Sep 23, 2011 ... particles called atoms. 2. Atoms are indivisible, they cannot be created or .... were
arranged based of three common traits: 1. Atomic Mass. 2.
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Chapter 5
Atomic Theory: The Nuclear Model of the Atom
Review Dalton’s Atomic Theory Some key laws Dalton knew: Law of Definite Composition the percentage of each element in a compound is the same regardless of its mass Law of Conservation of Mass in a chemical change, mass is conserved
Dalton’s Atomic Theory The theory is stated in 5 statements: 1. Each element is made up of tiny, individual particles called atoms. 2. Atoms are indivisible, they cannot be created or destroyed. 3. All atoms of each element are identical in every respect. 4. Atoms of one element are different from atoms of any other element. 5. Atoms of one element may combine with atoms of other elements, usually in the ratio of small, whole numbers, to form chemical compounds.
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Illustration Dalton’s Atomic Theory
Illustration of statements of Dalton’s Atomic Theory
Applications Dalton’s Atomic Theory In a chemical reaction: Each reacting substance(s) contain a certain number of atoms of different elements. As the reaction proceeds, the atoms are rearranged to form the product(s). The atoms are neither created nor destroyed, but arranged differently.
Law of Multiple Proportions When two elements combined to form more than 1 compound, different weights of one element that contains the same weight of the other element are in a simple ratio of whole numbers.
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Subatomic Particles During the 19th century, although Dalton’s atomic theory was getting accepted by the community, experiments would challenge it as scientists would prove there are smaller particles present in an atom. 1. Michael Faraday and William Crooks among the many scientists discovered the electron. However, Thomson was the scientist who discovered the properties of the electron. Mass of an electron = 9.109 x 10-28 g (0 u) Electrical Charge = -1 Symbol = e-
Subatomic Particles (cont’d) 2.
Ernest Rutherford is primary responsible for the discovery of the proton. Mass of an proton = 1.673 x 10-24 g (1u) Electrical Charge = +1 Symbol = p+ 3. James Chadwick is responsible for the discovery of the neutron. Mass of an neutron = 1.675 x 10-24 g (1u) Electrical Charge = 0 Symbol = no Overall, atoms of all elements are comprised of electrons, protons, and neutrons. All of these are subatomic particles.
Rutherford’s Experiment The complete understanding about the composition of an atom for a typical element were performed in the early 20th century by Ernest Rutherford, Hans Geiger, and Ernest Marsden. This would be known as the Gold-Foil Experiment.
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Gold-Foil Experiment
Figure 5.3-Rutherford scattering experiments.
Figure 5.4-Relative sizes of an atom and its nucleus. The diameter of an atom is approximately 10000 time the diameter of its nucleus.
Conclusions Gold-Foil Experiment From these studies, the conclusions are as follows: 1. Most of the mass of an atom is confined in the nucleus. 2. Most the atom’s volume is empty and other than the nucleus, electrons are moving around the nucleus in the atom. 3. For a neutral atom, the number of protons inside the nucleus must equal the number of electrons surrounding the nucleus in the atom.
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Isotopes An isotope is defined as a species which has the same atomic number but different atomic mass. Mass Number = # of protons + # of neutrons Atomic Number = # of protons
Isotopes (EXPRESSION) When writing an isotope, it is written in this format:
Mass Number
Atomic Number
A ZX
Nuclear Symbol
Practice Question Which of the following pairs is illustrates an isotope? Circle your answer.
3 3 7 Li & 6 Li
14 12 N & 7 6C 7 6 Li & 3 3 Li
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Practice Question Fill in the table below. Name of Element
Atomic Z
Number of Protons
Number of Neutrons
Mass Nuclear Number, Symbol A
56
56
82
138
Elemental Number, Symbol
Barium Ba
Name of Isotope
138 barium56 Ba 138
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Nitrogen
12
25 Indium111
Atomic Masses The atomic mass for each element is defined in units of amu. amu is for atomic mass unit and is defined as the mass of 1/12 of a carbon-12 isotope. 1 amu = 1.66 x 10-24 g A carbon-12 isotope has 6 protons and 6 neutrons. 12 u ∼ 12 nuclear subatomic particles 1 u ∼ 1 nuclear subatomic particle
Percentage Abundance of Some Natural Isotopes Symbol 1H 2H 12C 13C 39K 40K 41K
Mass (u) 1.007825035 2.014101779 12 (exactly) 13.003354826 38.9637074 39.9639992 40.9618254
Percent 99.9885 0.0115 98.93 1.07 93.2581 0.0117 6.7302
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Atomic Mass One can accurately observe the various stable isotopes of an element by perform a mass spectroscopy. Each stable isotope is provided on the chromatograph along with its natural abundances in percentage. Figure 5.5-Mass spectrum of neon (1+ ions). The relative abundance is the percentage of each isotope found in a natural sample of the pure element.
Calculation Atomic Mass To calculate the average atomic mass of an element, the following formula is utilized: Atomic Mass =
Percent Abundance × Isotope Mass1 + 100 Percent Abundance × Isotope Mass 2 + 100 Percent Abundance × Isotope Mass3 + .... 100
Sample Calculation Atomic Mass Calculate the average atomic mass for a chlorine atom with the following information: Atomic Mass(u) Percent Chlorine-35 34.968852721 75.78 Chlorine-37 36.96590262 24.22 Atomic Mass = 75.78 24.22 × 34.968852721u + × 36.96590262 u = 35.45253821u 100 100
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Periodic Table (History) The development of the first periodic tables were arranged based of three common traits: 1. 2. 3.
Atomic Mass Physical Properties Chemical Activity
Based on these traits, the scientists who are primary responsible for the modern periodic table we are familiarize with are Dmitri Mendeleev and Julius Meyer.
Figure 5.6-Periodic Table of the elements
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Periodic TABLE (Vocabulary) A set of elements arranged vertically is called a group or chemical families. GROUPS are indicated by a number and a letter. An array of elements arranged horizontally is called a period. PERIODS are indicated on the left side of the periodic table by numerical number behind group IA column.
Periodic TABLE (Vocabulary) Elements whose group number end in A are main group elements or representative elements. Elements whose group number end in B are transition elements or transition metals.
Periodic TABLE (Group Names) Group IA - Alkali Metals Group IIA - Alkaline Earth Metals Group VIIA - Halogens Group VIIIA - Noble Gases For the other main groups, the name of the family is based on the first element in the column. (i.e. Group IIIA-Boron Family, Group IVA-Carbon Family)
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METALS
NONMETALS
Summary PERIODIC TABLE If you are provide the group, period or other relevant information, one can identify the element. EXAMPLE: The name of an element whose a halogen and is located in period 3. (ANSWER: Cl or chlorine) Try these. Identify the element (name or symbol) for the following given information: a. group IVA, period 4 b. group IIIA, atomic number ≥ 31 c. an alkaline earth metal whose atomic number = 4
Periodic Table It is important that you get familiarize to the periodic table for common elements used frequently in chemistry. It is important to know the element name and connect it to its chemical symbol along with their respective group and period on the periodic table. Also, know by its chemical symbol the atomic number and its average atomic mass.
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Periodic Table
Figure 5.8 (a) Table of common elements, with symbols and atomic numbers.
Periodic Table (cont’d)
Figure 5.8 (b) Partial periodic table showing the symbols and locations of the more common elements
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