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Physical Science Chapter 17
Properties of Atoms and the Periodic Table
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Unit 4 The Nature of Matter
CLE: 32020.1.2.
Describe the structure and arrangement of atomic particles.
17:1 Structure of the Atom
• Scientists have developed their own shorthand for dealing with long, complicated names.
• Chemical symbols consist of one capital letter or a capital letter plus one or two smaller letters.
17:1 Scientific Shorthand
Elements are abbreviated in scientific shorthand—first letter or two of element’s name.
DefinitionofAtoms 2.11
17:1 The Scientific Shorthand
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• For some elements, the symbol is the first letter of the element's name.
• For other elements, the symbol is the first letter of the name plus another letter from its name.
• Because scientists worldwide use this system, everyone understands what the symbols mean.
17:1 Structure of the AtomAtomic Compounds
Aluminum…Al
Calcium……Ca
Carbon…….C
Chlorine……Cl
Copper…….Cu
Fluorine……F6
Gold………Au
Helium……He
Hydrogen…..H
Iodine………I
Iron………FeMagnesium..Mg
Memorize These. There will be quizzes often over the element and their symbols. STUDY.
17:1 Structure of the AtomAtomic Compounds
Mercury….Hg
Nitrogen….N
Oxygen……O
Potassium….K
Silver………Ag
Sodium…….Na7
Lead………..Pb
Radium……Ra
Chromium...Cr
Zinc………Zn
Neon………Ne
Platinum…..Pt
Sulfur………SMemorize These. There will be quizzes often over the element and their symbols. STUDY.
17.1 Irregular Chemical Symbols
The chemical symbols for the following elements are not abbreviations of their English names.
Copper is Cu, for cuprum.Gold is Au for aurum.Iron is Fe for ferrum.Lead is Pb for plumbum.Tin is Sn for stannum.Mercury is Hg for hydrargyrum.
Silver is Ag for argentum.Sodium is Na for natrium.Potassium is K for kalium. Antimony is Sb for stibium and Tungsten is W for wolfram.
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17:1 Structure of the Atom
• An element is matter that is composed of one type of atom. An atom is the smallest piece of matter that still retains the properties of the element.
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• Atoms are composed of particles called protons, neutrons, and electrons.
• Protons and neutrons are found in a small positively charged center of the atom called the nucleus that is surrounded by a cloud containing electrons.
• Protons are particles with an electrical charge of 1+.
17:1 Atomic Components
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• Protons and neutrons are made up of smaller particles called quarks.
17.1 Quarks—Even Smaller Particles
• So far, scientists have confirmed the existence of six uniquely different quarks.
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17:1 Atomic Components
• Electrons are particles with an electrical charge of 1–.
• Neutrons are neutral particles that do not have an electrical charge.
LookingInside2.34
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• Scientists theorize that protons are made of three quarks held together with the strong nuclear force.
• Another arrangement of three quarks produces a neutron.
17.1 Quarks—Even Smaller Particles
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17.1 Quarks—Even Smaller Particles
Protons and neutrons are made up of smaller particles called quarks.
Six quarks are known to exist; the sixth is called the top quark. 14
Quarks are studied by colliding accelerated charged particles with protons, which leave tracks in a bubble chamber.
• Scientists and engineers use models to represent things that are difficult to visualize—or picture in your mind.
17:1 Models—Tools for Scientists
Structure of the AtomStructure of the Atom
• Scaled-down models allow you to see either something too large to see all at once, or something that has not been built yet.
• Scaled-up models are often used to visualize things that are too small to see.
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• To study the atom, scientists have developed scaled-up models that they can use to visualize how the atom is constructed.
17.1 Models—Tools for Scientists
Scientists use scaled-up models to represent atoms.
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• In the 1800s, John Dalton, an English scientist, was able to offer proof that atoms exist. Dalton use a sphere as an early model of the atom.
17.1 The Changing Atomic Model
• Another famous Greek philosopher, Aristotle, disputed Democritus's theory and proposed that matter was uniform throughout and was not composed of smaller particles.
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• By 1926, scientists had developed the electron cloud model of the atom that is in use today.
17.1 The Electron Cloud Model
• An electron cloud is the area around the nucleus of an atom where its electrons are most likely found.
• The electron cloud model shows electrons traveling around in specific energy levels around a nucleus of protons and neutrons.
StructureofAtoms2.42
Section CheckSection Check
Question 1
A. atomB. quarkC. neutronD. proton
Which is the smallest piece of matter that still retains the property of the element?
Answer
The answer is A. An atom is the smallest piece of matter that still retains the property of the element.
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Question 2
A. protons and electrons
B. protons and neutronsC. neutrons and electronsD. quarks and electrons
What particles are found in the nucleus of an atom?
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Answer
The answer is B. Electrons are located in an electron cloud surrounding the nucleus of the atom.
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Question 3
What is the name of the small particles that make up protons and neutrons?
Answer
Protons and neutrons are made of smaller particles called quarks.
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17.2 Atomic Mass
• The nucleus contains most of the mass of the atom because protons and neutrons are far more massive than electrons.
• The mass of a proton is about the same as that of a neutron.
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17.2 Atomic Mass
• The mass of each proton and neutron is approximately 1,836 times greater than the mass of the electron.
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• The unit of measurement used for atomic particles is the atomic mass unit (amu).
• The mass of a proton or a neutron is almost equal to 1 amu.
• The atomic mass unit is defined as one-twelfth the mass of a carbon atom containing six protons and six neutrons.
17.2 Atomic Mass
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17.2 Protons Identify the Element
• The number of protons tells you what type of atom you have and vice versa. For example, every carbon atom has six protons. Also, all atoms with six protons are carbon atoms.
• The number of protons in an atom is equal to a number called the atomic number.
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17.2 Mass Number
• The mass number of an atom is the sum of protons and neutrons in the nucleus of an atom.
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17.2 Mass Number
• If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons.
number of neutrons = mass number – atomic number
Atomic Mass2.09
Atomic Number2.55
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Summary
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Learn These Facts.
Do the Practice Problems Now.
1. The atomic number is the number of protons.2. The number of protons is equal to the number
of electrons.3. The number of neutrons is the mass number
minus the protons.4. The number of neutrons plus the number of
protons is the mass number.5. The elements on the periodic table are
arranged by atomic numbers.
Element Symbol Atomic # Atomic Mass
# P #N #E
Helium He 2 4
Magnesium 12 12Zinc 30 65
Bromine 80 35
Aluminum 13 14
Uranium U 146 92
Sodium 11 12
Krypton 48 36
Calcium 40 20
Silver 47 61
2 2 2Mg 24 1212
Zn 303530
Br453535
Al 132713 92 92238
Na 23 11 11
36Kr 36 84Ca 20 20 20Ag 47 108 47 34
Calculate the atomic mass of these compounds. The unit for atomic mass is
amu (atomic mass unit).
1. PbO
2. CuO
3. HCl
4. SO2
5. Al2O3
6. ZnCl3
Copy these problems into your notebook. Begin now. If you don’t finish, this is your homework for tonight.
1. Pb = 207.2 x 1 = 207.2
O = 15.999 x 1 = 15.999
223.199 amu
2. Cu = 63.546 x 1 = 63.546
O = 15.999 x 1 = 15.999
79.545 amu
PbO
CuO
3. H = 1.008 x 1 = 1.008
Cl = 35.453 x 1 = 35.453
36.461 amu
4. S = 32.065 x 1 = 32.065
O2 = 15.999 x 2 = 31.998
64.063 amu
HCl
SO2
5. Al = 26.982 x 2 = 53.964
O3 = 15.999 x 3 = 47.997
101.961 amu
6. Zn = 65.409 x 1 = 65.409
Cl3 = 35.453 x 3 = 106.359
171.768 amu
Al2O3
ZnCl3
• Not all the atoms of an element have the same number of neutrons.
• Atoms of the same element that have different numbers of neutrons are called isotopes.
17.2 Isotopes
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• Models of two isotopes of boron are shown. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different.
• You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11.
17.2 Isotopes
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Isotopes1. Different isotopes have different properties.
2. Number of neutrons is equal to mass number minus atomic number.
3. Name of element followed by mass number identifies the isotope.
4. Average atomic mass is the weighted-average mass of an element’s isotopes.
5. Average atomic mass is closest to its most abundant isotope.
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17.2 Isotopes
• The average atomic mass of an element is the weighted-average mass of the mixture of its isotopes.
• For example, four out of five atoms of boron are boron-11, and one out of five is boron-10.
• To find the weighted-average or the average atomic mass of boron, you would solve the following equation:
Isotopes4.18
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Section CheckSection Check
Question 1
How is the atomic number of an element determined?
Answer
The atomic number of an element is equal to the number of protons in an atom of that element.
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Question 2
The element helium has a mass number of 4 and atomic number of 2. How many neutrons are in the nucleus of a helium atom?
Answer
Recall that the atomic number is equal to the number of protons in the nucleus. Since the mass number is 4 and the atomic number is 2, there must be 2 neutrons in the nucleus of a helium atom. 41
Question 3
How much of the mass of an atom is contained in an electron?
Answer
The electron’s mass is so small that it is considered negligible when finding the mass of an atom.
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Organizing the Elements
• Periodic means "repeated in a pattern."
• In the late 1800s, Dmitri Mendeleev, a Russian chemist, devised the first periodic table based on atomic masses.
17.3 The Periodic Table
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Organizing the Elements 17.3 The Periodic Table
• Because the pattern repeated, it was considered to be periodic. Today, this arrangement is called a periodic table of elements.
• In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties.
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Mendeleev’s Predictions17.3 The Periodic Table
• Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties.
• Mendeleev looked at the properties and atomic masses of the elements surrounding these blank spaces. His periodic table was arranged based on atomic mass.
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17.3 Improving the Periodic Table
• In 1913, the work of Henry G.J. Moseley, a young English scientist, made an arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses.
• The current periodic table uses Moseley's arrangement of the elements.
UsingtheModernPT6.24
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17.3 Electron Cloud Structure
• In a neutral atom, the number of electrons is equal to the number of protons.
• Therefore, a carbon atom, with an atomic number of six, has six protons and six electrons.
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17.3 Electron Cloud Structure
• Scientists have found that electrons within the electron cloud have different amounts of energy.
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17.3 Electron Cloud Structure
• Scientists model the energy differences of the electrons by placing the electrons in energy levels.
17.3 Electron Cloud Structure
• Energy levels nearer the nucleus have lower energy than those levels that are farther away.
• Electrons fill these energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus).
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17.3 Electron Cloud Structure
• Elements that are in the same group have the same number of electrons in their outer energy level.
• It is the number of electrons in the outer energy level that determines the chemical properties of the element.
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17.3 Energy Levels
• For example, energy level one can contain a maximum of two electrons.
• Energy level 2 can contain at most eight electrons.
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17.3 Energy Levels
Each row in the periodic table ends when an outer energy level is filled.
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Atomic Mass 17:2 Masses of Atoms
Electron Dot Diagrams
• Elements that are in the same group have the same number of electrons in their outer energy level.
• These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed.
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Electron Dot Diagrams
• An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level.
• Electron dot diagrams are used also to show how the electrons in the outer energy level are bonded when elements combine to form compounds.
• Not all elements will combine readily with other elements.
• The elements in Group 18 have complete outer energy levels.
• This special configuration makes Group 18 elements relatively unreactive.
Same Group—Similar Properties
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17.3 Regions on the Periodic Table
• The periodic table has several regions with specific names.
• The horizontal rows of elements on the periodic table are called periods.
• The elements increase by one proton and one electron as you go from left to right in a period.
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17.3 Improving the Periodic Table • The vertical columns in the periodic
table are called groups, or families, and are numbered 1 through 18.
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Copy this to your notes.
• All of the elements on the left side of the table are metals.
17.3 Regions on the Periodic Table
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Elements are classified as metals, nonmetals and metalloids.
• Those elements on the right side of the periodic table, in yellow, are classified as nonmetals.
17.3 Regions on the Periodic Table
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17.3 Regions on the Periodic Table
• The elements located on the stair-step dividing line are metalloids.
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A Growing Family
• In 1994, scientists at the Heavy-Ion Research Laboratory in Darmstadt, Germany, discovered element 111.
• Element 112 was discovered at the same laboratory.
• Both of these elements are produced in the laboratory by joining smaller atoms into a single atom.
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Elements in the Universe
• The same elements exist throughout the universe. Elements are synthesized in laboratories all over the world.
• Hydrogen and helium are the building blocks of other elements.
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Elements in the Universe
• Exploding stars, or supernovas, give scientists evidence to support this theory.
• Many scientists believe that supernovas have spread the heavier elements throughout the universe.
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Calculation—Atomic Mass
To calculate the atomic mass of a compound, add the atomic mass of each atom.
Example FeBr3
Fe = 55.845 x 1 =55.85
Br = 79.904 x 3 = 239.712
239.712 + 55.85 = 296.557 amu72
18:3 The Periodic Table
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Calculate the average atomic mass of these compounds.
1. Ca(NO2)4 4. NaCl
2. 2(H2SO4) 5. BaCl2
3. H2O 6. C6H12O6
Ca x 1 =40.078N x 4 = 56.028O x 8 = 127.992
224.098
H x 4= 4.032 S x 2 =64.130O x 8 =127.992 196.154
H x 2 = 2.016O x 1 =15.999 18.015
Na x 1 = 22.990Cl x 1 = 35.453 58.443
Ba x 1=137.327 Cl x 2 70.906 208.233
C x 6 = 72.066H x 12 =12.096O x 6 = 95.994 180.156
Section CheckSection Check
Question 1
How are the elements arranged in the periodic table?
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Answer
The elements are arranged by increasing atomic number and by changes in physical and chemical properties.
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Question 2
What do the elements in a vertical column of the periodic table have in common?
Answer
The vertical columns in the periodic table are called groups; elements in the same group have similar properties, such as electrical conductivity.
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Question 3
What do the dots in this electron dot diagram represent?
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Answer
The dots represent the electrons in the outer energy level.
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17. Review
• The central core of an atom is called the ______.
• The chart showing the classifications of elements according to their properties and increasing atomic numbers is called the __________.
nucleus
periodic table.
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17. Review
The mass of a ________ is about equal to the mass of a proton.
Elements arranged in vertical columns in the periodic table are called _______.
neutron
groups
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17. Review
The region around the nucleus occupied by the electrons is called ________.
The symbol for chlorine is ________.
Electron cloud
Cl
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17. Review
The maximum number of electrons in the second energy level of an atom is ________.
Two isotopes of carbon are carbon -12 and carbon 14. These isotopes differ from one another by two ________.
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neutrons
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17. Review
Metals are ___ conductors of heat and electricity.
Scientists believe that naturally occurring elements are manufactured within ____.
good
stars
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17. Review
So far, scientists have confirmed the existence of ___ different quarks.
In 1926, scientists developed the ____ model of the atom that is used today.
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Electron cloud
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17. Review
Electron ____ are used to show how electrons in the outer energy level are bonded when elements combine to form compounds.
The atomic number of an element is determined by its number of ____.
Dot diagrams
protons
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17. Review
According to present atomic theory, the location of an ____ in an atom cannot be pinpointed exactly.
Moving from left to right in a row of the periodic table, metallic properties _____.
electron
decrease
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17. Review
Each inner energy level of an atom has a maximum number of ____ it can hold.
Dot diagrams are used to represent____.
electrons
Outer level electrons
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17. Review
Particles of matter that make up protons and neutrons are ____.
A chemical symbol represents the ____ of an element.
quarks
name88
17. Review
Horizontal rows of the periodic table are called _____.
Atoms of the same element with different numbers of neutrons are called _______.
periods
isotopes89
17. Review
A particle that moves around the nucleus is a(n) ______.
Elements that are gases , are brittle, and are poor conductors at room temperature are ______.
electron
nonmetals 90
17. Review
A _____ is used to accelerate protons in the study of subatomic particles.
A certain atom has 26 protons, 26 electrons and 30 neutrons. Its mass number is _____.
tevatron
5691
17. Review
Suppose that you have discovered a new element and have named it neptunite. While studying your new element, you find that it has two isotopes –neptunite-220 and neptunite-250. What is the average atomic mass of your new element assuming that these two isotopes are present in equal amounts in nature?
235 amu92
17. Review
Assume that an element is composed of one isotope with a mass of 142 and another isotope with a mass of 145. For each atom with a mass of 142 there are three atoms with a mass of 145. What is the average atomic mass of the element?
144.2593
The End
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