1.1 Chemical Fundamentals - Father Michael McGivney
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Transcript 1.1 Chemical Fundamentals - Father Michael McGivney
1.1 Chemical Fundamentals
Isotopes
• When two atoms have the same number of
protons and electrons, but a different number
of neutrons, they are called isotopes (atomic
mass differs).
E.g., Hydrogen Isotopes
A
mass # = # of
protons + neutrons
X
Z
atomic # = # of
protons
Isotopes
• Radioisotopes are unstable isotopes whose
nuclei spontaneously break apart.
• The half-life of a particular radioisotope is
constant.
• They are used in radiometric dating and as
radioactive tracers.
E.g., Pygmy Woolly Mammoth
(1800 years old)
Radioisotopes
Name,
Symbol
Atomic
#
(Z)
Mass
#
(A)
Protons Neutron Relative Structur
s
Abunda al
nce
stability
Carbon-12
Carbon-13
Carbon-14
6
6
6
12
13
14
6
6
6
6
7
8
98.9%
1.1%
Trace
Stable
Stable
Radioacti
ve
Hydrogen-1
Hydrogen-2
Hydrogen-3
1
1
1
1
2
3
1
1
1
0
1
2
99.8%
0.2%
Trace
Stable
Stable
radioactiv
e
Characteristics of radioisotopes
• Half-life: the time it takes for one half of
the nuclei in a radioactive sample to decay
• Radiometric Dating: measure the ratio
between levels of stable and radioactive
isotopes to determine time elapsed
• Radioactive Tracers: radioisotopes used
to follow chemicals through chemical
reactions and trace their path as they
move through the cells and bodies of
http://www.mhhe.com/physsci/c
organisms
hemistry/essentialchemistry/flas
h/radioa7.swf
Chemical Bonding
• Electrons move around the atomic nucleus at
a distance determined by the amount of
energy the electron has.
• The further it is from the nucleus, the greater
its potential energy.
• Electrons in the outermost orbital are called
valence electrons.
• Valence electrons determine the chemical
behaviour of an atom.
Models of the Atom
• Bohr-Rutherford Model
of the Atom:
– Electrons move in the
space about the nucleus in
circular orbits like planets
revolve around the sun
• Lewis Dot Diagrams:
Diagrams showing only
the valence electrons of
the element since it is
these valence electrons
that are responsible for
the formation of chemical
bonds between atoms
•
• Quantum Mechanics
– A revision of the Bohr-Rutherford model since
it is impossible to know when exactly the
position and speed of electrons at any given
time
– A model that determines locations around the
nucleus where electrons are most likely to be
found. These volumes of space are called
orbitals.
•
ParticleWave
http://www.mhhe.
com/physsci/che
mistry/essentialc
hemistry/flash/hy
brv18.swf
• Energy levels: n=1, n=2, n=3, etc…
• Orbital Shapes: s, px, py, pz, d, f
Element
Helium
Carbon
Sulfur
B-R
Lewis-Dot
Quantum
Chemical Bonding
• Intramolecular Forces of Attraction: bonds that
hold atoms of a molecule or ions of an ionic solid
together
• An ionic bond is the force of attraction between
positive and negative charges.
E.g., Sodium Chloride (NaCl)
Chemical Bonds
Chapter 2 - Ionic
Bonding
Chemical Bonding
• A covalent bond forms when two atoms
share one or more pairs of valence electrons.
• Covalent bonds are stronger than ionic bonds.
Chapter 2 - Covalent
Bonding
E.g., Water (H2O)
Bond
Type
Entities Force of Chemical Lewis
attraction Formula diagram
Bond
strength
Ionic
Cation
and
anion
Electrostati
c attraction
between
oppositely
charged
ions
Weaker
than
covalent
bonds
Covalent
Neutral
atoms
Electrostati H2O
c attraction
between
nuclei and
valence
electrons
of neutral
atoms
Tutorial 2.1
Chemical Bond
Formation
NaCl
[Na+][C
l-]
O
H
H
Stronger
than ionic
bonds
Electronegativity
• A measure of an atom’s ability to attract a
shared electron pair when it is participating
in a covalent bond.
• The electronegativity difference (ΔEn)
allows one to determine the type of bond
formed between atoms or ions.
Molecular Shape
• Determines a molecule’s biological function
• When covalent bonds are formed, hybridization
occurs which changes the orientation of the
valence electrons
• VSEPR theory states that since electrons are all
negatively charged, valence electron pairs repel
one another and move as far apart as possible.
• Molecular Polarity: dependent upon bond
polarity and molecular shape
Polarity
Polar Covalent Bonds
• Unequal sharing of an electron pair results in
one atom attracting the pair more strongly than
the other atom.
• The atoms will take on a partial positive (δ +) or
partial negative (δ -) charge.
• Symmetrical molecular shapes
Chapter 2 - Polar
Covalent Bonding
What do
Microwaves do to
Water?
Polarity
Nonpolar Covalent Bonds
• Equal sharing of an electron pair.
• Includes hydrocarbons, such as methane.
• Asymmetrical molecular shapes
Intermolecular Bonds
• Bonds between molecules
• Determine physical state at a given temp
and pressure
• Weaker than intramolecular and ionic
bonds
• There are 3 types of intermolecular bonds:
London dispersion forces, dipole-dipole
forces, and hydrogen bonds
• A.k.a. van der Waals forces
London Dispersion forces
• Weakest forces found between all atoms
and molecules
• These forces exist due to the temporary
unequal distribution of electrons that are
attracted to the nuclei of neighbouring
atoms
Dipole-Dipole forces
• Hold polar molecules to one another
• The partially positive side on one molecule
is attracted to the partially negative side of
another molecule
Hydrogen bonds
• Strongest intermolecular forces
• Form between an electropositive H of one
polar molecule and an electronegative N,
O or F of a neighbouring polar molecule.
Chapter 2 - Hydrogen Bonding
WATER
• Function:
–
–
–
–
–
Controls body temp
Keeps surface moist
Gas exchange
Lubricates joints
Shock absorber
WATER
• Structure and Properties:
– Consists of polar covalent bonds and is a polar
molecule
– Molecular polarity allows ionic solids and other polar
molecules to dissolve in it readily
– Known as the universal solvent b/c so many different
solvents dissolve in it
Shockwave
Like Dissolves Like
• Miscible liquids dissolve in each other (e.g.
Ethanol and water)
dissolve
• Immiscible liquids do not dissolve in each
other (e.g. oil and water)
• Small non-polar molecules such as O2 and CO2
cannot form hydrogen bonds and therefore need
a protein carrier like hemoglobin. Large
nonpolar molecules also do not form hydrogen
bonds with water and are termed hydrophobic
(e.g. fats and oils) http://www.mhhe.com/physsci/chemistry/e
ssentialchemistry/flash/molvie1.swf
• Polar molecules dissolve in polar solvents
• Nonpolar molecules dissolve in nonpolar
solvents
Acids, Bases and Buffers
• Acids: Substances that increase the
concentration of H3O+ (aq) when dissolved in
water and that contain at least one ionisable
hydrogen atoms in their chemical structure.
– Acids taste sour and are able to conduct electricity
• Bases: substances that increase the
concentration of OH- (aq) ions in solution.
– Bases taste bitter, feel slippery and are able to
conduct electricity
Proton Exchnage
Neutralization
• Neutralization Reactions
http://www.mhhe.com/physsci/che
mistry/essentialchemistry/flash/bu
ffer12.swf
– The reaction of an acid and a base to produce water
and salt.
• pH
pH, the power of hydrogen
– Measure of the power of H+
– pH = -log10[H3O+(aq)]
• Buffers: systems used to resist significant
changes in pH
– These systems contain a substance that can donate
H+ ions when they are required and contain a
substance that can remove H+ ions where there are
too many in solution.
H2O (l) + CO2 (aq) H2CO3 (aq) HCO3- (aq) + H+ (aq)
Review
1. For a single atom of Sodium:
# of protons = ______
# of neutrons = _____
# of electrons = _____
# of valence electrons = _____
2. How many neutrons are found in an atom
of cobalt-60?
• For the molecule CO2:
– Draw a Lewis-dot diagram
– What kind of bonds are formed?
• Polar covalent, nonpolar, covalent or ionic
– Using the VSEPR theory what is the shape of
the CO2 molecule?
– Is CO2 polar or non-polar?
Radioisotopes
• Iodine-131 has a half life of 6 days. What
mass of Iodine-131 would remain from a
20 g sample after 30 days?
N = No (1/2) t / t ½
• No = Initial mass
• N = Final mass
• t = time
• t ½ = half-life time
Example 2
• How much of a 100.0 g sample of Au-195
is left after 8.10 days if its half-life is 2.70
days?
Questions??
• Homework
– Chemical Fundamentals Worksheet (on web)
– Download 1.2 powerpoint (on web)