Biology 101 PCC - Cascade Lab 3: Chemistry & Water 1 Lab Section: ____________________ Name: ______________________________________ Pre-lab Homework Lab 3: Chemistry & Water After reading over the lab and Chapter 2 in your textbook, answer these questions to be turned in at the beginning of the lab! 1. Refer to the periodic table on the last page, and then provide the atomic number and the atomic mass for each of the following elements. You may round off the atomic mass to one decimal place. atomic number atomic mass Calcium (Ca): ________ ________ Phosphorus (P): ________ ________ 2. Give the total number of electrons and the number of electrons in the outermost shell (valence shell) of each of the following elements. Element (symbol) Total electons Valence electrons Element (symbol) Total electons Valence electrons Carbon (C) Hydrogen (H): Oxygen (O): Nitrogen (N 3. The element fluorine (F) has the atomic number of 9, However, it has an approximate atomic weight of 19! Give the total number of each of the following particles fluorine in its neutral state. (recall the atomic weight is due primarily to the weight of the protons plus the neutrons, each of which weigh 1 ) # protons = ____ # electrons= ____ # neutrons = ____ 4. Match each description ion the left with an item in the right-hand column by placing a letter in each blank. a. A weak attraction between the positive region of one molecule and the negative region of another molecule. (Ex. between two water molecules.) ____ covalent bond b. An attraction between a particle that has a full positive charge with another particle that has a full negative charge. ____ polar c. An attraction where electrons are shared . ____ ionic bond d. The uneven distribution of electrons in a single molecule, producing regions of partial negative and regions of partial positive charge. ____ hydrogen bond
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Transcript
Biology 101 PCC - Cascade Lab 3: Chemistry & Water
We will review characteristics of atoms, elements and chemical bonding.
We will be exploring several unique properties of water resulting from its polar nature and
H-bonding including:
o Specific heat, its polar nature, cohesion, surface tension, adhesion, capillarity &
density.
OBJECTIVES: After successfully completing this lab a student will be able to:
Know the location and electrical charge on protons, neutrons and electrons
Explain how atomic number and atomic weight are determined
Use the periodic table to identify atomic number and atomic weight of several elements
Define ionic bond, covalent bond and hydrogen bond
Define specific heat
Relate the high specific heat of water to its property of hydrogen bonding
Define water cohesion and relate it to the surface tension of water
Define adhesion and cohesion and relate them to capillarity
Explain why water is more dense at 4oC than at 0oC
Overview:
92 elements exist naturally. Only about 25 are found in living organisms. Why are certain elements
consistently associated with life processes while others are not? The answer can be found in the
structure of atoms. This atomic structure determines the relationships between atoms (the interactions
necessary for life).
Atomic Structure
Matter- Anything that has mass and takes up space.
All matter is composed of atoms..
Note the form of the atom helium (figure 1), the atom’s nucleus with orbiting electrons.
Table 1. Characteristics of subatomic particles
Particle and Symbol Charge Mass (Daltons) Location
Electrons e- - 0* Orbits nucleus
Neutrons n None 1 Nucleus
Protons p + 1 Nucleus
*electrons have a small mass = 1/1,837 that of a proton
To aid in understanding atoms and elements, refer to the periodic table (last page)
Biology 101 PCC - Cascade Lab 3: Chemistry & Water
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Atomic number- is the number of protons in an atom.
For example, helium has 2 protons thus its atomic number is 2. The number of protons is usually the
same as the number of neutrons and the number of electrons. The number of protons determines the
element. For example boron has 5 protons, sulfur has 16 protons etc. (see periodic table)
Elements- A pure chemical substance composed of atoms
Atoms come in 92 natural forms based on their number of protons (see periodic table). These include
many familiar elements and their chemical symbol, iron Fe, carbon C, gold Au, potassium K, etc.
Isotopes- Atoms having the same number of protons, but differing numbers of neutrons.
Although all helium has 2 protons, the number of neutrons can vary. Helium has eight isotopes, 2He, 3He, 4He, 5He, 6He, 7He, 8He, 9He and 10He. The superscript indicates the number of protons plus
neutrons. Ex. Helium always has 2 protons. So, 5He has 2 protons and 3 neutrons.
1. How many protons and neutrons does isotope 8He have? ________ protons and _______ neutrons.
Atomic mass (weight) - is the mass of all the subatomic particles in an element.
The atomic mass is determined by averaging the various ratios of the isotopes for the element. The
periodic table indicates He has an atomic mass of 4.0026 (see last page). This number is due to
averaging all the relative weights of the eight He isotopes.
Electron orbital shells.
Electrons orbit their nucleus in defined orbitals called orbital shells. Rules apply to where these
electrons can be. Figure 2 shows this rule. The first shell holds a maximum of 2 electrons, the 2nd shell
can hold up to 8, the 3rd shell also can hold up to 8 electrons. This is the 2,8,8 rule
Figure 2. The first 18 elements and how electrons appear in orbital shells.
The Noble Gases
Note from above that helium, neon and argon all have full outer shells of e-. Having a full outer shell
means, these elements are stable; they do not form chemical bonds. All the other elements do not have
full outer shells, thus they will form chemical bonds (they are reactive).
Noble gasses
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Example of a reactive element: Carbon has 6 protons, thus it has an atomic number of 6. It has 6
electrons; 2 in the 1st shell, 4 e- in the second shell (table 2)