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Weeks one and two.doc

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McMaster University
Paul Hatala

Atoms - make up all matter - are made of protons (+), neutrons and electrons (-) - electrons are ridiculously small and light compared to protons - JJ Thompson (1890s) demonstrated that an atom has negative parts- electrons- and thus counter- discovered that there must be a positive part since the whole thing is neutral - Thompson- cathode shoots out electrons; using magnets, electrons bent towards the positive and away from the negative magnets. - Video film films at a different speed than the electrons move through a screen to create a picture - William Thompson (Lord Kelvin- Kelvin scale) responsible for plum pudding model - Rutherford tried to test plum pudding model- fired positive alpha particles at a thin foil of atoms and saw where they went- right through was expected outcome- BUT particles deflected away from the atom in the middle (the positive charge). He noticed it was concentrated in the centre. His model is a nucleus with electrons orbiting it - Discovery of neutrons: Bohr uses emission spectra of hydrogen to mathematically describe the energy given off by hydrogen when excited - Bohr-Rutherford model= electrons moving in set orbits around the nucleus, each orbit w a set # electrons (2, 8, 8, 18) - Current understanding (besides quantum-mechanic model): the number of protons determines which element it is. Atomic number- # protons Atomic mass- avg # of protons and neutrons In any neutral atom, the # of protons= # electrons Isotopes - if you add or remove protons, the atom is different, but we can change neutron number - sodium has 11 protons and either 12 or 13 neutrons (weight 23 or 24) - isotopes may be less stable (decay- can harvest energy or radiation) or may be stable over long periods of time (carbon- carbon dating with carbon of 8 neutrons instead of 6) - chalk river nuclear reactor makes Mo (which is used for medical imaging after 6 days, once it breaks down to make Tc and will decay in 6 hrs and not harm the patient in the long term) Periodic Table - columns are groups or families first group is alkalai metals (one valence electron), second= alkaline earth metals (2 valence electrons), middle= transition elements, third last=6 electrons in valence shell, second last= halogens (7 electrons), last group= noble gases (full valence shell) - rows are periods (number of shellsfirst period = one shell, second= two and third= three) • Sodium has 1 valence electron, so satisfying it will cause it to lose that electron, because they take the path of least resistance. Then, sodium becomes positively charged. (Positive ion or cation- the t is like a plus sign) • oxy2-n has 6 outer electrons, so it will gain two outer electrons, becoming negatively charged. (O ). It becomes an anion. • losing is harder than gaining, especially if one electron has already been removed, because the positive pull is stronger among the negative charges 2- -2 *** Charge on an atom number then symbol, i.e. O NOT O . • anions and cations will join to form neutral compounds. (i.e. NaCl or MgCl ) 2 • first column will always lose one (one positive cation) and second column will form two plus cation, whereas third last will form a two minus anion, etc. • KRIS KROSS RULE: write out atoms with their charges (cation first, anion second), cross the charges and bring them down to represent the number of each atom that is necessary (but always reduce to lowest terms) Mg and C = Mg C OR Mg C 4 2 2 Naming Compounds (IUPAC) - conventions have been created for consisting understanding of compounds (but there are still old names in use- salt, etc) - BINARY TYPE I: metal and a non-metal name each ion & anion: drop ending and add –ide example: NaCl= sodium chloride - BINARY TYPE II: transition metals have multiple valences, need to identify valence being used in the compound- use a roman numeral to identify the valence example: iron can be two or three plus- FeCl = I2on (II) Chloride OR FeCl = Iron 3III) Chloride - ALTERNATE BINARY TYPE II (ous-ic)- multi-valent ions- have more than one charge lower valence gets ous and ic goes to higher valence cations use their latin names- i.e. lead=plumb, tin= stann
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