Matter consists of chemical elements in pure form and in combinations called compoundsElements and CompoundsEssential Elements of LifeAn element’s properties depend on the structure of its atomsSlide 5IsotopesSlide 7The formation and function of molecules depend on chemical bonding between atoms1. Covalent BondsSlide 10Slide 11Slide 122. Ionic BondsSlide 143. Hydrogen bondSlide 16Chemical reactions make and break chemical bondsSlide 18The polarity of water molecules results in hydrogen bondingSlide 20Four emergent properties of water contribute to Earth’s fitness for lifeCohesionSlide 23Moderation of Temperature (due to high specific heat)Moderation of Temperature (by evaporative cooling)Insulation of Bodies of Water by Floating IceThe Solvent of LifeSlide 28Effects of Changes in pHSlide 30BuffersMatter consists of chemical elements in pure form and in combinations called compounds•Organisms are composed of matter•Matter is anything that takes up space and has mass•Matter is made up of elements •An element is a substance that cannot be broken down to other substances by chemical reactions•A compound is a substance consisting of two or more elements in a fixed ratio•A compound has characteristics different from those of its elementsElements and CompoundsSodium ChlorineSodiumchlorideEssential Elements of Life•About 25 of the 92 elements are essential to life•Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter•Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur•Trace elements are those required by an organism in minute quantities, e.g. Iodine(I), Iron(Fe)An element’s properties depend on the structure of its atoms•Each element consists of unique atoms•An atom is the smallest unit of matter that still retains the properties of an element•Atoms are composed of subatomic particles•Relevant subatomic particles include:–Neutrons (no electrical charge)–Protons (positive charge)–Electrons (negative charge)•Neutrons and protons form the atomic nucleus•Electrons form a cloud around the nucleus•Neutron mass and proton mass are almost identical and are measured in daltons•An element’s atomic number is the number of protons in its nucleus•An element’s mass number is the sum of protons plus neutrons in the nucleus •Atomic mass, the atom’s total mass, can be approximated by the mass numberIsotopes•All atoms of an element have the same number of protons but may differ in number of neutrons•Isotopes are two atoms of an element that differ in number of neutrons•Radioactive isotopes decay spontaneously, giving off particles and energy•Some applications of radioactive isotopes in biological research are:–Dating fossils–Tracing atoms through metabolic processes–Diagnosing medical disordersFig. 2-6TECHNIQUERESULTSCompounds includingradioactive tracer(bright blue)Incubators1 2345678910°C 15°C 20°C25°C30°C35°C40°C 45°C 50°C123Human cellsHumancells areincubatedwith compounds used tomake DNA. One compound islabeled with 3H.The cells areplaced in testtubes; their DNA isisolated; andunused labeledcompounds areremoved.DNA (old and new)The test tubes are placed in a scintillation counter.Counts per minute( 1,000)Optimumtemperaturefor DNAsynthesisTemperature (ºC)0101020203030 4050The formation and function of molecules depend on chemical bonding between atoms•Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms•These interactions usually result in atoms staying close together, held by attractions called chemical bonds.•Types of Chemical bonds 1. Covalent Bonds - results from Sharing of electrons 2. Ionic or electrovalent bonds - results from transfer of electrons 3. Hydrogen Bonds – results between Hydrogen atom of one molecule and an electronegative atom of another molecule1. Covalent Bonds•A covalent bond is the sharing of a pair of valence electrons by two atoms•In a covalent bond, the shared electrons count as part of each atom’s valence shell•A molecule consists of two or more atoms held together by covalent bonds•A single covalent bond, or single bond, is the sharing of one pair of valence electrons•A double covalent bond, or double bond, is the sharing of two pairs of valence electronsFig. 2-12Name andMolecularFormulaElectron-distributionDiagramLewis DotStructure andStructural FormulaSpace-fillingModel(a) Hydrogen (H2)(b) Oxygen (O2)(c) Water (H2O)(d) Methane (CH4)•Covalent bonds can form between atoms of the same element or atoms of different elements •A compound is a combination of two or more different elements•Bonding capacity is called the atom’s valence•Electronegativity is an atom’s attraction for the electrons in a covalent bond•The more electronegative an atom, the more strongly it pulls shared electrons toward itself•In a nonpolar covalent bond, the atoms share the electron equally•In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electron equally•Unequal sharing of electrons causes a partial positive or negative charge for each atom e.g. Water molecule –OHH++H2O2. Ionic Bonds•Atoms sometimes strip electrons from their bonding partners•An example is the transfer of an electron from sodium to chlorine•After the transfer of an electron, both atoms have charges•A charged atom (or molecule) is called an ion•A cation is a positively charged ion•An anion is a negatively charged ion•An ionic bond is an attraction between an anion and a CationFig. 2-14-2Na ClNaClNaSodium atomChlorine atomClNa+Sodium ion(a cation)Cl–Chloride ion(an anion)Sodium chloride (NaCl)•Compounds formed by ionic bonds are called ionic compounds, or salts•Salts, such as sodium chloride (table salt), are often found in nature as crystals Na+Cl–3. Hydrogen bond •Most of the strongest bonds in organisms are covalent bonds that form a cell’s molecules•Weak chemical bonds, such as ionic bonds and hydrogen bonds, are also important•Weak chemical bonds reinforce shapes of large molecules and help molecules adhere to each other•A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom•In living cells, the electronegative partners are usually oxygen or nitrogen atomsFig. 2-16 ++ +++Water (H2O)Ammonia (NH3)Hydrogen bondChemical