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1
Chapter 3 Atoms and Elements
3.1Classification of Matter
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Matter
Matter is the “stuff” that makes up all things.
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A pure substance is classified as
• matter with a specific composition.
• an element when composed of one type of atom.
• a compound when composed of two or more elements combined in a definite ratio.
Pure Substances
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Elements
Elements are • pure substances that
contains atoms of only one type.
Copper, CuLead, PbAluminum, Al
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Compounds
Compounds
• contain two or more elements in a definite ratio.
Salt (NaCl)Table sugar (C12H22O11)Water (H2O)
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Elements in a Compound
“Table salt” is a compound that contains the elements sodium and chlorine.
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Mixtures
A mixture is a type of matter that consists of• two or more substances that are physically mixed, not
chemically combined.• two or more substances in different proportions.• substances that can be separated by physical
methods.
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Physical Separation of a Mixture
Example: Pasta and water are separated with a strainer.
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Homogeneous Mixtures
In a homogeneous mixture,
• the composition is uniform throughout.
• the different parts of the mixture are not visible.
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Heterogeneous Mixtures
In a heterogeneous mixture, • the composition of
substances is not uniform.• the composition varies from
one part of the mixture to another.
• the different parts of the mixture are visible.
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Classification of Matter
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Identify each of the following as a pure substance or a mixture.
A. pasta and tomato sauce
B. aluminum foil
C. helium
D. air
Learning Check
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Identify each of the following as a pure substance or a mixture.
A. pasta and tomato sauce mixture
B. aluminum foil pure substance
C. helium pure substance
D. air mixture
Solution
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Identify each of the following as a homogeneous orheterogeneous mixture:
A. hot fudge sundae
B. air
C. sugar water
D. peach pie
Learning Check
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Identify each of the following as a homogeneous orheterogeneous mixture:
A. hot fudge sundae heterogeneous mixture
B. air homogeneous mixture
C. sugar water homogeneous mixture
D. peach pie heterogeneous mixture
Solution
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Chapter 3 Atoms and Elements
3.2Elements and Symbols
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Elements are• pure substances that cannot be separated into
simpler substances by ordinary laboratory processes.
• the building blocks of matter.
gold carbon aluminum
Elements
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Sources of Some Element Names
Some elements arenamed for planets,mythological figures,minerals, colors,scientists, andplaces.
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A symbol• represents the name of an element.• consists of 1 or 2 letters. • starts with a capital letter.
1-Letter Symbols 2-Letter SymbolsC carbon Co cobaltN nitrogen Ca calciumF fluorine Al aluminum O oxygen Mg magnesium
Symbols of Elements
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Several symbols are derived from Latin names as shownbelow.
Cu, copper (cuprum) Au, gold (aurum)
Fe, iron (ferrum) Ag, silver (argentum)
Symbols from Latin Names
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Physical Properties of Elements
The physical properties of an element • are observed or measured without changing its
identity.• include the following:
Shape DensityColor Melting pointOdor and taste Boiling point
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Physical Properties of Elements
Some physical properties ofcopper are:
Color Red-orangeLuster Very shinyMelting point 1083 °CBoiling point 2567 °CConduction of electricity ExcellentConduction of heat Excellent
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Select the correct symbol for each.A. Calcium
1) C 2) Ca 3) CA
B. Sulfur 1) S 2) Sl 3) Su
C. Iron1) Ir 2) FE 3) Fe
Learning Check
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Select the correct symbol for each.A. Calcium
2) Ca
B. Sulfur 1) S
C. Iron3) Fe
Solution
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Select the correct name for each symbol.A. N
1) neon 2) nitrogen 3) nickel
B. P1) potassium 2) phlogiston 3) phosphorus
C. Ag1) silver 2) agean 3) gold
Learning Check
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Select the correct name for each:A. N
2) nitrogen
B. P3) phosphorus
C. Ag1) silver
Solution
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Chapter 3 Atoms and Elements
3.3The Periodic Table
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Groups and Periods
On the periodic table,• elements are arranged according to similar
properties.
• groups contain elements with similar properties in vertical columns.
• periods are horizontal rows of elements.
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Groups and Periods
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Periodic Table
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Group Numbers
Group Numbers• use the letter A for the representative elements (1A to
8A) and the letter B for the transition elements.
• also use numbers 1-18 to the columns from left to right.
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Names of Some Representative Elements
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Alkali Metals
Group 1A (1), the alkali metals, includes lithium, sodium, and potassium.
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Halogens
Group 7A (17), the halogens, includes chlorine, bromine, and iodine.
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Identify the element described by the following:
A. Group 7A (17), Period 41) Br 2) Cl 3) Mn
B. Group 2A (2), Period 31) beryllium 2) boron 3) magnesium
C. Group 5A (15), Period 21) phosphorus 2) arsenic 3) nitrogen
Learning Check
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A. Group 7A (17), Period 41) Br
B. Group 2A (2), Period 33) magnesium
C. Group 5A (15), Period 2
3) nitrogen
Solution
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Metals, Nonmetals, and Metalloids
The heavy zigzag line separates metals and nonmetals.• Metals are located to the left.• Nonmetals are located to the right. • Metalloids are located along the heavy zigzag
line between the metals and nonmetals.
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Metals, Nonmetals, and Metalloids on the Periodic Table
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Metals• are shiny and ductile.• are good conductors of heat and electricity.
Nonmetals• are dull, brittle, and poor conductors.• are good insulators.
Metalloids• are better conductors than nonmetals, but not
as good as metals.• are used as semiconductors and insulators.
Properties of Metals, Nonmetals, and Metalloids
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Comparing a Metal, Metalloid, and Nonmetal
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Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid.
A. sodium ____B. chlorine ____C. silicon ____D. iron ____E. carbon ____
Learning Check
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Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid.
A. sodium 1 metalB. chlorine 2 nonmetalC. silicon 3 metalloidD. iron 1 metal E. carbon 2 nonmetal
Solution
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Match the elements to the description.
A. Metals in Group 4A (14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn
B. Nonmetals in Group 5A (15)1) As, Sb, Bi 2) N, P 3) N, P, As, Sb
C. Metalloids in Group 4A (14)1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb
Learning Check
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Match the elements to the description.
A. Metals in Group 4A (14)1) Sn, Pb
B. Nonmetals in Group 5A (15)2) N, P
C. Metalloids in Group 4A (14)2) Si, Ge
Solution
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Chapter 3 Atoms and Elements
3.4 The Atom
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Dalton’s Atomic Theory
In Dalton’s atomic theory, atoms• are tiny particles of matter. • of an element are similar and
different from other elements.• of two or more different elements
combine to form compounds.• are rearranged to form new
combinations in a chemical reaction.
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Subatomic Particles
Atoms contain subatomic particles.
• Protons have a positive (+) charge.• Electrons have a negative (-) charge.• Neutrons are neutral.• Like charges repel and unlike charges
attract.
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Rutherford’s Gold Foil Experiment
In Rutherford’s gold foil experiment, positively charged particles • were aimed at atoms of gold.• mostly went straight through the atoms. • were deflected only occasionally.
Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.
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Rutherford’s Gold Foil Experiment
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Structure of the Atom
An atom consists• of a nucleus that
contains protons and neutrons.
• of electrons in a large, empty space around the nucleus.
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Atomic Mass Scale
On the atomic mass scale,• 1 atomic mass unit (amu) has a mass equal to 1/12 of
the mass of the carbon-12 atom.• a proton has a mass of about 1 (1.007) amu.• a neutron has a mass of about 1 (1.008) amu.• an electron has a very small mass, 0.000 549 amu.
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Particles in the Atom
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Learning Check
Identify each statement as describing a1) proton, 2) neutron, or 3) electron.
A. found outside the nucleusB. has a positive chargeC. is neutralD. found in the nucleus
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Solution
Identify each statement as describing a1) proton, 2) neutron, or 3) electron.
A. 3 found outside the nucleusB. 1 has a positive chargeC. 2 is neutralD. 1, 2 found in the nucleus
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Chapter 3 Atoms and Elements
3.5Atomic Number and Mass Number
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The atomic number• is specific for each element. • is the same for all atoms of an element.• is equal to the number of protons in an atom.• appears above the symbol of an element.
Atomic Number
11Na
Atomic Number
Symbol
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Examples of atomic number and number of protons:
• Hydrogen has atomic number 1; every H atom has one proton.
• Carbon has atomic number 6; every C atom has six protons.
• Copper has atomic number 29; every Cu atom has 29 protons.
• Gold has atomic number 79; every Au atom has 79 protons.
Atomic Number and Protons
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State the number of protons in each. A. A nitrogen atom
1) 5 protons 2) 7 protons 3) 14 protons
B. A sulfur atom1) 32 protons 2) 16 protons 3) 6 protons
C. A barium atom1) 137 protons 2) 81 protons 3) 56 protons
Learning Check
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State the number of protons in each. A. A nitrogen atom
2) atomic number 7; 7 protons
B. A sulfur atom2) atomic number 16; 16 protons
C. A barium atom3) atomic number 56; 56 protons
Solution
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An atom • of an element is electrically neutral; the net charge
of an atom is zero.• has an equal number of protons and electrons.
number of protons = number of electrons
Aluminum has 13 protons and 13 electrons. The net(overall) charge is zero.
13 protons (13+) + 13 electrons (13 -) = 0
Electrons in An Atom
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Mass Number
The mass number• represents the number of particles in the nucleus.• is equal to the number of protons + the number
of neutrons.
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Atomic Models
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Number of protons = Atomic number
Number of protons + neutrons = Mass number
Number of neutrons = mass number – atomic number (protons)
Note: Mass number is given for specific isotopes only.
Study Tip: Protons and Neutrons
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An atom of zinc has a mass number of 65.A. How many protons are in this zinc atom?
1) 30 2) 35 3) 65
B. How many neutrons are in the zinc atom?1) 30 2) 35 3) 65
C. What is the mass number of a zinc atom that has37 neutrons?1) 37 2) 65 3) 67
Learning Check
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An atom of zinc has a mass number of 65.A. How many protons are in this zinc atom?
1) 30 (atomic number 30)
B. How many neutrons are in the zinc atom?2) 35 (65 – 30 = 35)
C. What is the mass number of a zinc atom that has 37 neutrons?
3) 67 (30 + 37 = 67)
Solution
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An atom has 14 protons and 20 neutrons.
A. Its atomic number is1) 14 2) 16 3) 34
B. Its mass number is1) 14 2) 16 3) 34
C. The element is1) Si 2) Ca 3) Se
Learning Check
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An atom has 14 protons and 20 neutrons.
A. It has atomic number1) 14
B. It has a mass number of3) 34 (14 + 20 = 34)
C. The element is1) Si (Atomic number 14)
Solution
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Chapter 3 Atoms and Elements
3.6Isotopes and Atomic Mass
24Mg 25Mg 26Mg12 12 12
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Isotopes• are atoms of the same element that have different
mass numbers.
• have the same number of protons, but different numbers of neutrons.
Isotopes
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An atomic symbol• represents a particular atom of an element.
• gives the mass number in the upper left corner and the atomic number in the lower left corner.
Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol:
mass number 23 Na
atomic number 11
Atomic Symbol
The atomic symbol for a specific atom of an element
gives the
• number of protons (p+),
• number of neutrons (n),
• and number of electrons (e-).
Information from Atomic Symbols
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Examples of number of subatomic particles for atoms
Atomic symbol
16 31 65O P Zn
8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n8 e- 15 e- 30 e-
Information from Atomic Symbols
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Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following:
12C 13C 14C6 6 6
protons ______ ______ ______ neutrons ______ ______ ______
electrons ______ ______ ______
Learning Check
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12C 13C 14C6 6 6
protons 6 p+ 6 p+ 6 p+
neutrons 6 n 7 n 8 nelectrons 6 e- 6 e- 6 e-
Solution
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Write the atomic symbols for atoms with the following subatomic particles:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________
Learning Check
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A. 8 p+, 8 n, 8 e- 16O8
B. 17p+, 20 n, 17e- 37Cl17
C. 47p+, 60 n, 47 e- 107Ag47
Solution
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Learning Check
1. Which of the pairs are isotopes of the same element?2. In which of the pairs do both atoms have 8 neutrons?
A. 15X 15X8 7
B. 12X 14X6 6
C. 15X 16X7 8
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Solution
B. 12X 14X6 6
The atomic symbols in “B.” represent isotopes of carbon with 6 protons each, but one has 6 neutrons and the other has 8.
C. 15X 16X7 8
These isotopes of nitrogen and oxygen have 8 neutrons.
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Isotopes of Magnesium
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Isotopes of Magnesium
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Isotopes of Sulfur
A sample of naturallyoccurring sulfur containsseveral isotopes with thefollowing abundancesIsotope % abundance
32S 95.02 33S 0.7534S 4.2136S 0.02
32S, 33S, 34S, 36S16 16 16 16
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Atomic Mass
The atomic mass of an element• is listed below the symbol of each element
on the periodic table.
• gives the mass of an “average” atom of each element compared to 12C.
• is not the same as the mass number.
Na22.99
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Isotopes of Some Elements and Their Atomic Mass
Most elements have two or more isotopes that contribute to the atomic mass of that element.
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Atomic Mass for Cl
The atomic mass of chlorine is• due to all the Cl isotopes.• not a whole number.• the average of two isotopes:
35Cl and 37Cl.
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Using the periodic table, specify the atomic mass ofeach element.A. calcium __________
B. aluminum __________
C. lead __________
D. barium __________
E. iron __________
Learning Check
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Using the periodic table, specify the atomic mass ofeach element: A. calcium 40.08 amu
B. aluminum 26.98 amu
C. lead 207.2 amu
D. barium 137.3 amu
E. iron 55.85 amu
Solution
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Calculating Atomic Mass
The calculation for atomic mass requires the
• percent(%) abundance of each isotope.
• atomic mass of each isotope of that element.
• sum of the weighted averages.
mass of isotope(1)x (%) + mass of isotope(2) x (%) + 100 100
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35Cl has atomic mass 34.97 amu (75.76%) and 37C has atomic mass 36.97 amu (24.24%). • Use atomic mass and percent of each isotope to
calculate the contribution of each isotope to the weighted average. 34.97 x 75.76 = 26.49 amu
10036.97 x 24.24 = 8.961 amu
100 • Sum is atomic mass of Cl 35.45 amu
Calculating Atomic Mass for Cl
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Calculating Atomic Mass Mg Isotope Mass Abundance
24Mg = 23.99 amu x 78.70/100 = 18.88 amu25Mg = 24.99 amu x 10.13/100 = 2.531 amu26Mg = 25.98 amu x 11.17/100 = 2.902 amu
Atomic mass (average mass) Mg = 24.31 amu
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Atomic Mass of Magnesium
The atomic mass of Mg• is due to all the Mg
isotopes.• is a weighted average.• is not a whole number.
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Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69Ga (atomic mass 68.926) atoms and 39.90% of 71Ga (atomic mass 70.925) atoms.
What is the atomic mass of gallium?
Learning Check
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69Ga 68.926 amu x 60.10 = 41.42 amu (from 69Ga)
10071Ga70.925 amu x 39.90 = 28.30 amu (from 71Ga)
100Atomic mass Ga = 69.72 amu
Solution
31
Ga
69.72
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Chapter 3 Atoms and Elements
3.7 Electron Energy Levels
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Energy Levels
Energy levels• are assigned numbers n =
1, 2, 3, 4, and so on.• increase in energy as the
value of n increases.• are like the rungs of a
ladder with the lower energy levels nearer the nucleus.
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Energy Levels
Energy levels have a maximum number of electrons equal to 2n2.
Energy level Maximum number of electronsn = 1 2(1)2 = 2(1) = 2 n = 2 2(2)2 = 2(4) = 8 n = 3 2(3)2 = 2(9) = 18
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Orbitals
An orbital• is a three-dimensional space around a nucleus,
where an electron is most likely to be found.
• has a shape that represents electron density (not a path the electron follows).
• can hold up to 2 electrons.
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Orbitals
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
An s orbital
•has a spherical shape around the nucleus.
•is found in each energy level.
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Orbitals
Electron Level Arrangement
In the electron level arrangement for the first 18 elements • electrons are placed in energy levels (1, 2, 3, etc.),
beginning with the lowest energy level• there is a maximum number in each energy level.
Energy level Number of electrons1 2 (up to He)2 8 (up to Ne)3 8 (up to Ar)4 2 (up to Ca)
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Learning Check
Write the electron level arrangement for each:
1. N
2. Cl
3. K
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Solution
Write the electron level arrangement for each:
1. N 2, 5
2. Cl 2, 8, 7
3. K 2, 8, 8, 1
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Learning Check
Identify the element with each electron level arrangement:
1. 2, 2
2. 2, 8, 3
3. 2, 7
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Solution
Identify the element with each electron level arrangement:
1. Be 2, 2
2. Al 2, 8, 3
3. F 2, 7
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Chapter 3 Atoms and Elements
3.8 Periodic Trends
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Valence Electrons
The valence electrons• determine the chemical properties of the elements.• are the electrons in the highest energy level.• are related to the group number of the element.
Example: Phosphorus has 5 valence electrons.5 valence electrons
P in Group 5A(15) 2, 8, 5
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All the elements in a group have the same number ofvalence electrons.
Example: Elements in group 2A (2) have two (2) valence electrons.
Be 2, 2Mg 2, 8, 2Ca 2, 8, 8, 2Sr 2, 8, 18, 8, 2
Groups and Valence Electrons
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Periodic Table and Valence Electrons
Representative Elements Group Numbers1 2 3 4 5 6 7 8 H He1 2
Li Be B C N O F Ne2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8
Na Mg Al Si P S Cl Ar2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8
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State the number of valence electrons for each.A. O
1) 4 2) 6 3) 8
B. Al1) 13 2) 3 3) 1
C. Cl1) 2 2) 5 3) 7
Learning Check
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State the number of valence electrons for each.A. O
2) 6
B. Al2) 3
C. Cl3) 7
Solution
110
State the number of valence electrons for each. A. calcium
1) 1 2) 2 3) 3
B. group 6A (16) 1) 2 2) 4 3) 6
C. tin 1) 2 2) 4 3) 14
Learning Check
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State the number of valence electrons for each. A. calcium
2) 2
B. group 6A (16) 3) 6
C. tin 2) 4
Solution
112
For the element with the following electron arrangement:1) State the number of valence electrons.2) Identify the element.
A. 2, 8, 5B. 2, 8, 8, 2C. 2, 7
Learning Check
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For the element with the following electron arrangement
1) State the number of valence electrons2) Identify the element.
A. 2, 8, 5 1) 5 2) phosphorus
B. 2, 8, 8, 2 1) 2 2) calcium
C. 2, 7 1) 7 2) fluorine
Solution
114
Electron-Dot Symbols
An electron-dot symbol• shows the valence electrons
around the symbol of the element.
• for Mg has 2 valence electrons as single dots on the sides of the symbol Mg.
. .·Mg · or Mg · or ·Mg or ·Mg
·
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Writing Electron-Dot Symbols
Electron-dot symbols for• groups 1A (1) to 4A (14) use single dots.
· ·Na · · Mg · · Al · · C ·
·
• groups 5A (15) to 7A (17) use pairs and single dots.
· · · ·· P · : O ·
· ·
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Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have thesame number of valence electrons (dots).
Example: Atoms of elements in Group 2A (2) each have 2 valence electrons.
· Be ·· Mg ·· Ca ·· Sr ·· Ba ·
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.A. X is the electron-dot symbol for
1) Na 2) K 3) Al
. .B. . X .
. is the electron-dot symbol of
1) B 2) N 3) P
Learning Check
118
.A. X is the electron-dot symbol for
1) Na 2) K
. .B. . X .
. is the electron-dot symbol of
2) N 3) P
Solution
119
Atomic Size
Atomic size is described
using the atomic radius;
the distance from the
nucleus to the valence
electrons.
120
Atomic Radius Within A Group
Atomic radius increasesgoing down each group of representative elements.
121
Atomic Radius Across a Period
Going across a period from left to right, • an increase in the number of protons increases
attraction for valence electrons.• atomic radius decreases.
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122
Learning Check
Select the element in each pair with the larger atomicradius.
A. Li or KB. K or BrC. P or Cl
123
Solution
Select the element in each pair with the larger atomicradius.
A. KB. KC. P
124
Ionization Energy
Ionization energy is the energy it takes to remove a valence electron.
Na(g) + Energy (ionization) -> Na+(g) + e-
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Ionization Energy In a Group
Going up a group ofrepresentative elements,• the distance decreases
between nucleus and valence electrons.
• the ionization energy increases.
126
Ionization Energy
• Metals have lower ionization energies.
• Nonmetals have higher ionization energies.
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127
Learning Check
Select the element in each pair with the higher ionizationenergy.
A. Li or KB. K or BrC. P or Cl
128
Solution
Select the element in each pair with the higher ionizationenergy.
A. Li B. BrC. Cl