BIO-1103 Lecture Notes - Lecture 2: Hydrogen Bond, Atomic Number, Sodium Chloride
Chapter 2: The Chemistry of Life
NPK Number : 16-4-8 :Found on fertilizers
Periodic Table of Elements
25 Elements are essential to life
Bulk elements
• Hydrogen
• Carbon
• Nitrogen
• Oxygen
• Phosphorous
• Magnesium
• Calcium
• Sodium
• Potassium
• Sulfide
Trace Elements
• V
• Cr
• Mn
• Fe
• Co
• Ni
• Cu
• Zn
• Mo
• B
• F
• Se
• I
Possibly essential trace elements
• Arsenic
• Br
• Sn
Atoms are Particles of Elements
Atom: the smallest pice of an element that retains the characteristics of the elements
Atoms are made up of 3 subatomic particles:
1. Proton: positive charge, nucleus
2. Neutron: neutral charge, nucleus
3. Electron: Negative charge, cloud
Example:
6- Atomic number (number of protons)
Carbon- Element
C- Symbol
12.0112- Atomic Mass (protons and neutrons)
Atoms are electrically neutral (the # of protons= the # of electrons)
Eight is Great: The octet Rule: An atom will try to fill its outer shell (with 8
electrons) by either losing or adding electrons
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Types of Bonding
Stealing Electrons: Ionic Bonding
• Attractions are formed where one atom will give up its electrons and the
other atom steals it to fill its outer shell
o The atom that loses its electrons gets a positive (+) charge and the
atom that gains an electron gets a negative charge (-)
• Ion: atom that’s gained or lost electrons
o Example: Na+Cl= NaCl
Sharing Electrons: Covalent Bonding
• Attraction between two elements formed when they share their electrons
• Two atoms share their electrons and they both complete their outer shells
Hydrogen Bonding
• Weakest of the chemical bonds
• Occurs between the hydrogen atoms of polar atoms
• (H20)- Oxygen atom is slightly negative, Hydrogen atoms get a positive
charge
• Any weak attraction between polar compounds (Many water molecules are
attracted to one another because of hydrogen bonding)
Hydrogen Bonding and DNA
• The bases of DNA are polar (have a slightly positive and a slightly negative
end) and the two strands are zipped together by hydrogen bonds
Carbon: The most social element
• C has 6 protons and electrons
• C can attach to many other elements
• C can share 4 pairs of electrons (must have 4 sticks surrounding C atom= 8
electrons)
• Example: CH4
Share and Share Alike?
Nonpolar covalent bond- both atoms have an equal attraction for electrons
Example: Hydrogen
Polar covalent bond: unequal sharing of electrons
Example: Water
• The covalent bond that forms between two oxygen atoms is a DOUBLE bond
o Both O have 6 electrons, need 8, so they share two electrons with each
other
1. Single Bond: 1 pair of electrons shared (ethane, propane, butane)
2. Double bond: 2 pairs shared (ethylene)
3. Triple bond: 3 pairs shared (acetylene)
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