1. Ch.2 Chemical Context of Life

2. Concept 2.1: Matter consists of chemical elements in pure form and in combinations called compounds Matter anything that takes up space and has mass 3 Forms Solid Liquid Gas Composed of elements 3. Element A substance that cannot be broken down to other substances by chemical reactions Composed of atoms Atom: smallest component of an element, contains nucleus of neutrons and protons, and electron cloud 4. Compound A substance consisting of two or more different elements combined in a fixed ratio. Example: NaCl (table salt) 1:1 ratio of Sodium (Na) to Chloride (Cl) Example: H20 (water) 2:1 ratio of Hydrogen (H) to Oxygen (O) 5. Elements-Table 2.1 92 Natural Elements (118 total) Essential elements: 20-25% of natural elements are needed by organisms to live a healthy life and reproduce. Vary amongst organisms 4 elements: Oxygen, Carbon, Hydrogen, and Nitrogen (96%) Remaining elements: Calcium, Phosphorus, Potassium, etc. Trace elements: required by an organism in small quantities Iron (Fe) needed by all forms of life, others only needed by certain organisms 6. Concept 2.2: An elements properties depend on the structure of its atoms Atom: smallest unit of matter that still retains the property of an element (no chemical change) Subatomic particles: form the atom Neutrons (neutral), protons (+), and electrons (-) 7. Figure 2.5Cloud of negative charge (2 electrons)Electrons Nucleus(a)(b) 8. Neutrons=Protons= ~1.7x10-24 g Very small unit to measure Assigned term Dalton Neutron=Proton=1 Dalton Electron=1/2000 Dalton **Not used when calculating atomic mass because its so small** 9. Atomic Number and Atomic Mass Atomic number: number of protons Unique to each element Charge is considered neutral on each atom Number of protons=number of electrons Mass number: sum of neutrons and protons in the nucleus of the atom. ~22.99