Transcript The Chemistry of Life Chapter 2

The Chemistry of Life
Chapter 2
Why should we study
chemistry in
Life depends on chemistry!
• When you eat food or inhale oxygen,
your body uses these materials in
chemical reactions that keep you alive.
• Just as buildings are made from bricks,
steel, glass, and wood, living things are
made from chemical compounds.
It all begins with…
• Atoms – the smallest unit of matter
History
• Greeks were first to try to explain chemical
reactions
• 400 BC: thought all matter composed of:
–
–
–
–
Fire
Earth
Water
Air
• Democritus first used word “atomos”, meaning
indivisible
• Atoms are composed of 3 main
particles: (subatomic particles)
– Protons (+)
– Neutrons (0)
– Electrons (-)
Protons and Neutrons
• Nucleus – Center of atom that
contains protons and neutrons.
• Both particles have about the
same mass.
Electrons
• Electrons are about 1/1840 the
mass of a proton.
• They are in constant motion in the
space surrounding the nucleus.
• Electron cloud model
• Atoms have equal numbers of
electrons and protons.
• This makes an atom neutral
The Elements
• 116 known elements
• 92 occur naturally
• Only 25 are important to living
organisms!
Elements
• Atomic number – number of protons
• Atomic mass – number of protons
and neutrons. (amu)
• Atomic symbol – letters naming the
element
Learning Check 1
State the number of protons for atoms of
each of the following:
A. Nitrogen
1) 5 protons
2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons
2) 16 protons
3) 6 protons
C. Barium
1) 137 protons 2) 81 protons
3) 56 protons
The Periodic Table
More Electrons
• Electrons reside in something
called shells.
• Shells are areas that surround
the center of an atom. (aka.
orbitals and energy levels)
More About Electrons
• Every shell can hold only so many
electrons
• The further from the nucleus, the
more electrons a shell can hold
Electrons
• Valence electrons - the electrons
on the outside shell of the atom
• This is where bonding takes place
• Atoms have no more than 8
valence electrons
Energy Level
(Shell)
Maximum
Number of
Electrons
Max number
of Valence
Electrons
1
2
2
2
8
8
3
18
8
4
32
8
5
50
8
6
72
8
7
98
8
The Octet Rule:
• Atoms will combine to form
compounds in order to reach eight
electrons in their outer energy level.
This is very stable!
•
Atoms with less than 4 electrons
tend to lose electrons.
•Atoms with more than 4
electrons tend to gain
electrons.
Review
1. How many protons, electrons, and
neutrons are in…
– Boron
– Chlorine
– Sodium
2. How many valence electrons does
each of these elements have?
3. What is the chemical formula for
water?
Compound
• Two or more elements chemically
combined in specific proportions
• Examples:
– Water
– Salt
– Sugar
H 2O
NaCl
C6H12O6
Chemical Formulas
are used to
represent
compounds
Two types of compounds:
Ionic
Covalent
Ionic Compounds
• Form when electrons are transferred
from one atom to another. (stealing)
Ions - Atoms with a net charge due to
gaining or losing electrons
– Gaining electrons gives an ion a negative charge
– Losing electrons gives an ion a positive charge
**If they have to choose, atoms
would rather be stable (with a full
“octet”) than neutral.
How Does This Happen?
Some atoms have a few too
many electrons
Some atoms only need a few
electrons
What do you do if you are a sodium (Na)
atom with one extra electron?
Go look for an atom that
wants it!
Ionic Bonding
• Negative ions and positive ions are held
together by ionic bond.
• https://www.youtube.com/watch?v=xweiQukBM_k
• Ionic compounds form between
metals and nonmetals
What If No One Will Give Up
An Electron?
• Covalent Bonds • Atoms with less than 8 valence electrons can
move close to each other and share their
electrons
• The electrons spend their time around both
atoms.
• And they lived happily ever after!
Covalent Bonds
• Sometimes the atoms share two pairs of
electrons and form a double bond, or three
pairs of electrons to form a triple bond.
• Structures formed by
covalent bonds are
molecules.
• Covalent compounds form between
2 nonmetals
Let’s summarize what we know!
Why do compounds form?
• Atoms are trying to get 8 valence electrons
How do compounds form?
• By ionic (e- transfer) or covalent (e- sharing)
bonding
How can you tell if a compound is ionic or
covalent?
• By the types of elements in the compound
(ionic = NM + M
covalent = NM + NM)
Learning Check 2:
Indicate whether a bond between the following
would be 1) Ionic
2) covalent
___
A.
sodium and oxygen
___
B.
nitrogen and oxygen
___
C.
phosphorus and chlorine
___
D.
calcium and sulfur
___
E.
chlorine and bromine
Dot structures – Bonding
How many bonds are formed?
•
•
•
•
Carbon
Nitrogen
Oxygen
Hydrogen
Make Some Molecules
•
•
•
•
•
•
Ammonia – NH3
Methane – CH4
Carbon Dioxide – CO2
Propane – C3H8
Urea – H4N2CO
Glucose – C6H12O6
Chemical Reactions
• When one set of chemicals changes
into another set of chemicals, a
chemical reaction occurs
• Bonds are either broken or formed
(or both!)
• Our bodies use nutrients through
chemical reactions!
• Reactants – molecules/elements prior
to reaction
• Products – molecule/elements
produced as a result of the reaction
Energy
C6H12O6 + O2
CO2 + H2O
Chemical Equations
• Represent a reaction
• Give the types and amounts of
substances that react and form
Reactants
2H2 + O2
“yields”
“yields”
Products
2H2O
Law of conservation of mass
• States that matter is not created or
destroyed during a chemical reaction
• Even though the matter may change
from one form to another, the same
number of atoms exists before and
after the change takes place!
Mass of
Reactants
Mass of
Products
Lets Make water!
2 H2
O2
2 H2O
Iron + Oxygen  Ironoxide
TAKE A
LOOK AT
THE
NUMBERS
Fe
Fe
Fe
Fe
How many Iron
molecules?
O2
Fe2O3
O2
Fe2O3
O2
How many
Oxygen
molecules?
What about
the
PRODUCT?
How do we write it?
Fe +
O2 
N 2 + H2 
KClO3 
Fe2O3
NH3
KCl + O2
CO2 + H2O 
C8H18 +
O2 
C6H12O6 +
CO2 +
O2
H2O
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Organic
Compounds
Organic Compounds
• Make up living organisms
• Contain the element carbon
4 valence
electrons =
4 covalent
bonds
Organic Compounds
• The carbon atom is versatile, it can
form large, complex compounds called
macromolecules
– Monomer –
– Polymer –
Organic Compounds
• Four main types of organic
macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids
Carbohydrates
• Made of C, H, & O
• H to O ratio is always 2:1
• Monomer – monosaccharide
– Ex. Glucose, sucrose
• Polymer – polysaccharide
– Ex. Starch, cellulose, fiber
• Main energy source for living
things
Carbohydrates
• Monosaccharide
• Examples:
• glucose – in many plant
and animal tissues, most
common monosaccharide
• fructose – in many fruits
• galactose – component of
milk
Carbohydrates
• polysaccharides
• Examples:
• glycogen – animals use to store
excess sugar
• plant starch – plants use to store
excess sugar
• cellulose – fibers that give plants
their rigidity & strength
Carb Sizes
Making bigger molecules
• Dehydration Synthesis – is a process
that connects two large molecules
– By removing a water molecule
Breaking down big molecules
• Hydrolysis – is a process that separates
two large molecules
– By adding a water molecule
Lipids
• Store a lot of energy
• Monomers – Glycerol
& Fatty acids
• Polymers – Fats & Oils
Lipids
• Important parts of cell
membranes and waterproof
coverings
• Steroids are lipids that act as
chemical messengers
Lipids
• If all carbons have single bonds, lipid is
saturated
• Ex: butter, lard, animal fat (usually solid at room
temperature)
• If any carbons have double or triple bonds,
lipid is unsaturated
• Ex: vegetable oil, fish oil, peanut oil
liquid at room temperature)
(usually
Fats vs. Oils
Proteins
• Contain C, H, O, and N
• Monomers – amino acids
– 25 different kinds (R groups)
• Polymers – proteins
Proteins
• Chains of AA’s are folded and twisted
giving each protein a unique shape
• Ionic charges and hydrogen bonds
help maintain protein’s shape
• Shape of protein is important to its
function!
• https://www.youtube.com/watch?v=TfYf_rPWUdY
Proteins
• Provide structure
– Ex: Collagen- makes up your skin,
muscles & bones
• Aid chemical activities in your body
– Ex: Enzymes- work to speed up
rxns in your body
• Transport substances into or out of
cells
• Help fight diseases
Dehydration synthesis!
Nucleic Acids
• Contain C, H, O, N plus
phosphorus (P)
• Monomer – Nucleotide
– 5 of them (A, T, C, G, U)
– Made of sugar, phosphate, and base
• Polymer – Nucleic Acid
– Ex. DNA, RNA
Nucleotide
Nucleic Acids
Nucleic Acids
• Store and transmit hereditary
information
–Ex: DNA (deoxyribonucleic acid)
RNA (ribonucleic acid)