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Chapter 2 : the Chemistry of Living Things
Key concepts :
*All consists of matter and enery. *The smallest functional unit of matter is an atom
*Chemical bonds form naturally because the molecules are more stable than the atoms that comprise them. One of
the most important naturally stable molecule is water
*Water is the universal biological solvent
*Living things harness energy and use it to make complex molecules not otherwise found in nature. The 4 classes of
“organic” molecules are proteins, carbohydrates, lipids and nucleic acids.
* Carbon is the common building block of all four classes of organic molecules, because of the many ways it can form
chemical bonds with other atoms.
1. All matter consists of elements – 2. Atoms combine to form molecules
Matter : All that has mass and occupies space
Element : Pure form of matter that cannot be broken down to a simpler form (100 know, eg aluminum, iron,…)
Atoms : smallest functional units of an element, that still retains physical and chemical properties of that element.
o Nucleus : protons (+ charged) and neutrons (neutral) in same amount, and same weight, together 99,9%
of weight/mass atom. (exception : smallest atom HYDROGEN => nucleus = 1 single proton)
Shell 1 (closest to Nucleus) can accommodate 2 electrons
Shell 2 : up to 8 electrons
Shell 3 (if exists) : up to 8 electrons
o Electrons : smaller (- charged) particals, orbit the nucleus. Constantly moving particles ! When moving to
a shell closer to the nucleus => loss of eneryg, when moving further away : has to absorb energy !
o Most cases : number of P and E = => entire atom is electrically neutral !!
Isotope : atoms with more/fewer neutrons than the usual number for that element => Same atomic number but
different atomic mass ! (e.g carbon : atomic number of 6 => 6 neurons and 6 protons => atomic mass of 12. Carbon-
14 has atomic mass of 14 because of 2 extra neutrons = an isotope of carbon)
o Radio-isotope : unstable isotope, gives off energy (radiation) and particles until reaches a stable state.
Scientific use : age rocks and fossibles (via carbon-14 isotopes)
Medical use : “tag” molecules with radiation sensors, power suplly in pace maker etc..;
Molecule : a stable association between 2 or more atoms. (NaCL = tablesalt)
Energy : the capacity to cause changes in matter ,to do “work”
o => stored in the bonds that hold atoms together (in living and nonliving matter) = Potential energy.
o => Energy in motion/doing work = kinetic energy
Living organisms : use certain molecules to store energy for own use : when chemical bonds of these molecules
are broken => potential energy becomes kinetic energy.
Chemical bonds = attractive forces holding atoms together to form molecules (external layers atoms used to bond
with eachother). Such chemical bonds can go from very simple to very complex. (eg. Kitchen salt = Na+ chl)
Each shell thus corresponds to a specific level of electron potential energy (shells further out : higher pot energy)
KEY CONCEPT : atoms are most stable when their outermost electron shell is completely filled with the max
number of electrons that it can accommodate = chemical bonds !!!
o Covalent bonds : ATOMS SHARE ELECTRONS ! type “deelverzameling” (bijv. 2 x H met 1 electron => H2 is
veel stabieler !! => elk complete cirkel van 2 electronen !) (H20 omdat O : 6 +1 = 7 maar moet 8 hebben
=> nog een H bijnemen)
o Ionic bonds : give up electrons (if 1 or 2in outermost circle) => circle less ! BUT will give the atom a net
charge because ther eare then fewer (or more) negative electrons than protons ! => such atom = ION
Electrolyte : ions in aqeous solutions, good conductors of electricity
o Hydrogen bonds : H2O : neutrale molecule maar deels pos geladen (hydrogeen deel) en deels neg geladen
(oxygen deel) omdat het sharen vd electronen op buitenste ringen unequal is !
o Poles : These partially charged regions !!
o Hydrogen bond = weak atractive force between oppositely charged regions of polar moleculs
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