Chemistry - Chemical Basis Of Life - Power Point

The Chemical Basis of Life Atoms, elements, compounds, & molecules How molecules interact Water is essential for life Acids, bases and salts Lectures by Tom Chen

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ELEMENTS, ATOMS, AND MOLECULES Chemicals play many more roles in life – Making up our bodies, those of other organisms, and the physical environment

2.1 Living organisms are composed of about 25 chemical elements • About 25 different chemical elements – Are essential to life • Trace elements – Are essential to life, but occur in minute amounts

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Atom: A unit of matter, the smallest unit of an element. 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

Table 2.1

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2.2: Trace elements are common additives to food and water • Dietary deficiencies in trace elements – Can cause various physiological conditions 0

Figure 2.2B Figure 2.2A

2.3 Elements can combine to form compounds 0

• Chemical elements – Combine in fixed ratios to form compounds

Sodium

Chlorine

Figure 2.3

Sodium Chloride

2.4 Atoms consist of protons, neutrons, and electrons • Atom: The smallest particle of matter that still retains the properties of an element Subatomic Particles • An atom is made up of protons and neutrons Located in a central nucleus • The nucleus is surrounded by electrons – – • Arranged in electron shells 2e

–

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Electron cloud

+ +

+ +

Nucleus 2 + Protons 2

Neutrons

2 – Electrons

Mass number = 4

Figure 2.4A

Differences in Elements • Atoms of each element

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– Are distinguished by a specific number of protons Electron cloud 6e–

++

Nucleus 6 + Protons 6

Figure 2.4B

Neutrons

6 – Electrons

Mass number = 12

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Isotopes

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The number of neutrons in an atom may vary • Variant forms of an element are called isotopes • Some isotopes are radioactive

Table 2.4

2.5 Radioactive isotopes can help or harm us • Radioactive isotopes are useful as tracers -

For monitoring the fate of atoms in living

Basic Research

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• Biologists often use radioactive tracers - To follow molecules as they undergo chemical changes in an organism Medical Diagnosis • Radioactive tracers are often used for diagnosis - In combination with sophisticated imaging instruments

Figure 2.5A

Figure 2.5B

How brain function is studied now? PET, CAT, MRI, etc.

Hearing,

speaking,

seeing,

thinking about words

Music Appreciation

2.6 Electron arrangement determines the chemical properties of an atom • Electrons in an atom

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– Are arranged in shells, which may contain different numbers of electrons 8 electrons) First electron shell (can hold 2 electrons)

Outermost electron shell (can hold

Electron

Figure 2.6

Hydrogen (H) Atomic number = 1

Carbon (C) Atomic number = 6

Nitrogen (N) Atomic number = 7

Oxygen (O) Atomic number = 8

Atoms whose shells are not full, tend to interact with other atoms and gain, lose, or share electrons. These interactions form chemical bonds Types of chemical bonds: 3. Ionic bond 4. Covalent bond 5. Hydrogen bond

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Ionic bonds are attractions between ions of opposite charge • When atoms gain or lose electrons – Charged atoms called ions are created

–

–

+

Transfer of electron

Na

Cl

Na Sodium atom

Cl Chlorine atom

–

Na

Na+ Sodium ion

Cl

Cl– Chloride ion

Sodium chloride (NaCl)

0 • Sodium and chloride ions – Bond to form sodium chloride, common table salt • An electrical attraction between ions with opposite charges

– Results in an ionic bond

Na+ Cl–

Figure 2.7B

Covalent bonds join atoms into molecules through electron sharing

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• In covalent bonds, two atoms share one or more pairs of outer shell electrons, forming molecules

0 Sharing of electrons may be EQUAL or UNEQUAL

• A molecule is nonpolar – When its covalently bonded atoms share electrons equally

• In a polar molecule

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– Electrons are shared unequally between atoms, creating a polar covalent bond (–)

(–)

O

H

Figure 2.9

(+)

H

(+)

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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 Hydrogen bonding occurs in other biologically important compounds such as proteins and DNA.

(–)

Hydrogen bond

(+) H

(+)

O

(–) (–) (+)

H (+ )

(–)

Can be used for recreation

Surrounds ¾ of the Earth’s surface

Used for hygienic purposes

Supplies body with essential minerals

Source of oxygen

Helps in maintaining homeostasis Serves as habitat for aquatic organisms

Used in food preparation

Makes up almost 70% of human’s body

Source of energy e.g hydroelectric power plants

Essential Minerals •are inorganic substances that exist naturally on and in the earth •14 minerals that have been shown by research to be essential to human health are: calcium, chromium, copper, fluorine, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, sodium and zinc • “Essential” because they comprise human tissue •Good sources of essential minerals include fruits, vegetables, meats, nuts, beans and dairy products. • Varying amounts of minerals can be obtained from WATER

Importance of minerals in body • crucial to the growth and production of bones, teeth, hair, blood, nerves, skin, vitamins, enzymes and hormones •For healthy functioning of nerve transmission • blood circulation •cellular integrity • energy production and muscle contraction

WATER’S LIFE-SUPPORTING PROPERTIES 0

Water is the solvent of life • Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions Na+

– + –

Cl–

Na+ Cl– +

+ – – +

+

– + – + –

–

– Ion in solution

Salt crystal

–

WATER’S LIFE-SUPPORTING PROPERTIES 0

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

Figure 2.11

WATER’S LIFE-SUPPORTING PROPERTIES 0 Water’s hydrogen bonds regulate temperature • Water’s ability to store heat (high heat capacity) – 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 0 Water has high heat of vaporization A water molecule takes energy with it when it evaporates • Leading to evaporative cooling Figure 2.12

Storm Turns Focus to Global Warming Is the rash of powerful Atlantic storms in recent years a symptom of global warming? some scientists have maintained that the rise in mean global temperatures over the last half a century — a well-documented trend widely linked to human activities such as the burning of fossil fuels — will inevitably have an effect on storms.

Ice is less dense than liquid water

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• 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

Hydrogen bond

Ice Hydrogen bonds are stable

Liquid water Hydrogen bonds constantly break and re-form

Living organisms are sensitive to acidic and basic conditions Acid = An ionic compound that releases H+ ions in solution Base = An ionic compound that accepts H+ ions or produces OHions in solution • Acidity is measured on the pH scale from 0 (most acidic) to 14 (most basic or alkaline)

pH scale

The pH scale

• Buffers are substances that resist pH change

OH– H+

OH–

H+

H+

H+ H+ Acidic solution

OH–

2

Lemon juice, gastric juice

3

Grapefruit juice, soft drink

4

Tomato juice

5 6

Human urine

7

Pure water Human blood

OH–

OH– H+ H+ – OH– OH H+ H+ H+ Neutral solution

OH–

Increasingly ACIDIC (Higher concentration of H+)

Is kept close to 7 (neutral) by buffers

H+

1

H+

+

OH–

OH– H+

OH–

OH– OH– – OH H+

NEUTRAL [H+]=[OH–]

8 Increasingly BASIC (Lower concentration of H+)

H

• The pH of most cells

0

0

Seawater

9 10 Milk of magnesia

11 Household ammonia

12 Household bleach

13 Oven cleaner

Basic solution

14

Figure 2.15

Acid precipitation threatens the environment

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• 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

Figure B Figure A

Salts Are formed when an acid and a base react with one another neutralizing the concentration of H+ ions  the process is called neutralization

Acid

Base

Salt

Importance of acids, bases and salts in living organisms 1. Life processes occur in neutral pH. 2.

Acids, bases and salts when dissolved in water serve as electrolytes.

3.

Salts are abundant in our body in the form of different body fluids like sweat and tears.

Electrolytes •are the elements necessary for electrochemical activity in our body. •Water (H20) – and the three minerals sodium, potassium and chloride are all necessary for the transmission of electrical impulses between cells

CHEMICAL REACTIONS

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2.17 Chemical reactions change the composition of matter • In a chemical reaction - Reactants interact, atoms rearrange, and products result

2 H2 Figure 2.17A

O2

2 H2O

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This is the general equation for photosynthesis—the process of capturing sunlight energy and converting it to chemical energy. Which of the following are the reactants of this reaction? • C6H12O6 and O2. • CO2 and H2O.