Atoms, Molecules, and Life

Atoms, Molecules, and Life
chapter 2 Atoms, Molecules, and Life 1

Chapter 2 At a Glance 2.1 What Are Atoms?
2.2 How Do Atoms Interact to Form Molecules? 2.3 Why Is Water So Important to Life? © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Elements
Cannot be broken down into simpler substances Cannot be converted into other substances by ordinary chemical reactions Processes that form or break binds between atoms Form all matter 92 occur naturally © 2017 Pearson Education, Ltd.

Atomic number = number of protons
Table 2-1 Table 2-1 Atomic number = number of protons Mass number = number of protons + neutrons © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Atom Smallest unit of an element
Retains all the chemical properties of that element Composed of subatomic particles Uncharged neutrons Positively charged protons Negatively charged electrons As a whole, neutral, as charges balance each other © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Subatomic particles are measured in atomic mass units Protons and neutrons each have a mass unit of 1 Mass of electrons is negligible (so small) Mass number Total number (equal to total mass) of the protons and neutrons contained in the nucleus of an atom Electrons are in constant motion about the nucleus © 2017 Pearson Education, Ltd.

(a) Hydrogen (H) 1 proton (b) Helium (He) 2 protons 2 neutrons
Figure 2-1 e electron shell e p+ p+ p+ n n atomic nucleus Figure 2-1 Atomic models These models are extremely simplified to make atoms easy to imagine. Atoms are never drawn to scale; if they were, and if this dot · were the nucleus, the electrons would be somewhere in the next room (or outside)—roughly 30 feet away! e+ (a) Hydrogen (H) 1 proton (b) Helium (He) 2 protons 2 neutrons © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Atomic number Number of protons in the nucleus
For example, hydrogen atoms have one proton, so the atomic number for hydrogen is one Defines each element For example, carbon has six protons and oxygen has eight © 2017 Pearson Education, Ltd.

Figure Appendix 2-1 Periodic Table of the Elements
Every hydrogen atom has one proton, every carbon atom has six, and every oxygen atom has eight, giving these atoms atomic numbers of 1, 6, and 8, respectively. The periodic table (Appendix II) organizes the elements according to their atomic numbers (rows) and their general chemical properties (columns). © 2017 Pearson Education, Ltd. 10

2.1 What Are Atoms? Isotopes
Atoms of the same element with different numbers of neutrons Distinguished by different mass numbers Some are radioactive (spontaneously break apart, releasing energy) and are used in research Radioactive isotopes are used in radioactive dating (of mummies, ancient trees, skeletons, artifacts), tracing physiological pathways, treating cancer (radiation therapy), and imaging. © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Nuclei and electrons play complementary roles in atoms Nuclei provide stability by resisting external forces (energy, heat, electricity) Electrons are dynamic Can capture and release energy Can forms bonds, linking atoms For example, the stable nuclei of a carbon atom (12C) keeps its carbonic identity regardless of the different structures in which it may be found. © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Electrons occupy electron shells
Three-dimensional regions around nucleus Each has a specific energy The farther from the nucleus, the greater the amount of energy stored in the electrons occupying that shell © 2017 Pearson Education, Ltd.

Figure 2-2 Electron shells in atoms
For simplicity, we depict these shells as increasingly large, concentric rings around the nucleus where electrons travel like planets orbiting a sun. © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Energy (heat, light) can excite an atom
Can cause an electron to jump from a lower-energy electron shell to a higher-energy shell Soon afterward, the electron falls back into its original shell, releasing the extra energy Life depends on electrons capturing and releasing energy Examples: incandescent light bulb, photosynthesis (photosystems). © 2017 Pearson Education, Ltd.

Figure 2-3 Energy capture and release in an incandescent bulb
The electron drops back into lower-energy shell, releasing energy as both heat and light. The energy boosts the electron to a higher-energy shell. An electron absorbs energy. heat energy heat light Figure 2-3 Energy capture and release in an incandescent bulb © 2017 Pearson Education, Ltd.

2.1 What Are Atoms? Each electron shell holds a specific number of electrons Shell nearest the nucleus can hold up to two More distant shells can hold up to eight (some more) Electrons fill the lowest-energy shell (nearest nucleus) first As atomic number increases, electrons fill shells increasingly distant from the nucleus Protons and electrons are balanced The two electrons in helium occupy the first electron shell. A carbon atom—with six electrons—will have two electrons filling its first shell and four occupying its second shell, which can contain a total of eight electrons. © 2017 Pearson Education, Ltd.

Figure 2-2 Electron shells in atoms
For simplicity, we depict these shells as increasingly large, concentric rings around the nucleus where electrons travel like planets orbiting a sun. Carbon (C) 6 protons 6 neutrons Oxygen (O) 8 protons 8 neutrons Phosphorus (P) 15 protons 16 neutrons Calcium (Ca) 20 protons 20 neutrons © 2017 Pearson Education, Ltd.

If an atom has 15 protons and 15 neutrons in its nucleus, how many electrons does it have?
2 4 8 15 Question: 2-2 Answer: d Diff: Easy Text Ref: Section 2.1 Skill: Factual Notes: This question reinforces the fact that the properties and reactivity of atoms depend on the number of subatomic particles. There are generally the same number of electrons in atoms as there are protons, making them electrically neutral. © 2017 Pearson Education, Ltd.

2.2 How Do Atoms Interact to Form Molecules?
Two or more atoms From the same or different elements Held together by interactions among their outermost electron shells Comprise matter For example, hydrogen and oxygen are linked to form water (H2O is two atoms of hydrogen and one atom of oxygen). Table salt is another example (NaCl); it is one atom of sodium and one atom of chloride). © 2017 Pearson Education, Ltd.

An atom will not react with other atoms if the outermost shell is completely empty or full Stable, inert An atom will readily react if the outermost shell is only partially full (features a vacancy) Reactive Some—free radicals—are so reactive that they pull other molecules apart Can contribute to aging, even death Example: Neon, with eight electrons in the outermost shell, is full and, therefore, inert. Oxygen, with six electrons in its outermost shell, can hold two more electrons, and so is susceptible to reacting. © 2017 Pearson Education, Ltd.

Chemical bonds hold atoms together in molecules Attractive forces Atoms gain, lose, or share electrons Three major types Ionic bonds Covalent bonds Hydrogen bonds Atoms, including those that are reactive, have equal numbers of protons and electrons. The equal number of protons and electrons gives atoms an overall neutral charge, but that does not make them stable. An atom with an almost empty outermost electron shell can become more stable by losing electrons and completely emptying the outer shell; this gives it a positive charge. An atom with a nearly full outer shell can become more stable by gaining electrons and filling the shell completely, giving it a negative charge. Hydrogen and oxygen atoms gain stability by interacting with each other. Single electrons from each of two hydrogen molecules fill the outer shell of an oxygen atom to form a water molecule. © 2017 Pearson Education, Ltd.

Ion An atom that has lost or gained electron(s), acquiring an overall positive or negative charge Oppositely charged ions that are attracted to each other are bound into molecules by ionic bonds Giving and taking of electrons Likely between atoms with an almost empty outermost electron shell and atoms with a nearly full outer shell Atoms that have lost electrons become positively charged ions (e.g., sodium: Na). Atoms that have gained electrons become negatively charged ions (e.g., chlorine: Cl). © 2017 Pearson Education, Ltd.

Figure 2-4 Ions and ionic bonds
An electron is transferred. Oppositely charged ions attract. Sodium atom (neutral) 11 protons 11 neutrons Chlorine atom (neutral) 17 protons 17 neutrons Sodium ion (+1) 11 protons 10 neutrons Chloride ion (1) 17 protons 18 neutrons (a) The formation of ions from atoms Figure 2-4 Ions and ionic bonds (b) An ionic molecule: NaCl © 2017 Pearson Education, Ltd.

Atoms with partially full outermost electron shells will likely form covalent bonds Most biological molecules Sharing of electrons Generally stronger than ionic bonds Two types Nonpolar covalent bonds Polar covalent bonds Because biological molecules must function in a watery environment where ionic bonds rapidly dissociate (break down), the atoms in most biological molecules, such as those found in proteins, sugars, and fats, are joined by covalent bonds. © 2017 Pearson Education, Ltd.

Nonpolar covalent bonds Form between atoms of the same element May also form between some atoms of different elements No charge on any part of the molecule formed Equal or nearly equal sharing of electrons Nuclei pull equally O2, N2, H2, CO2 © 2017 Pearson Education, Ltd.

Shared electrons spend equal time near each nucleus.
Figure 2-5 Neither atom has a full outer shell. Shared electrons spend equal time near each nucleus. Figure 2-5 Nonpolar covalent bonds Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond), and H2O. Hydrogen atom (reactive) Hydrogen atom (reactive) Hydrogen molecule (more stable) © 2017 Pearson Education, Ltd.

Polar covalent bonds Form when one nucleus attracts electrons more strongly Molecule has charged poles Unequal sharing of electrons H2O Often between H and O or H and N in biological molecules © 2017 Pearson Education, Ltd.

() slightly negative The nucleus with a larger positive charge
Figure 2-6 slightly negative The nucleus with a larger positive charge exerts a stronger pull on electrons. () Electrons spend more time near the nucleus with the larger charge. The nucleus with a smaller positive charge exerts a weaker pull on electrons. Figure 2-6 Polar covalent bonds Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond), and H2O. (+) slightly positive (+) © 2017 Pearson Education, Ltd.

Figure Appendix 2-1 Periodic Table of the Elements
The periodic table (Appendix II) organizes the elements according to their atomic numbers (rows) and their general chemical properties (columns). © 2017 Pearson Education, Ltd. 32

Hydrogen bonds Attraction between slightly positive and slightly negative poles of adjacent polar molecules—like water Partially positive H atom of one water molecule is attracted to the partially negative O atom of another Give water unique properties Comparatively weak but collectively strong Polar biological molecules can form hydrogen bonds with water, with each other, or even within the same molecule. © 2017 Pearson Education, Ltd.

(+) (+) (+) () hydrogen bonds (+) () (+) (+) (+) () () (+) (+) ()
Figure 2-7 (+) (+) (+) () hydrogen bonds (+) () (+) (+) (+) () () (+) Figure 2-7 Hydrogen bonds in water Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond), and H2O. (+) () (+) (+) (+) () © 2017 Pearson Education, Ltd.

Animation: Hydrogen Bonds in Water
Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond), and H2O. © 2017 Pearson Education, Ltd. 35

An inert atom __________.
forms covalent bonds with itself has a full outer electron shell has an empty outer electron shell does not react with other elements because it is unstable Question: 2-3 Answer: b Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: This question reinforces the fact that the number and position of the electrons affect the reactivity of the atom. © 2017 Pearson Education, Ltd.

The electrical attraction between positively and negatively charged ions forms a(n) ___________.
covalent bond hydrogen bond ionic bond oxygenated bond Question: 2-4 Answer: c Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: If students can remember this, it will be easier for them to understand the different types of bonds. © 2017 Pearson Education, Ltd.

How many electrons does sodium have in its outer shell?
1 2 4 8 Question: 2-5 Answer: a Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: This question will prepare students for a discussion on ions and ionic bonds. It is important to ask them if it is easier for sodium to lose one electron or to gain seven to achieve a full outer electron shell. © 2017 Pearson Education, Ltd.

After sodium loses an electron, it is a(n) ___________.
positive ion negative ion neutral ion isotope Question: 2-6 Answer: a Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: When sodium donates an electron from its outer electron shell to chloride, the sodium atom becomes a positively charged atom called an ion and its outer electron shell is completely empty. © 2017 Pearson Education, Ltd.

How many electrons does chlorine have in its outer shell?
1 2 4 7 Question: 2-7 Answer: d Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: This question continues to provide background for understanding the ionic bond that forms salt. Have students draw the atomic structure of chlorine. It is important to ask them if it is easier for chlorine to lose seven electrons or to gain one in order to achieve a full outer electron shell. © 2017 Pearson Education, Ltd.

How many electrons does chlorine have in its outer shell?
1 2 4 7 Question: 2-7 Answer: d Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: This question continues to provide background for understanding the ionic bond that forms salt. Have students draw the atomic structure of chlorine. It is important to ask them if it is easier for chlorine to lose seven electrons or to gain one in order to achieve a full outer electron shell. © 2017 Pearson Education, Ltd. 46

After chlorine gains an electron, it is a(n) ___________.
positive ion negative ion neutral ion isotope Question: 2-8 Answer: b Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: Upon accepting an electron from sodium, chlorine becomes a negatively charged atom called an ion and its outer electron shell is filled with electrons. © 2017 Pearson Education, Ltd.

How many electrons does sodium lose to chlorine to form an ionic bond?
1 2 4 8 Question: 2-9 Answer: a Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: This question goes a step further; it will confirm the students’ understanding of the final outcome of the ionic bond formed to make salt. © 2017 Pearson Education, Ltd.

Which of the following describes a nonpolar covalent bond?
Unequal sharing of electrons Charged Loss of electrons Equal sharing of electrons Question: 2-10 Answer: d Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: Explain that covalent bonds are different from ionic bonds because they share electrons. Break the discussion into two sections: one on nonpolar covalent bonds and one on polar covalent bonds. © 2017 Pearson Education, Ltd.

How many electrons does oxygen have in its outer shell?
1 2 4 6 Question: 2-11 Answer: d Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: Have students draw the atomic structure of oxygen. In the next question, they will figure out why the structure allows oxygen to form a double nonpolar covalent bond. © 2017 Pearson Education, Ltd.

How many nonpolar covalent bonds does oxygen form with itself?
1 2 4 8 Question: 2-12 Answer: b Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: Talk about how molecular oxygen exists as O2. This will come up again in the chapters on photosynthesis and cellular respiration, when students see that water splits into 1/2 O2 + 2 H+ + 2 electrons. This question will help them understand why the oxygen is written as 1/2 O2 rather than just an O. © 2017 Pearson Education, Ltd.

How many nonpolar covalent bonds does oxygen form with itself?
1 2 4 8 Question: 2-12 Answer: b Diff: Easy Text Ref: Section 2.2 Skill: Factual Notes: Talk about how molecular oxygen exists as O2. This will come up again in the chapters on photosynthesis and cellular respiration, when students see that water splits into 1/2 O2 + 2 H+ + 2 electrons. This question will help them understand why the oxygen is written as 1/2 O2 rather than just an O. © 2017 Pearson Education, Ltd. 56

How many covalent bonds can be made by the carbon atom in the figure below?
1 2 4 8 Carbon (C) 6 protons 6 neutrons Question: 2-19 Answer: c Diff: Moderate Text Ref: Sections 2.1 and 2.2 Skill: Conceptual Notes: Because the carbon atom has four electrons in its outer shell, it can make four covalent bonds with other atoms until this shell is complete with eight electrons. © 2017 Pearson Education, Ltd.

2.3 Why Is Water So Important to Life?
Hydrogen bonds among water molecules cause cohesion Molecules of a single type tend to stick together Droplet formation; flow Produces surface tension Surface of water tends to resist being broken This explains why a belly flop hurts. © 2017 Pearson Education, Ltd.

Figure 2-8 Water molecules have cohesive and adhesive properties
Water molecules cohere to form the droplets on a spider web. (a) Cohesion and adhesion (b) Cohesion causes surface tension © 2017 Pearson Education, Ltd.

Water exhibits adhesion Molecules of a different types tend to stick together Water adheres to molecules with charged regions (ions, other polar molecules) Responsible for capillary action Movement of water into very narrow spaces © 2017 Pearson Education, Ltd.

Figure 2-8 Water molecules have cohesive and adhesive properties
Water molecules adhere to a spider web. Capillary action allows water to move into the narrow spaces between cellulose fibers of a paper towel. (b) Cohesion causes surface tension (c) Capillary action © 2017 Pearson Education, Ltd.

Large plants, like trees, depend on cohesion and adhesion to supply water to all parts of the plant Hydrogen bonds cohering water molecules inside the vessels of the tree allow the water to overcome gravity Hydrogen bonds adhering water molecules to the walls of vessels allow capillary action against gravity © 2017 Pearson Education, Ltd.

Solvent Completely surrounds and disperses individual atoms or molecules of another substance Dissolves, yielding a solution Water is an excellent solvent Positive and negative poles of water attract other polar molecules and ions Hydrophilic (“water-loving”) © 2017 Pearson Education, Ltd.

Figure 2-9 Water as a solvent
Table salt is held together by ionic bonds between positively charged sodium ions and negatively charged chloride ions. When a salt crystal is added to water, the positively charged hydrogen poles of water molecules are attracted to the chlorine ions, and the negatively charged oxygen poles are attracted to the sodium ions. Water molecules surround the ions, preventing them from interacting with each other: the salt dissolves. © 2017 Pearson Education, Ltd.

Water moderates the effects of temperature changes Water has a high specific heat Energy input must be high enough to break hydrogen bonds and excite hydrogen molecules Water resists temperature change © 2017 Pearson Education, Ltd.

Water moderates the effects of temperature changes Water has a high heat of vaporization Energy input must be high enough to break hydrogen bonds and allow liquid to evaporate Water in sweat absorbs excess body heat, cooling us as it evaporates Heat of vaporization = amount of heat needed to cause a substance to evaporate (change from liquid to vapor). © 2017 Pearson Education, Ltd.

Water forms an unusual solid: ice Most substances become denser when they solidify from a liquid Ice is unusual because it is less dense than liquid water Water molecules spread farther apart than their average distance in liquid Icebergs and ice cubes float © 2017 Pearson Education, Ltd.

Water-based solutions can be acidic, basic, or neutral Small fraction of water molecules break apart into hydroxide and hydrogen ions H2O → OH– + H+ Pure water contains equal concentrations of OH– and H+ (neutral) When substances that release OH– or H+ are added to water, the solution no longer has an equal concentration © 2017 Pearson Education, Ltd.

() (+) water (H2O) hydroxide ion (OH) hydrogen ion (H+) Figure 2-13
Figure Some water is always ionized © 2017 Pearson Education, Ltd.

Solutions in which H+ > OH– are acidic An acid releases H+ when dissolved in water For example, hydrochloric acid ionizes in water HCl → H+ + Cl– H+ exceeds the concentration of OH– in the solution Lemon juice, vinegar © 2017 Pearson Education, Ltd.

Solutions in which OH– > H+ are basic A base combines with H+ when dissolved in water For example, sodium hydroxide ionizes in water NaOH  Na+ + OH– OH– exceeds the concentration of H+ in the solution Baking soda, chlorine bleach, ammonia © 2017 Pearson Education, Ltd.

H+ concentration in moles/liter
Figure 2-14 household ammonia (11.9) 1 molar hydrochloric acid (HCl) chlorine bleach (12.6) oven cleaner (13.0) drain cleaner (14.0) vinegar, cola (3.0) blood, sweat (7.4) seawater (7.8–8.3) washing soda (12) stomach acid (2) orange juice (3.5) lemon juice (2.3) black coffee (5.0) baking soda (8.4) hydroxide (NaOH) 1 molar sodium pure water (7.0) tomatoes (4.5) antacid (10) beer (4.1) urine (5.7) rain (5.6) milk (6.4) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Figure The pH scale pH value (H+ > OH) (H+ < OH) neutral increasingly acidic (H+ = OH) increasingly basic 100 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 H+ concentration in moles/liter © 2017 Pearson Education, Ltd.

Buffer Molecule that helps maintain nearly constant pH of a solution Accepts or releases H+ in response to small changes in H+ concentration In excess H+, a buffer combines with H+ In excess OH– , a buffer releases H+ A change in pH can alter the structure and function of biological molecules. pH of body fluids is maintained by several different buffers (e.g., bicarbonate). If the blood becomes too acidic, bicarbonate accepts (and absorbs) H to make carbonic acid: HCO3  H → H2CO3 bicarbonate + hydrogen ion → carbonic acid If the blood becomes too basic, carbonic acid liberates hydrogen ions to combine with OH to form water: H2CO3  OH → HCO3  H2O carbonic acid + hydroxide ion → bicarbonate + water © 2017 Pearson Education, Ltd.

What kind of bond holds the atoms of a single water molecule together?
Ionic Polar covalent Nonpolar covalent Hydrogen Question: 2-13 Answer: b Diff: Easy Text Ref: Section 2.3 Skill: Factual Notes: It is important to show students that ionic and covalent bonds hold the atoms of a molecule together, whereas hydrogen bonds are attractions between molecules. This question and the next illustrate how covalent bonds hold the atoms of a water molecule together, while hydrogen bonds hold water molecules together. © 2017 Pearson Education, Ltd.

What kind of bond forms between water molecules?
Ionic Polar covalent Nonpolar covalent Hydrogen Question: 2-14 Answer: d Diff: Easy Text Ref: Section 2.3 Skill: Factual Notes: Hydrogen bonds hold water molecules together, while polar covalent bonds hold the atoms within a single water molecule together. © 2017 Pearson Education, Ltd.

When you sweat, what property of water is functioning to cool you off?
Water is adhesive. Water has a high heat of vaporization. Water has a high surface tension. Water is neutral in pH. Question: 2-15 Answer: b Diff: Moderate Text Ref: Section 2.3 Skill: Conceptual Notes: Talk about how it takes a lot of energy (heat) to break the hydrogen bonds that hold water together. This can also lead to a discussion on Calories. © 2017 Pearson Education, Ltd.

The basilisk lizard takes advantage of which property of water as it runs along the surface of a pond or stream? Water is adhesive. Water has a high heat of vaporization. Water has a high surface tension. Water is neutral in pH. Question: 2-16 Answer: c Diff: Moderate Text Ref: Section 2.3 Skill: Conceptual Notes: All of the answers are correct statements, but (c) is the only correct answer. Adhesion applies to the polarity of water and its ability to stick to other polar surfaces. Surface tension applies to the cohesion of water, the tendency of water molecules to stick to each other via hydrogen bond formation. This question can be used to again illustrate hydrogen bonding, discussed earlier in Chapter 2, and how it contributes to the properties of water. © 2017 Pearson Education, Ltd.

Pure water is neutral in pH because __________.
the concentration of oxygen and hydrogen is equal hydrogen bonding reduces the formation of hydrogen ions ionization does not occur the concentration of hydroxide ions and hydrogen ions is equal Question: 2-17 Answer: d Diff: Moderate Text Ref: Section 2.3 Skill: Conceptual Notes: This question reinforces the concept of ionization. © 2017 Pearson Education, Ltd.

Atoms, Molecules, and Life

Similar presentations

Presentation on theme: "Atoms, Molecules, and Life"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Atoms, Molecules, and Life

Similar presentations

Presentation on theme: "Atoms, Molecules, and Life"— Presentation transcript:

Similar presentations

About project

Feedback