Download Expected paths Observed paths Nuclear atom • Rutherford

Expected paths
Observed paths
Nuclear atom
• Rutherford concluded that
o positive charge, and almost all the mass of the atom, is
concentrated in a small, central ‘nucleus,’ and
o most of the atom is empty space, and that the ‘orbits’ of
negative electrons around the nucleus define the diameter of
the atom.
• The neutron was discovered much later by James Chadwick.
• The atomic mass unit (u) is defined as 1/12 of the mass of one
12
C atom.
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Chemical Elements
• An element is a substance containing only atoms with the same
atomic number, that is, the same number of protons.
• Element symbols are abbreviations of names.
o Symbols are one or two letters.
– The first symbol is always capitalized.
– If present, the second symbol is always lower case.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
a b c d e f g h i j k l m n o p q r s t u v w x y z
• Isotopes are atoms with the same number of protons but
different numbers of neutrons.
12
6C
13
6C
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6C
• A sample of an element contains a mix of natural isotopes.
o The fraction of each isotope is its ‘percent natural abundance.’
o Natural boron contains 19.9% boron-10 and 80.1% boron-11.
• Ions are atoms that have gained electrons (anions) or lost
electrons (cations).
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• Recognize that the properties of ions are different from atoms.
o Use the correct formula!
• Isotope masses cannot be found by simple addition of the
masses of the constituent protons, neutrons, and electrons.
o A small amount of mass is converted to binding energy
• By definition, the mass of one atom of carbon-12 isotope = 12 u
exactly.
o The masses of atoms of all other isotopes are determined
relative to the mass of 12C by mass spectrometry.
All ions have a 1+ charge; lighter ions are deflected more.
Atomic Mass
• We encounter several different “numbers” and “masses”
o Atomic number (Z): number of protons; defines the element.
o Mass number (A): number of protons and neutrons in isotope.
o Isotopic mass: actual mass of an atom of an isotope.
o Atomic mass: weighted average of natural isotopes.
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• The atomic mass of an element is the weighted average
calculated using isotopic mass and abundance data:
atomic mass (weight) =
∑ fractional - abundance × isotopic - mass
i
i
isotope i
Determine the atomic mass of boron given these isotopic masses
and natural abundances:
10
B
10.0129370 u
19.9 %
11
B
11.0093054 u
80.1%
Introduction to the Periodic Table
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• Things you should know about the Periodic Table:
• Organized into vertical groups (columns, families) and
horizontal periods (rows).
o Groups are numbered left to right, from 1 to 18.
o Periods are numbered top to bottom, from 1 to 7.
• Elements are separated into three types, metals and nonmetals
(separated by a thick, stair-step line), and metalloids (or
semimetals) which occur along the boundary line.
• Certain Groups have family names:
o Group 1: Alkali Metals (excludes hydrogen)
o Group 2: Alkaline Earth Metals
o Group 16: Chalcogens
o Group 17: Halogens
o Group 18: Noble Gases (formerly also known as inert gases)
o Groups 1-2 & 13-18: Main Group or Representative elements
o Groups 3-12: Transition Metals
• Inner Transition Elements: the Lanthanides and the Actinides
(see figure)
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Naming Compounds: Organic and Inorganic Compounds
(Out-of-sequence from Chapter 3)
• Systematic nomenclature allows us to assign a unique name to
every compound.
o Different compounds with the same molecular formula may
be distinguished by their names.
o We avoid having to learn millions of trivial (non-systematic)
names such as water and ammonia.
Names and Formulas of Inorganic Compounds
• Binary compounds of metals and nonmetals:
o Usually are ionic.
o Rules for naming
– Write the unmodified name of the metal.
– Then the name of the nonmetal modified to end in –ide.
o Note that the name of the metal (cation) comes first in the
name and the formula.
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• Metals which may form several ions are distinguished by writing
the ionic charge in Roman numerals in parentheses after the
name of the element.
• The older endings –ous and –ic for metals with multiple charges
are still found, typically using the Latin name of the element.
Write names for the compounds CaH2, CuCl, Ag2S, Hg2Cl2
Write formulas for aluminum sulfide, magnesium nitride, and
vanadium(III) oxide
• Binary compounds of two nonmetals:
o Compounds are molecular (not ionic; no charges).
o First write the unmodified name of the nonmetal with the
more positive O.S.
o Then write the name of the second nonmetal modified to end
in –ide.
o Indicate the relative numbers of the atoms with prefixes:
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• Polyatomic ions: two or more atoms joined by covalent bonds
o Commonly contain only nonmetals
o Number of polyatomic anions » number of polyatomic cations
o Most end in –ite or –ate (oxoanions), a handful in –ide
o Some have hypo- (least O) or per- (most O) prefixes
o Oxoanion series occur; ex: Cl, Br, I, N, P, and S
o All common halogen polyatomic oxoanions: charge = 1–
o Variable H content placed in front of oxoanion
o Prefix thio- indicates S has replaced an O
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• Binary acids:
o An acid generates H+ ions in aqueous solutions.
– These H+ ions react rapidly with water molecules to form
hydronium ions, H3O+.
o A binary acid contains H and a nonmetal.
• Oxoacids:
o Ternary (3 elements) compounds with: H + O + nonmetal.
o Can be thought of being formed from H+ ions + an oxoanion.
o Oxoacid (molecular) and Oxoanion Salt (ionic) names can be
mapped to each other.
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• Some compounds of greater complexity
o In a hydrate each formula unit has a certain number of water
molecules associated with it
CoCl2 • 6H2O
CoCl2
Names and Formulas of Organic Compounds
• The variety of organic compounds is too vast for Chem 180!
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Back to Chapter 2:
The Concept of the Mole and the Avogadro Constant
• We cannot easily count large numbers atoms, ions, or
molecules, but we can easily weigh large numbers of these.
o
o
• A mole (mol) is the amount of a substance that contains the
same number of elementary entities as there are atoms in
exactly 12 g of pure C-12.
o
o
• Atomic masses in the periodic table do not have a unit specified.
o When referring to the mass of individual atoms we use ‘u’
o When referring to the mass of one mole of atoms ‘g’
o A mole of an element will contain a mixture of isotopes in
their natural abundances.
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Just how large is Avogadro’s number?
Using the Mole Concept in Calculations
You can obtain needed conversion factors from these equivalences.
1 mol Cu = 63.546 g Cu = 6.022 x 1023 Cu atoms
1 mol Pb = 207.2
g Pb = 6.022 x 1023 Pb atoms
1 mol Re = 186.207 g Re = 6.022 x 1023 Re atoms
206
Pb = 24.1%
Pb density = 11.34 g/cm3.
What is the mass of 2.35 x 1024 atoms of Cu?
Example: How many lead-206 atoms are present in a 22.6 g sample of lead
metal?
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How man Pb atoms are present in a small piece of lead with a volume of
0.105 cm3?
Rhenium-187 is a radioactive isotope that can be used to determine the age
of meteorites. A 0.100 mg sample of Re contains 2.02 x 1017 atoms of
187
Re. What is the percent abundance of rhenium-187 in the sample?
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