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ChemistryChemistryChapter 4: How Atoms DifferChapter 4: How Atoms Differ::• Atomic number = # pAtomic number = # p++ AND e AND e- -

(assume neutral atom for charge).(assume neutral atom for charge).• Rounded (whole number) mass Rounded (whole number) mass number = # pnumber = # p++ + # n + # n00..• Rounded average mass number – Rounded average mass number – Atomic number = #nAtomic number = #n00..• Symbol notation (Element; mass Symbol notation (Element; mass # and atomic #).# and atomic #).

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ChemistryChemistryIonsIons::

When atoms are When atoms are NOTNOT balanced for balanced for charge they are called ions.charge they are called ions.

• Positive ionPositive ion:: Atom has Atom has lostlost electrons. Called cations (symbol).electrons. Called cations (symbol).

• Negative ionNegative ion:: Atom has Atom has gained gained electrons. Called anions (symbol).electrons. Called anions (symbol).

• Symbol system for ions.Symbol system for ions.

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ChemistryChemistryIsotopesIsotopes::

When the number of neutrons is When the number of neutrons is different BUT the proton number is different BUT the proton number is the same…:the same…:• Chemical behavior is the same.Chemical behavior is the same.• The more neutrons, the greater the The more neutrons, the greater the

mass number (mass).mass number (mass).• Most elements found in nature are a Most elements found in nature are a

mixture of isotopes.mixture of isotopes.• Isotopes differ for their relative Isotopes differ for their relative

abundance in nature (show as a %).abundance in nature (show as a %).

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ChemistryChemistryAtomic and Mass # Atomic and Mass # ReviewReview::– The The atomic numberatomic number provides the provides the number of number of protonsprotons in the nucleus and in the nucleus and the number of the number of electronselectrons in a neutral in a neutral atom. atom. – The The mass numbermass number tells us the tells us the number of number of protonsprotons and and neutrons neutrons in the in the nucleus. The mass # minus the atomic nucleus. The mass # minus the atomic # provides the number of # provides the number of neutronsneutrons. . The mass # is different for The mass # is different for isotopesisotopes of of the same element. the same element.

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ChemistryChemistryIsotopes and Ions Isotopes and Ions ReviewReview::

– Different Different isotopesisotopes of the same element of the same element that are neutral for charge are different that are neutral for charge are different for for neutron #neutron # and and mass #;mass #; they are the they are the same for same for electron #electron # and and proton #.proton #.– IonsIons of the same element are different of the same element are different for for electron #electron # and and chargecharge ; they are the ; they are the same for same for atomic #atomic # and and mass #mass #..– CationsCations have a have a positivepositive charge because charge because electrons have electrons have leftleft the atom. the atom. AnionsAnions have have a a negativenegative charge because electrons charge because electrons have have entered intoentered into the atom. the atom.

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ChemistryChemistry

Average Atomic Mass:Average Atomic Mass:

– Chemists used a standard of C-12 as Chemists used a standard of C-12 as being 12 amu; 1 amu is 1/12 of C-12.being 12 amu; 1 amu is 1/12 of C-12.– Calculating average atomic massCalculating average atomic mass need number of naturally occurring need number of naturally occurring isotopes, their masses AND their isotopes, their masses AND their abundance (percentage of the total found abundance (percentage of the total found in the environment).in the environment).

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ChemistryChemistryAverage Atomic Mass:Average Atomic Mass:

–Round I:Round I: Calculate the atomic mass Calculate the atomic mass of element X and identify the element of element X and identify the element from the periodic table using the from the periodic table using the following data:following data:

• 6363X (62.930 amu; 69.2% abundance).X (62.930 amu; 69.2% abundance).• 6565X (64.928 amu; 30.8%)X (64.928 amu; 30.8%)

– Answer:Answer: 63.5 amu; Copper (Cu) 63.5 amu; Copper (Cu)

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ChemistryChemistryAverage Atomic Mass:Average Atomic Mass:– Round II:Round II: Calculate the atomic Calculate the atomic mass of element Y and identify the mass of element Y and identify the element from the periodic table using element from the periodic table using the following data:the following data:

• 5454Y (53.940 amu; 5.9% abundance).Y (53.940 amu; 5.9% abundance).• 5656Y (55.935 amu; 91.72%)Y (55.935 amu; 91.72%)• 5757YY (56.935 amu; 2.1% (56.935 amu; 2.1%

abundance)abundance)• 5858Y (57.933 amu; 0.28% abundance).Y (57.933 amu; 0.28% abundance).

– Answer:Answer: 55.844 amu; Iron (Fe) 55.844 amu; Iron (Fe)