Chapter 6

Chapter 6 - WATER Basic chemical notions Water molecule...

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WATER Basic chemical notions Water molecule Water’s thermal properties Water density
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Basic chemical notions Atom : The smallest unit which displays all the  properties of an element Nucleus : The center of the atom Protons : Positively charged particles Neutrons : Uncharged particles Electron shells : Electrons are negatively  charged particles which orbit the nucleus in  discrete shells, each of which can hold a  characteristic number of electrons Electrically stable atoms have the same number  of electrons as protons, and therefore 0 charge Ions  are atoms with either more protons than  electrons (positive ions,  cations ) or more  electrons than protons (negative ions,  anions ) ATOM ELECTRON SHELLS Hydrogen Oxygen proton (+ charge) neutron (0 charge) Shell has a maximum of two electrons Outer shell has a maximum of eight electrons Nucleus Electron shells
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Basic chemical notions Elemen t       Atoms with the same number of protons are the same element       The number of protons is the atomic number Hydrogen (H) has atomic number 1, carbon (C) is 6 Isotopes  of an element have the same number of protons but different numbers of  neutrons, and therefore different atomic weights.   Carbon-12 has an atomic number of 6 (6 protons) and an atomic weight of 12 (6  protons + 6 neutrons), which can be written  12 C 6 , or just  12 C. ISOTOPES OF CARBON Carbon-12 stable Carbon-13 stable Carbon-14 unstable (radioactive) Proton Neutron Electron images.encarta.msn.com/xrefmedia/aencmed/targets/illus/ilt/T050525A.gif
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Molecules  are formed of two or more (can be MANY more) bound atoms + 8+ Hydrogen Hydrogen Oxygen δ + δ + δ - δ - Water molecule Hydrogen and oxygen share electrons: they are  linked by (mostly)  covalent bonds Outer electron shells of both are now full        2 electrons per hydrogen orbit        8 electrons in the outer oxygen orbit Negative charge is concentrated on the oxygen,  and positive charge on the hydrogens: water is  dipolar Some other molecules There are a variety of illustrational conventions CAFFEINE CHLOROPHYLL DNA ALCOHOL DEHYDROGENASE VITAMIN B 12 Basic chemical notions
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www.chm.bris.ac.uk/pt/harvey/gcse/other.html The Water Molecule: H 2 O Dipolarity is the source of many of water’s special properties The two hydrogen atoms are separated by 105 °  in gaseous or liquid phase, and 109.5 °  in ice –  resulting in dipolar charge (+ on one end, - on the other) Water molecules tend to associate with each other via  hydrogen bonds  between a hydrogen  of one molecule and an oxygen of another - water is  cohesive
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Chapter 6 - WATER Basic chemical notions Water molecule...

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