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Nature’s chemical language Elements, Atoms, Molecules, Chemical Bonds Water’s life supporting properties Chemical reacti PowerPoint Presentation
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CHAPTER 2 The Chemical Basis of Life By Dr. Par Mohammadian. Nature’s chemical language Elements, Atoms, Molecules, Chemical Bonds Water’s life supporting properties Chemical reaction . Life requires about 25 chemical elements.

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CHAPTER 2The Chemical Basis of Life

By Dr. Par Mohammadian

  • Nature’s chemical language
  • Elements, Atoms, Molecules, Chemical Bonds
  • Water’s life supporting properties
  • Chemical reaction
life requires about 25 chemical elements
Life requires about 25 chemical elements
  • Living organisms are composed of matter. Matter: Anything that occupies space and has mass (air, water, etc.). Matter is found on the Earth in three physical states: Solid, Liquid, Gas
  • Matters are composed of elements.

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

elements can combine to form compounds
Elements can combine to form compounds
  • The smallest particle of an element is an atom
  • Different elements have different types of atoms
  • Chemical elements combine in fixed ratios to form compounds
  • An atom is made up of protons and neutrons located in a central nucleus
  • The nucleus is surrounded by electrons (The electrons orbit the nucleus)
  • The number of protons, the atomic number, determines which element it is
  • An atom’s mass number is the sum of the number of protons and neutrons
electron arrangement determines the chemical properties of an atom
Electron arrangement determines the chemical properties of an atom
  • Electrons are arranged in shells
    • The outermost shell determines the chemical properties of an atom
    • In most atoms, a full outer shell holds eight electrons
chemical bonds
Chemical Bonds
  • Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells
  • These interactions usually result in atoms staying close together
  • The atoms are held together by chemical bonds:

Ionic Bonds

Covalent Bonds

Hydrogen Bonds

ionic bonds sharing of electrons
Ionic bonds: Sharing of electrons

Covalent bonds, the sharing of electrons, join atoms into molecules

water is a polar molecule

THE PROPERTIES OF WATER

Water is a polar molecule
  • Atoms in a covalently bonded molecule may share electrons equally, creating a nonpolar molecule
  • If electrons are shared unequally, a polar molecule is created
water s polarity leads to hydrogen bonding and other unusual properties
Water’s polarity leads to hydrogen bonding and other unusual properties
  • 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 bond

the cohesion of water
The Cohesion of Water
  • Water molecules stick together as a result of hydrogen bonding

Hydrogen bonds make liquid water cohesive

Water’s hydrogen bonds moderate temperature

ice is less dense than liquid water
Ice is less dense than liquid water
  • as a solid
  • as a liquid
  • as a gas
  • Like no other common substance, water exists in nature in all three physical states:
water as the solvent of life
Water as the Solvent of Life
  • The dissolving agent is called the solvent
  • The dissolved substance is called the solute
  • A solution is a liquid consisting of two or more substances evenly mixed
  • aqueous solutions
the chemistry of life is sensitive to acidic and basic conditions
The chemistry of life is sensitive to acidic and basic conditions
  • Acid
    • A chemical compound that donates H+ ions to solutions
  • Base
    • A compound that accepts H+ ions and removes them from solution
  • Acidity is measured on the pH scale:
    • 0-7 is acidic
    • 8-14 is basic
    • Pure water and solutions that are neither basic nor acidic are neutral, with a pH of 7
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Buffers are substances that resist pH change

  • They accept H+ ions when they are in excess
  • They donate H+ ions when they are depleted
  • Cells are kept close to pH 7 by buffers
acid precipitation threatens the environment
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
chemical reactions
Chemical Reactions
  • Such changes in the chemical composition of matter are called chemical reactions
  • Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones
  • On the left side of the equation are the reactants, the starting materials
  • On the right side of the equation are the products, the end materials