conductor of heat and electricity.
A non-metal is an element that does not exhibit the characteristics of a metal. Most of
the nonmetals are gases.
Group 1
2 3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
Period
1
2
3
4
5
6
7
1
2
H
He
3
4
5
6
7
8
9
10
Li Be
B
C
N
O
F
Ne
11 12
13 14 15 16 17 18
Na Mg
Al Si
P
S
Cl Ar
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
55 56
Cs Ba
87 88
Fr Ra
*
**
* Lanthanides
** Actinides
I
Xe
72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Hf Ta W Re Os Ir
Pt Au Hg Tl Pb Bi Po At Rn
104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Key
Metals Metalloids Nonmetals
Periodic table showing position of metals and nonmetals.
13
Chemical elements of the body and importance of these elements and
their function:
Element
% mass in body
Oxygen (O)
65
Function
Toxic effects
Cellular respiration
Damage to eyes,
nervous system
and lungs at high
pressure.
Carbon (C)
18
Component of organic
Inhaled as
compounds.
Particles - lung
disease. (carbon
monoxide
poisoning)
Hydrogen (H)
10
Component of organic
acidosis, burns.
compounds.
Nitrogen (N)
3
Component of proteins,
harmful in oxide
Amino acids and cell
form.
membranes.
Calcium (Ca)
1.5
Bone and teeth
Nausea.
Phorphorus (P)
1.0
Call membranes
Liver damage.
The human body also contains amounts of sulphur (S), sodium (Na), Chlorine (Cl),
and trace amounts of Iron (Fe), Fluorine (F), Copper (Cu).
Elements of Biological Importance:
Oxygen (O):
It may seem obvious that people need to breathe oxygen to survive, but plants need
this element too. Many people think plants "breathe" carbon dioxide and "exhale"
oxygen. But in reality, plants also "breathe" oxygen at certain times. Without oxygen,
plants could not survive. Without plants, we wouldn’t have food to eat.
It is also worth mentioning that water is a compound of hydrogen and oxygen (H2O)
and that water is absolutely necessary for virtually all life as we know it. Water is
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incredibly important in our bodies. In fact, more than 50% of our bodies are made of
water. It dissolves other life-supporting substances and transports them to fluids in
and around our cells. It is also a place in which important reactions take place in our
bodies. Many people consider water to be the "blood of life".
When you consider the full importance of oxygen, it becomes clear that this versatile
element is the single most important substance to life.
Sodium (Na):
Since there no reserve store of sodium ions in the animal body, losses above the
amount of intake come from the functional supply of cells and tissues. Salt (sodium
chloride) is important in many ways. It is an essential part of the diet of both humans
and animals and is a part of most animal fluids, such as blood, sweat, and tears. It aids
digestion by providing chlorine for hydrochloric acid, a small but essential part of
human digestive fluid. Persons with hypertensive heart disease often must restrict the
amount of salt in their diet. 0.9% sodium chloride in water is called a physiological
solution because it is isotonic with blood plasma. It is known medically as normal
saline. Physiological solution is the mainstay of fluid replacement therapy that is
widely used in medicine in prevention or treatment of dehydration.
Calcium (Ca):
Approximately 99% of total body calcium is in the skeleton and teeth and 1% in
blood and soft tissues. Calcium has four major biological functions:
1. structural as stores in the skeleton
2. electrophysiological - carries charge during an action potential across
membranes
3. intracellular regulator, and 4) as a cofactor for extracellular enzymes and
regulatory proteins.
Calcium builds and maintains bones and teeth; regulates heart rhythm; eases insomnia;
helps regulate the passage of nutrients in & out of the cell walls; assists in normal
blood clotting; helps maintain proper nerve and muscle function; lowers blood
pressure; important to normal kidney function and in current medical research reduces
the incidence of colon cancer, and reduces blood cholesterol levels. Calcium
15
deficiency may result in arm and leg muscles spasms, softening of bones, back and
leg cramps, brittle bones, rickets, poor growth, osteoporosis (a deterioration of the
bones), tooth decay, depression.
Phosphorus (P):
Phosphorous is one of the most abundant minerals in the human body, second only to
calcium. This essential mineral is required for the healthy formation of bones and
teeth, and is necessary for our bodies to process many of the foods that we eat. It is
also a part of the body's energy storage system, and helps with maintaining healthy
blood sugar levels. Phosphorus is also found in substantial amounts in the nervous
system. The regular contractions of the heart are dependant upon phosphorus, as are
normal cell growth and repair.
Since phosphorus is found in almost all plant and animal food sources, a deficiency of
this mineral is rarely seen. However, phosphorus deficiency can and does occur,
particularly in people who take certain types of antacids for many years. Since
phosphorus is important in maintaining the bodys energy system and proper blood
sugar levels, it should seem logical that not getting enough of this mineral will affect
the energy level in the entire body. Indeed, feeling easily fatigued, weak and having a
decreased attention span can be symptoms of mild phosphate deficiency.
The human body must maintain a balance between magnesium phosphorus, and
calcium. Excess intake of phosphorus can occur in people with diets high in processed
foods, soft drinks, and meats, leading to osteoporosis.
16
Summary:
 Be familiar with most common elements and their atomic symbols e.g. oxygen,
carbon, nitrogen, sodium.
 Atomic number
Z = number of protons
 Atomic Mass number
A = number of protons + number of neutrons
For a neutral atom
Number of electrons = Number of protons
Symbol
12
6C
23
11Na
1
Name
Carbon
Sodium
Hydrogen
Chlorine
Mass Number (A)
12
23
1
35
Atomic Number (Z)
6
11
1
17
Protons
6
11
1
17
Neutrons
6
12
0
18
Electrons
6
11
1
17
1H
35
17Cl
17
Chemical Bonding:
Octet Rule:
A fundamental property of nature is that all atoms strive to have a full outer electronic
shell of electrons. In other words, all atoms want a full valence shell. When they can
achieve a full outer shell, the atoms are stable. This is a major driving force in
chemical bonding.
Many atoms gain or lose electrons in order to have a full valence shell (in order to
become stable). This loss or gain of electrons resulted in the formation of charged
atoms called ions.
An ion is an electrically charged particle obtained from an atom or chemically bonded
group of atoms by adding or removing electrons.
The numbers of electrons lost or gained is kept to a minimum – an atom will prefer to
gain 2 electrons rather than lose 6 e (or to lose 1e rather than gain 7e).
An atom that picks up an extra electron becomes a negatively charges ion called an
anion. (Note: remember that an electron is negatively charged so the addition of an
electron to an atom results in a negatively charged atom – anion).
An atom that loses an electron becomes a positively charged ion called a cation.
(Note: remember that an electron is negatively charged so the loss of an electron to an
atom results in a positively charged atom – cation).
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Example of a Cation: A sodium (Na) atom has 11 protons, 11 electrons and 12
neutrons. It has one electron in its valence (outer most shell – electronic shell number
3). Therefore in order to become stable the sodium atom wants to lose one electron so
it can than have a full valence shell (electronic shell number 2). When the sodium
atom loses this electron it forms a positively charged atom called a sodium cation.
Example of an Anion: A chlorine (Cl) atom has 17 electrons, 17 protons and 18
neutrons. It has seven electrons in its valence shell (electronic shell number 3). In
order to become stable, the chlorine atom needs to gain one electron in order to have a
full outer shell. When the chlorine atom gains an electron it becomes negatively
charged atom called a chlorine anion (Cl-).
When you are drawing the structure of an ion you have to put the structure of the
atom in square brackets and the charge of the ion (positive or negative) in the top right
had corner. The notation that one uses to signify an ion is the atomic symbol of the
element and the charge in superscript (Na+).
Na – e = Na+
Cl + e = Cl19
Ca -2e = Ca+2
O + 2e = O-2
Ions have different physical and chemical properties to the atoms from which they are
derived.
Sodium and lithium (metal atoms) react violently with water in a reaction which can
become explosive. Sodium ion, however, is found in table salt and is an important
constituent of human body fluids. Lithium ion is administered for the treatment of
anti-depressive conditions.
Chlorine atoms are too reactive to exist alone and in the absence of anything else to
react with they will react with themselves to form chlorine molecules (Cl2) which
forma greenish, toxic gas with a pungent odour. Chloride ion is found in table salt and
is the usual counter ion found widely distributed throughout the body to balance the
charges of the cations (Na+, K+).
The sodium and chlorine ions are singly charged but they can also be doubly charged
(Ca+2, O-2).
This leads us to chemical bonding..
The properties of a substance such as sodium chloride are determined in apart by the
chemical bonds that hold the atoms together. A chemical bond is a strong attractive
force that exists between certain atoms in a substance. There are two types of
chemical bonds – ionic (involves the losing or gaining of electrons) and covalent
(involves the sharing of electrons).
Ionic Bonding:
An ionic bond is a chemical bond formed by the electrostatic attraction between
positive and negative ions (particles with opposite electrical charges).
The bond forms between two atoms when one or more electrons are transferred from
the valence shell of one atom to the valence shell of another atom.
These two chemically bound atoms are then termed a compound (remember the
definition: a compound is a type of matter composed of two or more elements
chemically combined in fixed proportions).
Stable compounds are formed when the outermost shells of the atoms involved
are full.
20
The number of ions of each atom involved in ionic bonding is such that the positive
charge of the positive ions equal the negative charge on the negative ions.
Example: sodium chloride (NaCl) involves the sodium cation (Na+) and the chlorine
anion (Cl-). The sodium wants to lose one electron in order to have a full valence shell,
so it gives its electron to chlorine which wants an electron in order to have a full
valence shell. The overall charge on the compound is neutral.
Diagram of ionic bonding between sodium and chlorine.
Therefore, an ionic compound is a compound composed of cations and anions. The
strong attraction between positive and negative charges hold the ions together in a
regular pattern in space. For examples, in sodium chloride, each Na+ ion is surrounded
by six Cl- ions and each Cl- ion is surrounded by six Na+ ions. The result is a crystal,
which is a kind of solid having a 3-dimensional arrangement of atoms, molecules or
(in the case of NaCl) ions.
21
Example: LiF.
Li has 1 valence electron.
F has 7 valence electrons.
Therefore, Li loses an electron so it can have a full outer shell.
F gains an electron so it can have a full outer shell.
22
Covalent Bonding:
Many compounds do not contain ions.
These compounds consist of atoms bonded tightly together in molecules that result
when atoms share electrons instead of transferring electrons from one atom to another.
These are known as covalent compounds.
The bonds that hold atoms together in such molecules are covalent bonds.
Non-metals form covalent bonds with each other.
Diatomic molecules such as H2, O2, Cl2 are covalent molecules.
Compounds containing more than one non-metal are covalent compounds – NH3, CO2,
Therefore for covalent bonding there is sharing of electrons between atoms, so each
atom can achieve a full valence shell (octet rule).
Stable compounds are formed when the outermost shells of the atoms involved
are full.
Example: Hydrogen gas (H2).
Each hydrogen atom has 1 electron in its valence shell (electronic shell number 1). In
order for the hydrogen atom to be stable, the atom must have two electrons in its
valence shell (octet rule and the first electronic shell can only have a maximum of two
electrons). Therefore, there is a sharing of electrons between the two hydrogen atoms.
Only one electron from each atom is being shared so this is termed a single bond.
Both hydrogen atoms have one electron in their valence shell.
23
Each atom shares one electron each to form a H2 molecule. Both atoms are now stable
as they have full valence shells (electronic shell 1 can have a max. of 2 electrons).
In cases where there are two electrons being shared from each atom, this is termed a
double bond.
Example: Oxygen gas O2
In cases where there are three electrons being shared from each atom, this is termed a
triple bond.
There can also be covalent bonding between many atoms.
Example: Ammonia NH3
N has 5 valence electrons, and each hydrogen atom has 1 valence electrons. Therefore,
N shares one of its electrons with three H atoms, so N can have full valence shell.
24
For shorthand bonding between atoms can be shortened to a line or lines between
atoms. A single bond is represented by a single line; a double bond is represented by
two lines and a triple bond is represented by three lines.
H-H (H2), O-O (O2), O=C=O (CO2), N≡N (N2).
Double and triple bonds are classified as multiple bonds. Multiple bonds are shorter
and stronger than single bonds.
Organic Chemistry Example:
Organic chemistry involves the chemistry of the element carbon. Carbon never forms
ions (to lose or gain 4 electrons in one go would cost too much in energy terms).
Carbon always shares its 4 electrons but it is capable of multiple bonds. The carbon
atom can single bond to another carbon atom, or have double or triple bond to another
carbon.
ethene (contains a carbon carbon double bond, C=C).
ethane (contains a carbon carbon single bond, C-C).
ethyne (contains a carbon carbon triple bond).
acetone (contains a carbon oxygen double bond).
ethanol (contains a carbon carbon single bond and a carbon
oxygen bond).
25
Structure of Compounds:
A molecule has:

Fixed ratio of atoms always joined in the same way.

A definite shape in 3D space.

Particular bond lengths and bond angles.
Bond length is the distance between the nuclei of neighbouring atoms.
O
C
O
Linear
H
N
H
H
Trigonal planar.
H
C
H
H
H
Tetrahedral
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Valency:
Valency is simply the combining power of atoms or ions when forming compounds
and it is thus this which determines the ratios in which these combine together. In
ionic bonding the valency is simply the same as the charge on the ion.

Thus, sodium (Na) which has one electron in the outermost (valence) shell
which it needs to lose to form a singly charged positive ion Na+ has a valency
of 1.

Calcium (Ca) has two electrons in its valence shell, and so needs to lose 2
electrons to form a calcium cation (Ca+2) and so has a valency of 2.

Fluorine (F) has 7 electrons in its valence shell and so needs to gain another
electron in order to become stable (F-). Therefore, it has a valency of 1.

Oxygen has 6 electrons in its valence shell and so needs to gain 2 electrons in
order to become stable (O-2).
In ionic compounds all valencies must be satisfied, thus sodium chloride is NaCl
(each has a valency of 1) whereas calcium chloride is CaCl2 (here we require 2
chloride ions to satisfy the valency of 2 for calcium).
In covalent bonding the valency is the number of electrons actually used in bonding
(shared electrons).

Carbon (C) never form ions (to lose or gain 4 electrons in one go would cost
too much in energy terms) and always shares its 4 electrons, therefore having a
valency of 4.

Nitrogen (N) and Phosphorus (P) both have 5 electrons in their valence shell
and so may have a valency of either 3 or 5.
The valency of elements is shown on the periodic table:
All elements in group I – valency of 1. (H, Li, Na)
All elements in group II – valency of 2. (Be, Mg)
All elements in group 13– valency of 3. (B, Al)
All elements in group 14 – valency of 4. (C, Si)
All elements in group 15 – valency of 3/5. (N, P)
All elements in group 16 – valency of 2. (O, S)
All elements in group 17 – valency of 1. (F, Cl)
All elements in group 18 – valency of 0. (He, Ne, Ar – full valence shell).
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Therefore can predict how many atoms will combine together to form a compound.
Example:
NaCl
Na has a valency of 1, Cl has a valency of 1. You can switch these valencies to get the
molecular formula – NaCl.
CaCl2
Ca has a valency of 2. Cl has a valency of 1. When you switch these, you get the
molecular formula of CaCl2
CH4
C has a valency of 4. H has a valency of 1. Switch these and you get the molecular
formula of CH4
BF3
NH3
Therefore valency is a way of determining the combining ratios of atoms and ions in
molecules.
How to predict if a compound will undergo ionic or covalent bonding?
A convenient way of predicting the type of bonding involved between reacting atoms
is to use their electronegativity values.
Electronegativity is a measure of the ability of an atom in a molecule to draw
bonding electrons to itself.
Rule: If the electronegativity difference between reacting atoms is large the sharing of
electrons between them will be so uneven that the “shared” electrons will effectively
spend all their localised on the atom of greater electronegativity, thus a charged
species (ion) will be formed.
If the electronegativity difference is ≥ 1.98, ionic bonding takes place.
If the electronegativity difference is < 1.98, covalent bonding takes place.
Example: LiF (remember that both lithium (Li) and fluorine (F) both have a valency
of 1).
Li = electroneg. of 0.98
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F = electroneg. of 3.98. Difference is 3.00 – Ionic Bonding.
CN
C = electroneg. of 2.55.
N = electroneg. of 3.04. Difference is 0.49 – Covalent Bonding.
Polarity and solubility:

In the case of covalent bonding the atom of greater electronegativity acquires a
partial negative charge δ-, and the atom of lower electronegativity an equal
partial positive charge, δ+.

The bond then is said to be polar, ad the greater the difference in
electronegativity (but still less than 1.98), the greater the polarity.
It is the polarity of water, which allows ionic molecules to dissolve NaCl.
Ions are solvated and can move around with a greater degree of freedom.
Organic, non-polar substances do not dissolve in water.
Amino acids (building blocks of proteins) which have basic structure of +H3N-CHRCOO- - lots of polar bonds like O-H, N-H. Since they are polar, they are soluble in
water and can move around the body in the bloodstream.
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Hydrogen Bonds
When H is covalently bonded to an electronegative atom such as O or N (not C) in an
organic compound, e.g.
H
O
C
N
C
H
H
The bond will be polarised and the hydrogen will become slightly positively charged
(δ+). This slight positive charge can cause it to be attracted to another, slightly
negatively charged, electronegative atom (denoted as X) in another molecule. Thus
weak forces of attraction can be formed between molecules. These are known as
hydrogen bonds and are important in the chemistry of life.
Indeed it is hydrogen bonds which are the reason that water is a liquid, when the
corresponding compounds of atoms close to oxygen in the periodic table, combined
with hydrogen, are all gases.
Whilst, water may be expected to be a gas by comparison with its neighbours, it is
overall strength of many weak hydrogen bonds which constrain the water molecules
to remain close together as a liquid, at room temperature, rather than being free to
float away as a gas.
H
O
H
H
H
O
O
H
H
H
H
O
O
H
H
Of course if energy is supplied in the form of heat, this will break these weak forces
of attraction and the water molecules can escape by boiling off as water vapour.
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