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Chapter 2 notes

by: Megan Smith

Chapter 2 notes Biol 1103k

Megan Smith
GPA 3.6

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These notes are directly from the book and cover the main points.
Introductory biology I
David blaustein
Class Notes
Biology, Biology 1103K
25 ?




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This 6 page Class Notes was uploaded by Megan Smith on Friday January 29, 2016. The Class Notes belongs to Biol 1103k at Georgia State University taught by David blaustein in Summer 2015. Since its upload, it has received 24 views. For similar materials see Introductory biology I in Biology at Georgia State University.


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Date Created: 01/29/16
Date CHAPTER 2 – ATOMS, MOLECULES, AND LIFE A. ATOMS ARE THE BASIC STRUCTURAL UNITS OF ELEMENTS i. Element • A substance that cannot be separated into simpler substances, and cannot be converted into another substance by ordinary chemical reactions • Ex: gold ii. Atom • The smallest unit of an element, and each atom retains all the chem ical properties of that element • Ex: what makes up gold A. Atoms are Composed of Still Smaller Particles iii. Atoms are composed of subatomic particles: a. Neutrons (n) – no charge b. Protons (p+) – single positive charge c. Electrons (e -) – single negative charge • Measured in atomic mass units iv. Mass number • Total number (which equals the total mass) of the protons and neutrons in its nucleus v. Atomic nucleus • Protons and neutrons cluster together in the ce nter of the atom B. Elements are Defined by Their Atomic Number i. Atomic number • Number of protons in the nucleus - called the atomic number - is the feature that defines each element C. Isotopes Are of the Same Element with Different Numbers of Neutrons i. Isotopes • Atoms of the same element with different numbers of neutrons D. Some Isotopes are Radioactive i. Radioactive • Their nuclei spontaneously break apart, or decay. • Radioactive decay emits subatomic particles (such as neutrons) tha t carry large amounts of energy E. Some Radioactive Isotopes Damage Cells • Some radioactive isotopes release particles with enough energy that the can damage DNA, causing mutations. F. Nuclei and Electrons Play Complementary Roles in Atoms i. Nuclei (unless radioactive) provide stability by resistin g disturbances by outside forces ii. Electrons in contrast, are dynamic; they can capture and release energy iii. Electrons form bonds that link atoms together G. Electrons Occupy Complex Regions Around the Nucleus i. Electron shells • Electrons occupy complex three -dimensional regions, called electron shells, around the nucleus • Each shell has a specific energy associated with it • The farther away from the nucleus, the higher the energy of the electrons occupying the shell H. Electrons Can Capture and Release Energy i. Atoms excited by energy, such as light or heat, it can cause an electron to jump from a lower-energy electron shell to a higher -energy electron shell ii. Soon after the electron spontaneously falls back into its original electron shell and releases its extra energy I. As Atomic Number Increases, Electrons Fill Shells Increasingly Distant from the Nucleus i. The shell nearest the nucleus can hold only two ii. The larger more distant shells can hold eight iii. Electrons always fill the most inner shell first iv. Elements with larger num ber of protons in their nuclei require more electrons to balance these protons 2.2 HOW DO ATOMS INTERAC T TO FORM MOLECULES? i. Molecules • Atoms of the same or different elements linked together 2 A. Atoms Form Different Molecules to Fill Vacancies in Their Outer El ectron Shells • Electrons are most stable and less likely to interact with other atoms in the shells that are completely full • Atoms behave generally to two different principals: a. An atom will not react with other atoms when its outermost electron shell is com pletely full. o Such an atom (ex. Helium) is extremely stable and its described as inert o Inert – outermost shell is completely full b. An atom will react with other atoms if its outermost electron shell is only partially full (ex. Hydrogen). o Such an atom is described as reactive o Reactive – not completely full B. Chemical Bonds Hold Atoms Together in Molecules i. Chemical Bonds • Attractive forces that hold atoms together in molecules. • Bonds are formed when reactive atoms gain, lose, ro share electrons to gain stability and become less reactive • Three major types of bonds: a. Ionic b. Covalent c. Hydrogen C. Ionic Bonds Form Among Ions i. When an atom has more electrons than protons it becomes negatively charged ii. When an atom fewer electrons than protons it becomes positively charged iii. When an atom has acquired an overall positive or negative charge it is no longer an atom, but an ion o Ions with opposite charges attract one another o The attraction between positively and negatively charged ions forms ionic bonds iv. Ionic bonds • An electron is TRANSFERED between atoms creating positive and negative ions that attract one another D. Covalent Bonds Form by Sharing Electrons i. Covalent bonds • Atoms with partially full outermost electron shells can become stable by SHARING electrons with one another, filling both of their outer shells and forming covalent bonds. 3 E. Covalent Bonds May Produce Nonpolar or Polar Molecules i. Non polar covalent bonds • Electrons are shared equally between atoms ii. Polar covalent bonds • Electrons are shared unequally between atoms iii. Hydrogen bond • Attractions occur between polar molecules in which H is bonded to O or N • The slightly positive H attracts the slightly negative O or N of a nearby polar molecule iv. Free radicals • Unfilled outer shells • So reactive that the can tear other molecules apart F. Hydrogen Bonds Are Attractive Forces Between Certain Polar Molecules i. Hydrogen Bond • Attraction between a slightly positive hydrogen and slightly negative oxygen or nitrogen located in a nearby molecule or in another part of t he same molecule 2.3 WHY IS WATER SO IMPO RTANT TO LIFE? i. water • Is polar • Hydrogen bonds form among molecules A. Water Molecules Attract One Another i. Hydrogen bonds • Interconnect water molecules • Constantly break and reform allowing water to flow • Cause cohesion o Tendency for molecules of a single type to stick together ii. Cohesion among water molecules produces surface tension • The tendency for a water surface to resist being broken B. Water interact with Many Other Molecules i. Solvent • Substance that dissolves in some othe r substance ii. Solution • A dissolvable substance in a solvent 4 iii. Water dissolves polar molecules because its positive and negative poles are attracted to their oppositely charged poles iv. Hydrophilic • Ions and polar molecules are described as hydrophilic because of t heir electrical attraction for water molecules • Means “water loving” v. Hydrophobic • Larger molecules with nonpolar covalent bonds do not dissolve in water • Means “water-fearing” • Ex: oils and fats vi. Hydrophobic interaction • The tendency of oil molecules to clump to gether in water C. Water Moderates the Effects of Temperature Changes i. Specific heat • The energy required to heat 1 gram of a substance by 1degree C ii. Water has a very high specific heat • Hydrogen bonds need a large amount of heat energy to be broken D. It takes a Lot of Energy to Evaporate Water i. Heat of vaporization • Water has an extremely high heat of vaporization • The amount of heat needed to cause a substance to evaporate o Evaporate – to change from a liquid to a vapor ii. evaporation has a cooling effect because the (warmest) fastest moving molecules are the ones to evaporate…leaving the cool molecules behind E. Water forms an unusual solid: Ice i. Most liquids become denser when they become solid ii. Ice is less dense than liquid water (unusual) iii. Water freeing • Each molecule forms stable hydrogen bonds with four other water molecules • This creates an open, hexagonal (six -sided) arrangement F. Water based solutions can be Acidic, Basic, or Neutral i. Pure water contains equal concentrations of OH - and H+ ii. Acidic • If the concentration of H+ exceeds the concentration of OH - iii. Acid • A substance that releases hydrogen ions when it dissolves in water 5 iv. Basic • If the concentration of OH- is greater than the concentration of H+ v. Base • A substance that combines with hydrogen ions, reducing their number vi. pH Scale • goes 0-14 • measures how acidic or basic a solution is • Neutral pH (equal concentrations of H+ and OH -) is 7 • Acids have a pH below 7 • Pure water has a pH of 7 • Bases have a pH above 7 • Mammals, including humans, have pH in body fluids around 7.4 • Page 31 – examples of each vii. Buffer • Type of molecule that tends to maintain a solution at a constant pH by accepting or releasing H+ in response to small changes in H+ concentration • In the presence of excess H+, a buffer combines with the H+, reducing its concentration • In the presence of excess OH-, buffers release H+, which combines with OH- to form H2O. • THINK: Buffer always reacts with the H+ 6


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