HELP WITH 2 TOPIC QUES DUE IN 24 HOURS
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Chapter2.docxChapter 2: The Chemical Basis of Life
Objectives:
· Name and describe the subatomic parts of an atom.
· Describe and discuss the energy levels of an atom.
· Draw a simplified atomic structure of an atom with an atomic number less than 20.
· Distinguish between covalent, ionic, and hydrogen bonds.
· Describe the properties of water and their importance to living things.
· Define an acid and a base; describe the pH scale, and state the significance of buffers.
I. Living things obey the laws of _________________ and _______________ and are the product of chemical reactions. To better understand complex biological processes, we must often reduce them to simpler steps at a lower level of organization.
II. Matter is anything that takes up ________________ and has __________________. It may exist as _______________, __________________, or ______________.
III. Elements are basic types of matter, substances that cannot be broken down into simpler substances by ordinary chemical means. There are ________naturally occurring elements (+ more synthesized ones). Each element is represented by a symbol. Elements are essential for life. [FYI: The 12 most abundant elements include C HOPKNS CaFe Mg NaCl (C. Hopkins café (food tastes) mighty good with salt.)] The four elements that are most abundant in living things: ____________, __________, __________________, ____________________. Trace ________________, including I, Zn, Cu, etc., are present in very small amounts, but essential for health.
IV. The ______________ is the smallest unit of an element with properties of that element. At the core is a dense nucleus comprised of two subatomic particles: (1) _______________(positively charged, 1 amu) and ___________________ (no associated charge; neutral, 1 amu). Orbiting the nucleus is a cloud of another subatomic particle, ___________________ (negatively charged, negligible mass/not considered in calculations).
· An atom can be characterized by the number of protons it has or by its overall mass:
· _______________ number: the number of protons in the nucleus. Atoms with the same atomic number exhibit the same chemical properties and are considered to belong to the same element
e.g. 1H 6C 8O 11Na
· ______________number: the number of protons plus neutrons in the nucleus. (Electrons have negligible mass.)
e.g. 1H 12C 16O 23Na
· Electrons determine the chemical behavior of atoms. These subatomic components are the parts of the atom that interact. Electrons occupy energy levels outside the nucleus. Each can hold a maximum number of electrons.
· 1st – ______
· 2nd – ______
· 3rd – ______
· Energy levels may be subdivided into _________________ that hold a pair of electrons each. (Orbitals are where electrons are most likely to be found.) Electrons that are farther from the nucleus may have _____________potential energy (ability to do work) that those closer to the nucleus.
· Atoms are most stable when they have a ________________outer (valence) shell. If the outer shell is full when the atom is neutral, that element is ______________ (that is, it does not react with other atoms). In most elements, the outer shell is not full when the atom is neutral. The atom will then interact with others lose, gain, or share electrons) to achieve a full outer shell. This is called bonding. Bonding leads to the next level of organization (molecules!)
· As electrons move to a ________________ energy level, closer to the nucleus, energy is released. Moving electrons to energy levels farther out from the nucleus ___________________energy.
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Student self-check
A
B
What is the central area called? _________________
What 2 subatomic particles are found here? Charge? Size?
What subatomic particles are in rings around the nucleus? __________Charge? ____________ Size? ________________
If this atom is neutral, what is the atomic number? _____________
What element is this? ___________________
If this atom has the same # neutrons as protons, what would be its atomic mass? _________________
If you added another neutron, you would have a different _________________.
If you added another proton, you would have a different __________________.
Which electron – A or B – has more potential energy? ______________ Why? ____________________________
How many more electrons could fit in the outermost shell? ________
These shells are subdivided into ___________ that hold _____ electrons each.
Which atomic particle may be lost/gained in chemical reactions? _____________Why would atoms lose/gain them? _______________________
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V. Ions and Isotopes
· Ions – atoms that have gained or lost one or more electrons
· Isotopes: atoms of an element with different numbers of neutrons an, thus, different atomic mass. Ex. 12C (99% in nature) and 13C are stable, but 14C is radioactive; that is, it will decay and release particles and/or energy. It has a half-life of 5600 years. Most elements in nature exist as mixtures of different isotopes. Radioisotopes have value to science:
Because energy is released, radioactive isotopes can be used as “___________________” to follow an element in an organism. Because, they decay at a predictable rate, they can be used to date some rocks/fossils.
VI. Molecules and Compounds
· _________________: Two or more atoms held together by attractions called bonds.
· _____________________: Two or more different elements combined in a fixed ratio. The properties of a compound can be quite different from those of the elements composing it. Ex. Sodium (explosive when neutral + chlorine (a toxic gas when neutral) = sodium chloride (common table salt)
VII. A chemical formula is a short-hand method for describing the chemical composition of a molecule/compound.
· __________________ formula – shows the number of atoms of each element present.
Ex. H2O CaCO3
· ___________________ formula – shows the arrangement of atoms in a molecule
· ___________________ are molecules with the same molecular formulas but different structural formulas.
VIII. Chemical equations describe chemical reactions._________________ form when atoms are joined by chemical bonds. The chemical behavior of an atom is determined primarily be the number of electrons in its ____________ ____________. Atoms will associate with other atoms in order to achieve full outer shells. This is called chemical bonding.
(1.) Ionic bonding
_______________: atom that has lost/gained one or more electrons and is, thus, charged.
· Cation: positively charged
· Anion: negatively charged
· ______________ ______________: attraction between oppositely charged ions. Molecules comprised of these bonds are often most stable as crystals; ex.: formation of NaCl (table salt). Ionic bonds are strong when dry, but easily broken by water. Ionic compounds include _________________, ________________, and ______________.
(2.) __________________ bonds: involve the “sharing” of a pair or pairs of electrons, so that each has a full outer shell. Each pair of electrons is represented in structural formulas by a solid dash. Covalent bonds are very __________________ bonds. They may be polar or nonpolar:
· Nonpolar: electrons are shared equally by atoms in the bond resulting in no net charge anywhere on the molecule.
· Polar: pair of electrons is pulled closer the more electronegative atom resulting in one end of the bond having a slight positive charge and the other having a slight negative charge.
(3.) Hydrogen bond: occurs between a hydrogen that is covalently bonded to one atom (usually O or N) and that is electrostatically attracted to another atom
Ex. ammonia, water
Hydrogen bonds are represented by . . . in structural formulas. H bonds are very weak individually, but many create a fairly strong attraction; they work in holding together parts of large molecules (DNA and proteins). Water molecules are polar and can form hydrogen bonds with each other.
IX. Water Is Essential to Life
· Organisms are 70-90% water; varies by: species, _________, age.
· About ¾ of Earth’s surface is covered by water, ice, and water vapor. Water is the only common substance to exist is all three physical states at the same place/time.
· Water plays a critical role in metabolism.
· Water has many exceptional properties because it is a polar molecule that forms four hydrogen bonds. (This makes it a “sticky” molecule.) (1.) Water is ______________ – it sticks to itself. (2.) Water is ______________ – it sticks to many other substances. (3.) Water is attracted to any substance that has a charge. A substance that attracts water is _______________. Water is not attracted to nonpolar substances (those that have no charge). Such substances are _____________________.
· Exceptional Properties of Water – Resulting from its Polar Nature
1. Water is an excellent _______________. Water can dissolve polar/ionic (hydrophilic) substances. Water cannot dissolve nonpolar (hydrophobic) substances.
2. ________________ action: movement of water into a porous substance due to adhesion to the substance and cohesion to itself. Ex. Movement of water into a paper towel, sponge, or capillary tube. Imbibition is special type of capillary action resulting in swelling; ex. Seeds swelling in water, important in germination
3. Surface _______________: clinging together of water molecules at surface of water body, forming a tight layer. Ex. Skipping rocks, insects walking on water, belly flop, water beading up
4. Buoyant support: support resulting from water molecules within a water body clinging together; allows organisms to swim/float
5. Water displays great resistance to temperature change (high ____________ heat). Because water is cohesive, water heats up and cools down slowly compared to other liquids; a lot of energy is required to break hydrogen bonds and allow more movement associated with temperature increase. It also takes time for water molecules to form hydrogen bonds and cool down. This is important in maintaining stable temperatures in and around water habitats and within the bodies of organisms – that are made mostly of water!
6. Water has a high heat of ______________. The cohesiveness of ware slows down evaporation. Heat energy is used in breaking hydrogen bonds. This allows evaporative cooling in terrestrial organisms (sweating, panting, transpiration)
7. Water ____________ when it freezes. Because it forms structured hydrogen bonds as it cools down, water is less dense (occupies more space) as a solid than as a liquid; this makes water a major force of weathering (rocks breaking down into solid just as pipes and soda cans burst when frozen). Because ice floats, it insulates water bodies in winter. Solutes increase the boiling point of water (______◦C) and decrease the freezing point (____◦C). Plants convert starch to sugar in the sap to avoid freezing. Fish in cold habitats have higher ion or protein content in blood to serve as “antifreeze.”
8. Water ionizes. The covalent bond within a water molecule sometimes breaks spontaneously. This produces a positively hydrogen ion (H+) and a negatively charged hydroxide ion (OH-). The amount of ionized hydrogen from water in a solution can be measured as pH. The pH scale is _____________, which means that a pH scale difference of 1 unit actually represents a ____-fold change in hydrogen ion concentration. Pure water has a pH of 7. There are equal amounts of [H+] relative to [OH-]. It is neutral. [H+] = [OH-] A change in the balance of H+ and OH- can damage living tissues, esp. _______________.
· ______________– any substance that dissociates in water and increases the [H+]; acidic solutions have pH values below 7
· ______________ – any substance that combines with [H+] when dissolved in water; basic solutions have pH values above 7
The pH in most living cells and their environments is fairly close to _______. Proteins involved in metabolism are sensitive to any pH changes. Organisms use ___________ to minimize pH disturbances. A buffer is a chemical substance that takes up or releases hydrogen ions.
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