Post on 05-Jan-2016
Matter – anything that takes up space and has weight; composed of elements
Elements – composed of chemically identical atomsas of 2002, 114 elements known, though only 92 are naturally occurring
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Structure of Matter
CHNOPS
Bulk elements include Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur
Table 2.1a
Table 2.1b
Atoms
Atoms – smallest particle of an elementAtoms - composed of subatomic particles:
protons – carry a positive charge neutrons – carry no electrical charge electrons – carry a negative charge
Nucleus• central part of atom• composed of protons and neutrons• electrons move around the nucleus
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Atomic Structure
Subatomic Particles
Since the nucleus contains protons and neutrons, the nucleus contains a positive charge
Generally, the number of electrons is equal to the number of protons, so there is a net neutral charge for the atom
Atomic Number • number of protons in the nucleus of one atom • each element has a unique atomic number• equals the number of electrons in the atom
Atomic Weight/Mass Number• the number of protons plus the number of neutrons in one atom • electrons do not contribute to the weight of the atom
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Atomic Number and Mass Number
Question
What is the atomic number and atomic weight for the 3 examples in the previous slide?
Isotopes• atoms with the same atomic numbers but with different atomic weights• atoms with the same number of protons and electrons but a different number of neutrons• oxygen often forms isotopes (O16, O17, O18)• unstable isotopes are radioactive; they emit subatomic particles 2-6
Isotopes
Question
What is the atomic number and atomic weight for the 3 isotope examples on the previous slide?
Molecules – particle formed when two or more atoms chemically combine
Compound – particle formed when two or more atoms of different elements chemically combine
Molecular formulas – depict the elements present and the number of each atom present in the molecule
H2 C6H12O6 H2O
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Molecules and Compounds
• found in regions of space called electron shells (energy shells)• each shell can hold a limited number of electrons• for atoms with atomic numbers of 18 or less, the following rules apply:
• the first shell can hold up to 2 electrons• the second shell can hold up to 8 electrons• the third shell can hold up to 8 electrons
• lower shells are filled first• if the outermost shell is full, the atom is stable; inert
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Electrons
Octet Rule
Atoms tend to interact so that they have 8 electrons to fill the outer shell
Ion• an atom that has gained or lost an electron(s)• an electrically charged atom• atoms form ions to become stable
Cation• a positively charged ion• formed when an atom loses an electron(s)
Anion• a negatively charged ion• formed when an atom gains an electron(s)
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Ions
• an attraction between a cation and an anionIonic Bond
• formed when electrons are transferred from one atom to another atom
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Ionic Bond
Formed when atoms share electrons
•Hydrogen atoms form single bonds•Oxygen atoms form two bonds•Nitrogen atoms form three bonds•Carbon atoms form four bonds
H ― HO = ON ≡ NO = C = O
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Covalent Bond
Structural formulas show how atoms bond and are arranged in various molecules
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Structural Formulas
Polar Molecule• molecule with a slightly negative end and a slightly positive end• results when electrons are not shared equally in covalent bonds• water is an important polar molecule
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Polar Molecules
Hydrogen Bond• a weak attraction between the positive end of one polar molecule and the negative end of another polar molecule• formed between water molecules• important for protein and nucleic acid structure
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Hydrogen Bonds
Solution – a mixture of one or more substances called solutes, dispersed in a dissolving medium called a solvent
Solutes – Na+ & Cl-
Solvent – H2O
Most biological activities occur in aqueous (water-based) solutions.
hydrophilic molecules – dissolve in waterhydrophobic molecules – repel wateramphipathic molecules -have both
hydrophilic and hydrophobic properties
Chemical reactions occur when chemical bonds form or break among atoms, ions, or molecules
Reactants are substances being changed by the chemical reaction
Products are substances formed at the end of the chemical reaction
NaCl ’ Na+ + Cl-
Reactant Products2-15
Chemical Reactions
Synthesis Reaction – chemical bonds are formed A + B ’ AB
Decomposition Reaction – chemical bonds are brokenAB ’ A + B
Exchange Reaction – chemical bonds are broken and formed AB + CD ’ AD + CB
Reversible Reaction – the products can change back to the reactants
A + B AB2-16
Types of Chemical Reactions
Electrolytes – substances that release ions in water
Acids – electrolytes that release hydrogen ions in waterHCl H+ + Cl-
Bases – substances that release ions that can combine with hydrogen ions
NaOH Na+ + OH-
Salts – electrolytes formed by the reaction between an acid and a base
NaCl Na+ + Cl-
HCl + NaOH H2O + NaCl2-17
Acids, Bases, and Salts
pH scale - indicates the concentration of hydrogen ions insolution
Neutral – pH 7; indicates equal concentrations of H+ and OH-
Acidic – pH less than 7; indicates a greater concentration of H+
Basic or alkaline – pH greater than 7;indicates a greater concentration of OH-
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Acid and Base Concentrations
Organic molecules • contain C and H• usually larger than inorganic molecules• dissolve in water and organic liquids• carbohydrates, proteins, lipids, and nucleic acidsInorganic molecules • generally do not contain C• usually smaller than organic molecules• usually dissolve in water or react with water to release ions• water, oxygen, carbon dioxide, and inorganic salts
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Organic vs Inorganic
• provide energy to cells
• supply materials to build cell structures
• water-soluble• contain C, H, and O• ratio of H to O close to 2:1 (C6H12O6)• monosaccharides – glucose, fructose• disaccharides – sucrose, lactose• polysaccharides – glycogen, cellulose
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Organic SubstancesCarbohydrates
• soluble in organic solvents• fats (triglycerides)
• used primarily for energy• contain C, H, and O but less O than carbohydrates (C57H110O6)• building blocks are 1 glycerol and 3 fatty acids per molecule• saturated and unsaturated
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Organic SubstancesLipids
• phospholipids
• building blocks are 1 glycerol, 2 fatty acids, and 1 phosphate per molecule
• hydrophilic and hydrophobic
• major component of cell membranes
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Organic SubstancesLipids
• steroids• connected rings of carbon• component of cell membrane• used to synthesize hormones• cholesterol
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Organic SubstancesLipids
• structural material• energy source• hormones• receptors• enzymes• antibodies
• building blocks are amino acids
• amino acids held together with peptide bonds
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Organic SubstancesProteins
Four Levels of Structure
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Organic SubstancesProteins
• constitute genes• play role in protein synthesis• building blocks are nucleotides
• DNA (deoxyribonucleic acid) – double polynucleotide• RNA (ribonucleic acid) – single polynucleotide 2-29
Organic SubstancesNucleic Acids
Table 2.6
Prokaryotes vs Eukaryotes
Size smaller Larger
Nucleus - +
Organelles - +
Chromosomes 1 circular Multiple, linear
Ribosomes smaller 70s Larger 80sr