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Lecture 2: Atoms and Elements
Lecture Outline Defining matter and its types Elements and symbols The periodic table The atom Atomic number and mass number Isotopes and atomic mass Electron energy levels Electron configuration Periodic trends
(as in before, group activity takes center and front in the lecture)
2
Defining Matter and its types
Matter: Matter is stuff. it is what makes up a substance. Matter makes things we see everyday such as water, wood, cooking pan, clothes, shoes, etc.
3
Properties of Matter
Type of Properties
PhysicalObtained without changing identity
(No color, shape, taste, or density change)
ChemicalObtained by changing identity(New color, shape, taste, etc)
Physical ChangeChange without changing identity
and no new substances formed
Chemical ChangeChange in which new substancesare formed by changing identity
4
Elements and Symbols
Robert Boyle (1627-1691: Elements are substances that cannot be separated into simpler substances
Robert had no preconceived ideas about how many elements there might be …
Elements are the building blocks of matter
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
gold carbon aluminum
5
Number of Elements
Matter is composed of 115 different elements (88 naturally occurring) millions of compounds
In comparison, English language has 26 letters millions of words and sentences
Elements not evenly distributed 9 elements in the earth’s crust make up 98% of the mass Oxygen is the most abundant: 20% of air, almost 50% of earth’s
crust Elements in living matter also not evenly distributed selected for
biological function Oxygen is still most abundant, followed by carbon, hydrogen, and
nitrogen Calcium, phosphorus, magnesium, potassium, sodium, chlorine,
sulfur, and iron are all present in significant amounts
6
Element Names
Element named after many things: Places of discovery Planets minerals People (Scientists) Colors Mythology
7
Symbols of Elements
Learn the FIRST 20 elements and their names (TEST Material)
8
Symbols from Latin Names
Some symbols are derived from Latin names as shownbelow:
Cu, copper (cuprum) Au, gold (aurum)
Fe, iron (ferrum) Ag, silver (argentum)
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
9
The Periodic Table: Groups vs. Periods
• Groups contain elements with similar properties in vertical columns.
• Periods are horizontal rows of elements.
10
The Periodic Table
11
Group Numbers
Group Numbers Use the letter A for the representative elements (1A to 8A) and
the letter B for the transition elements Also use numbers 1-18 to the columns from left to right Several groups of representative elements have common names
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
12
The heavy zigzag line separates metals and nonmetals Metals are located to the
left Nonmetals are located to
the right. Metalloids are located
along the heavy zigzag line between the metals and nonmetals
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
Metals, Nonmetals, and Metalloids
13
Properties of Metals, Nonmetals, and Metalloids
Metals Are shiny and ductile Are good conductors of heat and electricityNonmetals Are dull, brittle, and poor conductors of heat and
electricity Are good insulatorsMetalloids Are better conductors than nonmetals, but not as good
as metals Are used as semiconductors and insulators
14
Pause: ALE 2
Group activity: all groups work on problems on ALE IIB worksheet, problems 3-6
Need volunteers to work on the problems written on the board. If no volunteers immediately, will call names. Everyone will do problems on the board sooner or later
While working on the problems, ask if you have any questions. I’m more than happy to help
15
Dalton’s Atomic Theory
Atoms
Are tiny particles of matter
Of an element are similar and different from other elements
Of two or more different elements combine to form compounds
Are rearranged to form new combinations in a chemical reaction
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
16
Subatomic Particles
Atoms contains subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral Coulomb's law: Like charges repel
and unlike charges attract
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
17
An atom consists
Of a nucleus that contains protons and neutrons
Of electrons in a large, empty space around the nucleus
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
Structure of the Atom
18
Atomic Mass Scale
On the atomic mass scale for subatomic particles 1 atom mass unit (amu) is defined as 1/12 of the mass of
the carbon-12 atom A proton has a mass of about 1 (1.007) amu A neutron has a mass of about 1(1.008) amu An electron has a very small mass, 0.000549 amu
19
Atomic Number and Mass Number
The atomic number Is specific for each element and is the same for all atoms
of an element. Is equal to the number of protons in an atom. Appears above the symbol of an element.
• The mass number : represents the number of particles in the nucleus and is equal to sum of protons and neutrons in the nucleus. Number of protons + Number of neutrons
11
Na
Atomic Number
Symbol
20
Atomic Number and Protons
Examples of atomic number and number of protons:
Hydrogen has atomic number 1, every H atom has one proton.
Carbon has atomic number 6, every C atom has six protons.
Copper has atomic number 29, every Cu atom has 29 protons.
Gold has atomic number 79, every Au atom has 79 protons.
21
Number of Electrons in Atom Atoms are neutral In each atom, number of protons is equal to that
of electrons
number of protons = number of electrons
For instance, an aluminum atom has 13 protons and 13 electrons. The net charge is zero
13 protons (13+) + 13 electrons (13 -) = 0
22
Isotopes and Isotopic Notation
Isotopes
Elements of same type, same number of protons, but different number of neutrons.
Isotopes have identical properties, mass, and sometimes radioactivity
Nuclear Symbol
atomic number zmass number aX
atomic number 11mass number 23N
a
Example: Sodium atom
23
For an atom, the nuclear symbol gives the number of Protons (p+) Neutrons (n) Electrons (e-)
16 31 65
O P Zn 8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n 8 e- 15 e- 30 e-
Nuclear Symbols
24
Atomic Mass
The atomic mass of an element
Is listed below the symbol of each element on
the periodic table.
Gives the mass of an “average” atom of each
element compared to 12C.
Is not the same as the mass number
Na22.99
Summary
Atomic mass = average mass of an atom in each element
Mass number = # of protons + # of neutrons in the nucleus
Atomic number = number of protons in an atom
Learning Check
Fill the following table for neutral atoms:
25
Element Name
Symbol Atomic Number
Mass Number
Number of
Protons
Number of
Neutrons
Number of Electrons
Boron 10
Cl 35
8 16
92 146
8 6
26
Elements and Their Atomic Mass
Most elements have two or more isotopes that contribute to the atomic mass of that element.
27
Calculating Average of Masses
To calculate an atomic mass, the contribution of each isotope is determined by multiplying the mass of each isotope by its percent abundance and adding the results
Example: magnesium has three isotopes, Mg-24 (23.99 amu, 78.70%), Mg-25 (24.99 amu, 10.13%) and Mg-26 (25.98 amu, 11.17%). Calculate the atomic mass of magnesium.
Isotope: Mass x Abundance (%) = Contribution to average Mg amu
24Mg25Mg26Mg
23.99
24.99
25.98
78.70/100
10.13/100
11.17/100
Average Atomic Mass:
18.88
2.532
2.902
24.31
28
Pause: ALE 2
Group activity: all groups work on problems on ALE 2 worksheet, problems 1and 2, 7-9
While working on the problems, ask if you have any questions. I’m more than happy to help
29
Lecture 2: Atoms and Elements
Electron Energy Levels
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
30
Electron Energy Levels
Electrons are arranged in
specific energy levels that Are labeled n = 1, n = 2, n =
3, and so on.
Increase in energy as n increases.
Have the electrons with the lowest energy in the first energy level (n=1)closest to the nucleus.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
31
Energy Level Changes
An electron absorbs energy to “jump” to a higher energy level.
When an electron falls to a lower energy level, energy is emitted.
In the visible range, the emitted energy appears as a color.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
32
Energy Emitted
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
33
Sublevels
Sublevels Contain electrons with the same energy. Are found within each energy level. Are designated by the letters s, p, d, f.
The number of sublevels is equal to the value of the principal quantum number (n).
34
Number of Sublevels
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
35
Energy of Sublevels
In any energy level, The s sublevel has the lowest energy. The s sublevel is followed by the p, d, and f sublevels
in order of increasing energy. Higher sublevels are possible, but only s, p, d, and f
sublevels are needed to hold the electrons in the atoms known today.
36
Orbitals
An orbital Is a three- dimensional space
around a nucleus where an electron is most likely to be found.
Has a shape that represents electron density (not a path the electron follows).
Can hold up to 2 electrons. Contains two electrons that must
spin in opposite directions.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
37
s Orbitals
An s orbital Has a spherical shape
around the nucleus. Increases in size around the
nucleus as the energy level n value increases.
Is a single orbital found in each s sublevel.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
38
p Orbitals
A p orbital Has a two-lobed shape. Is one of three p orbitals that make up each p
sublevel. Increases in size as the value of n increases.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
39
Sublevels and Orbitals
Each sublevel consists of a specific number oforbitals. An s sublevel contains one s orbital. A p sublevel contains three p orbitals. A d sublevel contains five d orbitals. An f sublevel contains seven f orbitals.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
40
Electrons in Each Sublevel
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
41
Pause: ALE 2
Group activity: all groups work on problems on ALE 2 worksheet, problems 11 and 12
Need volunteers to work on the problems written on the board. If no volunteers immediately, will call names. Everyone will do problems on the board sooner or later
While working on the problems, ask if you have any questions. I’m more than happy to help
42
Lecture 2: Atoms and Elements
Electron Configurations
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
43
Energy levels are filled with electrons In order of increasing energy. Beginning with quantum number n = 1. Beginning with s followed by p, d, and f.
Order of Filling
44
Energy Diagram for Sublevels
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
45
An orbital diagram shows Orbitals as boxes in each sublevel. Electrons in orbitals as vertical arrows. Electrons in the same orbital with opposite spins (up
and down vertical arrows).
Orbital diagram for Li
1s2 2s1 2p filled half-filled empty
Orbital Diagrams
46
Order of Filling
Electrons in an atom Fill orbitals in sublevels of the same type with
one electron until half full, Then pair up in the orbitals using opposite spins.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
47
Writing Orbital Diagrams
The orbital diagram
for carbon consists of Two electrons in the 1s
orbital. Two electrons in the 2s
orbital. One electron each in
two of the 2p orbitals
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
48
Write the orbital diagrams for
A. Nitrogen
B. oxygen
C. magnesium
Individual Learning Check
49
An electron configuration Lists the sublevels filling with electrons in order of
increasing energy. Uses superscripts to show the number of electrons
in each sublevel. For neon (10 electrons) is as follows:
number of electrons
sublevel 1s2 2s2 2p6
Electron Configuration
50
Example: Period 1 Configurations
In Period 1, the first two electrons enter the 1s orbital
51
Abbreviated Configurations
An abbreviated configuration shows The symbol of the noble gas in brackets that
represents completed sublevels. The remaining electrons in order of their sublevels,
Example: Chlorine has a configuration of
1s2 2s2 2p6 3s2 3p5
[Ne]
The abbreviated configuration for chlorine is
[Ne] 3s2 3p5
52
Period 2 Configurations
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
53
A. The correct electron configuration for nitrogen is 1) 1s2 2p5 2) 1s2 2s2 2p6 3) 1s2 2s2 2p3
B. The correct electron configuration for oxygen is 1) 1s2 2p6 2) 1s2 2s2 2p4 3) 1s2 2s2 2p6
C. The correct electron configuration for calcium is1) 1s2 2s2 2p6 3s2 3p6 3d2
2) 1s2 2s2 2p6 3s2 3p6 4s2
3) 1s2 2s2 2p6 3s2 3p8
TAPPS Learning Check
54
Write the electron configuration and abbreviated configuration for each of the following elements:
A. Cl
B. S
C. K
TAPPS Learning Check
55
Sublevel Blocks on the Periodic TableThe periodic table consists of sublevel blocks arranged in order of increasing energy.
Groups 1A-2A = s level Groups 3A-8A = p level Groups 3B to 2B = d level Lanthanides/Actinides = f level
56
Sublevel Blocks
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
57
Using the periodic table, write the electron configuration for silicon.
SolutionSilicon is in group 4A, period 3, thus we would stop at
3p and it would have 2 electrons in the 3p orbital:
all the sublevel blocks in order gives:
1s2 2s2 2p63s2 3p2
Writing Electron Configurations
58
The 4s orbital has a lower energy than the 3d orbitals.
In potassium K, the last electron enters the 4s orbital instead of the 3d
1s 2s 2p 3s 3p 3d 4s
Ar 1s2 2s2 2p63s2 3p6
K 1s2 2s2 2p63s2 3p64s1
Ca 1s2 2s2 2p63s2 3p64s2
Sc 1s2 2s2 2p63s2 3p6 3d1 4s2
Ti 1s2 2s2 2p63s2 3p6 3d2 4s2
Electron Configurations d Sublevel
59
Exceptions in Sublevel Block Order
Within the filling of the 3d sublevel, exceptions occur for chromium and copper Both Cr and Cu, in the 3d sublevel, are close
to either a half-filled or filled sublevel Cr has only 1 electron in the 4s and 5 e-s in
the 3d sublevel …half-filled 3d, added stability Cu has 1 e- in 4s and 10 e-s in 3d sublevel …
completely filled 3d, stable After 4s and 3d, 4p is filled
60
Using the periodic table, write the electron configuration for manganese.
Solution1s2 2s2 2p63s2 3p6 4s2 3d5
Writing Electron Configurations
61
A. The last two sublevel blocks in the electron configuration for Co are
1) 3p64s2
2) 4s24d7 3) 4s23d7
B. The last three sublevel blocks in the electron configuration for Sn are
1) 5s25p24d10
2) 5s24d105p2
3) 5s25d105p2
Learning Check
62
Learning Check
Give the symbol of the element that has
A. [Ar]4s2 3d6
B. Four 3p electrons
C. Two electrons in the 4d sublevel
D. The element that has the electron configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d2
63
Pause: ALE 2
Group activity: all groups work on problems on ALE 2 worksheet, problems 12-15
Need volunteers to work on the problems written on the board. If no volunteers immediately, will call names. Everyone will do problems on the board sooner or later
While working on the problems, ask if you have any questions. I’m more than happy to help
64
Lecture 2: Atoms and Elements
Periodic Trends
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
65
Valence Electrons
The valence electrons Determine the chemical properties of the elements. Are the electrons in the highest energy level. Are related to the Group number of the element.
Example: Phosphorus has 5 valence electrons 5 valence electrons
P Group 5A(15) 1s2 2s2 2p6 3s2 3p3
66
All the elements in a group have the same number of
valence electrons.
Example: Elements in Group 2A(2) have two (2) valence electrons.
Be 1s2 2s2
Mg 1s2 2s2 2p6 3s2
Ca [Ar] 4s2
Sr [Kr] 5s2
Groups and Valence Electrons
67
Periodic Table and Valence Electrons
68
Electron-Dot Symbols
An electron-dot symbol Indicates valence electrons
as dots around the symbol of the element.
Of Mg shows two valence electrons as single dots on the sides of the symbol Mg.
. .· Mg · or Mg · or · Mg or ·
Mg
· Electron-dot symbolCopyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
69
Writing Electron-Dot Symbols
The electron-dot symbols for Groups 1A(1) to 4A(14) use single dots.
· · Na · · Mg · · Al · · C ·
· Groups 5A(15) to 7A(17) use pairs and single dots.
· · · · · P · : O · · ·
70
State the number of valence electrons for each:A. O
1) 4 2) 6 3) 8
B. Al
1) 13 2) 3 3) 1
C. Cl
1) 2 2) 5 3) 7
Learning Check
71
State the number of valence electrons for each.
A. 1s2 2s2 2p6 3s2 3p1
B. 1s2 2s2 2p6 3s2
C. 1s2 2s2 2p5
Learning Check
72
Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have the same number of valence electrons (dots).
Example: Atoms of elements in Group 2A(2) each have 2 valence electrons.
2A(2)· Be ·
· Mg ·
· Ca ·
· Sr ·
· Ba ·
73
A. X is the electron-dot symbol for
1) Na 2) K 3) Al
B. X is the electron-dot symbol of
1) B 2) N 3) P
Learning Check
74
Atomic Size
Atomic size is Described using
the atomic radius. The distance from
the nucleus to the
valence electrons.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
75
Atomic Radius Within A Group
Atomic radius Increases going
down each group of representative elements.
Decreases going across each period.
Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings
76
Ionization Energy
Ionization energy Is the energy it takes to remove a valence electron.
Na(g) + Energy (ionization) Na+(g) + e-
77
Ionization Energy
The ionization
energies of
Metals are low
Nonmetals are high
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
78
Pause: Group Work
Do all the problems in group activity 2 as group