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Chapter 2: The Chemical Basis of Life The Nature of Matter Matter is anything that takes up space and has mass Matter is composed of elements which are substances that cannot be broken down any smaller by normal chemical processes CHNOPS are six important elements for life:Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur Atomic Structure Names are represented by atomic symbols Atomic mass is dependent on the number of protons, neutrons, and electrons Protons are positive, electrons are negative, and neutrons are neutral Protons and neutrons are in the nucleus, electrons orbit around the nucleus. Atomic Structure Continued Atomic mass usually equals the sum of protons and neutrons as electrons have very little mass Each proton and neutron weighs one atomic mass unit The atomic number is equal to number of protons Periodic Table olumns are groups ows are Periods Group 8 is the noble ases Isotopes Atoms of the same element that differ in number of neutrons Named by the atomic symbol and atomic mass (C14) Can be unstable and omit radioactive particles Arrangement of Electrons in an Atom It is impossible to pinpoint an electrons exact location as they are moving very quickly Electrons are arranged in electron shells that contain set numbers of electrons Arrangement of Atoms in an Electron Continued The first shell can hold two electrons After the first shell, an atom is most stable when its outer shell contains eight electrons The number of valence (outer shell) electrons an element has determines its reactivity Types of Chemical Bonds A group of atoms is a molecule Two or more atoms of different elements joining forms a compound Ionic Bonding Atoms are held by attracting opposite charges after an electron transfers Salts are ionic bonds Ionic bonds can dissociate or break apart in many biological environments Covalent Bonds Formed when atoms share one or more electrons Can form complex three dimensional shapes In a structural formula a line illustrates a bond Hydrogen, Oxygen, and Nitrogen molecules are all bonded covalently Chemical Reactions Displayed in an equation Reactants are on the left, products are on the right Equations must be balanced with the same number of atoms of each element on both sides Water's Importance to Life The Structure of Water Atoms differ in electronegativity (how equally they share electrons) Polarity can result where one side of a molecule is slightly positive and the other side is slightly negative Water forms a V shape with Oxygen at the point of the V which is slightly negative, the hydrogens are slightly positive Water molecules can form hydrogen bonds with each other making them cohesive Properties of Water Water is a Solvent Because of it polarity, water dissolves many substances Substances that easily dissolve in water are hydrophilic Substances that do not easily dissolve in water are hydrophobic Water Molecules are Cohesive and Adhesive Cohesion is the ability of water molecule to stick together through hydrogen bonding Adhesion is the ability of water to stick to polar surfaces Cohesion and adhesion are essential to water transport in plants Water Has High Surface Tension Cohesion causes surface water to stick together which is important to many aquatic organisms Water Has a High Heat Capacity Hydrogen bonds allow water to absorb a lot of heat without changing temperatures Water also has a high heat of vaportization Mediterranean climates are created when water absorbs heat through the summer and slowly releases it during Water is Less Dense than Ice Water expands as it freezes so ice is less dense than liquid water so ice floats on water This allows aquatic organisms to survive winter Acids and Bases When water dissociates it releases hydrogen and hydroxide ions Acidic Solutions Release a high concentration of hydrogen ions Often taste sour Basic Solutions Have a high concentration of hydroxide ions Have a bitter taste and feel slippery pH and pH scale The pH scale is a mathematical way of representing Hydrogen ion concentration It is a logarithmic scale so a pH of 2 has ten times the concentration of a pH of 3 Buffers and pH In most organisms pH must be kept in a narrow range Buffers are chemicals that keeps pH within normal limits