Transcript Biochemistry I (CHE 418 / 5418)

Introduction to Organic and
Biochemistry
(CHE 124)
Reading Assignment
General, Organic, and Biological Chemistry: An Integrated
Approach
4th. Ed. Raymond
Chapter 2
Atoms and Elements
Answers to odd numbered problems in textbook are found in
the book’s index.
Atom
• The building block of matter.
– Greek (Atomos meaning indivisible).
• Atoms are composed to three subatomic particles
– Draw a diagram of carbon.
Subatomic
Particle
Mass (g)
Mass
(amu)
Charge
Location
Proton
1.6726 x 10- 24 1.0073
+
Nucleus
Neutron
1.6750 x 10-24 1.0087
0
Nucleus
(neutral)
Electron
9.110 x 10-28
5.486 x 10-4
Amu = atomic mass unit also called Dalton.
-
Outside
of
Nucleus
Elements
• Ancient Greeks recognized four elements
– Earth, air, fire and water.
• Modern definition
– Element - substance that contains only on type of atom.
• Elements cannot be broken down into substances
with different properties by chemical means.
– 112 known elements (91 naturally occurring)
• Elements are organized on the Periodic Chart. (See
next slide).
• Learn the elements / symbols on the handout.
Elements Have Two Important Numbers
A
Z
X
• Atomic Mass, A
• Atomic Number, Z
• Symbol of Element, X
Element Defined by Number of Protons
• Atomic Mass, A
12
= # protons + # neutrons
C
• Atomic Number, Z
6
= # protons
protons = electrons
The number of protons (atomic number)
defines an element.
Periodic Chart
• See the inside front cover of your textbook.
– Dmitri Mendeleev (1836-1907), along with others, arranged elements
by chemical properties onto primitive Periodic Table (1869)
• Left space for elements unknown at the time
• Predicted detailed properties for elements as yet unknown
G
r • Period -horizontal row, numbered 1 - 7
– Numbered top to bottom, organized by atomic number
o
u • Group or Family - vertical column,
– Numbered 1 – 8 A and B’s
p
– “New” system 1 – 18 (L to R).
– Elements in a group have similar chemical properties. 8A
1A
3A
2A
Period
3B
4B
5B
6B
7B
8B
1B
2B
4A
5A
6A
7A
– Main group elements
Note location of
• groups A’s 1, 2, 13 – 18
Metals
– Transition Metals
Nonmetals
• B’s groups 3 – 2
Metalloids
– Lanthanides
• elements 58 - 71
– Actinides
• elements 90 - 103
Metals vs Nonmetals
Metals
Nonmetals Metalloids
Conduct electricity
and heat
Lustrous
Malleable
Ductile
Nonconductor
Intermediate
Nonlustrous
Brittle
Brittle
Intermediate
Intermediate
Intermediate
• Lustrous
– Shiny
• Malleable
– Able to pound on without breaking
• Ductile
– Able to stretch into a wire
– Groups with common names
1A
2A
–
–
–
–
3B
Group 1 (1A) = Alkali Metals
Group 2 (2A) = Alkaline Earth Metals
3A
4A
Group 17 (7A) = Halogens
Group 18 (8A)= Noble Gases
4B
5B
6B
7B
8B
1B
2B
8A
5A
6A
7A
Trends
• Electronegativity
– Measure of how tightly an element holds onto its electrons.
Conversion Factors
Mole (Avagadro’s number)
• Atoms are very small
– How do we keep track of the number of atoms?
• Mole (n) = 6.022 X 1023 atoms / 1 mole
– the mass in grams of one mole of a substance is
numerically equal to its formula mass (molecular mass).
• By knowing Avogadro’s number and the atomic mass, it is now
possible to calculate the mass of a single atom in grams. In the
laboratory, substances are weighed on balances, in units of grams
• Significance of the Mole
– The mole allows us to relate the number of grams of a substance to
the number of atoms or molecules of a substance
Problems
• How many Carbon atoms are in 30 g of
Carbon?
• What is the weight in grams of 0.45 moles
of gold (Au)?
Bohr Model of the Atom
• Protons and neutrons are located in the nucleus.
• Electrons orbit the nucleus in specific orbits with
each orbit corresponding to a different energy level.
– Ground state (most stable state) when electrons are in
energy levels as near as possible to the nucleus
– Excited state when electrons is pushed into an orbit farther
from the nucleus.
• When electrons move from an excited state (higher energy level) to
the ground state (lower energy level), the energy produced is given
off often as light.
• Worked well to explain the emision spectrum of hydrogen, but not
other elements.
– Figure 2.12 p. 47. Line spectrum.
Quantum Mechanic Model of the Atom
• In 1926, Erwin Schrodinger wrote a
series of mathematical equations
that described electron energy
levels in a new way.
• Quantum Mechanics
– Energy levels called atomic orbitals
• Orbitals are three-dimensional regions of
space where there is a high probability of
finding an electron (electron cloud).
• See Figure 2.13 p. 48.
• Maximum number of electrons per energy
level = 2n2
• N=energy level.
– Table 2.5 p. 49 Give the Ground State
Electron Distribution for the first 20
elements. (use periodic chart and
board to demonstrate)
Energy
Level
(n)
Maximum
Number of
Electrons
1
2
2
8
3
18
4
32
Valence Electrons
• Valence electrons
– Electrons in the highest numbered, occupied
energy level.
– These are the “reactive” electrons.
– NOTE: elements in the same group, have the
same number of electrons in the valance shell.
Electron Dot Structures (Lewis dot
structures)
• Representation of the number of electrons
in an elements valence shell.
– Draw only the valence electrons.
– See figure 2.15 p. 51
An Element May Differ in Number
of Neutrons
• Isotope - element with the same number
of protons, but different number of
neutrons.
Atomic
Mass
Atomic
Number
# protons
12
C
6
13
14
C
6
= atomic number
C
6
Eight isotopes
of carbon are
(A = 9 – 16)
# neutrons = atomic weight - atomic number
An Element May Differ in Number
of Neutrons (Cont’)
Atomic
Mass
Atomic
Number
12
C
6
13
14
C
6
C
6
# protons
6
6
6
# neutrons
6
7
8
Isotopes of hydrogen
• 1H = hydrogen
• 2H = deuterium
• 3H = tritium
• Each isotope of hydrogen has a name.
• Z = 1 for each isotope of H.
• SEE TABLE 2.8 Page 59 for list of radioisotopes
used in medicine!
Half Life
• Time required for one half of atoms of
radioisotope to decay.
• Examples
– Radon – 222
– Plutonium 239
– Uranium 238
3.8 days
24,000 yrs.
4.5 million yrs.
Types of Radiation
Name
Alpha
particles
Beta
particles
Positrons
Gamma
rays
Sym
α
β
β+
γ
Make up
2 protons + 2
neutrons
(He nucleus)
Electron
Positively
charged electron
Electronmagnetic
raditation
Charge
Stopped
by
paper
2+
1-
plastic
1+
plastic
0
Concrete /
lead
See Table 2.7 for type of radiation emitted by particular isotopes.