4U Biology Exam Review PDF

The Fundamental Chemistry of Life RECALL: Chemistry Matter makes up everything in the universe, including all living organisms. Element - pure substance (cannot be broken down)...

The Fundamental Chemistry of Life RECALL: Chemistry Matter makes up everything in the universe, including all living organisms. Element - pure substance (cannot be broken down) Atom - smallest particle of an element Atoms bond together in ratios to form molecules and compounds.  Organic Compounds Made up of: C, H, O, and sometimes N Make up 96% of the weight of a living organism The other 4% is mostly composed of: Ca, P, K, S, Na, Cl, Mg  What is the major difference between the living and the non-living things? Atomic Structure RECALL: Atoms are composed of three subatomic particles: protons, neutrons and electrons Protons determine the identity of an atom. Why not electrons? Or neutrons? The mass of an atom is equal to the sum of its protons and neutrons. Subatomic Particle Summary Protons Neutrons Electrons CHARGE + neutral - LOCATION nucleus nucleus outer orbitals HOW TO CALCULATE atomic number atomic number atomic mass - atomic number Isotopes and Radioisotopes Isotope - an atom of an element with the same number of protons, but a different number of neutrons, giving it a different mass *Isotopes of the same element behave the same way during a chemical reaction because they have the same number of protons and electrons  Radioisotopes Radioisotope - occurs when the nuclei of some isotopes of an element are unstable and tend to break down, or decay, giving off particles of matter that can be detected as radioactivity During the decay process, the unstable radioisotope is transformed into a more stable atom of another element. I.e. 14C → 14N  In beta decay, one of the neutrons from 14C becomes a proton, making 14N. Reaction antineutrino +e- + 14 How is C used to date fossils?  The ratio of 14C:12C is 1:1x1012 (one to one trillion). When scientists compare the ratio of 14C to 12C in a fossil, they can determine how long ago the organism died. The half life of 14C is 5730 years. This number is used in the calculation. Electron Arrangements in Orbitals Electrons are equal to protons, thus atoms are neutral Electrons occupy orbitals, which are around the nucleus Electron orbitals are grouped into shells, often numbered 1, 2, 3, etc. The 1st shell is closest to the nucleus, and holds 2 electrons; the 2nd and 3rd shells are further away and hold 8 and 18 electrons respectively The first shell is s (stands for sharp), the second shell is s and p (stands for primary), other shells use d and f (for diffuse and fundamental) In case you wondered where these letters came from…  Electron Shells The first shell is called: 1s ○ It holds 2 e- and is spherical in shape The second shell is  called: 2s ○ It holds 2 e-, is spherical in shape, and is larger than 1s The third shell is called: 2p ○ There are three 2p orbitals ○ Each one has two tear-drop shaped orbitals running in opposing directions (think two balloons tied together) and each tear drop can hold 1 e- for a total of 6 e- What atom is this? 3 x 2p = 2 e 1s = 2 e  2s = 2 e Ans. NEON Valence Electrons Valence Electrons - electrons in the outermost shell of an atom RECALL: Shells that are not full are chemically reactive. *All the elements in living organisms have unfilled outermost shells and can therefore participate in chemical reactions with other atoms. Valence electrons are used when drawing Lewis dot structures for atoms. Giving, Taking and Sharing Atoms with 3 or less electrons in their outer orbital tend to lose electrons to become positively charged cations Atoms with 5 or more electrons in their outer orbital tend to gain electrons to become negatively charged anions  Atoms that are nonmetals will share electrons to create full outer orbitals - when shells from two different atoms overlap, they are called hybridized electron orbitals Chemical Bonds in Biological Molecules Ionic bond - a bond that results from the attraction between two oppositely charged atoms or molecules (i.e. cation and anion) Ions are very strongly attracted to water molecules and tend to dissociate and dissolve in water, forming hydrated ions Chemical Bonds in Biological Molecules (cont’d) Covalent bonds - form when atoms share one or more pairs of valence electrons  The strength of a covalent bond depends on the electronegativity of the atoms involved in the sharing of the electron pair Electronegativity is the measure of an atom’s attraction for additional electrons H–H or H:H This or this represents a shared pair of electrons in molecular diagrams. Chemical Bonds in Biological Molecules (cont’d) The shared orbitals that form covalent bonds extend between atoms at specific angles and directions, giving covalently bound molecules distinct three-dimensional forms. I.e. CH4 (methane) The bonds between the carbon and hydrogen atoms are arranged in four symmetrical orbitals, so the hydrogen atoms are 109.5° from each other. The overall arrangement of this molecule is tetrahedral. Chemical Bonds in Biological Molecules (cont’d) The number and tetrahedral arrangement of the bonds around a carbon atom allows carbon atoms to link together in  more complicated biological compounds. Polar Molecules Electronegativity and Polarity The more electronegative an atom is, the more strongly it attracts electrons Electronegativity is influenced by the atomic number and the distance between the valence electrons and the nucleus of an atom Electronegativity increases as the distance between the electrons and the nucleus decreases Polar Molecules  The unequal sharing of electrons between two atoms with different electronegativity results in a polar covalent bond. This means that one atom attracts electrons more strongly than the other atom. The atom that attracts the valence electrons more strongly carries a partial negative charge, which results in the other atom carrying a partial positive charge. Because the atoms carry partial charges, the whole molecule may have a non-uniform charge distribution. This is the polarity of the molecule. Determining Polarity Ionic bond - the difference in electronegativity between two elements is >1.7 Polar covalent bond - the difference in electronegativity between two elements is between 0.4 and 1.7 Non-polar covalent bond - the difference in electronegativity between two elements is