Chapter 2 - The Chemical Context Of Life + Test Review

Question 1

Explain why table salt has emergent properties.

Answer 1

Sodium and chlorine bind together to create the compound sodium chloride. Apart, these elements are a metal and a toxic gas; however, together they interact and form the new compound NaCl, showing that it has different properties than a metal and a poisonous gas as it is edible. As the two elements interact they become more complex.

Question 2

Is a trace element an essential element? Explain.

Answer 2

Yes, as it is required by an organism. However, a trace element is only needed by an organism in minute amounts whereas an essential element is required in larger amounts.

Question 3

What is an element?

Answer 3

A substance that cannot be broken down into another substance by chemical reactions. Example - gold, carbon, oxygen, copper, etc. The most basic form.

Question 4

What is a compound?

Answer 4

A substance consisting of two or more different elements combined in a fixed ration. A compound has characteristics that are different than its elements. Example - NaCl (Sodium chloride, table salt) H2O (Water).

Question 5

What are essential elements? What are the four essential elements in the human body?

Answer 5

Essential elements are required for an organism to live, survive, and reproduce. The four elements 1) Oxygen, O 2) Carbon C 3) Hydrogen H and 4) Nitrogen N, account for 96% of living matter.

Question 6

What are trace elements? Give some examples.

Answer 6

Trace elements are required by an organism, but only in minute quantities. Example - Calcium Ca, Potassium K, Sodium Na, Magnesium Mg, etc.

Question 7

In humans, iron is a trace element required for the proper functioning of hemoglobin, the molecule that carries oxygen in red blood cells. What might be the effects of an iron deficiency?

Answer 7

An effect of low oxygen levels can be fatigue. Anemia.

Question 8

Explain how natural selection might have played a role in the evolution of species that are tolerant of serpentine soils.

Answer 8

The plants adapted with an ability to tolerate elevated levels of the elements in serpentine soils and could then grow and reproduce there. The offspring of these plants would vary, with the most capable of thriving under serpentine conditions growing best and reproducing most. Many generations continued to adapt like this.

Question 9

A lithium atom has 3 protons and 4 neutrons. What is its mass number?

Answer 9

7

Question 10

A nitrogen atom has 7 protons, and the most common isotope of nitrogen as 7 neutrons. A radioactive isotope of nitrogen has 8 neutrons. Write the atomic number and mass number of this radioactive nitrogen as a chemical symbol with a subscript and superscript.

Answer 10

N - atomic number 7 - mass number 15

Question 11

How many electrons does fluorine have? How many electron shells? Name the orbitals that are occupied. How many electrons are needed to fill the valence shell?

Answer 11

A) 9 electrons
B) 2 shells
C) 1s, 2s, 2p - three orbitals
D) 1 electron is needed to fill the valence shell

Question 12

In Figure 2.7 (Periodic Table showing electron distribution), if two or more elements are in the same row, what do they have in common? If two ore more elements are in the same column, what do they have in common?

Answer 12

A) The number of electron shells

B) The number of valence electrons in their valence shells

Question 13

What do an elements properties depend on?

Answer 13

The structure of the atom.

Question 14

What is the definition of an atom? What 3 subatomic particles make up an atom? What are their electronic charges?

Answer 14

The smallest unit of matter that retains the properties of the element. 1) Proton - 1 unit of positive charge, 2) neutron - electrically neutral, and 3) electron - 1 unit of negative charge.

Question 15

What is an atomic nucleus?

Answer 15

Protons and neutrons packed together in a dense core at the center of an atom.

Question 16

What is an electron? Explain how it works, basically.

Answer 16

A subatomic particle that holds 1 unit of negative charge. Electrons form a cloud of negative charge around the nucleus and the attraction of opposite charges keeps the electrons in the vicinity of the nucleus.

Question 17

What is the unit used to measure the mass of subatomic particles?

Answer 17

Dalton - or atomic mass unit. Neutrons and protons have a mass close to 1 dalton.

Question 18

What is an atomic number?

Answer 18

The number of protons which is unique to that element (written to the left of the symbol for that element). All atoms of a particular element have the same number of protons in their nuclei. Extra - Unless otherwise noted, an atom is neutral in electrical charge, meaning protons must be balanced by an equal amount of electrons.

Question 19

What is the mass number?

Answer 19

The sum of protons and neutrons in the nucleus. (Written to the left of the element symbol on top of the atomic number).

Question 20

What is atomic mass?

Answer 20

The total mass of an atom. Actually, an average of the atomic masses of all the element’s naturally occurring isotopes.

Question 21

What are isotopes?

Answer 21

The different atomic forms of the same element. All atoms of a given element have the same number of protons, but some atoms have more neutrons than other atoms of the same element and therefore have a greater mass. Even though isotopes have slightly different masses, they behave identically in different chemical reactions.

Question 22

What is a radioactive isotope?

Answer 22

One in which the nucleus decays spontaneously. When this decay changes the number of protons, it transforms the atom to a different element. Example - when (^14)C (carbon) decays, it becomes (^14N) (nitrogen)

Question 23

Explain “half life”.

Answer 23

A “parent” isotope decays into its “daughter” isotope at a fixed rate and is expressed as the “half life” of the isotope. The amount of time it takes for 50% of a sample of radioactive isotope to decay.

Question 24

Explain radiometric dating.

Answer 24

Radiometric dating measures the ratio of different isotopes and can calculate how many “half lives” (in years) have passes since the organism was fossilized.

Question 25

What is energy?

Answer 25

The capacity to cause change.

Question 26

What is potential energy?

Answer 26

The energy that matter possesses because of its location or structure. The more distant an electron is from the nucleus, the greater its potential energy.

Question 27

What is an electron shell?

Answer 27

An energy level of electrons at a characteristic average distance from the nucleus of an atom. Show in 2D as concentric circles surrounding the nucleus. When an electron absorbs energy, it moves to a shell further out from the nucleus.

Question 28

What is a valence electron?

Answer 28

An electron in the outermost electron shell.

Question 29

What is the valence shell?

Answer 29

The outermost electron shell of an atom.

Question 30

Explain electron ORBITALS.

Answer 30

An orbital is the 3D space where an electron is found 90% of the time. The first electron shell has only one spherical s orbital (called 1s), but the second shell has four orbitals: one large spherical s orbital (called 2s) and three dumbbell shaped p orbitals (called 2p orbitals). The third shell and other higher electron shells also have s and p orbitals, as well as orbitals of more complex shapes.

Question 31

Why does the structure H - C = C - H fail to make sense chemically?

Answer 31

Each carbon atom has only three covalent bonds instead of the required four.

Question 32

What holds the atoms together in a crystal of magnesium chloride (MgCl2)?

Answer 32

The attraction between oppositely charged ions, forming ionic bonds.

Question 33

If you were a pharmaceutical researcher, why would you want to learn the 3D shapes of naturally occurring signaling molecules?

Answer 33

If you could synthesize molecules that mimic these shapes, you might be able to treat diseases or conditions caused by the inability of affected individuals to synthesize such molecules. Example - endorphins and morphine.

Question 34

Explain how atoms interact.

Answer 34

Atoms with incomplete valence shells interact with other atoms in such a way that each partner completes its valence shell. (Share or transfer valence electrons)

Question 35

What is a chemical bond?

Answer 35

An attraction between 2 atoms resulting from a sharing of outer shell electrons or the presence of opposite charges in atoms. The bonded atoms gain complete outer electron shells. The strongest chemical bonds are called covalent bonds.

Question 36

What is a covalent bond?

Answer 36

The sharing of a pair of valence electrons by two atoms.

Question 37

What is a molecule?

Answer 37

2 atoms held together by a covalent bond. Example - H1 + H1 = H2.

Question 38

What is a single bond?

Answer 38

A pair of shared valence electrons by 2 atoms.

Question 39

What is a double bond?

Answer 39

A double covalent bond. The sharing of 2 pairs of valence electrons by 2 atoms.

Question 40

Explain valence. What are the valences of hydrogen, oxygen, nitrogen, and carbon?

Answer 40

The bonding capacity is called the atoms valence and usually equals the number of unpaired electrons required to complete the valence shell. H = 1, O = 2, N = 3, C = 4

Question 41

What is methane?

Answer 41

1 carbon atom bonds with 4 hydrogen atoms. CH4

Question 42

Explain electronegativity.

Answer 42

The attraction of a particular atom for the electrons of a covalent bond. The more electronegative an atom is, the stronger it pulls shared electrons toward itself.

Question 43

What is a non polar covalent bond?

Answer 43

A covalent bond between 2 atoms of the same element. The electrons are shared equally because the 2 atoms have the same electronegativity. Example - H2, O2

Question 44

What is a polar covalent bond?

Answer 44

This type of bond happens when an atom is bounded to a more electronegative atom. The electrons of the bond are not shared equally. Oxygen is one of the most electronegative elements

Question 45

What are ions? What are the 2 types of ions?

Answer 45

Opposite charged atoms. An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge. 1) cation - positively charged, 2) anion - negatively charged.

Question 46

What is an ionic bond?

Answer 46

Two ions of opposite charge attracted to each other. Example - NaCl

Question 47

What are ionic compounds?

Answer 47

(Salts) Compounds formed by ionic bonds and does not consist of molecules.

Question 48

What is a hydrogen bond?

Answer 48

An attraction between a hydrogen and an electronegative atom. (Electronegative partners are usually oxygen or nitrogen). Example - Ammonia (NH3) + Water (H2O) - Results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia.

Question 49

Explain van dear Waals interactions.

Answer 49

Weaker attractions between molecules or parts of molecules that result from transient local partial charges. (Occur only when molecules and atoms are close together)

Question 50

Give an example of molecular shape and how that affects function. Why is it important?

Answer 50

Shapes of atoms and molecules depend on positions of atoms orbitals. Molecular shape is crucial as it determines how biological molecules recognize and respond to one another with specificity. Structure affects the function. Example - morphine and endorphins.

Question 51

When is an element inert and non-reactive?

Answer 51

When the element has a complete valence shell.

Question 52

How do radioactive elements become stable?

Answer 52

In order to radioactive elements to stabilize, they omit rays of energy. *Example - alpha, beta, or gamma rays (gamma being the harshest and most damaging)

Question 53

Figure 2.10 - Covalent bonding.

Answer 53

See photos for diagram.

Question 54

Which type of chemical reaction occurs faster at equilibrium, the formation of products from reactants or reactants from products?

Answer 54

At equilibrium, the forward and reverse reactions occur at the same rate.

Question 55

Write an equation that uses the products of photosynthesis as reactants and the reactants of photosynthesis as products. Add energy as another product. This new equation describes a process that occurs in your cells. Describe this equation in words. How does this equation relate to breathing?

Answer 55

C6H12O6 + 6 O2 –> 6 CO2 + 6 H2O + Energy. Glucose and oxygen react to form carbon dioxide and water, releasing energy. We breathe in oxygen because we need it for this reaction to occur, and we breathe out carbon dioxide because it is a byproduct of this reaction.

Question 56

What are chemical reactions?

Answer 56

The making and breaking of chemical bonds. Matter is conserved in a chemical reaction as reactions cannot create or destroy atoms but can only rearrange or redistribute the electrons among them.

Question 57

What is a reactant?

Answer 57

The starting material in a chemical reaction. Example - H2 or O2

Question 58

What is a product?

Answer 58

The material resulting from a chemical reaction. Example - H2O

Question 59

What is the chemical shorthand for photosynthesis?

Answer 59

6 CO2 (carbon dioxide) + 6 H2O (water) –> C6H12O6 (glucose) + 6 O2 (oxygen)

Question 60

Discuss the reversibility of reactions.

Answer 60

All chemical reactions are reversible, with the products of the forward reaction becoming the reactants for the reverse reaction. Example - 3 H2 (hydrogen) + N2 (nitrogen) –>–

Question 61

Explain chemical equilibrium.

Answer 61

Chemical equilibrium is reached when the forward and reverse actions occur at the same rate. The relative concentrations of products and reactants stop changing and the reactions offset one another exactly.

Question 62

What are the 3 weak bonds that hold complex molecules together?

Answer 62

1. Ionic bond - exists between ions dissociated in water
2. Hydrogen bond - the attraction between a hydrogen and an electronegative atom
3. Van der waals interactions - electrons accumulate by chance in one part of a molecule distributing unevenly. The results are ever changing regions of positive and negative charge that enable all atoms and molecules to stick to one another. These interactions are individually weak and occur only when atoms and molecules are very close together

Question 63

What is typically the strongest bond?

Answer 63

Covalent bond.