CHM 109 SUROVIEC FALL 2015 Atoms and Elements. I. Atoms and Atomic Theory An element is composed of...
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Transcript of CHM 109 SUROVIEC FALL 2015 Atoms and Elements. I. Atoms and Atomic Theory An element is composed of...
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CHM 109SuroviecFall 2015
Atoms and Elements
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I. Atoms and Atomic Theory
An element is composed of tiny particles called atoms All atoms of the same element have the same chemical properties
Compounds are formed when two or more atoms of different element combine
Chemical reactions involve only separation, combination or rearrangement or atoms
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A. Fundamental Laws of Matter
There are three fundamental laws of matter Law of conservation of mass
Law of constant composition
Law of multiple proportions
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A. Law of conservation of mass
In a chemical reaction matter is neither created or destroyed
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B. Law of Definite Proportions
In 1797 Joseph Proust noticed that elements of a given compound always combined in definite proportions in all samples of a compound.
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C. Law of Multiple Proportions
This law asserts that when 2 elements (A&B) form two different compounds, the masses of element B that combine with 1 gram of element A can be expressed as a ratio of small whole numbers.
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D. Atomic Theory
John Dalton explained the 3 previous laws along with his Atomic Theory which states:
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II. Structure of an atom
Atom: basic unit of an element that can enter into chemical combination
Atom possesses structure: Electron Proton Neutron
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A. Electrons
First evidence for subatomic particles came from the study of the conduction of electricity by gases at low pressures J.J. Thomson, 1897 Rays emitted were called cathode rays Rays are composed of negatively charged particles called electrons
Electrons carry unit negative charge (-1) and have a very small mass (1/2000 the lightest atomic mass)
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Cathode Ray Apparatus10
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02_05.JPG11
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III. Structure of the Atom
Since the overall atom is neutral, and we know that they contain electrons they must have a positive particle to balance the atom out.
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II. Structure of the Atoms
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A. Protons and Neutrons – The Nucleus
Ernest Rutherford, 1911Bombardment of gold foil with α particles
Expected to see the particles pass through the foil
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Rutherford Backscattering
Found that some of the alpha particles were deflected by the foil
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B. Current Atomic Model
1. Most of the atom’s mass and all of its positive charge are contained in a small cone called the nucleus
2. Most of the volume of atoms is empty space which is where the electrons are
3. There are as many electrons as protons
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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
If the atom is a football stadium, then the nucleus is a marble on the 50-yard line.
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VI. Proton, Neutron and Electron
Amu = 1/12 the mass of a carbon atom containing 6 protons and 6 neutrons. This makes the proton ~1amu.
The proton and electron have electrical charge
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A. Elements
What makes elements unique is the number of protons, neutrons and electrons in an atom of the element.
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B. Isotopes
All atoms of a given element have same number of protons, but the number of neutrons can change
This means that one element can have different masses.
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B. Isotopes
Atomic number (Z) = number of protons in the nucleus
Mass number (A) = number of protons and neutrons in the nucleus
Isotope = atoms of the same element (X) with different numbers of neutrons in their nuclei
XAZ
Mass Number
Atomic NumberElement Symbol
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Do You Understand Isotopes?
How many protons, neutrons, and electrons are in C14
6 ?
How many protons, neutrons, and electrons are in C11
6 ?
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C. Molecules and Ions
Molecules: aggregate of two or more atoms in a definite arrangement held together by chemical forces
Ion: atom or group of atoms with a net charge due to the loss or gain of electrons.
H2 H2O NH3 CH4
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C. Molecules and Ions
Cation: ion with a positive charge
Anion: ion with a negative charge
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Do You Understand Ions?
How many protons and electrons are in ?Al2713
3+
How many protons and electrons are in ?Se7834
2-
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Polyatomic ions26
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V. Periodic Law and Table
Mendeleev constructed a periodic table based on the elements known at the time.
He noticed that certain groups of elements had similar properties
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A. Ions and Periodic Table
Metals tend to lose electronsNonmetals tend to gain electrons
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VI. Atomic Mass
Since isotopes have different masses for the same element an atomic mass is a weighted average of the isotopes
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VII. Molar Mass
We would like to know the number of atoms in a given mass of atoms.
Since atoms are so small we count them by weight.
A. The Mole.We use a mole to
count the amount of material containing 6.022 x 1023
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B. Mole conversion
Using conversion factors we can convert between moles and atoms.
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C. Moles and Mass
The next question is what is the mass of that many atoms.
It has been determined that the mass of 1 mole of atoms is equal to its atomic mass in amu
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