Chapter 2- Chemistry - Chemistry of Life 2010 D Julian...

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1/7/2010 1 Chemistry of Life © 2010: D. Julian Elements Organisms are composed of matter Matter is anything that takes up space and has mass An element is a substance that cannot be broken down to other substances by chemical reactions. A compound is a substance consisting of two or more elements combined in a fixed ratio (e.g., NaClconsists of 1:1 Na and Cl). A compound has characteristics different from those of its elements © 2010: D. Julian Sodium Chlorine Sodium chloride Essential elements of life add Ca, P and K to reach >99%. C, O, H and N make up 96% of living matter… Life requires about 25 elements. © 2010: D. Julian Table 2.1
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1/7/2010 2 Atoms © 2010: D. Julian Cloud of negative charge (2 electrons) Nucleus Electrons Subatomic particles An element’s properties depend on the structure of its atoms. An atom is the smallest unit of matter that still retains the properties of an element. Atoms are composed of subatomic particles. There are hundreds of types, but only three are relevant in the context of this course: 1. Neutrons 2. Protons 3. Electrons © 2010: D. Julian Nucleus Fig 2.5 Atomic number and atomic mass Atoms of the various elements differ in number of subatomic particles An element’s atomic number is the number of protons in its nucleus An element’s mass number is the sum of protons plus neutrons in the nucleus Atomic mass , the atom’s total mass, can be approximated by the mass number © 2010: D. Julian
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1/7/2010 3 Isotopes All atoms of an element have the same number of protons but may differ in number of neutrons Isotopes are two atoms of an element that differ in number of neutrons Radioactive isotopes decay spontaneously, giving off particles and energy © 2010: D. Julian Energy levels of electrons Energy is the capacity to cause change Potential energy is the energy that matter has because of its location or structure © 2010: D. Julian Fig 2.8 (a) A ball bouncing down a flight of stairs provides an analogy
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