1 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)
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1 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.
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1
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 …
• 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
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
Atoms contains subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral Coulomb's law: Like charges repel
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
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.
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
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.
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
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.