atomic structure topic 1 copyright © the mcgraw-hill companies, inc. permission required for...
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Atomic StructureAtomic Structure
Topic 1Topic 1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Atomic - Molecular Atomic - Molecular Theory of MatterTheory of Matter
The The Atomic - Molecular Atomic - Molecular Theory of MatterTheory of Matter
states that all matter states that all matter is composed of small, is composed of small, fast moving particles fast moving particles called atoms. These called atoms. These
atoms can join atoms can join together to form together to form
molecules. molecules.
This theory is really This theory is really thousands of thousands of
individual theories individual theories that provide evidence that provide evidence for the whole theory.for the whole theory.
Where did it all Where did it all begin?begin?
The word “atom” The word “atom” comes from the comes from the
Greek word Greek word ““atomos”atomos” which which
means means indivisibleindivisible..
The idea that all The idea that all matter is made up matter is made up of atoms was first of atoms was first proposed by the proposed by the
Greek philosopher Greek philosopher DemocritusDemocritus in the in the 5th century B.C5th century B.C..
AtomsAtomsThe The smallestsmallest particle of an particle of an element element that that retains the retains the properties properties of that of that element.element.
Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small particles called atoms.
3. Atoms of different elements can combine in simple whole number ratios to form compounds.
4. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.
2.1
2. All atoms of a given element are identical. The atoms of one element are different from those of any other element
Electrons, protons & neutronsElectrons, protons & neutrons
Which one of Dalton’s assumptions is Which one of Dalton’s assumptions is wrong?wrong?
ElectronElectron
negatively charged subatomic particlenegatively charged subatomic particle
Sir Joseph J Thomson experimented Sir Joseph J Thomson experimented with cathode rayswith cathode rays
He found (1897) that cathode rays He found (1897) that cathode rays could be deflected by electrically could be deflected by electrically charged plates, towards (+) side platecharged plates, towards (+) side plate
J.J. ThompsonJ.J. Thompson
e- charge = -1.60 x 10-19 C
Thomson’s charge/mass of e- = -1.76 x 108 C/g
e- mass = 9.10 x 10-28 g
Measured mass of e-
(1923 NobelPrize in Physics)
Millikan's Oil Drop Experiment
2.2
ProtonProton
1840x heavier than an electron1840x heavier than an electron
Approx 1AMU (atomic mass unit)Approx 1AMU (atomic mass unit)
A hydrogen atom stripped of an A hydrogen atom stripped of an electronelectron
(+) charged particle(+) charged particle
NeutronNeutron
Discovered in 1932 by Discovered in 1932 by ChadwickChadwick
No chargeNo charge
Mass is equal to that of a Mass is equal to that of a protonproton
Chadwick’s Experiment (1932)Chadwick’s Experiment (1932)
H atoms - 1 p; He atoms - 2 p
mass He/mass H should = 2
measured mass He/mass H = 4
+ 9Be 1n + 12C + energy
neutron (n) is neutral (charge = 0)
n mass ~ p mass = 1.67 x 10-24 g2.2
Subatomic Particles Subatomic Particles
Particle Mass
(g) Charge
(Coulombs) Charge (units)
Electron (e-) 9.1 x 10-28 -1.6 x 10-19 -1
Proton (p) 1.67 x 10-24 +1.6 x 10-19 +1
Neutron (n) 1.67 x 10-24 0 0
mass p = mass n = 1840 x mass e-
2.2
Structure of the AtomStructure of the Atom
Rutherford discovered the Rutherford discovered the nucleus of the atomnucleus of the atom
The nucleus is composed of The nucleus is composed of protonsprotons and and neutronsneutrons
HISTORYHISTORY OF THE ATOMOF THE ATOM
1910 Ernest Rutherfordoversaw Geiger and Marsden carrying out his
famous experiment.
they fired Helium nuclei at a piece of gold
foil which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
1910
1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)4. TeacherTube - Rutherford\'s experiment
particle velocity ~ 1.4 x 107 m/s(~5% speed of light)
(1908 Nobel Prize in Chemistry)
2.2
NucleusNucleus
(+ ) charge(+ ) charge
Occupies a small volumeOccupies a small volume
Contains protons and neutronsContains protons and neutrons
High densityHigh density
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
Rutherford’s Model of the Atom
2.2
Outside the nucleusOutside the nucleus
Electron are found outside Electron are found outside the nucleusthe nucleus
Electrons occupy most of the Electrons occupy most of the volumevolume
Is this really an Atom?Is this really an Atom?
The model above represents The model above represents the most modern version of the most modern version of
the atom. the atom.
(Artist drawing)(Artist drawing)
Many of the models that you Many of the models that you have seen may look like the one have seen may look like the one
below. It shows the parts and below. It shows the parts and structure of the atom. Even structure of the atom. Even
though we do not know what an though we do not know what an atom looks like, scientific atom looks like, scientific models must be based on models must be based on
evidence. evidence.
How can Indirect How can Indirect Evidence be Gathered?Evidence be Gathered?
Click here to visit a lClick here to visit a lab where actual scieab where actual scientific research on atntific research on atoms is conducted.oms is conducted.
Identifying features of AtomsIdentifying features of Atoms
A. Atomic Number (Z)A. Atomic Number (Z)
The The numbernumber of of protonsprotons in the nucleus in the nucleus of the atom of a certain element. of the atom of a certain element. This identifies the element.This identifies the element.
The atom is electrically neutral The atom is electrically neutral therefore it must also have therefore it must also have eight eight electrons around its nucleuselectrons around its nucleus
Atomic Mass Unit (AMU)Atomic Mass Unit (AMU)
Mass of the pMass of the p++ and n and n00 are very small are very small
1.67 x 101.67 x 10-24-24gg
This unit is called theThis unit is called the Atomic Mass Unit Atomic Mass Unit
The AMU isThe AMU is 1/12 the mass of a 1/12 the mass of a Carbon – 12 atom that contains 6p Carbon – 12 atom that contains 6p and 6nand 6n
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
# OF NEUTRONS = mass number – atomic number
XAZ
H11 H (D)2
1 H (T)31
U23592 U238
92
Mass Number
Atomic NumberElement Symbol
2.3
ISOTOPESISOTOPES
The nuclei of atoms must contain The nuclei of atoms must contain the same # of protons but the same # of protons but
neutrons may varyneutrons may vary
ISOTOPESISOTOPES
Atoms that have same # of p+Atoms that have same # of p+
Different # of neutronsDifferent # of neutrons
Different mass numbersDifferent mass numbers
How many protons, neutrons, and electrons are in C146 ?
How many protons, neutrons, and electrons are in C116 ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
Do You Understand Isotopes?Isotope Maker
2.3
Atomic Mass CalculationsAtomic Mass CalculationsAtomic MassAtomic Mass
The weighted average of the masses The weighted average of the masses of the isotopes of that element. Most of the isotopes of that element. Most elements occur as elements occur as twotwo or more or more isotopesisotopes in nature in nature
Similar to your class averageSimilar to your class average
An ion is an atom, or group of atoms, that has a net positive or negative charge. An atom that has lost or gained one or more electronscation – ion with a positive charge
If a neutral atom loses one or more electronsit becomes a cation.
anion – ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons Cl-
17 protons18 electrons
2.5
A monatomic ion contains only one atom
A polyatomic ion contains more than one atom
2.5
Na+, Cl-, Ca2+, O2-, Al3+, N3-
OH-, CN-, NH4+, NO3
-
13 protons, 10 (13 – 3) electrons
34 protons, 36 (34 + 2) electrons
Do You Understand Ions?
2.5
How many protons and electrons are in Al2713 ?3+
How many protons and electrons are in Se7834
2- ?
Some Polyatomic Ions (Table 2.3)Some Polyatomic Ions (Table 2.3)
NH4+ ammonium SO4
2- sulfate
CO32- carbonate SO3
2- sulfite
HCO3- bicarbonate NO3
- nitrate
ClO3- chlorate NO2
- nitrite
Cr2O72-
dichromate SCN- thiocyanate
CrO42- chromate OH- hydroxide
2.7
The Development of Atomic The Development of Atomic ModelsModels
The timeline shoes the development of The timeline shoes the development of atomic models from 1803 to 1911.atomic models from 1803 to 1911.
5.1
Electrons in AtomsElectrons in AtomsDaltonDalton– IndivisibleIndivisibleThomsonThomson– Raisin bun modelRaisin bun modelRutherfordRutherford– Dense , emptyDense , emptyBohrBohr– Definite ;energyDefinite ;energy– Circular fixed distance from the nucleusCircular fixed distance from the nucleus– Greater; electronGreater; electron– Energy levels or shellsEnergy levels or shells
The Development of Atomic The Development of Atomic ModelsModels
The timeline shows the development of The timeline shows the development of atomic models from 1913 to 1932.atomic models from 1913 to 1932.
5.1
QuantaQuanta
Photons ; Photons ; bundles of energybundles of energy
The energy that is absorbed as The energy that is absorbed as electrons jump to higher energy electrons jump to higher energy levels and it is levels and it is emittedemitted when they fall when they fall to to their lower energy levelstheir lower energy levels
If electrons remain in their orbit If electrons remain in their orbit they they don’t lose energydon’t lose energy
NielsNiels Bohr and The Planetary Model of t Bohr and The Planetary Model of the Atomhe AtomAll atoms that are in the lowest energy All atoms that are in the lowest energy
level are in their normal state or level are in their normal state or groundground statestate
b. Principle Energy levelsb. Principle Energy levelsElectrons normally occupy the Electrons normally occupy the lowestlowest energy energy
levels. If an atom absorbs energy from an levels. If an atom absorbs energy from an outside source, it may cause the electrons outside source, it may cause the electrons to move to a to move to a higher energy levelshigher energy levels. This is . This is called the called the excited state This state is excited state This state is unstable.unstable.
Principle Energy levelPrinciple Energy level
The PEL denotes how far the electron The PEL denotes how far the electron is from the nucleusis from the nucleus
K- 1K- 1 ________________________
L-2L-2 ________________________
M-3M-3 ________________________
Similar to rungs on a ladderSimilar to rungs on a ladder
INC
RE
AS
ING
PE
The Bohr ModelThe Bohr ModelLike the rungs of the Like the rungs of the strange ladder, the strange ladder, the energy levels in an energy levels in an atom are not equally atom are not equally spaced. spaced.
The higher the energy The higher the energy level occupied by an level occupied by an electron, the less electron, the less energy it takes to energy it takes to move from that energy move from that energy level to the next higher level to the next higher energy level.energy level.
5.1
Spectral LinesSpectral Lines
When electrons in an atom are in the When electrons in an atom are in the excited state and return to lower excited state and return to lower energy levels the energy is emitted energy levels the energy is emitted as as
Radiant energy of a specific Radiant energy of a specific frequency which produces a frequency which produces a characteristic spectral line which can characteristic spectral line which can be used to identify elementsbe used to identify elements
+P+P
22
33
44
656 nm
700 nm700 nm400 nm400 nm
-e-e
Balmer series for Hydrogen
Atom
11
-e-e
-e-e
55
-e-e
486 nm
434 nm
-e-e 410 nm
n=1
n=2
n=3
n=4
Spectrum
UV
IR
Vi s ible
Ground State
Excited State
Excited StateExcited State unstable and drops back down
•Energy released as a photon
•Frequency proportional to energy drop
Excited State
But only as far as n = 2 this time
BOHR VS BOHR VS ORBITAL MODEL OF THE ATOMORBITAL MODEL OF THE ATOM
It does not represent electrons as It does not represent electrons as moving in moving in planetary orbits around planetary orbits around the nucleusthe nucleus
Electrons occupy regions of space Electrons occupy regions of space aroundaround the nucleus (not circular the nucleus (not circular paths)paths)
Electrons occupy orbitals that may Electrons occupy orbitals that may differdiffer in size, shape, or orientation in in size, shape, or orientation in spacespace
Electron ConfigurationsElectron Configurations
Ground StateGround State
The The ground stateground state is the most stable is the most stable energy state of an atom. It is the energy state of an atom. It is the nature of things to seek the lowest nature of things to seek the lowest possible energy levels. Therefore, possible energy levels. Therefore, high energy systems are high energy systems are unstableunstable
Electron ConfigurationsElectron Configurations
The way in which electrons are The way in which electrons are arranged around the nuclei of atomsarranged around the nuclei of atoms
1s1s22 2s 2s2 2 2p 2p3 3 ground stateground state
1s1s2 2 2s2s1 1 2p2p4 4 excited state excited state
Energy levelsEnergy levels
The energy levels are represented by The energy levels are represented by quantum numbersquantum numbers
N is equal to the number of the N is equal to the number of the principle energy level as referred to principle energy level as referred to under the Bohr atom and is the same under the Bohr atom and is the same as the as the period number in the periodic period number in the periodic table (horizontal)table (horizontal)
SublevelsSublevels
The energy levels may be divided The energy levels may be divided into sublevels. Every PEL has one or into sublevels. Every PEL has one or more sublevels within it. The number more sublevels within it. The number of sublevels in the PEL is the same as of sublevels in the PEL is the same as the principle quantum #the principle quantum #
PEL 1 has 1 Sublevel PEL 1 has 1 Sublevel s s
PEL 2 has 2 SublevelsPEL 2 has 2 Sublevels ss pp
PEL 3 has 3 SublevelsPEL 3 has 3 Sublevels s p ds p d
PEL 4 has 4 SublevelsPEL 4 has 4 Sublevels ss pp dd ff
OrbitalsOrbitals
Each Each sublevelsublevel may consist of one or may consist of one or more more orbitals orbitals ..
Only two electrons to occupy each Only two electrons to occupy each orbitalorbital
These two electrons have opposite These two electrons have opposite spinsspins
Atomic OrbitalsAtomic OrbitalsThe numbers and kinds of atomic orbitals The numbers and kinds of atomic orbitals depend on the energy sublevel. depend on the energy sublevel.
5.1
Atomic OrbitalsAtomic OrbitalsDifferent atomic orbitals are denoted by Different atomic orbitals are denoted by letters. The letters. The ss orbitals are spherical, and orbitals are spherical, and pp orbitals are dumbbell-shaped.orbitals are dumbbell-shaped.
5.1
Atomic OrbitalsAtomic OrbitalsFour of the five Four of the five dd orbitals have the same orbitals have the same shape but different orientations in space.shape but different orientations in space.
5.1
Atomic OrbitalsAtomic Orbitals
The number of electrons allowed in each of The number of electrons allowed in each of the first four energy levels are shown here.the first four energy levels are shown here.
5.1
Electron ConfigurationsElectron Configurations– Aufbau PrincipleAufbau Principle
According to the According to the aufbau principleaufbau principle, , electrons occupy the orbitals of lowest electrons occupy the orbitals of lowest energy first. In the aufbau diagram below, energy first. In the aufbau diagram below, each box represents an atomic orbital.each box represents an atomic orbital.
5.2
3 Rules3 Rules
Pauli Exclusion PrinciplePauli Exclusion Principle– An orbital may contain only An orbital may contain only 2 electrons 2 electrons
at the most with opposite spinsat the most with opposite spins
Hunds RuleHunds Rule– Electrons occupy orbitals of equal Electrons occupy orbitals of equal
energy energy 1 electron enters each orbital 1 electron enters each orbital until all orbitals contain one electron until all orbitals contain one electron with parallel spinswith parallel spins
What do electron configurations tell What do electron configurations tell us?us?
Principle energy level (PEL)Principle energy level (PEL)
Type of sublevelType of sublevel
The The numbernumber of electrons in the of electrons in the sublevelsublevel
Atomic Electron ConfigurationsAtomic Electron Configurations
1s1s22PEL
Type of sublevel and # of Orbitals
# of electrons in orbital
Valence ShellValence Shell
The outer most occupied PEL, the The outer most occupied PEL, the electrons in this shell are called electrons in this shell are called valence electronsvalence electrons an atom can’t have an atom can’t have more than 8 electrons in its more than 8 electrons in its valence valence shellshell
** ** The chemical properties of an The chemical properties of an element are determined mainly by element are determined mainly by the arrangement of electrons in the the arrangement of electrons in the valence shell**valence shell**
KernelKernel
The part of the atom including the The part of the atom including the nucleusnucleus that is stripped of its that is stripped of its valence valence electronselectrons
Ground Vs. Excited StateGround Vs. Excited State
Na 2- 8- 1Na 2- 8- 1
Na 2 – 7 -2 Na 2 – 7 -2
What element is this?What element is this?
2-8-7-3 2-8-7-3
Is it in the ground or excited state?Is it in the ground or excited state?
Ionization Energy (IE)Ionization Energy (IE)
The amount of energy needed to The amount of energy needed to remove the most loosely held remove the most loosely held electron from a neutral atomelectron from a neutral atom
Highest – Highest – noble gasesnoble gases
Metallic – Metallic – smallest IEsmallest IE
Non – Metallic – Non – Metallic – largest IElargest IE
ionic compounds consist of a cation and an anion
• the formula is always the same as the empirical formula
• the sum of the charges on the cation and anion in each formula unit must equal zero
The ionic compound NaCl
2.6
A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds
H2 H2O NH3 CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5
A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance
An empirical formula shows the simplest whole-number ratio of the atoms in a substance
H2OH2O
molecular empirical
C6H12O6 CH2O
O3 O
N2H4 NH2
2.6
Formula of Ionic Compounds
Al2O3
2.6
2 x +3 = +6 3 x -2 = -6
Al3+ O2-
CaBr2
1 x +2 = +2 2 x -1 = -2
Ca2+ Br-
Na2CO3
1 x +2 = +2 1 x -2 = -2
Na+ CO32-
Chemical NomenclatureChemical NomenclatureIonic CompoundsIonic Compounds– often a metal + nonmetaloften a metal + nonmetal– anion (nonmetal), add “ide” to element nameanion (nonmetal), add “ide” to element name
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2 magnesium hydroxide
KNO3 potassium nitrate
2.7
Transition metal ionic compoundsTransition metal ionic compounds– indicate charge on metal with Roman numeralsindicate charge on metal with Roman numerals
FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride
FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride
Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide
2.7
Molecular compoundsMolecular compounds– nonmetals or nonmetals + metalloidsnonmetals or nonmetals + metalloids– common namescommon names
HH22O, NHO, NH33, CH, CH44, C, C6060
– element further left in periodic table is 1element further left in periodic table is 1stst
– element closest to bottom of group is 1element closest to bottom of group is 1stst
– if more than one compound can be formed if more than one compound can be formed from the same elements, use prefixes to from the same elements, use prefixes to indicate number of each kind of atomindicate number of each kind of atom
– last element ends in idelast element ends in ide
2.7
HI hydrogen iodide
NF3 nitrogen trifluoride
SO2 sulfur dioxide
N2Cl4 dinitrogen tetrachloride
NO2 nitrogen dioxide
N2O dinitrogen monoxide
Molecular Compounds
2.7
TOXIC!
Laughing Gas
An acid can be defined as a substance that yields hydrogen ions (H+) when dissolved in water.
HCl•Pure substance, hydrogen chloride•Dissolved in water (H+ Cl-), hydrochloric acid
An oxoacid is an acid that contains hydrogen, oxygen, and another element.
HNO3 nitric acid
H2CO3 carbonic acid
H2SO4 sulfuric acid2.7