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Lecture 6

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Biological Sciences

Chapter 2 • element- cant be changed or broken down further by ordinary chemical reactions o chemical symbols eg: O,C, H, N, P, S, Na, Cl, Fe o C, H, O, N comprise 96% mass of most organisms • Atomic Structure- o Atom- smallest part of element that retains chemical properties o Subatomic Particles  Protons- 1 unit of positive charge, in atomic nucleus  neutrons- no charge, in atomic nucleus  electron- 1 unit of negative charge, outside of nucleus o neutral in charge- # of electrons = to # of protons o atomic number- number of protons that are in the nucleus  all atoms of particular element have sath atomic number o atomic mass- protons and neutrons – 1.7*10^(-24 ) G’s(1AMU-atomic mass unit- dalton)  number of protons and neutrons o Electrons- 1/1800 mass of proton • Isotope- form of an element with different number of neutrons but same number of protons and electrons o radioisotope- nucleus breaks and is unstable- emits radiation during decay  decay can be measured • Molecule- compound in which two or more atoms in a fixed-ratio and joined strongly to form stable particle • chemical formula- describes type of atoms and how many of each • molecular mass- sum of atomic masses of atoms o ex: H2o H=1 and O= 16 AMU’s = 18AMU’ s • Chemical Equation- description of chemical reaction o reactantsproducts • Chemical Bonds o e- : move around nucleus in orbitals o valence electrons- outer most electrons o occupy the valence shell o H and He valence shell is full with two electrons o all other atoms valence shell full with 8 electrons • Bonds o result of how atoms share electrons o represent certain amount of bond energy • Bond energy- represent certain amount of chemical energy o by forming bonds, cell stress energy o by breaking bonds cells release energy • electronegativity- measure of attraction for electrons in chemical bonds o the more electronegative an atom is the more strongly it pulls e- toward itself o Comparison: o O-3.5 o S-2.5 o H-2.1 o C-2.5 o N-3.0  Difference in electronegativity between 2 atoms determines type of bond which forms  if same or very similar then electrons are shared equally • NON-POLAR Covalent bond  if difference is less than 2 then e- is shared unequally • POLAR Covalent bond  If difference is greater than 2 • e- is captured by one atom o IONIC BOND • Covalent Bond o Sharing of e- between atoms o result in each atom having filled valence shell o strong bond • “Characteristic number of bonds” o covalent bonding properties Element #
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