The chemical basis of life
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The Chemical Basis of Life. Elements, Atoms and Molecules Water’s Life-Supporting Properties Chemical Reactions. Living Organisms are Made of Elements. Living organisms composed of matter Matter: anything that occupies space and has mass

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The Chemical Basis of Life

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The chemical basis of life

The Chemical Basis of Life

  • Elements, Atoms and Molecules

  • Water’s Life-Supporting Properties

  • Chemical Reactions

Living organisms are made of elements

Living Organisms are Made of Elements

  • Living organisms composed of matter

  • Matter: anything that occupies space and has mass

  • Element: substance that cannot be broken down to other substances by ordinary chemical means

  • Chemists recognize 92 natural elements

    • Life requires 25 of these

Chemicals of life

Chemicals of Life

  • Four make up about 96% of the human body

  • Ca, P, K, S, Na, Cl, Mg make up most of the rest

  • Trace: B, Cr, Co, Cu, F, I, Fe, Mn, Mo, Se, Si, Sn, V, Zn

Elemental deficiencies

Elemental Deficiencies

  • Iron (Fe): anemia

    • Added to cereal

  • Iodine (I): goiter

    • Added to salt

  • New avenue: genetically improved foods (GM crops): Vitamin A

Elements form compounds

Elements form Compounds

  • Compounds are composed of elements

  • Some have 2 elements, some have more

  • Compounds have novel properties

  • Some compounds have the same elements in the same proportions, but act differently



  • Smallest unit of matter that retains the properties of the element

  • Split into 3 particles:

    • Protons (+ charge)

    • Neutron (0 charge)

    • Electrons (- charge)

  • Nucleus: protons and neutrons

  • Electrons orbit the nucleus

The chemical basis of life

If the atom is the size of Yankee stadium, the nucleus is a fly in the center of the

field and the electrons are the size of gnats buzzing around outside the stadium

Elemental differences

Elemental Differences

  • The number of protons defines an element: atomic number

  • Mass number: sum of protons and neutrons

  • Atomic mass: also includes electrons (very light)

  • Isotopes: differing numbers of neutrons- behave chemically identically to each other

Radioactive isotopes

Radioactive Isotopes

  • Basic Research

    • Used to trace elements in organisms to see where they are active, where they go, etc.

    • We can literally see what happens to each atom in a compound as it is utilized

  • Medical Diagnosis

    • Can be used to find centers of chemical activity (cancer tissues have more activity)

  • Dangers

    • Damage to DNA (some man created some natural)

Electrons affect chemical properties

Electrons Affect Chemical Properties

  • Electron orbits are called shells:

    • The inner-most: 2 e-

    • The outer shell for most elements: up to 8 e-

    • # in the outermost shell determines the reactivity of the element

  • Magic number: 8

Covalent bonds

Covalent Bonds

  • Strong chemical bond

  • Two atoms share one or more pairs of outer shell electrons

  • Forms molecules (two or more atoms physically held together)

  • Two types:

    • Polar (unequal charges)

    • Non-polar (equal charges)

Ionic bonds

Ionic Bonds

  • Tends to occur between elements with many/few electrons in outer shell

  • Element with many electrons takes one/some from element with few electrons

  • Forms ions (positive or negative charge)

Hydrogen bonds

Hydrogen Bonds

  • H atoms involved in polar covalent bonds carry a slight positive charge

  • They can be attracted to atoms with slight negative charges (N, O are common)

  • H-bonds help define the properties of water, hold proteins together, hold DNA together, etc.

    • Biologically very important

Chemical reactions

Chemical Reactions

  • Reactants ‘before’ arrow, products ‘after’

  • Must be balanced

Water s properties

Water’s Properties

  • Cohesion: H-bonds hold water molecules to each other

    • Trees, water-walkers

  • H-bonds help moderate temperature

    • Coastal areas have milder temps than inland areas (think SD compared to IE)

    • Evaporative cooling: when water evaporates, the molecules left behind have lower energy (cooler)

      • Used to cool greenhouses, people

More water properties

More Water Properties

  • Ice is less dense than water (UNUSUAL)

    • Each molecule forms H-bonds with 4 neighbors

    • Molecules end up maximally spaced

    • Ice floats!

  • Water is the solvent of life

    • Solution: liquid consisting of a uniform mixture of two or more substances

    • Solvent: dissolving agent

    • Solute: substance that is dissolved

    • Polar molecules dissolve readily in water. Why?

The chemical basis of life


  • Compound that accepts H ions: base

    • Example: NaOH (sodium hydroxide)

  • Compound that donates H ions: acid

    • Example: HCl (hydrochloric acid)

  • Scale from 0 - 14

Acid precipitation

Acid Precipitation

  • pH lower than 5.2

  • Mostly caused by presence of sulfur and nitrogen oxides

  • Rain with pH 2 recorded on east coast, fog with pH 1.7 recorded in LA (probably Riv.)

  • Results from burning fossil fuels

    • How many drive SUVs?

  • Damaging forests, nutrient cycling, cities, ocean more acidic

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