Regents Warm-Up The atomic mass of an element is calculated using the (1) atomic number and the ratios of its naturally occurring isotopes (2) atomic number.

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Presentation transcript:

Regents Warm-Up The atomic mass of an element is calculated using the (1) atomic number and the ratios of its naturally occurring isotopes (2) atomic number and the half-lives of each of its isotopes (3) masses and the ratios of its naturally occurring isotopes (4) masses and the half-lives of each of its isotopes

Oxidation Numbers AIM: How do we assign oxidation numbers? Do Now: What is oxidation? What is reduction?

OXIDATION STATES RULES FOR ASSIGNING OXIDATION STATES 1)Group one elements are always 1+ in compounds or asfree (aq) ions. Ex in NaCl EACH Na has an oxidation state of 1+. in K 2 SO 4 EACH Na has an oxidation state of 1+. A Li +1 (aq) free ion has an oxidation number of 1+.

OXIDATION STATES 2) Group two elements have an oxidation state of 2+ in compounds and as free (aq) ions. Example: in BaCl 2 EACH Ba has an oxidation state of 2+ In Ca 3 (PO 4 ) 2 EACH Ca has an oxidation state of 2+. A free Mg +2 has an oxidation state of 2+.

OXIDATION STATES 3) The oxidation state of any ion is its charge. Example: a Fe +3 (aq) ion has an oxidation state of 3+.

OXIDATION STATES 4) Any atom that is uncombined and has a neutral charge has an oxidation state of 0, this is called the elemental state Example Cu(s) has an oxidation state of 0, as does Fe(s): IMPORTANT - remember if no charge is shown, assume it is 0 – not one as is algebra. the exceptions H 2, O 2, N 2, Cl 2, Br 2, I 2, F 2 exist as diatomic molecules in the elemental state and have oxidation states of 0.

OXIDATION STATES 5) The oxygen rules: Oxygen USUALLY has an oxidation state of 2- in compounds, 0 in O 2. EXAMPLE: in H 2 O oxygen is 2- In H 2 SO 4 EACH oxygen is 2- EXCEPTION #1– when oxygen is contained in a PEROXIDE, it has an oxidation state of 1-. o H 2 O 2, Li 2 O 2, K 2 O 2 are peroxides, each O is 1- EXCEPTION #2 – when oxygen is combined with Fluorine, its oxidation state is 1+ or 2+. Fluorine is electronegative enough to oxidize oxygen EXAMPLE in FO the oxygen is 1+ in F 2 O each oxygen is 2+

OXIDATION STATES 6) Fluorine is always 1- in its compounds 7)Halogens (Group 17) are usually 1- EXCEPT when in table E polyatomic ions, where their oxidation states can vary (multiple oxidation states).

OXIDATION STATES 8)The sum of the oxidation states of all the elements in a compound MUST equal the charge of the compound, even if it is neutral. Example: in NaOH all the oxidation states equal neutrality, 0 Na = +1 O = -2 H = +1 total = 0

OXIDATION STATES 9)The hydrogen rule: the oxidation state of hydrogen is usually 1+ EX in H 2 O each hydrogen is 1+ EXCEPTION – in metal hydrides the hydrogen is 1-, hydrogen is electronegative enough to oxidize group one metals. Example: NaH, KH etc the hydrogen is 1-

OXIDATION STATES 10) ELEMENTS WITH MULTIPLE OXIDATION STATES LISTED ON THE PERIODIC TABLE Some elements have many oxidation states, determined by what other elements they combine with. For example N, Mn, Cr have multiple oxidation states in their compounds. NOTE elements like Zn only have one state from your periodic table, so just look it up!

OXIDATION STATES KMnO 4 (NOTE, this is a neutral compound, charge is 0) K = +1 (Rule 1) = +1 O = -2 (Rule 2) = 4(-2) Mn = ? (Rule 10) = X. total = 0 Mn (-2) + X = 0 (solve for X) +1 + (-8) + X =0 (-7) + X = 0 X = 7, Mn = +7