Transcript of Unit 3 - Elements, Atoms and Ions 1.The Elements 2.Symbols for Elements 3.Dalton’s Atomic Theory...
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- Unit 3 - Elements, Atoms and Ions 1.The Elements 2.Symbols for
Elements 3.Daltons Atomic Theory 4.Formulas of Compounds
5.Structure of the Atom 6.Modern Concept of Atomic Structure
7.Isotopes 8.Introduction to the Periodic Table 9.Natural States of
Elements 10.Ions 11.Compounds That Contain Ions pages 82-113 1
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- Unit 3 - Elements, Atoms and Ions Upon completion of this unit,
you should be able to do the following: 1.Determine the number of
protons, neutrons and electrons in an atom based on the element
name or the atomic number and atomic mass. 2.Write the symbols of
common elements and write the names of common elements given their
symbols. 3.Differentiate between a chemical symbol and a chemical
formula. 4.Explain the significance of subscripts. 5.Given a
formula, state the number of atoms of each element present. 6.Use
the periodic table to predict the charge and formula of a monatomic
ion. 7.Use the periodic table to identify metals and non-metals.
8.Use the periodic table to identify alkali metals, alkaline earth
metals, halogens and noble gases. 2
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- Element a substance that cannot be broken down into other
substances by chemical methods. Sometimes chemists use the word
element is used to mean a single atom of that element. This is the
microscopic form. Other times the word element is used to mean a
sample large enough to weigh on a balance. This is the macroscopic
form. The term element is also used in generic form. When we say
the human body contains sodium, that does not mean elemental sodium
is present, rather atoms of some form of sodium are present. The
Elements 3
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- Currently there are 118 elements, 88 of which occur naturally.
The 9 most abundant elements listed below account for 98% of the
mass of the earths crust. ElementMass Percent Oxygen (O)49.2
Silicon (Si)25.7 Aluminum (Al)7.50 Iron (Fe)4.71 Calcium (Ca)3.39
Sodium (Na)2.63 Potassium (K)2.40 Magnesium (Mg)1.93 Hydrogen
(H)0.87 The Elements 4
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- Symbols are used as abbreviations for element names One or two
letters in symbol First letter is upper case, second letter is
lower case Origin of some symbols come from Greek or Latin name The
symbol for lead is Pb from the Latin word for heavy, plumbum. The
name for bromine comes from a Greek word meaning stench. Table 4.3
on page 87 lists 44 common elements with their symbols memorize
them Symbols for Elements 5
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- The Elements Song The Elements Song by Tom Lehrer Harvard
scientist and musician Background song set to the tune of The Very
Model of a Modern Major-General from The Pirates of the Penzance by
Gilbert and Sullivan Daniel Radcliffe version Karaoke - Your Turn
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- Daltons Atomic Theory 1.Most natural materials are mixtures of
pure substances. 2.Pure substances are either elements or
combinations of elements called compounds. 3.A given compound
always contains the same proportions (by mass) of the elements.
This is known as the law of constant composition. For example,
water always contains 8 grams of oxygen for each gram of hydrogen.
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- Daltons Atomic Theory 1.Elements are made of tiny particles
called atoms. 2.All atoms of a given element are identical. 3.The
atoms of a given element are different from those of any other
element. 4.Atoms of one element can combine with atoms of other
elements to form compounds. A given compound always has the same
relative numbers and types of atoms. 5.Atoms are indivisible in
chemical processes. Atoms are not created or destroyed in chemical
reactions. The reaction only changes the way the atoms are grouped
together. 8
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- Formulas of Compounds Compound a distinct substance that is
composed of the atoms of two or more elements and always contains
exactly the same relative masses of those elements. A compound can
be broken down into those elements by chemical methods. Example
Water (H 2 O) can be broken down into hydrogen and oxygen. Water
always contains 2 hydrogen atoms for each oxygen atom. 9
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- Formulas of Compounds A chemical formula expresses the types of
atoms and numbers of each atom in a given compound. Water has 2
atoms of hydrogen for each atom of oxygen. The chemical name for
table salt is sodium chloride. The chemical formula for sodium
chloride is NaCl. It contains 1 atom of sodium and 1 atom of
chlorine. 10
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- Formulas of Compounds Rules for writing formulas 1.Each atom
present is represented by its element symbol. 2.The number of each
type of atom is indicated by a subscript written to the right of
the element symbol. 3.When only 1 atom of a given type is present,
the subscript 1 is not written. Page 90, example 4.1 Self check
exercise 4.1 11
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- Structure of the Atom Scientists believed that elements
consisted of atoms and that compounds are a specific collection of
atoms bound together in some way. But what is an atom like? Does it
consist of smaller parts, and if so, what are the subatomic
particles? Video 1 - Atoms and the Periodic Table Video 2 - J.J.
Thomson and the electron Video 3 - Ernest Rutherford and the
nucleus 12
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- Structure of the Atom 13
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- Structure of the Atom Atoms consist of: Electron a negatively
charged particle Proton a positively charged particle, same size of
charge as an electron, but positive Neutron a neutral particle with
a mass relatively close to that of proton Protons and neutrons are
located in a small dense center called the nucleus. Most of the
mass of an atom is due to the nucleus. Electrons are located
outside of the nucleus in a negatively charged cloud. Most of the
volume of an atom is due to the electrons. 14
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- Modern View of Atomic Structure If all atoms are composed of
the same components, why do different atoms have different chemical
properties? The answer lies in the number and arrangement of the
electrons. The space in which the electrons move accounts for most
of the atomic volume. The electrons are the parts of the atom that
intermingle when atoms combine to form molecules. The number of
electrons a given atom possesses greatly affects the way it can
interact with other atoms. 15
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- Modern View of Atomic Structure 1 Angstrom = 1 x 10 -10 meters
Electron cloud 16
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- Isotopes The identity of an element is determined by the number
of protons it has. The number of protons is called the atomic
number. Isotopes of an element have the same number of protons, and
therefore the same atomic number, but different numbers of
neutrons. The total number of protons and neutrons in an atom is
called the mass number. The mass number is used in naming to
identify isotopes, such as Carbon-14, which has a mass number of
14. Carbon-12 has a mass number of 12. 17
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- Isotopes Ag Silver 47 Z, atomic number = Number of protons 108
A, mass number = Number of protons and neutrons X, element symbol
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- Isotopes Iodine - 127; 53 protons, 74 neutrons
Iodine-123Iodine-123 (half-life 13 hours) is the isotope of choice
for nuclear medicine imaging of the thyroid gland, which naturally
accumulates all iodine isotopesnuclear medicine HW - Page 117-118
Problems 38 and 42 19
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- Metals Good conductors of heat and electricity Shiny (have
luster) Malleable - can be hammered into sheets Ductile - can be
drawn into wires 21
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- Nonmetals Good insulators (absorb electricity) Dull appearance
Most are gases or easily vaporized solids and liquids Solids are
brittle 22
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- Metalloids Exhibits some properties of both metals and
nonmetals. 23
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- Groups All elements in a group have similar chemical
properties. Group 1 Alkali Metals Group 2 Alkaline Earth Metals
Groups 3-12 Transition Metals Group 17 Halogens Group 18 Noble
Gases 24
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- Natural State of Elements Gas Liquid Solid 25
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- Diatomic Molecules Mnemonic to help remember - H 2, I 2, N 2,
Cl 2, Br 2, O 2, F 2 HINClBrOF Or 7 from 7 + H 26
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- Ions An atom has a certain number of protons in its nucleus and
an equal number of electrons in the space around the nucleus,
giving the atom a net zero charge. Adding or removing an electron
from a neutral atom will create a charged ion. Ions are always
formed by adding or removing electrons, not by changing the number
of protons. 27
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- A positive ion, called a cation, is produced when an atom loses
one or more electrons. Na Na + + e - A cation is named using the
name of the parent atom. Na + is called the sodium ion. Ions
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- A negative ion, called an anion, is produced when an atom gains
one or more electrons. Cl + e - Cl - An anion is named by taking
the root name of the atom and changing the ending. Cl - is called
the chloride ion. Ions 29
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- Similarly, other Group 17 nonmetals gain one electron to form
anions. The fluorine anion is called fluoride, the bromine anion is
called bromide and the iodine anion is called iodide. Oxygen and
sulfur add two electrons to form anions. The oxygen anion is called
oxide and the sulfur anion is called sulfide. Ions 30
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- Atoms do not form ions on their own. Most commonly, ions are
formed when metallic elements combine with nonmetallic elements.
When metals and nonmetals react, the metal atoms tend to lose one
or more electrons, which are gained by the atoms of the nonmetals.
Reactions between metals and nonmetals tend to form compounds that
contain metal cations and nonmetal anions. Ions 31
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- Group 1 metals form ions with a +1 charge Group 2 metals form
ions with a +2 charge Group 13 metals form ions with a +3 charge
Many Group 3-12 metals form ions with multiple charges Group 17
atoms form ions with a -1 charge Group 16 atoms form ions with a -2
charge Metals always form cations. The tendency to lose electrons
is a fundamental characteristic of metals. Ions 32
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- Sodium Chloride example NaCl is a solid and does not conduct
electricity Pure (distilled) water does not conduct electricity
NaCl dissolved in water does conduct electricity Why? Compounds
that contain Ions 33
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- Electric current can travel when electrons are free to move. In
ionic substances, ions carry the current Substances that contain
ions can conduct an electric current only if the ions can move.
Distilled water contains no ions. When NaCl is dissolved in water
it ionizes and the electrons are free to move. Compounds that
contain Ions 34
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- Whenever a compound is formed between a metal and non-metal, it
can be expected to contain ions. These substances are called ionic
compounds. A chemical compound must have a net charge of zero.
There must be positive ions (cations) and negative ions (anions)
present. The number of cations and anions must result in a net
charge of zero. When writing the formula for a compound, the cation
is always written first. Use subscripts to balance charges on
compounds. Compounds that contain Ions 35
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- Writing Formulas Examples:Na + + Cl - NaCl Mg 2+ + Cl - MgCl 2
Al 3+ + Cl - AlCl 3 Li + + N 3- Li 3 N PracticeCa 2+ + Cl - Na + +
S 2- Ca 2+ + P 3- Homework Page 119 problems 76, 78, 84 Compounds
that contain Ions 36