General Biology I Chapter 2 PDF

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General Biology I : Bio201 Chapter 2 : The Chemical Basis of Life ➢ Overview • Elements are substances that cannot be broken down into simpler substances by chemical reactions. One of the most abundant elements are : O, C, H, N, Ca, and P (they are around 98% of mass of living organisms. • Atoms are the smallest forms of matter that retain the chemical characteristics of a given element. They contain a nucleus which have protons and neutrons, and they have clouds of electrons surrounding the nucleus. • Of course, a proton has +1 charge and 1 AU, a neutron has no charge but a mass of 1.005AU, and the electron has a -1 charge and a mass of 5.5 x 10-4 AU . • In the periodic table, columns refer to the number of valence electrons; rows refer to the location of the electrons (which orbital they occupy). • The number of protons : The atomic number : Z. It defines the element. In an uncharged atom, The Number of Protons = The Number of electrons. The atomic weight = Number of Protons + Number of Neutrons. • Isotopes are elements carrying the same number of protons, but different number of neutrons. They can be radioactive (help tracing some compounds, and can have bigger weight so it’s easier to work with). • Energy levels of the e- are called shells. The outermost one is the valence shell. The farther away the electron is from the nucleus, the greater is the energy. Orbitals are the circles we draw around the nucleus; they are K, L, M, N …

➢ Types of Bonds :  Covalent Bonds : In covalent bonds, there is sharing of electrons, two electrons are shared per bond. Atoms share electrons covalently to fill their outer shells, they become stable. There are simple covalent bonds, double, and triple .

 Ionic bonds : In ionic bonds, there is gain/loss of electrons. An electronegative atom steals an electron from another to fill its valence shell. So elements in group V, VI, and VII tend to steal 3, 2, and 1 electron, respectively, in order to become stable. Cations are ions with + charge, they steal (attract) an electron. Anions are ions with – charge, they lose (donate) an electron. Water easily dissolves salts because it forms hydrations shells around the ions Water : solvent/ Salt : solute. To dissolver in water, solutes must be polar/ionic  Polar Covalent Bonds : Electronegative atoms like O, S, N, pulls an electron from H in water, this causes a partial + charge on the H, and a partial – on the oxygen; partial charges are indicated by (δ). Soo, the bonds between O and H are called polar covalent bonds.  Hydrogen Bonds : To form this type of bonds, we need a Hydrogen atom, an electronegative atom like (O, N, S) to be bonded with that hydrogen atom, and we need an electronegative atom to pull an electron from the hydrogen. Van der Waals Interaction : on the surface of molecules, there is some shortlived charges that induce opposite charges in long molecules.

➢ Reduction and Oxidation : o Reduction is the gain of an electron. .Oxidant + e- ---> Product.. o Oxidation is the loss of an electron. Reductant ---> Product + e- . o Redox reactions involve the transfer of electrons; and in reality, it happens a lot.

➢ The Properties of Water :  Since H2O covers 70% of the earth’s surface, Earth is called a water planet.  H2O is essential for life and constitute 50-95% of all living things.  Water is polar since O pulls an electron from H and they end up partially charged. It also forms hydrogen bonds with the interactions of partial charges. As water freezes, it forms a crystal because H bonding lasts longer.  The higher the temperature, the greater the movement.

 Water has a high specific heat. It takes 1 calorie/g of water to raise the To 1oC.  Water has high heat of vaporization. 540 calories change 1 g from liquid to vapor.  For water to boil and evaporate, it takes 100oC; and for it to freeze, To must be 0. Without water temperature would fluctuate greatly from day to night, season to season Water has high surface tension; it sticks to itself strongly and forms meniscus and droplets. It is a superb solvent since it masks ions to attract them; makes hydration shells around an ion; and solvates the ionic and polar compounds. Water is sticky because of H bonding. It is cohesive (sticks to itself) and adhesive (sticks to other things). The meniscus is due to this property. Water involves making & breaking molecules by hydrolysis & condensation. ❖ To break 2 stuck molecules, we add water: Hydrolysis Reaction ( + Enzyme ! ) ❖ To join 2 sugars, we remove water by taking H from an element and OH from the other; this is the Condensation – Dehydration Reaction. ( + Enzyme ! )

➢ Acids, Bases, and Buffers : ⬧ Acids release protons (proton donors). Bases absorb protons (proton acceptor). ⬧ Ph is the measure of the concentration of free H+. Ph = -log [H+]. ⬧ In water, Ph = 7; It’s neutral. When we have excess in protons, it’s an acid (Ph > 7) and when we have a reduced number of protons, it’s a base (Ph < 7). ⬧ Normal physiological Ph is usually close to 7.4 ⬧ [OH-] x [H3O+] = 10-14 Neutral I-----------------------------I---------------------------I 0 Acids 7 Bases 14 If asked about the Ph unit difference, we do the higher – the small : 5 – 3 = 2 If asked about the Ph concentration difference, each unit is valued as 10 > So if there is 2 units in differences, it’s going to be 10 x 10 = 100. Polar molecules dissolve in water (polar too). All charged molecules are polar. Even hydrogen bonds are polar since they have partial charges. Buffers are molecules that act like acids or bases or both. They are weakly ionizing; they help stabilizing and balancing things that get out of hand. Acids and bases combine to form salts and water. When salts dissolves in water, the components separate as ions, which in turn are referred to as electrolyte, because they can carry current (courant). Polars aren’t electrolytes....