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AtomicAtomic
ConceptsConcepts
Unit 3:
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What is an atom?What is an atom?
y The smallest particle ofan element that
retains the properties of that element.
Individualatoms can be
seen using what is called
a scanning, tunneling
microscope (invented
1981.) This is an image is
of gold atoms.
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John DaltonJohn Dalton18031803
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Daltons Theory Cont.Daltons Theory Cont.y 3. Atoms of different elements can_______________________ or can
___________________ with one another in
simple whole-numberratios to formcompounds (law of constant composition)
y
4. ___________________ occur when atomsare separated, joined, orrearranged. Atoms of
one element can _____________ ________
into atoms ofanother element as aresult ofa
chemicalreaction.
physically mix togetherchemically combine
Chemical reactions
never be changed
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Daltons Model (1803)Daltons Model (1803)
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A penny contains 2.4 x 1022
copper atoms.
There are 6.95 x 109 peopleon Earth.
Thats a lot of atoms!
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The Subatomic ParticlesThe Subatomic Particles
y Electrons - ___________________________________________________
Charge ____
Mass (amu) ________
Mass (grams) ____________
Are negatively chargedsubatomic particles
-1 1
1840 amu
9.11 x 10-28
g
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Cathode RayTubeCathode RayTube
y
Cathode RayVideo
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y Protons - ________________________
________________________________
Charge ______________
Mass (amu) ______________Mass (grams) ______________
Are positively charged
subatomic particles
+1
11.67 x 10-24g
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y eutrons - ______________________
________________________________
Charge ______________
Mass (amu) ______________
Mass (grams) ______________
subatomic particles with
no charge. Found in nucleus
0
1
1.67 x 10-24
g
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y A typicalatomic radius is about 100pm,
whereas the radius ofan atomic nucleus is
about 5 x 10-3pm Imagine that in an atomwere the size of the Houston Astrodome, the
volume of its nucleus would be comparable to
that ofa small marble.
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y ucleus - ________________________
_________________________________________
Central core of an atom
composed of protons and neutrons
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ohr modelBohr model Planetary ModelPlanetary Model
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Modern TheoryModern Theory
y In the modern theory (the wave-mechanical model) electrons are
considered to be found in an area of
probability known as electron clouds.
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Atomic StructureAtomic Structurey
Atomic Number - ___________________________________________________
The elements on the periodic table arearranged according to atomic number.
The atomic number identifies the element.
Since atoms are electrically neutral: the # of
__________ in the nucleus ofan atom
=the number of __________ outside the
nucleus
The number ofprotons in the nucleus of an atom
protonselectrons
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y Mass number - ____________________
_________________________________
Nuclear symbol: Used to represent the
composition ofan atom in shorthandnotation, the symbol of the element with
two additional numbers to the left are used.
Sum of the number of
protons and neutrons a whole #
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Nuclear SymbolNuclear Symbol
y The _________ number is written as thesubscript and the _______ number is
written as the superscript.
Heatomic
2
mass
4
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OtherrepresentationsOtherrepresentations
y Helium 4
y He 4
The number given after the name ofan
element is the _______ number.
4He
mass
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y In the previous examples, why is it ok to
omit the atomic number from our
representations?
Since the atomic number identifies
an element, you can check the
periodic table to find the atomic
number when given the symbol
because it never changes!
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Symbol At. # Mass # # p # n # e-
9 10
14 15
47 22
55 25
Complete the following table:
F 9 919
14Si 1429
2222Ti 25
25Mn 2530
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y Isotopes - ________________________
_________________________________________________________________
y
Since isotopes have the same number ofprotons, isotopes must be of the same
element.
y Remember that only protons and neutrons
contribute to the mass number, therefore,
isotopes must have different mass numbers.
Atoms containing the
same number of protons, but have adifferent mass number (# of n)
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y Despite these differences, isotopes are
chemicallyalike because theyhave
identical numbers of protons andelectrons. These subatomic particles are
responsible for the characteristic
chemical behavior of each element.
y To find the most abundant isotope using
atomic mass, round atomic mass to the
nearest whole number.
y Ex: atomic mass of oxygen is 15.9994,
most abundant isotope = O-16
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The three isotopes ofhydrogen are:The three isotopes ofhydrogen are:
y H 1 H 2 H 3
__p __n __p __n __p __n1 0 1 1 1 2
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Ions - ____________________________
________________________________
________________________________
atoms that lost or gained
electrons during a chemical reaction to
become electrically charged.
Symbol At. # Mass # # p # n # e-
24Mg 12
24Mg2+
35Cl
35Cl-
24 12 12 12
12 24 12 12 10
17 35 17 18 17
17 35 17 18 18
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Atomic MassAtomic Mass
y The mass of even the largest single atom is
too small to e measured on a balance. The
mass ofa single atom can be determinedusing __________________a mass spectrometer
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Mass SpectrometerMass Spectrometer
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y The mass ofan individualatoms is useful
information, but these values are inconvenient
and impractical to work with. Instead, it ismore useful to compare the relative masses of
atoms using an isotope of carbon, carbon 12,
as a basis. The isotope carbon 12 wasassigned a mass of exactly 12.00000 amu.
Therefore one amu is defined as:
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y Atomic mass unit (amu) - _____________
_________________________________
y An atom of carbon 12 has
__________________________; therefore,the mass ofa single proton or neutron is
about _______amu.
defined as 1/12
the mass of a carbon-12 atom.
6 protons and 6 neutrons
one
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y Since the mass ofa single atom depends
on the number of protons and neutrons
in the nucleus, one would think that the
atomic mass ofan element_____________________________should be a whole number
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y This is not the case due to the existence of
________.
y The atomic mass ofan element is the
____________________of the atoms in a
________________ sample of the
elements.
isotopes
weighted average mass
naturally occuring
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Calculating Atomic MassCalculating Atomic Mass
y To calculate the average atomic mass of
an element, one must know the number
of stable isotopes of that element, mass of
each isotope, and the natural percentabundance of each isotope.
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Example:
A sample of cesium is ,
19.7% 132Cs, and 5.49% 134Cs. What is itsaverage atomic mass?
Cs-132
Cs-134
(132 amu)
(134 amu)
(0.197)
(0.0549)
= 26.0 amu
= 7.36 amu
Add together 132.86 amu
132.9 amu
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y Electron Configurations_________________________________
__________________________
In all natural phenomena, change proceeds
towards the lowest possible energy state.
y Principal Energy Levels -___________
_________________________________
y The reference tables use a type of shorthand
which expresses the number of electrons in
each PEL.
placement of electrons around the
nucleus
(PELs) are
designated by the period number
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Looking at your Periodic TableLooking at your Periodic Table
2 e-
in 1st
PEL, 4 e-
in 2nd
PEL
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ExamplesExamples
y Neon _______________
y Magnesium ____________________
Ground State Electron Configurations
Lowest energy state ofan atom (most
stable.) These are given on the periodic
table.
2-8
2-8-2
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y Excited state electron configurations -
________________________________
________________________________________________________________
______.
When an electron in an atom gains a
specific amount of energy, that electronmoves to a higher energy state
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Example: HeliumExample: Helium
y Ground state He: 2
Excited state He: 1-1
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Example: NitrogenExample: Nitrogen
Ground State:2-5
Excited State:2-4-1
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Important note:Important note:
yThe number of electrons in
the ground state electron
configuration and theexcited state electron
configuration are the same!
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A sample regents question
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Acceptable answersAcceptable answers
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Try it yourself!Try it yourself!
y
What are some possible excited stateconfigurations forO?
y Ground state: 2-6
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Lewis Dot Diagrams orLewis Dot Diagrams or
Structures (Electron Dot)Structures (Electron Dot)
y Use only the ________ electrons.
y These are the electrons in the outermost
principle energylevel
valence
Therefore sodium
will have oneelectron in its
Lewis diagram
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y Represent electrons as dots (or circles or
Xs) around the element symbol.
y To draw a Lewis diagram foran atom,
follow the fill order:
two on top, then around the clock!
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y Therefore our example can be expressed
in two ways:
Na Na
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Other ExamplesOther Examples
M
g O
F
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BrightBright--Line SpectrumLine Spectrum
y
Every element emits light if it is heated bypassing electricity through its gas or vapor.
The atoms absorb energy, then lose the
energyand ___________.
y Please add: The energyabsorbed and emitted
is in discrete quantities. These quantities are
the difference in the principle energylevelsof the ground state configuration and the
excited state configuration
emit light
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The step are
analogous ofthe energy
levels, the ball
is analogous ofthe electrons!
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y Passing the light througha prism
(spectroscope) gives the ____________
__________(spectrallines) of the element.
This spectrum is unique for each element aseach element has a different number of
electrons, so ______
_______________________________________.
emissions
spectrum
no
two elements have the sameenergy
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Various Emissions SpectraVarious Emissions Spectra