CAS BI 105 Lecture Notes - Lecture 2: Chemical Polarity, Unpaired Electron, Covalent Bond

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9/9: Chemistry for Biology
Terms
Matter - anything that takes up space and has mass
Elements - substances that cannot be broken down into other substances
Atoms - the smallest functional units of matter (building blocks)
Composed of protons (+), electrons (-) and neutrons
Contains an equal number of protons and neutrons (electrical charge = 0)
Protons and neutrons cluster around the nucleus (center of the atom)
Electrons move in an orbit around the nucleus
Electron Orbits
Inner ring can only have 2 electrons
Outer rings can hold up to 8 electrons
The more electrons an atom has, the more shells they have
Electron Importance
Form bonds
Two neighboring atoms can form bonds and share electrons
Determine if atom is an ion
Ion - if an atom gains or loses an electron
Form of an element that has a different number of electrons
Anions - ions with an extra electron
Cations - ions missing an electron
Capture and transfer energy
In some elements, electrons can capture free energy and lose it later
Form destructive free radicals
Free Radical - when an atom or molecule has a single and unpaired electron in its outer shell
Can harm a cell’s DNA and essential functions
Cigarettes and UV rays contribute to the formation of this
Antioxidants
Vitamin C/E beta caroine
Bonds & Molecules
Molecule - two or more atoms linked by bonds
Covalent Bonds
Two atoms sharing a pair of electrons
ex: Hydrogen Fluoride (HF)
Can predict the total number of covalent bonds in an atom by knowing the number of unpaired
electrons are in the outer shell
Atoms are MOST stable when all electrons are paired, so some atoms are prone to forming covalent
bonds
Are stable in a watery environment
In some bonds, the electrons are shared closer to one nucleus then the other
Polar v. Non polar Covalent bonds
Non polar Molecules - when a molecule is composed of non polar covalent bonds there is no end
with more or less charge, the entire molecule has the same charge all over
C-C and C-H are examples of non polar covalent bonds
Polar Molecules - molecules that have a positive charge on one end and a negative charge on the
other end
The O-H and N-H bonds are considered a polar covalent bonds
SUMMARY: strong bonds, joined atoms share a pair of electrons
Ionic Bonds
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