Chapter 2 Essential Chemistry for Biology Power Point

Chapter 2 Essential Chemistry for Biology Power. Point® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko © 2013 Pearson Education, Inc.

SOME BASIC CHEMISTRY • Take any biological system apart, and you eventually end up at the chemical level. • Chemical reactions are always occurring in the human body. • Water is the chemical solvent (liquid) in which chemical reactions in organisms takes place. © 2013 Pearson Education, Inc.

Matter: Elements and Compounds • Matter is anything that occupies space and has mass.

Matter: Elements and Compounds • Matter is composed of chemical elements. – An element is a substance that cannot be broken down into other substances by chemical reactions. – There are 92 naturally occurring elements on Earth. – Carbon, Nitrogen and Oxygen are examples. – There are dozens of man-made chemical elements. • All of the elements are listed in the periodic table. © 2013 Pearson Education, Inc.

Figure 2. 1 a Atomic number (number of protons) 6 C Element symbol H 12 Mass number (number of protons plus neutrons) He Li Be B Na Mg Al Si P C N O F Ne S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Figure 2. 1 b Mercury (Hg)

Figure 2. 1 c Copper (Cu)

Figure 2. 1 d Lead (Pb)

Matter: Elements and Compounds • Twenty-five elements are essential to people. • Four elements make up about 96% of the weight of most cells: – oxygen, – carbon, – hydrogen, and – nitrogen. © 2013 Pearson Education, Inc.

Figure 2. 2 Carbon (C): 18. 5% Oxygen (O): 65. 0% Calcium (Ca): 1. 5% Phosphorus (P): 1. 0% Potassium (K): 0. 4% Sulfur (S): 0. 3% Sodium (Na): 0. 2% Chlorine (Cl): 0. 2% Hydrogen (H): 9. 5% Nitrogen (N): 3. 3% Magnesium (Mg): 0. 1% Trace elements: less than 0. 01% Boron (B) Chromium (Cr) Cobalt (Co) Copper (Cu) Fluorine (F) Iodine (I) Iron (Fe) Manganese (Mn) Molybdenum (Mo) Selenium (Se) Silicon (Si) Tin (Sn) Vanadium (V) Zinc (Zn)

Matter: Elements and Compounds • Trace elements are – required in only very small amounts and – essential for life. • An iodine deficiency causes goiter. • Fluorine – is added to dental products and drinking water and – helps to maintain healthy bones and teeth. © 2013 Pearson Education, Inc.

Figure 2. 3 a

Matter: Elements and Compounds • Elements can combine to form compounds. – Compounds are substances that contain two or more elements in a fixed ratio. – Common compounds include – Na. Cl (table salt) and – H 2 O (water). © 2013 Pearson Education, Inc.

Atoms • Each element consists of one kind of atom. – An atom is

The Structure of Atoms • Atoms are composed of subatomic particles. – A proton is positively charged (+) – An electron is negatively charged (-) – A neutron is electrically neutral. • Most atoms have protons and neutrons packed tightly into the nucleus. – The nucleus is the atom’s central core. – Electrons orbit the nucleus. © 2013 Pearson Education, Inc.

Figure 2. 4 2 Nucleus Protons 2 Neutrons 2 Electrons Nucleus 2 e– Electron cloud

The Structure of Atoms • Elements differ in the number of subatomic particles in their atoms. – The number of protons, the atomic number, determines which element it is. – Mass is a measure of the amount of material in an object. – An atom’s mass number is the sum of the number of protons and neutrons in its nucleus. © 2013 Pearson Education, Inc.

Isotopes • Isotopes are alternate mass forms of an element. • Isotopes – have

Table 2. 1

Isotopes • The nucleus of a radioactive isotope decays spontaneously, giving off particles and energy. • It is usually the heavier isotopes that are radioactive. • C-14 is a radioactive isotope of Carbon. • Even the human body has very small amounts of C -14. © 2013 Pearson Education, Inc.

• Radioactive isotopes have many uses in research and medicine. – They can be used to determine the fate of atoms in living organisms. – They are used in PET scans to diagnose heart disorders and some cancers.

Figure 2. 5

Isotopes • Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA. – The 1986 Chernobyl nuclear accident released large amounts of radioactive isotopes. Many people were harmed by the release of radioactive energy. – Naturally occurring radon gas may cause lung cancer. © 2013 Pearson Education, Inc.

Electron Arrangement and the Chemical Properties of Atoms • Of the three subatomic particles, only electrons are directly involved in the chemical activity of an atom. • Electrons orbit the nucleus of an atom in specific electron shells. • The farther an electron is from the nucleus, the greater its energy. • The number of electrons in the outermost shell determines the chemical properties of an atom – that is the types of chemical reactions that occur. © 2013 Pearson Education, Inc.

Figure 2. 6 Electron First electron shell (can hold 2 electrons) Hydrogen (H) Atomic number 1 Outer electron shell (can hold 8 electrons) Carbon (C) Atomic number 6 Nitrogen (N) Atomic number 7 Oxygen (O) Atomic number 8

Chemical Bonding and Molecules • Chemical reactions enable atoms to give up or acquire electrons, filling their outer shells. • Chemical reactions usually result in atoms – staying close together and – being held together by attractions called chemical bonds. © 2013 Pearson Education, Inc.

Ionic Bonds • Ionic bonds form when an atom loses or gains electrons. • When an atom loses or gains electrons, it becomes electrically charged. – Charged atoms are called ions. – Ionic bonds are formed between oppositely charged ions. – The negative atom is called an anion while the positive atom is called a cation © 2013 Pearson Education, Inc.

Figure 2. 7 -1 Na Cl Na Sodium atom Cl Chlorine atom

Figure 2. 7 -2 Complete outer shells Na Cl Na Cl– Na Sodium atom Cl Chlorine atom Na Sodium ion Cl– Chloride ion Sodium chloride (Na. Cl)

Covalent Bonds • A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. • Covalent bonds are the strongest of the various bonds. • Covalent bonds hold atoms together in a molecule. • The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell. © 2013 Pearson Education, Inc.

Figure 2. 8 Electron configuration H H Hydrogen gas (H 2) O O Oxygen gas (O 2) H H C H Methane (CH 4) H Structural formula Space-filling model Ball-and-stick model

Covalent Bonds • Hydrogen – 1 covalent bond • Oxygen – 2 covalent bonds

Polar Covalent Bonds • Water is a compound in which the electrons in its covalent bonds are not shared equally. – This causes water to be a polar molecule, one with an uneven distribution of charge. – Electrons spend more time around the oxygen atom causing it to be partially negatively charged. – Electrons spend less time around the hydrogens making them partially positively charged. © 2013 Pearson Education, Inc.

– These bonds are thus called polar covalent bonds. © 2013 Pearson Education, Inc.

Figure 2. UN 02 (slightly ) H H O (slightly −) (slightly )

Hydrogen Bonds • The polarity of water results in weak electrical attractions between neighboring

Figure 2. 9 Hydrogen bond Slightly positive Slightly charge negative charge

https: //www. youtube. com/watch? v=Py. C 5 r 2 m. B 4 d 4 Hydrogen Bonding (8. 59)

Review – Types of Chemical Bonds • There are four types of chemical bonds

Chemical Reactions • Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones. – Such changes in the chemical composition of matter are called chemical reactions. – A simple example is the reaction between oxygen gas and hydrogen gas that forms water. © 2013 Pearson Education, Inc.

Figure 2. UN 03 2 Hydrogen gas + O 2 2 H 2 O Oxygen gas Water Reactants Products

Chemical Reactions • Chemical reactions include – reactants, the starting materials, and – products, the end materials. • Chemical reactions – can rearrange matter – but cannot create or destroy matter. © 2013 Pearson Education, Inc.

https: //www. youtube. com/watch? v=Mi. Iuwtn. E 0 do Chemical Reactions (8. 25)

Water’s Life-Supporting Properties • The polarity of water molecules and the hydrogen bonding that results explain most of water’s lifesupporting properties: 1. Water molecules stick together. 2. Water has a strong resistance to change in temperature. 3. Frozen water floats. 4. Water is a common solvent for life. © 2013 Pearson Education, Inc.

The Cohesion of Water • Water molecules stick together as a result of hydrogen bonding. – This tendency of molecules of the same kind to stick together is called cohesion. – Cohesion is vital for the transport of water from the roots to the leaves of plants. © 2013 Pearson Education, Inc.

The Cohesion of Water • Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid. – Hydrogen bonds give water an unusually high surface tension. – Some spiders can walk on water because their foot pads are electrically charged and repel water © 2013 Pearson Education, Inc.

Figure 2. 12

How Water Moderates Temperature • Because of hydrogen bonding, water has a strong resistance to temperature change. • Heat and temperature are related, but different. – Heat how much total energy is stored – Temperature measures the intensity of heat (how quickly the molecules are moving – thermometer) • Water can absorb and store large amounts of heat while only changing a few degrees in temperature. • Note how a steel pot will heat up very fast but the water in the pot takes a lot of time to heat up and change temperature. © 2013 Pearson Education, Inc.

How Water Moderates Temperature • Water can moderate temperatures. – Earth’s giant water supply causes temperatures to stay within limits that permit life. – Evaporative cooling occurs when a substance evaporates and the surface of the liquid remaining behind cools down. © 2013 Pearson Education, Inc.

Figure 2. 13

The Biological Significance of Ice Floating • When water molecules get cold enough, they move apart, forming ice. • A chunk of ice has fewer water molecules than an equal volume of liquid water. (Ice is less dense than water. ) • Ice floats because it is less dense than liquid water. © 2013 Pearson Education, Inc.

Figure 2. 14 Hydrogen bond Liquid water Hydrogen bonds constantly break and re-form. Ice Stable hydrogen bonds hold molecules apart, making ice less dense than water.

https: //www. youtube. com/watch? v=HVT 3 Y 3_g HGg Properties of Water (11. 16)

Water as the Solvent of Life • A solution is a liquid consisting of a homogeneous mixture of two or more substances. – The dissolving agent is the solvent. – The dissolved substance is the solute. • When water is the solvent, the result is an aqueous solution. • Dissolved salt in water is the solute while water which does the dissolving is the solvent. • Dissolved sugar in water is the solute while water which does the dissolving is the solvent. © 2013 Pearson Education, Inc.

Figure 2. 15 Sodium ion in solution Chloride ion in solution Cl– Na Cl – Salt crystal Na

Acids, Bases, and p. H • A chemical compound that releases H+ to a solution is an acid (example: HCl – hydrochloric acid) • A compound that accepts H+ and removes them from solution is a base. (example: Na. OH – sodium hydroxide) • To describe the acidity of a solution, chemists use the p. H scale. (0 – 14 with 7 being neutral) • Lower than 7 = acid; higher than 7 = base. © 2013 Pearson Education, Inc.

Figure 2. 17 14 Oven cleaner Basic solution 13 Lower H concentration OH− − OH−OH − OH H OH− H 12 Household bleach Household ammonia 11 Milk of magnesia 10 9 Seawater 8 Neutral solution H H OH− H H − OH H H Acidic solution [H ] [OH−] Human blood 7 Pure water 6 Urine Greater H concentration OH− H H OH− − OH H − OH H 5 4 Black coffee Tomato juice 3 Grapefruit juice, soft drink 2 Lemon juice, stomach acid Battery acid 1 0 p. H scale

Figure 2. 17 a OH− − OH OH− H − OH − OH H Basic solution OH− H H OH− − OH H − OH H H − H OH H − OH H H Neutral solution Acidic solution H

Acids, Bases, and p. H • Buffers are substances that resist p. H change. • Buffers – accept H+ ions when they are in excess and – donate H+ ions when they are depleted. • Increases in global CO 2 concentrations may lead to – the acidification of the oceans and – ecological disasters. © 2013 Pearson Education, Inc.

https: //www. youtube. com/watch? v=Xeuyc 55 Lqi Y Acids Bases and p. H (8. 53)

Figure 2. 18