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Transcript of Mec chapter 2
Chapter 2
The Structure of the Atom and the Periodic Table
Denniston Topping Caret
7th Edition
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2.1 Composition of the Atom
• Atom - the basic structural unit of an element
• The smallest unit of an element that retains the chemical properties of that element
2.1
Com
posi
tion
of
the
Ato
m
• Nucleus - small, dense, positively charged region in the center of the atom
- protons - positively charged particles
- neutrons - uncharged particles
Electrons, Protons, and Neutrons
• Atoms consist of three primary particles• electrons• protons• neutrons
2.1
Com
posi
tion
of
the
Ato
m Characteristics of Atomic Particles
• Electrons are negatively charged particles located outside of the nucleus of an atom
• Protons and electrons have charges that are equal in magnitude but opposite in sign
• A neutral atom that has no electrical charge has the same number of protons and electrons
• Electrons move very rapidly in a relatively large volume of space while the nucleus is small and dense
Mass
number
Atomic number
Charge of particle
Symbol of the atom
2.1
Com
posi
tion
of
the
Ato
m Symbolic Representation of an Element
CAZ X
• Atomic number (Z) - the number of protons in the atom
• Mass number (A) - sum of the number of protons and neutrons
Atomic Calculations
number of protons + number of neutrons = mass number
2.1
Com
posi
tion
of
the
Ato
m
number of neutrons = mass number - number of protons
number of protons = number of electrons IF positive and negative charges cancel, the atom charge = 0
2.1
Com
posi
tion
of
the
Ato
m
Calculate the number of protons, neutrons, and electrons in each of the following:
B115
Fe5526
2.1
Com
posi
tion
of
the
Ato
m Atomic Composition Calculations
4
Hydrogen(Hydrogen - 1)
Deuterium(Hydrogen - 2)
Tritium(Hydrogen - 3)
2.1
Com
posi
tion
of
the
Ato
m
Isotopes of Hydrogen
• Isotopes - atoms of the same element having different masses– contain same number of protons– contain different numbers of neutrons
Isotopes
2.1
Com
posi
tion
of
the
Ato
m Isotopic Calculations
• Isotopes of the same element have identical chemical properties
• Some isotopes are radioactive
• Find chlorine on the periodic table
• What is the atomic number of chlorine?
17
• What is the mass given?
35.45
• This is not the mass number of an isotope
2.1
Com
posi
tion
of
the
Ato
m Atomic Mass• What is this number: 35.34?
• The atomic mass - the weighted average of the masses of all the isotopes that make up chlorine
• Chlorine consists of chlorine-35 and chlorine-37 in a 3:1 ratio
• Weighted average is an average corrected by the relative amounts of each isotope present in nature
2.1
Com
posi
tion
of
the
Ato
m Atomic Mass Calculation
Calculate the atomic mass of naturally occurring chlorine if 75.77% of chlorine atoms are chlorine-35 and 24.23% of chlorine atoms are chlorine-37
Step 1: convert the percentage to a decimal fraction:
0.7577 chlorine-35
0.2423 chlorine-37
Step 2: multiply the decimal fraction by the mass of that isotope to obtain the isotope contribution to the atomic mass:
For chlorine-35:0.7577 x 35.00 amu = 26.52 amu
For chlorine-370.2423 x 37.00 amu = 8.965 amu
Step 3: sum these partial weights to get the weighted average atomic mass of chlorine:
26.52 amu + 8.965 amu = 35.49 amu
2.1
Com
posi
tion
of
the
Ato
m
2.1
Com
posi
tion
of
the
Ato
m Atomic Mass Determination• Nitrogen consists of two naturally occurring
isotopes– 99.63% nitrogen-14 with a mass of 14.003 amu
– 0.37% nitrogen-15 with a mass of 15.000 amu
• What is the atomic mass of nitrogen?
2.1
Com
posi
tion
of
the
Ato
m
Ions and Charges
• Ions - electrically charged particles that result from a gain or loss of one or more electrons by the parent atom
• Cation - positively charged– results from the loss of electrons– 23Na 23Na+ + 1e-
• Anion - negatively charged– results from the gain of electrons– 19F + 1e- 19F-
K3919
-23216S
22412 Mg2.
1 C
ompo
siti
on o
f th
e A
tom Calculating Subatomic Particles
in Ions• How many protons, neutrons, and electrons
are in the following ions?
2.2 Development of Atomic Theory
• Dalton’s Atomic Theory - the first experimentally based theory of atomic structure of the atom
2.2
Dev
elop
men
t of
Ato
mic
The
ory
Postulates of Dalton’s Atomic Theory
1. All matter consists of tiny particles called atoms
2. An atom cannot be created, divided, destroyed, or converted to any other type of atom
3. Atoms of a particular element have identical properties
4. Atoms of different elements have different properties
5. Atoms of different elements combine in simple whole-number ratios to produce compounds (stable aggregates of atoms)
6. Chemical change involves joining, separating, or rearranging atoms
Postulates 1, 4, 5, and 6 are still regarded as true.
2.2
Dev
elop
men
t of
Ato
mic
The
ory
• Electrons were the first subatomic particles to be discovered using the cathode ray tube.
Indicated that the particles were negatively charged.
2.2
Dev
elop
men
t of
Ato
mic
The
ory
Subatomic Particles: Electrons, Protons, and Neutrons
2.2
Dev
elop
men
t of
Ato
mic
The
ory
Evidence for Protons and Neutrons
• Protons were the next particle to be discovered, by Goldstein– Protons have the same size charge but opposite in sign
– A proton is 1,837 times as heavy as an electron
• Neutrons
– Postulated to exist in 1920’s but not demonstrated to exist until 1932
– Almost the same mass as the proton
2.4 The Periodic Law and the Periodic Table
• Dmitri Mendeleev and Lothar Meyer - two scientists working independently developed the precursor to our modern periodic table
• They noticed that as you list elements in order of atomic mass, there is a distinct regular variation of their properties
• Periodic law - the physical and chemical properties of the elements are periodic functions of their atomic numbers
Classification of the Elements2.
4 T
he P
erio
dic
Law
an
d th
e P
erio
dic
Tab
le
Important Biological Elements2.
4 T
he P
erio
dic
Law
an
d th
e P
erio
dic
Tab
le
Parts of the Periodic Table
• Period - a horizontal row of elements in the periodic table. They contain 2, 8, 8, 18, 18, and 32 elements
• Group - also called families, and are columns of elements in the periodic table.
• Elements in a particular group or family share many similarities, as in a human family.2.
4 T
he P
erio
dic
Law
an
d th
e P
erio
dic
Tab
le
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able Families of the Periodic Table
• Representative elements - Group A elements
• Transition elements - Group B elements
• Alkali metals - Group IA
• Alkaline earth metals - group IIA
• Halogens - group VIIA
• Noble gases - group VIIIA
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
Category Classification of Elements
• Metals - elements that tend to lose electrons during chemical change, forming positive ions
• Nonmetals - a substance whose atoms tend to gain electrons during chemical change, forming negative ions
• Metalloids - have properties intermediate between metals and nonmetals
Classification of Elements Metals
• Metals: – A substance whose atoms tend to lose
electrons during chemical change– Elements found primarily in the left 2/3 of
the periodic table
• Properties:– High thermal and electrical conductivities– High malleability and ductility– Metallic luster– Solid at room temperature
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
Classification of Elements Nonmetals
• Nonmetals: – A substance whose atoms may gain
electrons, forming negative ions– Elements found in the right 1/3 of the
periodic table
• Properties:– Brittle– Powdery solids or gases– Opposite of metal properties
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
Classification of Elements Metalloids
• Metalloids: – Elements that form a narrow diagonal band
in the periodic table between metals and nonmetals
• Properties are somewhat between those of metals and nonmetals
• Also called semimetals
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
Atomic Number and Atomic Mass
• Atomic Number:
– The number of protons in the nucleus of an atom of an element
– Nuclear charge or positive charge from the nucleus
• Most periodic tables give the element symbol, atomic number, and atomic mass
2.4
The
Per
iodi
c L
aw
and
the
Per
iodi
c T
able
Element Information in the Periodic Table
20 atomic number
Ca symbol
Calcium name
40.08 atomic mass
Using the Periodic Table
• Identify the group and period to which each of the following belongs:
a. P
b. Cr
c. Element 30
• How many elements are found in period 6?
• How many elements are in group VA?2.
4 T
he P
erio
dic
Law
an
d th
e P
erio
dic
Tab
le
2.5 Electron Arrangement and the Periodic Table
• The electron arrangement is the primary factor in understanding how atoms join together to form compounds
• Electron configuration - describes the arrangement of electrons in atoms
• Valence electrons - outermost electrons– The electrons involved in chemical bonding
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able Valence Electrons
• The number of valence electrons is the group number for the representative elements
• The period number gives the energy level (n) of the valence shell for all elements
Valence Electrons and Energy Level
• How many valence electrons does Fluorine have?
– 7 valence electrons
• What is the energy level of these electrons?
– Energy level is n = 2
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Electron Arrangement by Energy Level
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Valence Electrons - Detail• What is the total number of electrons in
fluorine?
– Atomic number = 9
– 9 protons and 9 electrons
• 7 electrons in the valence shell, (n = 2 energy level), so where are the other two electrons?– In n = 1 energy level
– Level n = 1 holds only two electrons
Determining Electron ArrangementList the total number of electrons, total number ofvalence electrons, and energy level of the valenceelectrons for silicon.
1. Find silicon in the periodic table• Group IVA • Period 3• Atomic number = 14
2. Atomic number = number of electrons in an atom
• Silicon has 14 electrons
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Determining Electron Arrangement #2List the total number of electrons, total number of valence electrons, and energy level of the valence electrons for silicon.
3. As silicon is in Group IV, only 4 of its 14 electrons are valence electrons
• Group IVA = number of valence electrons
4. Energy levels:• n = 1 holds 2 electrons• n = 2 holds 8 electrons (total of 10)
• n = 3 holds remaining 4 electrons (total = 14)
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Determining Electron ArrangementPractice
List the total number of electrons, total number of valence electrons, and energy level of the valence electrons for:
• Na
• Mg
• S
• Cl
• Ar
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able Energy Levels and Subshells
PRINCIPAL ENERGY LEVELS
• n = 1, 2, 3, …
• The larger the value of n, the higher the energy level and the farther away from the nucleus the electrons are
• The number of sublevels in a principal energy level is equal to n
– in n = 1, there is one sublevel
– in n = 2, there are two sublevels
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Principal Energy Levels
• The electron capacity of a principal energy level (or total electrons it can hold) is
2(n)2
– n = 1 can hold 2(1)2 = 2 electrons
– n = 2 can hold 2(2)2 = 8 electrons
• How many electrons can be in the n = 3 level?– 2(3)2 = 18
• Compare the formula with periodic table…..
n = 1, 2(1)2 = 2
n = 2, 2(2)2 = 8
n = 3, 2(3)2 = 18
n = 4, 2(4)2 = 32
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Sublevels
• Sublevel: a set of energy-equal orbitals within a principal energy level
• Subshells increase in energy:
s < p < d < f
• Electrons in 3d subshell have more energy than electrons in the 3p subshell
• Specify both the principal energy level and a subshell when describing the location of an electron
Principle energy level (n)
Possible subshells
1 1s
2 2s, 2p
3 3s, 3p, 3d
4 4s, 4p, 4d, 4f
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able Sublevels in Each Energy Level
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Orbitals
• Orbital - a specific region of a sublevel containing a maximum of two electrons
• Orbitals are named by their sublevel and principal energy level
– 1s, 2s, 3s, 2p, etc.
• Each type of orbital has a characteristic shape
– s is spherically symmetrical
– p has a shape much like a dumbbell
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able Orbital Shapes
• s is spherically symmetrical
• Each p has a shape much like a dumbbell, differing in the direction extending into space
Subshell Number of
orbitals
s 1
p 3
d 5
f 7
• How many electrons can be in the 4d subshell?
•10
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Quantum Mechanical Model• Each orbital within a
sublevel contains a maximum of 2 electrons
• Energy increases as n, shell number increases, but ALSO increases as you move from s to p to d to f sublevels
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Incr
easi
ng E
nerg
y4s
4p
4d
4f
••
•• •• ••
•• •• •• •• ••
••••••••••••••
Electron
Orbital
Sublevel
Shell 4
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Electron Spin• Electron configuration - the
arrangement of electrons in atomic orbitals
• Aufbau principle - or building up principle helps determine the electron configuration– Electrons fill the lowest-energy orbital that
is available first– Remember s<p<d<f in energy– When the orbital contains two electrons,
the electrons are said to be paired
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able Electron Filling Order
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Rules for Writing Electron Configurations
• Obtain the total number of electrons in the atom from the atomic number
• Electrons in atoms occupy the lowest energy orbitals that are available – 1s first
• Each principal energy level, n contains only n sublevels
• Each sublevel is composed of orbitals• No more than 2 electrons in any orbital• Maximum number of electrons in any principal
energy level is 2(n)2
Electron Distribution• This table lists the number of electrons in each
shell for the first 20 elements• Note that 3rd shell stops filling at 8 electrons even though
it could hold more
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Orbital Energy-level Diagram2.
5 E
lect
ron
Arr
ange
men
t an
d th
e P
erio
dic
Tab
le
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Writing Electron Configurations
• H– Hydrogen has
only 1 electron– It is in the
lowest energy level & lowest orbital
– Indicate number of electrons with a superscript
– 1s1
• Li– Lithium has 3
electrons– First two have
configuration of Helium – 1s2
– 3rd is in the orbital of lowest energy in n=2
– 1s2 2s1
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
ableElectron Configuration Examples
• Give the complete electron configuration of each element
– Be
– N
– Na
– Cl
– Ag
The Shell Model and Chemical Properties
• As we explore the model placing electrons in shells, we will see that the pattern which emerges from this placement correlates well with a pattern for various chemical properties
• We will see that all elements in a group have the same number of electrons in their outermost (or valence) shell2.
5 E
lect
ron
Arr
ange
men
t an
d th
e P
erio
dic
Tab
le
Groups Have Similar Chemical Properties and Appearances
• Examples of different elements that have similar properties and are all in group VA– Nitrogen
– Phosphorus
– Arsenic
– Antimony
– Bismuth
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
What noble gas configuration is this?
•Neon•Configuration is written: [Ne]3s23p1
Shorthand Electron Configurations
• Uses noble gas symbols to represent the inner shell and the outer shell or valance shell is written after
• Aluminum- full electron configuration is: 1s22s22p63s23p1
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
• Remember:
– How many subshells are in each principle energy level?
– There are n subshells in the n principle energy level.
– How many orbitals are in each subshell?
– s has 1, p has 3, d has 5, and f has 7
– How many electrons fit in each orbital?
– 22.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Shorthand Electron Configuration Examples
• N
• S
• Ti
• Sn
Use this breakdown of the Periodic Table and you can write the configuration of any element.
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
Classification of Elements According to the Type of
Subshells Being Filled
Classification of Elements – by Group
• Representative element: An element in which the distinguishing electron is found in an s or p subshell
• Distinguishing electron: The last or highest-energy electron found in an element
• Transition element: An element in which the distinguishing electron is found in a d subshell
• Inner-transition element: An element in which the distinguishing electron is found in a f subshell
2.5
Ele
ctro
n A
rran
gem
ent
and
the
Per
iodi
c T
able
2.6 The Octet Rule
• The noble gases are extremely stable– Called inert as they don’t readily bond to other
elements
• The stability is due to a full complement of valence electrons in the outermost s and p sublevels:– 2 electrons in the 1s of Helium – the s and p subshells are full in the outermost
shell of the other noble gases (eight electrons)
Octet of Electrons
• Elements in families other than the noble gases are more reactive– Strive to achieve a more stable electron
configuration– Change the number of electrons in the atom to
result in full s and p sublevels
• Stable electron configuration is called the “noble gas” configuration2.6
The
Oct
et R
ule
2.6
The
Oct
et R
ule
The Octet Rule
• Octet rule - elements usually react in such a way as to attain the electron configuration of the noble gas closest to them in the periodic table– Elements on the right side of the table move right to the
next noble gas– Elements on the left side move “backwards” to the
noble gas of the previous row
• Atoms will gain, lose or share electrons in chemical reactions to attain this more stable energy state
2.6
The
Oct
et R
ule
NaSodium atom
11e-, 1 valence e-
[Ne]3s1
Na+ + e-
Sodium ion10e-
[Ne]
Ion Formation and the Octet Rule
• Metallic elements tend to form positively charged ions called cations
• Metals tend to lose all their valence electrons to obtain a configuration of the noble gas
2.6
The
Oct
et R
ule
AlAluminum atom13e-, 3 valence e-
[Ne]3s23p1
Al3+ + 3e-
Aluminum ion10e-
[Ne]
• All atoms of a group lose the same number of electrons
• Resulting ion has the same number of electrons as the nearest (previous) noble gas atom
Ion Formation and the Octet Rule
O + 2e-
Oxygen atom8e-, 6 valence e-
[He]2s22p4
O2-
Oxide ion10e-
[He]2s22p6 or [Ne]
2.6
The
Oct
et R
ule
Isoelectronic• Isoelectronic - atoms of different elements having
the same electron configuration (same number of electrons)
• Nonmetallic elements, located on the right side of the periodic table, tend to form negatively charged ions called anions
• Nonmetals tend to gain electrons so they become isoelectronic with its nearest noble gas neighbor located in the same period to the right
2.6
The
Oct
et R
ule
Using the Octet Rule
• The octet rule is very helpful in predicting the charges of ions in the representative elements
• Transition metals still tend to lose electrons to become cations but predicting the charge is not as easy
• Transition metals often form more than one stable ion– Iron forming Fe2+ and Fe3+ is a common example
Examples Using the Octet Rule
• Give the charge of the most probable ion resulting from these elements– Ca
– Sr
– S
– P
• Which of the following pairs of atoms and ions are isoelectronic?– Cl-, Ar
– Na+, Ne
– Mg2+, Na+
– O2-, F-2.6
The
Oct
et R
ule
2.7 Trends in the Periodic Table
• Many atomic properties correlate with electronic structure and so also with their position in the periodic table– atomic size– ion size– ionization energy– electron affinity
2.7
Tre
nds
in th
e P
erio
dic
Tab
leAtomic Size
• The size of an element increases, moving down from top to bottom of a group
• The valence shell is higher in energy and farther from the nucleus traveling down the group
• The size of an element decreases from left to right across a period
• The increase in magnitude of positive charge in nucleus pulls the electrons closer to the nucleus
2.7
Tre
nds
in th
e P
erio
dic
Tab
leVariation in Size of Atoms
2.7
Tre
nds
in th
e P
erio
dic
Tab
leCation Size
Cations are smaller than their parent atom• More protons than electrons creates an increased
nuclear charge• Extra protons pull the remaining electrons closer
to the nucleus• Ions with multiple positive charges are even
smaller than the corresponding monopositive ions– Which would be smaller, Fe2+ or Fe3+? Fe3+
• When a cation is formed isoelectronic with a noble gas the valence shell is lost, decreasing the diameter of the ion relative to the parent atom
2.7
Tre
nds
in th
e P
erio
dic
Tab
leAnion Size
Anions are larger than their parent atom.
• Anions have more electrons than protons
• Excess negative charge reduces the pull of the nucleus on each individual electron
• Ions with multiple negative charges are even larger than the corresponding monopositive ions
2.7
Tre
nds
in th
e P
erio
dic
Tab
leRelative Size of Select Ions and
Their Parent Atoms
ionization energy + Na Na+ + e-2.7
Tre
nds
in th
e P
erio
dic
Tab
leIonization Energy
• Ionization energy - The energy required to remove an electron from an isolated atom
• The magnitude of ionization energy correlates with the strength of the attractive force between the nucleus and the outermost electron
• The lower the ionization energy, the easier it is to form a cation
2.7
Tre
nds
in th
e P
erio
dic
Tab
leIonization Energy of Select Elements
• Ionization decreases down a family as the outermost electrons are farther from the nucleus
• Ionization increases across a period because the outermost electrons are more tightly held
• Why would the noble gases be so unreactive?
Br + e– Br– + energy
2.7
Tre
nds
in th
e P
erio
dic
Tab
leElectron Affinity
• Electron affinity - The energy released when a single electron is added to an isolated atom
• Electron affinity gives information about the ease of anion formation
– Large electron affinity indicates an atom becomes more stable as it forms an anion
2.7
Tre
nds
in th
e P
erio
dic
Tab
lePeriodic Trends in Electron
Affinity
• Electron affinity generally decreases down a group
• Electron affinity generally increases across a period