Chapter 2 Atoms, Molecules, and Ions PDF

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CHEMISTRY 120/121

Chapter 2 Atoms, Molecules and Ions

Overview: 

History of Chemistry

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Notation for Atoms

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Ionization

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Isotopes

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Chemical Bonds

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Periodic Table

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Naming of Simple Compounds

Atoms, Molecules, and Ions – Ch. 2.1 – 2.9 History of Chemistry 

400 B.C., Greek philosophers proposed that all mater was composed of four fundamental substances o ____________________ o ____________________ o ____________________ o ____________________

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Greek philosophers Democritus, proposed the existence of small indivisible pieces that made up ____________________. Democritus named these ultimately small pieces ____________________ meaning “indivisible”. o No experiments to test idea, did not gain acceptance

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2000 years of Alchemy o Attempts to turn metals into gold o Prepared mineral acids and isolated elements such as mercury, sulfur and antimony o Fake Emeralds “Take white lead, one part, and of any glass you choose, two parts, fuse together in a crucible and then pour the mixture. To this crystal, add the urine of an ass and after forty days you will find emeralds.”

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Robert Boyle (1627-1691) was seen as the first “chemist” to perform truly quantitative experiments. o Quantitative behavior of gases o Element cannot be broken down into two or more simpler substances o List of known elements grew o He was not always right 1 J. Zhou Summer 2018

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Georg Stahl (1660-1734), German chemist tried to explain the nature of combustion. o Suggested a substance called phlogiston flowed out of the burning material

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Antoine Lavoisier (1743-1794), French chemist, explained the true nature of combustion. Like Boyle, regarded measurement as essential operation of chemistry. o Suggested that mass is neither created nor destroyed o Law of ____________________ of ____________________

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Joseph Proust (1754-1826), French chemist, showed that a given compound always contains exactly the same proportion of elements by mass o Law of ____________________ ____________________

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John Dalton (1766-1844), English schoolteacher, showed that when two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

o Law of ____________________ ____________________ o 1808 presented his theory of atoms (Marked the beginning of “modern chemistry”) 

Each element is made up of tiny particles called atoms

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The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways

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Chemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms.

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Chemical reactions involve reorganization of the atoms – changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

o Prepared first table of atomic masses, based on the relative masses of elements in known compounds 

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Made many incorrect assumptions

The experimental work of the French chemist Joseph Gay-Lussac in 1808 and the interpretation of these experimental results by Amedeo Avogadro in 1811 paved the way for determination of absolute formulas o Gay-Lussac discovered that when gases formed compounds, they always did so in small whole number ratios, which became to be known as the law of ____________________ ____________________

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o Avogadro hypothesized that at the same ____________________ and ____________________, equal ____________________ of different gases contain the same number of “____________________”

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The hypothesis only makes sense if the space between the particles is very large compared to the size of the particles themselves

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If so, the volume of a gas is determined by the number of particles present, not by the size of the individual particles

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Stanislao Cannizzaro (1826-1910), Italian chemist presented his ideas at the First International Chemical Congress in 1860 o Accepted that compounds contained whole numbers of atoms as Dalton suggested and that Avogadro’s hypothesis was correct – equal volumes of gases under the same conditions contain the same number of molecules o Presented his ideas: 

Assigned the H2 molecule a relative mass of 2

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Measured the relative molecular masses of a large number of compounds

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Led to approximate values of the relative atomic masses

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J.J. Thomson (1856-1940), English physicist, performed the first important experiment that led to an understanding of the composition of the atom o Experimented with Cathode-ray tubes and determined the charge-to-mass ratio of an electron

o Proposed the first atomic model: ____________________ distributed randomly in a diffuse ____________________ cloud

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Robert Millikan (1868-1953) determined the charge of an electron

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In 1896 French scientist Antoine Henri Becquerel found a mineral containing uranium can produce an image on a photographic film in the absence of light. His student, Marie Curie (Founder of Radioactivity) called it radioactivity. o Certain elements spontaneously produce high energy of radiation o 3 types of radiation 

____________________ ____________________ (γ): high energy light

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____________________ ____________________ (β): high speed electrons

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____________________ ____________________ (α): 2+ ion (mass 7300 x larger than the electron

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Ernest Rutherford (1871-1937) performed experiments to deduce something about the distribution of electrons in the atom o Bombarded gold foil with high energy α particles (+ve)

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o This experiment led to the following conclusions: 

Atom is mostly ____________________ ____________________

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Massive positive center (____________________) containing protons and neutrons

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Electrons moved around the nucleus at a relatively large distance

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An atom is neutral (equal number of electrons and protons)

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Notation for Atoms

Where X= Z= A= # of neutrons = 

All atoms of the same ____________________ have the same number of ____________________ and ____________________ but they can have different number of neutrons

Example: Indicate the number of protons, neutrons, and electrons and nucleons in

Ionization 

Process by which an atom or a molecule acquires a negative or positive charge by gaining or losing an electron to form ions

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When the atom loses or gains electrons it’s identity won’t change but becomes an ion

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Neutral species gaining 1 or more electrons: Negative ion – anion O

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+ 2e-

 O2-

Losing 1 or more electrons from a neutral species: Positive ion – cation Li



Li+ + e-

Example: Write an appropriate symbol for the species consisting of 29 protons, 34 neutrons, and 27 electrons.

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Isotopes 

Atoms of the same element with different number of neutrons are called ____________________. e.g. There are three isotopes for hydrogen

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In nature, most elements contain a mixture of isotopes.

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The percentage of an isotope occurring in a natural sample of an element is called its ____________________ ____________________. o The sum of the percentages of the specific isotopes must add up to 100%. e.g. Chlorine gas is mainly composed of two isotopes, 35Cl and 37Cl

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The relative atomic mass is the weighted average of the isotopic masses.

*Atoms that have the same mass number but different atomic number are known as ____________________.

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Chemical Bonds 

Chemical bonds are the forces that hold atoms together in compounds.

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____________________ Bonds o Two atoms share one or more pairs of electrons o Atoms in molecules are held together by covalent bonds o A molecule is the simplest particle or unit that represents that pure substance o Tend to form between nonmetallic elements eg; CO2, H2O, NO2

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____________________ Bonds o Result from the electrostatic attraction between oppositely charged ions o Na+ + Cl- form ____________________, sodium chloride o NH4+ and SO42- combine to form ____________________, ammonium sulfate o Ionic solids have a geometrical arrangement of ions that maximizes the attraction between opposite charges and minimizes the repulsion between like charges o Metallic atoms tend to form cations o Nonmetallic atoms tend to form anions o Tend to form between a combination of a metal plus a non-metal (or two polyatomic ions)

Periodic Table 

Arrangement of known elements in order of increasing atomic number

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Leads to a natural grouping of elements of similar chemical properties

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Metallic elements are on the left side of the Periodic table

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Non metallic elements are on the right side

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The majority of elements are metallic

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Naming Simple Compounds 

You are expected to review chemical nomenclature (i.e. naming simple compounds – section 2.9)

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In addition to reviewing the general procedure for naming the different classes of compounds in section 2.9, you are required to know the following: o The first 36 elements by name and symbol o The ions in tables 2.3, 2.4 (only the systematic name) and 2.5; note that some of the ions are based on parent elements that are beyond the first 36 elements and you are required to know them o The prefixes used to denote the number of atoms present in binary covalent (i.e. molecular) compounds in table 2.6 o The acids in tables 2.7 and 2.8

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