Elements and the cell

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Elements and the cell

  1. 1. Ch.2 “Chemical Context of Life”
  2. 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. 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. 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. 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. 6. Concept 2.2: An element’s 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. 7. Figure 2.5 Cloud of negative charge (2 electrons) Electrons Nucleus (a) (b)
  8. 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 it’s so small**
  9. 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

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