Download 3.1 Basic Chemistry

Basic Chemistry
Atoms and Elements
Matter
•
Matter: The material
from which all
substances are made
•
Matter
1. Has mass
2. Takes up space
3. Is composed of atoms
Atoms
• Atom - the smallest unit of
matter
• Atoms are composed of smaller
subatomic particles
– Proton: (+) charge
– Electron: (-) charge
– Neutron: no charge
• Atoms are electrically neutral
• Atoms have two major zones:
– Atomic nucleus
• Contains most of the
energy and atomic mass
• Contains protons and
neutrons
– Electron cloud
• Determines reactivity
Electron cloud
He (Helium)
Elements: Properties of Atoms
•
The properties of an atom are determined by the
structure of an atom
Number of protons, neutrons, and electrons
•
1. Distance of the electron cloud from the nucleus
2. Arrangement of electrons in the cloud
•
Element: Matter composed of only one type of
atom
–
•
Ex. C and H are elements, but CH4 is not!
Elements are arranged by structure (and
therefore by properties) in the Periodic Table of
Elements
Periodic Table of Elements
/
http://www.ptable.com
The other
2% of
elements
in organisms
are called
trace
elements
98% of the mass of all
living organisms is composed
of the six yellow elements
CHONP(S)
Atomic Number
• Atomic number: The
number of protons in an
atom
• An element is defined by
its atomic number
– Ex. If an atom has 2 protons
(atomic # 2) it is helium, 3
protons it is lithium, etc.
• atomic # = # protons = #
electrons; remember
atoms are electrically
neutral!!
Atomic Mass
• Atomic mass: the weight
of an atom in Daltons (1
Dalton = 6.02 x 10-23
grams)
– Recognize that number?
• The atomic mass (in
Daltons) of an element is
roughly equal to the # of
protons + # of neutrons in
the atom
– # neutrons = rounded
atomic mass – atomic
number
• How many neutrons does a
standard helium atom
have?
Determining the numbers of subatomic particles in a carbon
atom using the Periodic Table of Elements:
1. Find carbon in the table: it has atomic number 6 and
atomic mass 12.011
2. Atomic number 6 means that carbon has 6 protons and 6
electrons (atomic number = # protons = # electrons)
3. Round the mass number to the nearest whole number
and subtract the # protons (or atomic number) to get #
neutrons
•
•
•
# neutrons = rounded atomic mass – atomic number
12.011 ≈ 12; 12-6 = 6 neutrons
Carbon has 6 protons, 6 electrons, and 6 neutrons
• Determine the numbers of subatomic
particles (protons, neutrons, and electrons)
in the following atoms {use a periodic
table}:
– 6C
– 8O
– 17Cl
– 7N
– 3Li
• Answers:
– 6C
–
–
–
–
= 6 protons, 6 neutrons, 6 electrons
8O = 8 protons, 8 neutrons, 8 electrons
17Cl = 17 protons, 18 neutrons, 17 electrons
7N = 7 protons, 7 neutrons, 7 electrons
3Li = 3 protons, 3 neutrons, 3 electrons
Electrons and Periodicity
• A row in the Periodic Table is called a
period and corresponds to an energy level
– The first period along the top contains the
elements H and He
– H and He contain only 1 energy level in their
electron clouds
• A column in the Periodic Table is called a
group; members of a group have similar
reactivity
(Group 1) (Group 2)
(Period 1)
(Period 2)
(Period 3)
(Group 3)
Electron Cloud: Energy Levels
• The electron cloud is divided into electron shells or
energy levels
• An atom’s outer energy level is its valence shell
and the electrons it contains are valence electrons
– An atom has as many energy levels as the period (row)
it is in {periodic table}
– An atom has a number of valence electrons = to its
Group (column)
• Remember that some periodic tables count transition metals as
groups; on these tables subtract 10 from the nonmetal group
numbers to get the valence electron. Ex: group 14 = 4 valence
electrons
– Valence electrons determine reactivity
• Determine the numbers of energy levels and
valence electrons in the following atoms {use
a periodic table}:
– 6C
– 8O
– 15P
– 7N
– 1H
• Answers:
– 6C
–
–
–
–
= 2 energy levels, 4 valence electrons
8O = 2 energy levels, 6 valence electrons
15P = 3 energy levels, 5 valence electrons
7N = 2 energy levels, 5 valence electrons
1H = 1 energy level, 1 valence electrons
Alternative Elements: Isotopes
• Isotope: an atom that has a number of neutrons different
from the average for that element
• Regular atoms usually more stable
• Isotopes occur naturally; the average mass numbers of
isotopes and normal atoms of one type is atomic weight
mass ≈ 1.000
2H mass ≈ 2.012
3H mass ≈ 3.014
+______________
6.026
Div by 3
________________
Atomic Wt ≈ 1.008
1H
Alternative Elements: Radioisotopes
(Radionuclides)
• Radioisotopes: Isotopes with unstable nuclei that
may emit high energy particles
– ‘Adding’ neutrons weakens the strong nuclear force and
destabilizes the nucleus
– The nucleus will regain stability by ejecting particles
• Radiation: Energy particles emitted by a
radioisotope
Uses for Radioisotopes
• Used in body scans
• Used as radiotracers to determine
steps of internal chemical
processes
– Radioisotopes were used to puzzle
out the steps of photosynthesis,
cellular respiration, and viral
infection among others
• Can be used date rocks, artifacts,
and bones
– Called radiometric dating
• Used to treat cancer
(chemotherapy) and other
disorders
• Massive or prolonged exposure
causes damage to organisms
Fiestaware Demo
Electron Clouds
• Divided into energy levels
• Energy levels divided into
orbitals
Orbitals
The Octet Rule
• Lewis dot diagram: A diagram of a period 1,
2, or 3 element that shows the distribution
of valence electrons in an atom
• Octet rule: A period 2 or 3 element has a full
valence shell when it has or can share 8
valence electrons
• Lewis dot diagrams are used to determine
whether and how two elements will
covalently bond
• Do a Lewis Dot Diagram of the following
atoms:
– 6C
– 1H
– 8O
– 7N
– 15P
– 16S
Basic Chemistry
ELECTRON PHYSICS
Physics - Background
• In order to do work, all machines must transform energy
from one form to another
– Work is what is accomplished when a force operates on an object
over a distance.
– Energy is the capacity to do work, or the capacity to change.
– Force is defined as a push, pull on an object
• The transformation of energy is a requirement of life (part
of metabolism)
– Energy transformations are linked to chemical transformations in
cells
• Remember: Energy → Force → Work
Physics- Potential Energy
All forms of energy can
be placed in two
categories:
…is realized
• Potential energy is stored
energy—as chemical
bonds, concentration
gradient, charge
imbalance, etc.
• Once energy is actually
converted, it is no longer
potential energy; it is real
energy
Potential energy….
Question:
• Just as energy can be converted from potential to
real, it can be converted from one type to another.
There are many types of energy; can you name
some?
Physics - Thermodynamics
There are two rules for the conversion of energy (the
Laws of Energy):
1. Energy is neither created nor destroyed. The
total amount of energy before a transfer equals
the amount of energy after (in a closed system).
2. No conversion or transfer of energy is 100%
efficient. The amount of energy useable for work
after a conversion is less than before the
conversion. The “lost energy” escapes as waste
heat. This phenomenon is called entropy.
Problem:
• A hypothetical car converts the chemical energy in gas to
kinetic energy (via the engine), and kinetic to electrical (via
the alternator) to power the radio. If both the engine and
the alternator are 20% efficient, and there is 100 calories
of energy in the gas, how much is left to power the radio
after conversion? How much energy is lost?
Answer:
• A hypothetical car converts the chemical energy in gas to
kinetic energy (via the engine), and kinetic to electrical (via
the alternator) to power the radio. If both the engine and
the alternator are 20% efficient, and there is 100 calories
of energy in the gas, how much is left to power the radio
after conversion? How much energy is lost?
– 100 cal (chemical) to 100 cal (.20) kinetic to 100 cal
(.20)(.20) electrical. 100 cal → 20 cal → 4 cal
– 4 calories are left for the radio. 96 calories were wasted.
Problem:
• An mechanic with little grasp of Thermodynamics
proposes an electrical car that uses an alternator claiming
that the alternator will charge the car battery and keep the
car going forever. What is wrong with his plan?
Answer:
• An mechanic with little grasp of Thermodynamics
proposes an electrical car that uses an alternator claiming
that the alternator will charge the car battery and keep the
car going forever. What is wrong with his plan?
– The alternator will actually drain all the power in the
engine! For example: Imagine that the battery, which
powers the car, has 100 cal of energy with a 20%
efficient energy conversion rate. When the electrical
energy is converted to kinetic energy, 20 cal will be
usable
Atomic Electrodynamics
• Electrons have
potential energy
proportional to their
distance from their
nucleus
– Farther = longer
distance to fall = more
potential energy!
• Electrons in their
original state are said
to be in a ground state,
but we can add energy
to make them jump to
a higher energy level;
an excited state.
– The jump lasts
microseconds before
the electron is snatched
up by a nearby atom or
falls back to the ground
state.
• Jumping electrons may go from a high
energy state to a low or vice versa
• The difference in energy is released or
stored
– Any stored energy can then be used to build
ATP
– Released energy emerges as heat or
fluorescence (light emissions)
• Some electrons may jump completely away
from their atoms! The atoms are not
ionized
Basic Chemistry
MOLECULES, REACTIONS &
BONDING
Elements vs. Molecules
• Elements are composed of only one kind of atom
(Ex O2)
– Six elements make up 98% of organic molecule mass
– Carbon, hydrogen, oxygen, nitrogen, phosphorus, and
sulfur CHONP(S)
• Molecules are composed of multiple kinds of atoms
chemically bound together (Ex H2O)
• Bonding occurs as a result of a chemical reaction,
an interaction of atoms in which molecules change
partner atoms to form new compounds*
Covalent Bonds
• Covalent bonds: Bond
in which atoms share
one or more pairs of
electrons, so that the
valence shells are filled
• May bond double or
triple
The Octet Rule
• Lewis dot diagram: A diagram of a period 1,
2, or 3 element that shows the distribution
of valence electrons in an atom
• Octet rule: A period 2 or 3 element has a full
valence shell when it has or can share 8
valence electrons
• Lewis dot diagrams are used to determine
whether and how two elements will
covalently bond
Determine a possible structural formula of hydrogen and
carbon
1. Find the elements on the Periodic Table and determine
the number of valence electrons each has
•
Carbon is #4 (Group 4, so 4 valence) and hydrogen is #1 (Group
1 so 1 valence)
2.
Do a Lewis dot diagram of each element
3.
Determine where valence electrons can pair up
• Do a Lewis Dot Diagram of the following
atoms:
– 6C
– 1H
– 8O
– 7N
– 15P
– 16S
Covalent bonds can be
• Single—sharing one pair of
electrons
C H
• Double—sharing two pairs of
electrons
C C
• Triple—sharing three pairs of
N N
electrons
Polar Covalent Bonds - Water
•
Polar covalent bonds
–
–
–
–
Generate a polar
(magnetic) molecule
H2O is the classic
example
Molecules become
magnetically ‘bent’
Causes the formation of
a magnetic field with a
(+) and a (–) end
Unpaired electrons & shape
Water is polar: it
possesses two
magnetic
dipoles. Here
the molecules
are attracted to
a statically
charged
balloon.
Hydrogen Bonds