BIOL 112 Lecture Notes - Lecture 8: Atomic Number, Electronegativity, Mass Number
16 May 2018
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BIOL 112-Lecture 1: Chemistry
Atoms:
Nucleus: protons and neutrons, larger mass
Electrons: negative charge, little mass
Elements:
Mass number: number of protons + neutrons,
mass in Daltons (D)
Atomic number: number of protons, identity of the element
Mass is not always a round number due to the fact that certain elements
have isotopes. (ex: C12 and C14)
In the atmosphere, there is a large quantity of C12 and a small fraction of C14, so the
average mass of one C atom becomes 12.03
Radiocarbon Dating: Used to determine the age of bones, fossils, etc.
Periodic Table:
Columns: similar chemistry, same number of
electrons in the outermost shell
Rows: similar size, same number of shells
Valence: number of unpaired electrons
Elements in biology: H, O, N, C, S, Mg, P, Na and Cl
* For chemical bonds, only electrons are important
* Electrons are arranged in orbitals (contain 1 or 2 e-)
1. Covalent Bond:
- STRONGEST BOND
- A covalent bond is made of 2 electrons
- These 2 electrons are shared (one electron comes from
each atom) to form an orbital
- Atoms can form bonds until their outermost shell is saturated
Ex: H2, CH4, NH3, H2O
Nonpolar covalent bond: e- are shared equally
Polar covalent bond: e- are not shared equally (O is more
electronegative than H, so partial charges exist on the O & H
atoms)
Electronegativity: H<C<N<O<F, increases proportionally to the number of protons
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Document Summary
Mass number: number of protons + neutrons, mass in daltons (d) Atomic number: number of protons, identity of the element. Mass is not always a round number due to the fact that certain elements have isotopes. (ex: c12 and c14) In the atmosphere, there is a large quantity of c12 and a small fraction of c14, so the average mass of one c atom becomes 12. 03. Radiocarbon dating: used to determine the age of bones, fossils, etc. Columns: similar chemistry, same number of electrons in the outermost shell. Elements in biology: h, o, n, c, s, mg, p, na and cl. * for chemical bonds, only electrons are important. * electrons are arranged in orbitals (contain 1 or 2 e-: covalent bond: A covalent bond is made of 2 electrons. These 2 electrons are shared (one electron comes from each atom) to form an orbital. Atoms can form bonds until their outermost shell is saturated.
