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Transcript of How to access School Files 1)Google “ocdsb” 2)Go to the students drop down menu and select “My...
How to access School Files
1) Google “ocdsb”
2) Go to the students drop down menu and select “My Docs-Active Directory”
3) Enter student number and password
4) Then choose: Data 1 on “ADLTFS1.ad.osdsb.ca”(X:)
5) Click on “Handout”
6) Scroll down and click “SBI4U”
The Chemical Basis of Life
Atoms, elements, compounds, & molecules
How molecules interact
Water is essential for life
pH and buffers
ELEMENTS, ATOMS, AND MOLECULES• Living organisms are
composed of matter
• Matter has mass and occupies space
Atom: A unit of matter, the smallest unit of an element.
Living organisms are composed of about 25 chemical elements
Trace elements
– Are essential to life, but occur in minute amounts
Element: A substance composed of atoms having an identical number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.
Carbon, hydrogen, oxygen, and nitrogen Make up the bulk of living matter
Trace elements are common additives to food and water
•Dietary deficiencies in trace elements can cause various physiological conditions
Elements can combine to form compounds• Chemical elements
– Combine in fixed ratios to form compounds
Sodium Chlorine Sodium Chloride
Subatomic Particles• An atom is made up of protons, neutrons and electrons
• The nucleus contains neutrons and protons and is surrounded by electrons
+
+
– –
+
–
2
2
2
Protons
Neutrons
Electrons
Massnumber = 4
++
2e–
Electroncloud
Nucleus
Atoms consist of protons, neutrons, and electrons
• Atom: The smallest particle of matter that still retains the properties of an element
Differences in Elements
•Atoms of each element are distinguished by a specific number of protons
+6
6
6
Protons
Neutrons
Electrons
Massnumber = 12
++
6e–
Nucleus
Electroncloud
6
Isotopes The number of neutrons in an atom may vary
• Variant forms of an element are called isotopes • Some isotopes are radioactive
Table 2.4
Radioactive isotopes are useful as tracers for monitoring the fate of atoms in living organisms
The half-life of a radioisotope is the time required for half of the atoms in a sample to decay
During beta-minus decay, a neutron in an atom's nucleus turns into a proton, an electron and an antineutrino.
Medical Diagnosis• Radioactive tracers are often used for diagnosis
- In combination with sophisticated imaging instruments
Research
• Biologists often use radioactive tracers to follow molecules as they undergo chemical changes in an organism
How brain function is studied PET, CAT, MRI, etc.
Music Appreciation
Hearing, speaking, seeing, thinking about words
PET•Positron emission tomography (PET) is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body.
•The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule
PET Scan
CT•Computed tomography (CT) is a medical imaging method employing tomography created by computer processing.
•Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation
MRI•Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging (NMRI), is primarily a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body
•Unlike CT, MRI uses no ionizing radiation. Rather, it uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body
MRI
Electron arrangement determines the chemical properties of an atom
•Electrons in an atom are arranged in shells, which may contain different numbers of electrons
Hydrogen (H)Atomic number = 1
Electron
Carbon (C)Atomic number = 6
Nitrogen (N)Atomic number = 7
Oxygen (O)Atomic number = 8
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
•Atoms whose shells are not full, tend to
interact with other atoms
•Atoms gain, lose, or share
electrons
•These interactions form
chemical bonds
Electron arrangement
Chemical Bonds
Types of Bonds
1) Ionic bonds are attractions between ions of opposite charge
• When atoms gain or lose electrons
– Charged atoms called ions are created
Transfer of electron
NaSodium atom
ClChlorine atom
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
Na Cl ClNa
+ ––
–
• Sodium and chloride ions
– Bond to form sodium chloride, common table salt
Na+
Cl–
• An electrical attraction between ions with opposite charges
– Results in an ionic bond
2) Covalent bonds join atoms into molecules through electron sharing
• In covalent bonds, two atoms share one or more pairs of outer shell electrons, forming molecules
Electronegativity•Electronegativity refers to the tendency of an atom to attract electrons in a covalent bond
•Oxygen (3.5) has a high electronegativity
•Hydrogen (2.1) and Carbon (2.5) have lower affinities
•A bond between carbon and hydrogen will have nearly equal sharing of electrons (non polar)
•A bond between oxygen and hydrogen will be highly polar
•If the atoms have a large difference in electronegativity (>1.8) then the electron is shared so unevenly that it produces an ionic bond.
Electronegativity
In a polar covalent bond electrons are shared unequally between atoms, creating a polar molecule
(–) (–)
(+) (+)
O
HH
3) Hydrogen Bonds
Hydrogen bonds are weak bonds important in the chemistry of life
• The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules
• This attraction forms weak bonds called hydrogen bonds
• Hydrogen bonding occurs in other biologically important compounds such as proteins and DNA.
Hydrogen
bond (+)
(+)
H
H(+)
(+)
(–)
(–)
(–)
(–)
O
Molecular Shape
Shapes of Molecules
Water is the solvent of life• Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions
+
–
–
–
–
–
–
–
–
––
++
+
++
Na+
+
Na+
Cl–
Ion insolution Salt
crystal
Cl–
WATER’S LIFE-SUPPORTING PROPERTIES
Hydrophobic and Hydrophilic molecules•Nonploar molecules do not form hydrogen bonds with water and are ‘excluded’ from associating with water
•These molecules are said to be hydrophobic
•Hydrophobic molecules such as oxygen require carrier proteins for transportation in the body
•Polar molecules can form hydrogen bonds with water and are said to be hydrophilic
Cell Membrane
WATER’S LIFE-SUPPORTING PROPERTIES
Hydrogen bonds make liquid water cohesive
• Due to hydrogen bonding
– Water molecules can move from a plant’s roots to its leaves by adhesion• Insects can walk on water due to surface
tension
• Created by cohesive water molecules
Water’s hydrogen bonds moderate temperature
• Water’s ability to store heat
– Moderates body temperature and climate
• It takes a lot of energy to disrupt hydrogen bonds
- So water is able to absorb a great deal of heat energy without a large increase in temperature
• As water cools
- A slight drop in temperature releases a large amount of heat
WATER’S LIFE-SUPPORTING PROPERTIES
Liquid waterHydrogen bonds
constantly break and re-form
IceHydrogen bonds are stable
Hydrogen bond
Figure 2.13
Ice is less dense than liquid water• Hydrogen bonds hold molecules in ice farther apart than in liquid water
• Ice is therefore less dense than liquid water which causes it to float
• Floating ice protects lakes and oceans from freezing solid
The chemistry of life is sensitive to acidic and basic conditions
A compound that releases H+ ions in solution is an acid
And one that accepts H+ ions in solution is a base• Acidity is measured on the pH scale from 0 (most
acidic) to 14 (most basic or alkaline)
The pH scale
Basic solution
Oven cleaner
Acidic solution
Neutral solution
pH scale0
1
2
3
4
5
6
7
8
9
10
11
12
Lemon juice, gastric juice
Grapefruit juice, soft drink
Tomato juice
Human urine
Pure waterHuman blood
Seawater
Milk of magnesia
Household ammonia
Household bleach
Incr
easi
ngly
AC
IDIC
(Hig
her
conc
entr
atio
n of
H+)
NEUTRAL[H+]=[OH–]
H+ H+
H+ OH– H+
H+ H+
OH– H+ H+
OH–
OH–
H+ H+OH–
OH– OH–
H+ H+H+
OH–
OH–
OH– OH–
OH–OH– H+
Incr
easi
ngly
BA
SIC
(Low
er c
once
ntra
tion
of H
+)
OH–
H+
14
13
Figure 2.15
• The pH of most cells
Is kept close to 7 (neutral) by buffers
• Buffers are substances
that resist pH change
Acid precipitation threatens the environment
• Some ecosystems are threatened by acid precipitation
• Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids
• Can kill trees and damage buildings
Acid, Bases and Buffers
Ionization of Water
• in pure water the concentration of the hydronium ion is 1.0x10-7mol/L
• the pH is defined as the negative logarithm of the hydronium ion concentration
• In pure water the pH=-log1.0x10-7
= 7
Strong Acids and Bases• Strong acids and bases completely ionize in water
Weak Acids and Bases
•Ionize partially in water
Weak Base
•10% ionization
Buffers
• a chemical system containing a substance that can donate H+ ions when required or remove H+ when too many are in solution
•therefore resist changes in pH
Functional groups
Functional groups are reactive clusters of atoms attached to the carbon backbone of organic molecules
Bonding Capacity
Element Bonding Capacity
Examples
H 1 Water, ethane
O 2 Oxygen, methanol
S 2 Hydrogen sulphide,
N 3 Nitrogen (N2), hydrogen cyanide (HCN)
C 4 Methane, carbon dioxide
P 5 Phosphate ion
Four classes of Biological Macromolecules
Macromolecule Subunit
Complex carbohydrate (starch)
Simple sugars (glucose)
Lipid (triacylglycerol) Glycerol and fatty acids
Protein Amino acids
Nucleic acid (DNA or RNA)
nucleotides
Condensation reaction (dehydration synthesis)
•A chemical reaction that creates a covalent bond between two interacting subunits, linking them to each other
•An anabolic reaction is a reaction that produces large molecules from smaller subunits
Hydrolysis Reaction
A hydrolysis reaction is a catabolic reaction in which a water molecule is used to break a covalent bond holding subunits together