BIOL 235 Midterm 2 (version A) exam study guide solution Athabasca UniversitiesChapter 2 objectives
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1. Identify, by name and symbol, the principal chemical elements of the human body.
-Oxygen (O): part of water and many organic (carbon-containing) molecules; used to generate ATP, a molecule used by cells to temporarily store chemical energy
-Carbon (C): forms backbone chain and rings of all organic molecules – carbs, lipids, proteins and nucleic acids (DNA and RNA)
-Hydrogen (H): part of water and most organic molecules; ionized form H+ makes body fluids more acidic
-Nitrogen (N): part of all proteins and nucleic acids
-Calcium (Ca): contributes to hardness of bones and teeth; ionized form (Ca2+) needed for blood clotting, release of some hormones, contraction of muscle, and many other processes
-Phosphorus (P): part of nucleic acids and ATP; required for normal bone and tooth structure
-Potassium (K): ionized form (K+) is the most plentiful cation (+ charged particle) in intracellular fluid; needed to generate action potentials
-Sulfur (S); part of some vitamins and many proteins
-Sodium (Na): ionized form (Na+) is the most plentiful cation in extracellular fluid; essential for maintaining water balance; needed to generate action potentials
-Chlorine (Cl): ionized form (Cl -) is the most plentiful anion (- charged particle) in extracellular fluid; essential for maintaining water balance
-Magnesium (Mg): Ionized form (Mg2+) is needed for action of many enzymes, molecules that increase the rate of chemical reactions in organisms
-Iron (Fe): Ionized forms (Fe2+ and Fe3+) are part of hemoglobin (oxygen-carrying protein in red blood cells) and some enzymes
-Trace elements include: aluminum (Al), boron (B), chromium (Cr), cobalt (Co), fluorine (F), iodine (I), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), and zinc (Zn)
2. Describe the basic structure of an atom, ion, molecule and compound.
-Atoms are the smallest units of matter that retain the properties and characteristics of the element – hydrogen atoms, the smallest atoms, have a diameter of less than 0.1 nanometers, and the largest atoms are only five times larger
-Subatomic particles compose different atoms – there are only 3 that are important in understanding the chemical reactions of the human body: protons, neurons and electrons
-Atoms of the same element have the same number of protons – atoms of each element have a unique way of losing, gaining, or sharing their electrons with interacting with other atoms to achieve stability
-Ions are electrically charged atoms – ions have positive or negative charges because of an unequal number of protons and electrons – ionization is the process of losing or gaining electrons – this is symbolized by writing the chemical symbol, followed by the number of its (+) or (-) charges – so Ca2+ is a calcium ion that has 2 positive charges because it has lost two electrons / IONS ARE FORMED WHEN ATOMS LOSE OR GAIN ONE OR MORE VALENCE ELECTRONS (positively and negatively charged ions are attracted to each other)
-A molecule is the combination of two or more atoms sharing electrons – a molecular formula indicates the elements and the number of atoms of each element that make up a molecule – a molecule can consist of two atoms of the same kind, like in oxygen (O2), - the ‘2’ indicating that the molecule contains two atoms of oxygen
-A compound is a substance that contains atoms of two or more different elements –water (H20) and table salt (NaCl) are common compounds – oxygen (02) is not a compound because it consists of atoms of only one element
3. Explain, briefly, how ionic, covalent and hydrogen bonds are formed.
-An ionic bond is the force of attraction that holds together ions with opposite charges (opposites attract) – in general, ionic compounds exist as solids, with an orderly, repeating arrangement of ions, such as a crystal of salt
– a crystal of salt can be large or small – the number of ions can vary, but the ratio of Na(+) to Cl(-) is always 1:1 – an ionic compound that breaks apart into (+) and (-) ions in a solution is called an electrolyte
– Below is a list of the names and symbols of common ions in the body
-Below is how table salt is formed BOOM (ions and ionic bond formation)
-When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them (they can share 1, 2, or 3 pairs of valence electrons) – the larger number of electron pairs that are shared, the stronger the bond – covalent bonds can be formed between atoms of the same element (molecules) or of different elements (compounds)
-A single covalent bond results when two atoms share 1 electron pair (like when a MOLECULE of hydrogen is
formed by 2 hydrogen atoms sharing their single valence electrons)
-A double covalent bond is formed when 2 atoms share 2 pairs of electrons (like in an oxygen molecule)
-A triple covalent bond occurs with 2 atoms share 3 pairs of electrons (like a hydrogen molecule)
-The same principles of covalent bonding that applies to atoms of the same element also apply to covalent bonds between atoms of different elements
-A nonpolar covalent bond is when two atoms share the electrons equally – one atom does not attract the shared electrons more strongly than the other (the bonds between 2 identical atoms are always nonpolar covalent bonds)
-In a polar covalent bond, the sharing of electrons between two atoms is unequal – the nucleus of one atom attracts the shared electrons more strongly than the other – when these bonds forms, the molecule has a partial negative charge near the atom that attract electrons more strongly (this atom has greater electronegativity; the power to attract electrons to itself) – and at least one other atom in the molecule with have a partial positive charge (these partial charges are indicated by a delta symbol followed by a + or -)
-A hydrogen bond is made up from polar covalent bonds that form between hydrogen atoms and other atoms – a hydrogen bond forms when a hydrogen atom with a partial positive charge attracts the partial negative charge of electronegative atoms – SOOO hydrogen bonds are formed by attracting oppositely charged parts of molecules, rather than sharing electrons like in covalent bonds or the loss or gain of electrons as in ionic bonds
-Hydrogen bonds are weak compared to ionic/covalent bonds, and therefore cannot bind atoms into molecules
4. Define the term “chemical reaction,” and explain the basic differences between synthesis, decomposition, exchange and reversible reactions.
-A chemical reaction occurs when new bonds form or old bonds break between atoms – the interactions of valence electrons are the basis of all chemical reactions – for instance, how hydrogen and oxygen molecules [Show Less]