Biology 1020: Unit. One, Chapter 2. The Chemical Context of Life

What is an ion?

- Molecules that are electrically. charged

What elements make the remaining 3.7% of percent of Body Mass?

-Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, and Magnesium.

What constitutes a chemical reaction?

-The making of chemical bonds -The breaking of chemical bonds -Changes in the composition of matter

What feature is key in compounds?

- A compound has characteristics different from those of its elements - The metal sodium (highly reactive) combines with the poisonous gas chlorine, forming the edible compound sodium chloride, or table salt

What is a half-life? What. are its "descendants called?"

- A half life is the amount of time it. takes for 50% of a sample of a radioactive isotope to decay. - A "parent" isotope decays into its "daughter" isotope at a fixed rate.

What is a dalton? Why is it used?

- A measure of mass for atoms and subatomic particles; the same as the atomic mass unit or amu. - Used because utilizing grams and other conventional measurements were too minuscule.

What is a compound?

- A substance consisting of two or more different elements combined in a fixed ratio. - Table Salt, NaCl, is fixed into a 1:1 ratio - Water (H2O) consists of a ratio of 2:1 Hydrogen to Oxygen

What is an element?

- A substance that cannot be broken down to other substances by chemical reactions. - Today, there are 92 elements that occur in nature.

What is an electron shell?

- An electron shell is an energy level of electrons at a characteristic average distance from the nucleus of an atom. - An electron's energy level is correlated with its average distance from the nucleus

Is H2 and O2 considered pure elements or compounds?

- Pure Elements - Because. a compound is a combination of two or more different elements

How are radioactive tracers used?

- Cells use radioactive atoms just as they would use nonradioactive isotopes. - Isotopes are incorporated into biologically active molecules, which are then used as trackers t. track atoms during metabolism.

How are electron's energy levels partitioned?

- Changes in electrons PE occurs in a series of fixed amounts - An electron having a certain amount of energy is similar to something like a ball on a staircase. - Different Electron Shells

What are the draw backs to using radioactive isotopes?

- Decaying isotopes also pose a hazard to life by damaging cellular molecules. - Severity depends on the type and amount of radiation an organism absorbs.

What is an Isotope?

- Different atomic forms of the same element - One of several atomic forms of. an element, each with the. same number of protons but a different number of neutrons, thus differing atomic mass.

Why do electrons have potential energy?

- Due to their distance from the nucleus. The negatively charged electrons are attracted to the positively charged nucleus. - It takes work to move a given electron. farther. away. from the nucleus - More distant an electron has from a nucleus = The more PE

Why are half-lives valuable tools to deciphering when an organism died?

- Each radioactive isotope has a characteristic. half-life that is not affected by temperature, pressure, or any other environmental variable.

What is energy? What varies in the amount of energy it possesses?

- Energy is defined as the capacity to cause change - An atom's electrons vary in the amount of energy they posses

What are key. to. function. for. molecules?

-The Molecules characteristic size and shape

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

-The attraction between oppositely charged ions, forming ionic bonds

How do opiates work?

- Opiates relieve pain and alter mood by weakly binding to specific receptor molecules soon the surfaces of the brain. - Opiates are able to do this because they have a similar structure to Endorphins, and are able to bind to Endorphin receptors.

What is an atom's valence?

-The bonding capacity of a given atom - The number of covalent bonds that an atom can form, which usually equals the number of unpaired electrons in its shells.

What is the atomic mass? Why isn't it exact?

- The atomic mass is. the TOTAL mass of an atom. - Neutrons and protons each have a mass very close to 1 dalton, so the mass number is close to, but slightly different. from, the total mass of an atom. - Atomic mass is also. the. average mass of the naturally occurring isotopes, weighted by their abundance) - Because elements sometimes have 2 or more isotopes, elements vary in atomic mass and neutrons.

What is an atom's electronegativity?

- The attraction of a particular atom for the electrons of a covalent bond. - The more electronegative an atom is, the more strongly it pulls shared electrons towards itself. - In a covalent bond of two of the same element, electrons are shared equally because they have the same electronegativity.

How is a chemical's behavior determined?

- The distribution of electrons in the atom's electron shells. - The chemical behavior of an atom depends mostly on the number of electrons in the outermost shell

What is the atomic number? Why are protons so important?

- The number of protons in the nucleus of an atom, unique for each element and designated by a subscript. - Each element has a unique number of protons! - Unless otherwise indicated, an atom is neutral in charge. Therefore, the atomic number of. an element reveals the number of protons and neutrons.

What happens when an atom forms a covalent bond?

- The orbitals in its valence shell. undergo a rearrangement

What is the mass number? Why is it important in deducing the number of neutrons?

- The total number of protons and neutrons in an atom's nucleus. - Subtracting the atomic number by the mass number reveals the number of neutrons.

Why is it called an electron orbital?

- We can never describe the exact location of an electron. - Therefore, we utilize the three-dimensional space where an electron is found 90% of the time.

How do hydrogen bonds work?

- When a hydrogen atom is covalently bonded to an electronegative atom, the hydrogen has a partial positive charge that allows it to be attracted to a different electronegative atom nearby. - Electronegative partners are. usually oxygen and nitrogen

What happens when an electron gains energy? Loses Energy?

- When electrons absorbs energy, it moves to a. shell farther out from the nucleus - When an electron loses energy, it "falls back" to a shell closer to the nucleus, and the lost energy is usually entered into the environment as heat.

Want is an ionic compound?

-A compound resulting from the formation of an ionic bond; also called a salt. - Each salt crystal is an aggregate of vast numbers of cations and anions bonded by their electrical attraction and arranged in a three-dimensional lattice.

What is an ionic bond?

-A chemical bond resulting from the attraction between oppositely charged ions. - The transfer of an electron is not, by itself, the formation of a bond, rather it allows a bond to form between it results in two ions of opposite charges. -Any two ions of opposite charge can form an ionic bond.

What is radiometric dating? When is it used?

-A method for determining the absolute age of rocks and fossils, based on the half-life of radioactive isotopes. - Scientist employ this when they measure the ratio of different isotopes and calculate the number of years have passed since an organism was fossilized or a rock was formed.

What is a cation?

-A positively charged ion - Cat- Eye- Ons

What is a neutron?

-A subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7x10^-24g, found in the nucleus of an atom.

What is an electron?

-A subatomic particle with a single negative electrical charge and a mass about 1/2000 that of a neutron or proton. One or more electrons move around the nucleus atom.

What is a proton?

-A subatomic particle with a single positive electrical charge, with a mass of about 1.7x10^-24g, found in the nucleus of an atom.

What is a hydrogen bond?

-A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of the same molecule.

Why are emergent properties important in compounds?

-Allows an explosive metal and poisonous gas to combine to form Table Salt.

What is an atom?

-An atom is thee smallest unit of matter that still retains the properties of an element. -We symbolize atoms with the same abbreviations used for elements that is made up of those atoms (Example: Carbon= The element and a single carbon atom.)

What are chemical bonds?

-An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. - The bonded atoms gain completer outer electron shells

What is a radioactive isotope? What's an example?

-An isotope that is unstable; thus the nucleus decays spontaneously, giving off the detectable particles and energy. -When the radioactive decay leads to a change. in. the. number of protons, it. transforms the. atom to an atom of. a. different. element. - When an atom of carbon-14 decays, it loses a proton, becoming. an. atom of nitrogen-14

What is an anion?

-Anions are negative ions -Anus

What is matter?

-Anything which takes up space and has mass - Example: Rocks, Metals, Oils, Gases, and Living Organisms

What is an example of a naturally occurring toxic element to humans?

-Arsenic -Millions of people in Asia have been inadvertently exposed to arsenic-laden water due to mining.

What does inert mean?

-Chemicals that are unreactive. -Noble gases are considered inert

What subatomic particle is directly involved in chemical reactions?

-Electrons are directly involved in chemical reactions

What are atoms mostly?

-Empty space - If an atom of helium were the size of a typical football stadium, the nucleus would be the size of a pencil eraser in the center of the field. -Moreover, the electrons would be like two tiny gnats buzzing around the stadium.

What are the times of half-lives?

-Half-lives can range from a few seconds to extremely long (Uranium-238 has a half. life. of. 4.5. billion years)

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

-In this structure, each carbon atom has only three covalent bonds instead of the required four.

What are some ways that researchers can help clean up toxic heavy metals in contaminated areas?

-Some species of plants have become adapted to environments containing elements that are usually toxic. -Example being a Serpentine, contains elevated concentrations of elements such as chromium, nickel, and cobalt. -Researches may use serpentine plants to help dispose of some contaminated metals.

What is the weights of protons and neutrons in daltons? Electrons?

-Neutrons and protons have masses close to 1 dalton, electrons. is about 1/2000 of. a proton or neutron. (Need. 2000 electrons to equal ONE proton) -Because the mass of an electron is so small, we can ignore electrons when computing the total mass of an atom.

Around what percentage of elements do we need? What are they called?

-Of the 92 natural elements, about 20-25% are essential elements that an organism needs to reproduce and to live healthily. - Essential Elements- A chemical element required for an organism, to survive, grow, and reproduce. - Humans need 25 elements while plants only need 17.

What is the atomic nucleus? What are its features?

-Protons and neutrons form the atomic nucleus, forming an atom's central core - Protons give the nucleus a positive charge -Atomic Nucleus is very dense (Think of 6.6 Billion cars in a box of 1ft by 1ft)

What are the reactants? Products?

-Reactants, known as the starting materials -Products, known as the resulting materials

What keeps the electrons within the vicinity of the nucleus?

-The rapidly moving electrons form a "cloud" of negative charge around the nucleus, and it is the attraction between opposite charges that keeps the electrons within the vicinities of the nucleus.

What is a covalent bond?

-The sharing of a pair of valence electrons by two atoms. -Two or More atoms held together via covalent bonds constitute a molecule.

What are the strongest bonds?

-The strongest kind of chemical bonds are covalent bonds and iconic bonds in dry compounds. - Ionic bonds in aqueous or water based solutions are weak interactions.

What are trace elements? What are some examples of trace elements.

-Trace elements are required by an organism in only minute qualities. -Iron (needed in all forms of life), Iodine (Essential ingredient of a hormone produced by the thyroid gland).

What are Valence Electrons? Valence Shells?

-Valence electrons are electrons in the outermost electron shell. - Valence shell is the outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.

What are Van der Waals interactions?

-Weak attractions between molecules or parts of molecules that result from transient local partial charges. - Think of the kids on the school's analogy - Occurs because electrons are not always EVENLY distributed -This makes one molecule may have a slightly positive or negative charge to it

Why are weak interactions needed?

-Weak interactions may form not only between molecules but also between parts of a large molecule. - The cumulative effect of weak interactions is to reinforce the three-dimensional shape of the structure.

What is a polar bond?

-a covalent bond in which electrons are shared unequally - Bonds between oxygen and hydrogen atoms of a molecule are quite polar.

Why is molecular shape crucial in biology?

-it determines how biological molecules recognize and respond to one another with specificity -Biological molecules often bind temporarily to each other. by forming weak interactions, but only if their shapes are complementary.

What is Chemical Equilibrium?

-the point at which the reactions offset one another exactly -This is a dynamic equilibrium, reactions are still going in both directions.

At what temperature do atoms completely stop moving?

0 Kelvin

How many atoms can the second shell hold?

10 electrons

4. Which statement is true of all atoms that are anions? A. The atom has more electrons than protons. B. The atom has more protons than electrons. C. The atom has fewer protons than does a neutral atom of the same element. D. The atom has more neutrons than protons.

A. The atom has more electrons than protons.

1. In the term trace element, the adjective trace means that A. the element is required in very small amounts. B. the element can be used as a label to trace atoms through an organism's metabolism. C. the element is very rare on Earth. D. the element enhances health but is not essential for the organism's long-term survival.

A. the element is required in very small amounts.

How do isotopes behave in chemical reactions?

Although they have different masses, they behave identically in chemical reactions.

6. We can represent atoms by listing the number of protons, neutrons, and electrons—for example, 2p+,2n0,2e− for helium. Which of the following represents the 18O isotope of oxygen? A. 7p+,2n0,9e− B. 8p+,10n0,8e− C. 9p+,9n0,9e− D. 10p+,8n0,9e−

B. 8p+,10n0,8e−

3. The reactivity of an atom arises from A. the average distance of the outermost electron shell from the nucleus. B. the existence of unpaired electrons in the valence shell. C. the sum of the potential energies of all the electron shells. D. the potential energy of the valence shell.

B. the existence of unpaired electrons in the valence shell.

7. The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound. A. HS B. HS2 C. H2S D. H4S

C. H2S

8. What coefficients must be placed in the following blanks so that all atoms are accounted for in the products? C6H12O6→⎯⎯⎯⎯⎯⎯⎯C2H6O+⎯⎯⎯⎯⎯⎯⎯CO2 A. 2; 1 B. 3; 1 C. 1; 3 D. 2; 2

D. 2; 2

5. Which of the following statements correctly describes any chemical reaction that has reached equilibrium? A. The concentrations of products and reactants are equal. B. The reaction is now irreversible. C. Both forward and reverse reactions have halted. D. The rates of the forward and reverse reactions are equal.

D. The rates of the forward and reverse reactions are equal.

2. Compared with 31P, the radioactive isotope 32P has A. a different atomic number. B. one more proton. C. one more electron. D. one more neutron.

D. one more neutron.

How do electrons like to exist?

Electrons, Like all matter, tend to exist in the lowest available state of potential energy.

How many shells can accompany an orbital?

No more than two electrons can occupy a single orbital.

What are the four main elements that make up 96% of living matter?

Oxygen- 65.0% Carbon- 18.5% Hydrogen- 9.5 % Nitrogen- 3.3%

O=O; What do the lines represent?

The double line represents a double covalent bond

What is Potential Energy?

The energy that matter possesses because of its location or structure.

H-H; What does the line represent?

The line represents a single bond, a pair of shared electrons

What is a molecular formula?

The molecular formula gives the actual numbers of atoms in a molecule.

What is the atomic number?

The number of protons within an atom.

How many atoms can the first shell hold?

Two atoms

What is a non-polar bond?

a covalent bond in which electrons are shared equally

What is a structural formula?

a formula that shows the visual arrangement of atoms in the molecule of a compound.