Chapter 2: Atoms, Molecules & Life What are atoms? What are molecules? Why do atoms interact? How do atoms interact? Why is water so important to life?

Table 2-1 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. Living things are composed of chemical elements

Matter is composed of elements

Matter - Elements Atoms (p. 22) 1. Nucleus a.Protons and neutrons 2. Electrons a. Electron shells, orbitals, energy levels

Figure 2-1 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. electron shell Helium (He)Hydrogen (H) nucleus e–e– e–e– e–e– p+p+ p+p+ p+p+ n n Representations of atomic structure

Figure 2-2 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. Carbon (C)Calcium (Ca)Phosphorus (P)Oxygen (O) 2e–2e– 6p+6p+ 6n6n 8p+8p+ 8n8n 15p + 16n 20p + 20n 4e–4e– 2e–2e– 6e–6e– 2e–2e– 8e–8e– 5e–5e– 2e–2e– 8e–8e– 8e–8e– 2e–2e– CaPOC

Figure 2-3 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. light energy 3 Electron drops back into lower- energy shell, releasing energy as light. 2 The energy boosts the electron to a higher energy level. 1 An electron absorbs energy. Electrons are energized moving particles (p. 23)

How do we know orbitals exist?

Atoms of most elements interact with other atoms Chemical bonds & chemical reactions (p. 25) H H

Chemically bonded atoms form molecules & compounds (p. 23) Lactose

Why do atoms form bonds? Reactive Inert

Table 2-2 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.

Matter – Chemical bonds 1.Bonds between individual atoms a. Ionic b. Covalent 2.Bonds between polar molecules a. Hydrogen bonds

Ionic bonding (p. 25) Stable?

Figure 2-4ab Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. 11p + 11n 17p + 18n Electron transferred Chloride ion (–)Sodium ion (+) Chlorine atom (neutral) Sodium atom (neutral) Attraction between opposite charges (a) (b) 11p + 11n 17p + 18n

Figure 2-4c Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. (c) An ionic compound: NaCl Na + Cl – Na + Cl – Na + Cl –

Covalent bonding (p. 26)

Covalent bonding (p. 28)

Covalent bonding can form polar molecules (p. 26)

Nonpolar covalent bonding (p. 26)

Sodium (Na), atomic number 11, has a tendency to lose an electron in the presence of chlorine. After losing the electron, Na will have _________ protons in its nucleus.

Bonds form between atoms because 1.Atoms seek to have an equal number of protons and electrons 2.All atoms form bonds 3.Atoms attempt to become electrically neutral 4.Atoms seek a full outer shell of electrons

Hydrogen bonds 1.Are used to form all molecules involving hydrogen 2.Are only used to form a hydrogen molecule (H2) from two hydrogen atoms 3.Occur between all covalently bonded molecules 4.Occur between polar molecules

none How many single covalent bonds can this phosphorus atom form?

1. Because helium has the same number of protons as electrons. 2. Its outermost electron shell has 8 electrons. 3. The outermost electron shell is empty. 4. Because its atomic number is an even number 5. Its outermost electron shell has 2 electrons. Why is a helium atom (atomic number = 2) more stable than a hydrogen atom (atomic number =1)?

Lithium (Atomic # = 3) can become stable by which of the following types of bonds? 1)Ionic 2)Covalent 3)Hydrogen 4)All of these 5)Both 1 and 2

An atom of sulfur (Atomic #16) 1)Is stable and nonreactive 2)Can form a stable compound with beryllium (Be) through a double covalent bond (S=Be) 3)Can become stable by forming 2 single covalent bonds 4)Both 2 & 3

Chemical bonding activity If your birth month was your atomic number, what would you bond with?

Why is water so important to life? Water, the solvent of polar and ionic molecules (p. 28)

O H

Water-based solutions can have different pHs (p. 31) hydrogen ion (H + ) hydroxide ion (OH – ) water (H 2 O) (+)(–)

Figure 2-15 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. H + concentration in moles/liter increasingly acidic increasingly basic neutral (H + = OH – ) (H + > OH – )(H + < OH – ) –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 1molar sodium hydroxide (NaOH) 1molar hydrochloric acid (HCI) stomach acid (2)lemon juice (2.3)"acid rain" (2.5–5.5)tomatoesbeer (4.1) vinegar, cola (3.0) orange (3.5)black coffee (5.0)normal rain (5.6) water from faucet urine (5.7) milk (6.4)pure water (7.0) seawater (7.8–8.3)salivablood, sweat (7.4)baking soda (8.4) toothpaste (9.9)household ammonia (11.9)washing soda (12)oven cleaner (13.0)chlorine bleach (12.6)phosphate detergents drain cleaner (14.0) pH value

Water and life Water moderates temperature changes (p. 32)

Why is water so important to life? Water is less dense as a solid than as a liquid (p. 33) -How is this important for life?

Water and life Water and chemical reactions 1. Hydrolysis 2. Dehydration synthesis 3. Photosynthesis 4. Respiration