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2.1 Atoms, Ions, and Molecules KEY CONCEPT All living things are based on atoms and their interactions. 2.1 Atoms, Ions, and Molecules Living things consist of atoms of different elements. • An atom is the smallest basic unit of matter. • An element is one type of atom. Hydrogen atom (H) H Oxygen atom (O) O 2.1 Atoms, Ions, and Molecules Energy Levels • Electrons move around the nucleus in regions called energy levels. • Energy Levels: Where electrons are found outside the nucleus. • Different energy levels can hold different numbers of electrons. 2.1 Atoms, Ions, and Molecules Energy Levels • Outermost Energy Level: – Atoms are most stable when they have a full outermost energy level. – Determine how atoms form ions or covalent bonds. 2.1 Atoms, Ions, and Molecules • An atom has a nucleus and electrons. – The nucleus has protons and neutrons. – Electrons are in energy levels outside nucleus. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-) 2.1 Atoms, Ions, and Molecules • A compound is a substance made up of atoms of different elements bonded together in a certain ratio. – water (H2O) _ O H + H + 2.1 Atoms, Ions, and Molecules • A compound is a substance made up of atoms of different elements bonded together in a certain ratio. – water (H2O) – carbon dioxide (CO2) 2.1 Atoms, Ions, and Molecules • A compound is a substance made up of atoms of different elements bonded together in a certain ratio. – water (H2O) – carbon dioxide (CO2) – many other carbon-based compounds in living things 2.1 Atoms, Ions, and Molecules Ions form when atoms gain or lose electrons. • An ion is an atom that has gained or lost one or more electrons. • Ionic bonds form between oppositely charged ions due to electrical attraction.. gained electron Na loses an electron to CI Sodium atom (Na) Chlorine atom (CI) ionic bond Sodium ion (Na+) Chloride ion (CI-) 2.1 Atoms, Ions, and Molecules Positive and Negative ions – positive ions: Formed when atoms lose electrons; tend to be formed by atoms with few outer energy levels. – negative ions: Formed when atoms gain electrons; tend to be formed by atoms with nearly a full outer energy level. 2.1 Atoms, Ions, and Molecules Atoms share pairs of electrons in covalent bonds. • A covalent bond forms when atoms share one or more pairs of electrons. • A molecule is formed when atoms are bonded together by covalent bonds; it is not necessarily a compound..forms when atoms share one or more pairs of electrons. covalent bonds Oxygen atom (O) Carbon atom (C) Carbon dioxide (CO2 ) Oxygen atom (O) 2.1 Atoms, Ions, and Molecules KEY CONCEPT Water’s unique properties allow life to exist on Earth. 2.1 Atoms, Ions, and Molecules Life depends on hydrogen bonds in water. • Water is a polar molecule. – Polar molecules have slightly charged regions due to an uneven pull on the electrons. _ O H + H + – Nonpolar molecules do not have charged regions due to equal pull on the electrons. – Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms like oxygen. 2.1 Atoms, Ions, and Molecules Atom: Oxygen _ + H O H Charge: Slightly Negative + _ + H O Atom: Hydrogen H + Charge: Slightly positive 2.1 Atoms, Ions, and Molecules Check for understanding • What does it mean for a molecule to be polar? 2.1 Atoms, Ions, and Molecules • Hydrogen bonds are responsible for three important properties of water. – high specific heat – cohesion – adhesion 2.1 Atoms, Ions, and Molecules High Specific Heat • Large amount of energy needed to produce an increase in temperature. 2.1 Atoms, Ions, and Molecules Cohesion • Water molecules “stick” to each other. 2.1 Atoms, Ions, and Molecules Adhesion • Water molecules” stick” to other substances. • Water has greater adhesion than cohesion. 2.1 Atoms, Ions, and Molecules Person on the left of each table: • Explain to your partner the difference between cohesion and adhesion 2.1 Atoms, Ions, and Molecules Many compounds dissolve in water. • A solution is formed when one substance dissolves in another. – A solution is a homogeneous mixture (a mixtures of substances that are the same throughout). – Solvents dissolve other substances. They are present in a greater amount. – Solutes dissolve in a solvent. They are present in a lesser amount. solution 2.1 Atoms, Ions, and Molecules Person on the right of each table: • Explain the difference between a solute and a solvent 2.1 Atoms, Ions, and Molecules • “Like dissolves like.” – Polar solvents dissolve polar solutes. – Nonpolar solvents dissolve nonpolar solutes. – Polar substances and nonpolar substances generally remain separate. 2.1 Atoms, Ions, and Molecules Some compounds form acids or bases. • An acid releases a hydrogen ion when it dissolves in water. – high H+ concentration – pH less than 7 stomach acid pH between 1 and 3 more acidic 2.1 Atoms, Ions, and Molecules • A base removes hydrogen ions from a solution. – low H+ concentration – pH greater than 7 bile pH between 8 and 9 more basic 2.1 Atoms, Ions, and Molecules • A neutral solution has a pH of 7. It is neither acidic or basic. pure water pH 7 2.1 Atoms, Ions, and Molecules KEY CONCEPT Carbon-based molecules are the foundation of life. 2.1 Atoms, Ions, and Molecules Carbon atoms have unique bonding properties. • Carbon forms covalent bonds with up to four other atoms, including other carbon atoms. • Carbon-based molecules have three general types of structures. – straight chain – branched chain – ring 2.1 Atoms, Ions, and Molecules • Many carbon-based molecules are made of many small subunits bonded together. – Monomers are small molecules that are the single units in a much larger molecule. – Polymers are large molecules (macromolecules) formed from many monomers bonded together. 2.1 Atoms, Ions, and Molecules Four main types of carbon-based molecules are found in living things. • Carbohydrates – Made of carbon, hydrogen, and oxygen. • Function – Broken down to provide a source of energy. – Make up plant cell walls. • Monomer Example: Glucose 2.1 Atoms, Ions, and Molecules Four main types of carbon-based molecules are found in living things. • Carbohydrates are made of carbon, hydrogen, and oxygen. – Carbohydrates include sugars and starches. – Monosaccharides are simple sugars. – Polysaccharides include starches, cellulose, and glycogen. 2.1 Atoms, Ions, and Molecules • Carbohydrates can be broken down to provide energy for cells. • Some carbohydrates are part of cell structure. Polymer (starch) Starch is a polymer of glucose monomers that often has a branched structure. Polymer (cellulose) monomer Cellulose is a polymer of glucose monomers that has a straight, rigid structure 2.1 Atoms, Ions, and Molecules • Lipids – nonpolar molecules that include fats, oils, and cholesterol. – Many contain carbon chains called fatty acids. – Fats and oils contain fatty acids bonded to glycerol. Triglyceride 2.1 Atoms, Ions, and Molecules • Lipids have several different functions. – broken down as a source of energy – make up cell membranes – used to make hormones 2.1 Atoms, Ions, and Molecules • Fats and oils have different types of fatty acids. – saturated fatty acids – unsaturated fatty acids 2.1 Atoms, Ions, and Molecules • Phospholipids make up all cell membranes. – Polar phosphate “head” – Nonpolar fatty acid “tails” Phospholipid 2.1 Atoms, Ions, and Molecules • Proteins are polymers of amino acid monomers. – Many functions: enzymes, oxygen transport, oxygen transport, and muscle movement. – Polymer: polypeptide (protein) – Monomer: amino acids – Twenty different amino acids are used to build proteins in organisms. 2.1 Atoms, Ions, and Molecules • Proteins are polymers of amino acid monomers. – Twenty different amino acids are used to build proteins in organisms. – Amino acids differ in side groups, or R groups. 2.1 Atoms, Ions, and Molecules • Proteins are polymers of amino acid monomers. – Twenty different amino acids are used to build proteins in organisms. – Amino acids differ in side groups, or R groups. – Amino acids are linked by peptide bonds. 2.1 Atoms, Ions, and Molecules • Proteins differ in the number and order of amino acids. – Amino acids interact to give a protein its shape. Hemoglobin hydrogen bond – Incorrect amino acids change a protein’s structure and function. 2.1 Atoms, Ions, and Molecules • Nucleic acids are polymers of monomers called nucleotides. 2.1 Atoms, Ions, and Molecules • Nucleic acids are polymers of monomers called nucleotides. – Nucleotides are made of a sugar, phosphate group, and a nitrogen base. – Functions: Store genetic information; build proteins. A phosphate group deoxyribose (sugar) nitrogen-containing molecule, called a base 2.1 Atoms, Ions, and Molecules • Nucleic acids are polymers of monomers called nucleotides. – Nucleotides are made of a sugar, phosphate group, and a nitrogen base. – Types: DNA and RNA DNA – DNA stores genetic information. RNA – RNA builds proteins. 2.1 Atoms, Ions, and Molecules Warm-up: • Write at least 3 sentences describing how you think each of these terms are related to one another: – Chloroplast – Chemical reactions – Cellular respiration – Photosynthesis – Mitochondria. 2.1 Atoms, Ions, and Molecules Talking Drawing: • Create a graphic representation (drawing) of the following words. If you do not know what they are use your best judgment to draw a picture: – Atom – Chemical reaction – Proton – Neutron – Electron – Photosynthesis 2.1 Atoms, Ions, and Molecules KEY CONCEPT Life depends on chemical reactions. 2.1 Atoms, Ions, and Molecules Bonds break and form during chemical reactions. • Chemical reactions change substances into different ones by breaking and forming chemical bonds. – 1. Reactants: Substances changed by a chemical reaction. – 2. Direction of the reaction – 3. Products: Substances formed during a chemical reaction. CO2 + H2O H2CO3 2.1 Atoms, Ions, and Molecules • Bond energy: is the amount of energy that breaks a bond, or the amount of energy released when a bond forms. – Energy is added to break bonds. – Energy is released when bonds form. • Chemical Equilibrium: Reversible reactions can occur in both directions. A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3 2.1 Atoms, Ions, and Molecules Chemical reactions release or absorb energy. • Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction. • 4. Reactants • 5. Activation Energy 2.1 Atoms, Ions, and Molecules • Exothermic reactions: release more energy than they absorb. – Reactants have higher bond energies than products. – Excess energy is released by the reaction. 6. Total Energy Released 7. Products 2.1 Atoms, Ions, and Molecules • Endothermic reactions: absorb more energy than they release. – Reactants have lower bond energies than products. – Energy is absorbed by the reaction to make up the difference. 8. Reactants 9. Activation Energy 10. Total Energy Released 11. Products 2.1 Atoms, Ions, and Molecules KEY CONCEPT Enzymes are catalysts for chemical reactions in living things. 2.1 Atoms, Ions, and Molecules A catalyst lowers activation energy. • A Catalyst: is a substance that speeds up chemical reactions. 1. decreases activation energy 2. increases reaction rate 2.1 Atoms, Ions, and Molecules Enzymes allow chemical reactions to occur under tightly controlled conditions. • Enzymes are catalysts in living things. – Enzymes are needed for almost all processes. – Most enzymes are proteins. 2.1 Atoms, Ions, and Molecules • Disruptions in homeostasis can prevent enzymes from functioning. – Enzymes function best in a small range of conditions. – Changes in temperature and pH can break hydrogen bonds. – An enzyme’s function depends on its structure. 2.1 Atoms, Ions, and Molecules • Enzyme structure and function: An enzyme’s structure allows only certain reactants to bind to the enzyme. – Substrates – Reactants that bind to the active site of an enzyme. substrates (reactants) enzyme Substrates bind to an enzyme at certain places called active sites. 2.1 Atoms, Ions, and Molecules • The lock-and-key model helps illustrate how enzymes function. – substrates brought together – The enzyme only works when specific substrates bind. Substrates bind to an enzyme at certain places called active sites. The enzyme brings substrates together and weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme.