Chemistry Basics Fact Sheet.pdf

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Department
Biology
Course
BIOL 108
Professor
James Stark
Semester
Spring

Description
Chemistry Basics Fact Sheet Basic General Chemistry  Matter is composed of elements, the simplest forms into which matter can be broken down using ordinary chemical techniques. Examples are hydrogen (H), carbon (C), oxygen (O), etc.  Atoms are the smallest units of elements, and are in turn composed of o Protons (positively charged) o Electrons (negatively charged) o Neutrons (not charged, neutral) o In all atoms, the number of protons = the number of electrons.  The nucleus is the core of an atom. Protons plus (usually) neutrons are found there.  Atoms of an element always have the same number of protons, but sometimes have different numbers of neutrons. For example, carbon always has 6 protons, but can have 6, 7 or 8 neutrons. Variants such as these are called isotopes. Some isotopes are radioactive, and have been extensively used as tracers to elucidate complex biochemical pathways.  The electrons orbit the nucleus in electron shells. For biology, we need only consider the first 3 shells. They have maximum electron carrying capacities: o 1 (inner) shell: 2 electrons max nd o 2 (further from the nucleus): 8 max o 3 : 8 max  Atoms with full outer (valence) shells are unreactive, for example helium (safe for balloons).  Atoms with incomplete outer shells are reactive, for example hydrogen (unsafe for balloons). Reactive atoms will transfer or share electrons with other atoms, forming chemical bonds. o Ionic bonds result from electron transfer from one atom to another. Example:  Na (sodium) can lose an electron to Cl (chlorine).  Both elements are now ions (atoms or molecules that have gained or + - lost one or more electrons): Na and Cl . Their opposite charges hold them together. This is known as an ionic bond. o Covalent bond result from electron sharing. For example, two hydrogen atoms will share a pair of valence (outer shell) electrons to form 2 . Covalent bonds can be either 1  Non-polar. When electrons are equally shared, due to both atoms having equal or nearly equal attraction for electrons. Carbon (C) and hydrogen (H) are about equal in electron attraction, so C-H bonds are non-polar.  Polar. When electrons are unequally shared, due to one atom having a much greater attraction for electrons than the other. The shared electrons are more frequently found near the stronger attracting atom, creating small differences in charge distribution, or poles. Oxygen and nitrogen are the two most important strong electron attractors in biochemistry. Bonds such as O—H, N—H, C—N, C—O, etc., are polar.  Water, H2O, is a polar compound, due to the stronger attraction for electrons of oxygen.
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