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Chapter 2 The Chemistry of Life Atoms • Atoms – The study of chemistry begins with the basic unit of matter, the atom. – Placed side by side, 100 million atoms would make a row only about 1 centimeter long. – Atoms contain subatomic particles that are even smaller. Atoms – The subatomic particles that make up atoms are • Protons –Positively Charged • Neutrons - No Charge • Electrons – Negatively Charged Atoms • The subatomic particles in a helium atom. Atoms • Protons and neutrons have about the same mass, 1 amu • Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. Atoms • The electron with 1/1840 the mass of a proton. • Electrons are in constant motion in the space surrounding the nucleus because of the energy of their motion. Atoms • Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutral. Elements and Isotopes • Elements and Isotopes • A chemical element is a pure substance that consists entirely of one type of atom. • Elements are represented by a one- or two-letter symbol. – C stands for carbon. – Na stands for sodium. Elements and Isotopes • The number of protons in an atom of an element is the element's atomic number. • Carbon has 6 protons, so its atomic number is 6. Elements and Isotopes – Isotopes • Atoms of the same element that differ in the number of neutrons they contain are known as isotopes. • The sum of the protons and neutrons in the nucleus of an atom is called its mass number. Elements and Isotopes Isotopes of Carbon 6 electrons 6 protons 6 7 8 neutrons Chemical Compounds • Chemical Compounds • In nature, most elements are found combined with other elements in compounds. • A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. Chemical Bonds • Chemical Bonds • The atoms in compounds are held together by chemical bonds. • Bond formation involves the electrons that surround each atomic nucleus. • The electrons that are available to form bonds are called valence electrons. Chemical Bonds – The main types of chemical bonds are: • ionic bonds – transfer electrons • covalent bonds – share electrons Chemical Bonds Chlorine ion (Cl-) Sodium atom (Na) Sodium ion (Na+) Chlorine atom (Cl) Protons Electrons +11 - 11 10 Protons Electrons +17 18 - 17 Charge +10 Charge -10 Chemical Bonds • In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom. Chemical Bonds – Ionic Bonds • An ionic bond is formed when one or more electrons are transferred from one atom to another. • An atom that loses electrons has a positive charge. • An atom that gains electrons has a negative charge. • These positively and negatively charged atoms are known as ions. Chemical Bonds – Covalent Bonds • Sometimes electrons are shared by atoms instead of being transferred. • Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms. Chemical Bonds • A covalent bond forms when electrons are shared between atoms. • When the atoms share two electrons, the bond is called a single covalent bond. • When atoms share four electrons it is called a double bond. • When atoms share six electrons it is called a triple bond. Chemical Bonds • The structure that results when atoms are joined together by covalent bonds is called a molecule. • A molecule is the smallest unit of most compounds. Chemical Bonds – Van der Waals Forces • When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. • Chemists call such intermolecular forces of attraction van der Waals forces, after the scientist who discovered them. Chemical Bonds • Although van der Waals forces are not as strong • as ionic bonds or covalent bonds, they can hold • molecules together, especially when the molecules • are large. Chemical Bonds • For example, van der Waals forces form between the molecules on the surface of a gecko’s foot and the molecules on the surface of the wall. • The combined strength of all the van 2-2 Properties of Water • Water stores heat efficiently – Water retains heat longer than many other substances – Water is essential in maintaining homeostasis 2-2 Properties of Water • Polarity – Water is considered to be a polar molecule due to an uneven distribution of charge. – The electrons in a water molecule are shared unevenly between hydrogen and oxygen. – The polarity of water makes it effective at dissolving other polar substances such as sugars, ionic compounds, and some proteins. Polar Water Molecule + - 2-2 Properties of Water • A hydrogen bond is the force of attraction between a positive charge of one molecule and negative charge of another. 2-2 Properties of Water • Cohesion and Adhesion – Cohesion is an attractive force that holds molecules of a single substance together, such as water molecules – Adhesion is the attractive force between two particles of different substances, such as water molecules and glass molecules. 2-2 Properties of Water • Solutions – A solution consists of a solute dissolved in a solvent • i.e. Chocolate milk – Milk is the solvent – Chocolate powder is the solute 2-2 Properties of Water • Acids and Bases – Ionization of Water • Water ionizes into hydronium ions (H3O+) and hydroxide ions (OH–) 2-2 Properties of Water • Acids – Acidic solutions contain more hydronium ions (H3O+) than hydroxide ions (OH–) 2-2 Properties of Water • Bases – Basic solutions contain more hydroxide ions (OH–) than hydronium ions (H3O+). 2-2 Properties of Water • pH – Scientists have developed a scale for comparing the relative concentrations of hydronium ions (H3O+) and hydroxide ions (OH–) in a solution. – This scale is called the pH scale, and it ranges from 0 to 14. 2-2 Properties of Water • Buffers – Buffers are chemicals that neutralize the effects of an acid or a base by adding small amounts of the opposite (either an acid or a base) to a solution. 2-3 Carbon Compounds • • • • Carbon is the element of life Organic compounds – carbon containing Inorganic compounds- carbon lacking Carbon has 4 valence e– Will make 4 strong covalent bonds Carbon found in many forms – Straight chain – Branched chain 2-3 Carbon Compounds • Carbon found in many forms – Carbon ring – Double bonded – Triple bonded 2-3 Carbon Compounds • Macromolecules – “giant molecules” – Small units called monomers, come together in a process called polymerization • They form polymers 2-3 Carbon Compounds • Carbohydrates (CHO) – C1H2O1 – Main energy source – Only source of brain food (glucose) – 4cal/1gram – 1 cal = amount of energy needed to raise 1g of water, 1 °C 2-3 Carbon Compounds • Carbohydrates – Sugars • Monosaccharides – simple sugars, I ring of carbon – glucose • Disaccharides- 2 sugars, 2 rings – sucrose • Polysaccharides- many sugars – starches 2-3 Carbon Compounds • Lipids – Fats – Insulate, protect, shock absorber, energy storage, cell membranes – 9cal/1gram 2-3 Carbon Compounds • Lipids – Fatty Acid Chains • Unsaturated -CH=CH- (double bonds) -liquids • Saturated –CH2-CH2- (single bonds) -solids 2-3 Carbon Compounds • Nucleic Acids – DNA, RNA • Nucleotide – 5 Carbon sugar – Nitrogen base – Phosphate group 2-3 Carbon Compounds • Proteins – Building blocks of the body – 4cal/1 gram – Made of Amino Acids- 20 A.A. • We produce 12 A.A. • 8 essential A.A. we must consume – Enzymes • Varying functions in the body 2-4 Chemical Reactions and Enzymes • Energy and Chemical Reactions – Chemical rxns always involve changes in chemical bonds • Reactants are substances that enter chemical reactions. • Products are substances produced by chemical reactions. 2-4 Chemical Reactions and Enzymes • Energy and Chemical Reactions – Energy is released or absorbed whenever chemical bonds form or are broken • Some rxns release energy (exothermic) • Some rxns absorb energy (endothermic) 2-4 Chemical Reactions and Enzymes • Energy and Chemical Reactions 2-4 Chemical Reactions and Enzymes • Energy and Chemical Reactions • Activation Energy – Amount of energy necessary for a reaction to begin – Enzymes can lower activation energy level – A Catalyst is a substance that speeds up a chemical reaction – Enzymes are Catalysts