KEY CONCEPTS Molecules form when atoms bond to each other. Chemical bonds are based on electron sharing. The degree of electron sharing varies from nonpolar.

KEY CONCEPTS Molecules form when atoms bond to each other. Chemical

bonds are based on electron sharing. The degree of electron sharing varies from nonpolar covalent bonds, to polar covalent bonds, to ionic bonds.

Chemical reactions tend to be spontaneous if they lead to lower potential energy and higher entropy (more disorder). An input of energy is required for nonspontaneous reactions to occur.

Water is a small, highly polar molecule. As a result, it is an extremely efficient solvent and has a high capacity for absorbing energy.

KEY CONCEPTS

Water is a small, highly polar molecule. As a result, it is an extremely efficient solvent and has a high capacity for absorbing energy.

• Radioactive isotopes have unstable nuclei that emit particles of radiation (energy) to form new daughter isotopes. This is known as radioactive decay. The energy may be released as beta particles (electrons), gamma rays (pure energy), or alpha particles (helium nuclei – positively charged and large).

Each element has a characteristic number of protons. The number of neutrons can vary; forms of an element with different numbers of neutrons are called isotopes.

Each radioactive isotope decays at a constant rate quantified as its half-life

How Old Is the Earth?

• Meteorites formed 4.58 Ga, and the Moon formed 4.51 Ga. Earth must be about the same age, but no direct radiometric dating is possible because Earth was initially molten (Figure 2.4).

How Does Covalent Bonding Hold Molecules Together?

• Atoms are most stable when each orbital has two electrons. Atoms can be joined by a covalent bond in which each atom’s unpaired electrons are shared by both nuclei to fill their orbitals (Figure 2.7).

Bond Angles and the Shapeof Molecules

• Molecular shape depends on bond angles, which in turn depend on the orbitals in the bond (Figure 2.12).

CHECK YOUR UNDERSTANDINGCovalent bonds are based on electron sharing, while ionic bonds are based on electrical attraction between ions with opposite charges. Covalent bonds can be polar or nonpolar, depending on whether the electronegativities of the two atoms involved are the same or different…

CHECK YOUR UNDERSTANDING…You should be able to (1) draw the structural formulas of methane (CH4) and ammonia (NH3) and add dots to indicate the relative locations of the covalently bonded electrons, and (2) draw the electron shells around sodium ions (Na+) and chloride ions (Cl-) and explain why table salt (NaCl) exists.

What Is Energy?• Energy is the ability to do work or supply heat. Stored energy is called potential energy, and the energy of movement is called kinetic energy or thermal energy, which is measured as temperature.

The first law of thermodynamics states that energy is conserved—it cannot be created or destroyed, but it can be transferred or transformed

The Roles of Temperature and Concentration in Chemical

Reactions

• High temperatures and high concentrations cause more reactant collisions and faster reaction rates.

2.4 The Composition of the Early Atmosphere: Redox Reactions and the Importance of Carbon

• Volcanic gases (mostly CO2, N2,

and H2O) probably dominated Earth’s

early atmosphere, but H2, NH3, and

CH4 were also present in sufficient

amounts to form H2CO and HCN.

What Is a Redox Reaction?

• In a reduction-oxidation (redox) reaction, one molecule loses electrons (is oxidized), another gains electrons (is reduced), and an electron donor is always paired with an electron acceptor (Figure 2.20).

Functional Groups

• Carbon provides the structural framework of organic compounds, and functional groups containing H, N, or O atoms bonded to C determine their behavior (Table 2.1).

2.5 The Early Oceans andthe Properties of Water

• Life originated in and is based on water because water is a great solvent (substances dissolve easily in it).

• Water has several striking physical properties: it expands as it changes from a liquid to a solid, and it has an extraordinarily large capacity for absorbing heat.

Water is Denser as a Liquid than as a Solid

• Hydrogen bonds in ice connect water molecules in an open crystal pattern. In liquid water, there are fewer hydrogen bonds and the water molecules can pack more tightly, making water denser than ice (Figure 2.27).

Water has several striking physical properties: it expands as it changes from a liquid to a solid, and it has an extraordinarily large capacity for absorbing heat.

• Water’s temperature-buffering capacity would have protected dissolved HCN and CH2O from

energy sources in Earth's early environment (such as asteroid bombardment, volcanism, and sunlight) that could have broken them apart.

Acid-Base Reactions and pH

• In acid-base reactions, a proton donor (acid) transfers a proton to a proton acceptor (base).

Thalidomide effect – Fig. 3.291 optical isomer is a safe tranquilizer – mirror image inhibits blood vessel formation – use as anticancer drug?

Thalidomide taken during narrow windows of limb formation gave reduced or no arms or legs –

apparently by affecting blood vessel formation

How Do Amino Acids Linkto Form Proteins?

THE PEPTIDE BOND

CHECK YOUR UNDERSTANDING

Amino acids are small molecules with a carbon atom bonded to a carboxyl group, an amino group, a hydrogen atom, and a side chain called an R-group. Each amino acid has distinctive chemical properties because each has a unique R-group. You should be able to draw the general form of an amino acid.

When the carboxyl group of one amino acid reacts with the amino group of another amino acid, a strong covalent bond called a peptide bond forms. Polypeptides are polymers made up of peptide-bonded amino acids. Small polypeptides are called oligopeptides, and large polypeptides are called proteins. You should be able to draw and label two amino acids linked by a peptide bond.

3.3 What Do Proteins Look Like?

Quaternary Structure

QUATERNARY STRUCTURE

How Do Enzymes Work?

• Enzymes bring substrates together in specific positions that facilitate reactions and are very specific as to which reactions they catalyze.

Escherichia coli – LPS/O antigens, OMPs, flagella, peptidoglycan, inner membrane, DNA, ribosomes,

tRNA, various protein assemblies