Chapter ThreeAtoms and the Periodic

Table

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OutlineOutline

3.1 Atomic Theory3.1 Atomic Theory3.2 Elements and Atomic Number3.2 Elements and Atomic Number3.3 Isotopes and Atomic Weight3.3 Isotopes and Atomic Weight3.4 The Periodic Table3.4 The Periodic Table3.5 Some Characteristics of Different Groups3.5 Some Characteristics of Different Groups3.6 Electronic Structure of Atoms3.6 Electronic Structure of Atoms3.7 Electron Configurations3.7 Electron Configurations3.8 Electron Configurations and the Periodic Table3.8 Electron Configurations and the Periodic Table3.93.9 Electron-Dot SymbolsElectron-Dot Symbols

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GoalsGoals

1.1. What is the modern theory of atomic What is the modern theory of atomic structure?structure?  Be able to explain the major assumptions Be able to explain the major assumptions of atomic theory.of atomic theory.

2.2. How do atoms of different elements differ?How do atoms of different elements differ?  Be able Be able to explain the composition of different atoms to explain the composition of different atoms according to the number of protons, neutrons, and according to the number of protons, neutrons, and electrons they contain.electrons they contain.

3.3. What are isotopes, and what is atomic weight?What are isotopes, and what is atomic weight?  Be Be able to explain what isotopes are and how they affect able to explain what isotopes are and how they affect an elementan element’’s atomic weight.s atomic weight.

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Goals Contd.Goals Contd.

4.4. How is the periodic table arranged?How is the periodic table arranged?  Be able to Be able to describe how elements are arranged in the periodic describe how elements are arranged in the periodic table, name the subdivisions of the periodic table, and table, name the subdivisions of the periodic table, and relate the position of an element in the periodic table relate the position of an element in the periodic table to its electronic structure.to its electronic structure.

5.5. How are electrons arranged in atoms?How are electrons arranged in atoms?  Be able to Be able to explain how electrons are distributed in shells and explain how electrons are distributed in shells and subshells around the nucleus of an atom, how valence subshells around the nucleus of an atom, how valence electrons can be represented as electron-dot symbols, electrons can be represented as electron-dot symbols, and how the electron configurations can help explain and how the electron configurations can help explain the chemical properties of the elements.the chemical properties of the elements.

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3.1 Atomic Theory3.1 Atomic TheoryChemistry is founded on four fundamental Chemistry is founded on four fundamental assumptions about atoms and matter, which together assumptions about atoms and matter, which together make up modern make up modern Atomic TheoryAtomic Theory::

1.1. All matter is composed of atoms.All matter is composed of atoms.

2.2. The atoms of a given element differ from the The atoms of a given element differ from the atoms of all other elements.atoms of all other elements.

3.3. Chemical compounds consist of atoms combined Chemical compounds consist of atoms combined in specific ratios.in specific ratios.

4.4. Chemical reactions change only the way the Chemical reactions change only the way the atoms are combined in compounds; the atoms atoms are combined in compounds; the atoms themselves are unchanged.themselves are unchanged.

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► Atoms are composed of tiny Atoms are composed of tiny subatomic particlessubatomic particles called called protons, neutrons, protons, neutrons, andand electrons electrons. .

► The masses of atoms and their constituent The masses of atoms and their constituent subatomic particles are very small when measured subatomic particles are very small when measured in grams. Atomic masses are expressed on a in grams. Atomic masses are expressed on a relative mass scale. One atom is assigned a mass, relative mass scale. One atom is assigned a mass, and all others are measured relative to it. and all others are measured relative to it.

► The basis for the relative atomic mass scale is an The basis for the relative atomic mass scale is an atom of carbon that contains 6 protons and 6 atom of carbon that contains 6 protons and 6 neutrons. This carbon atom is assigned a mass of neutrons. This carbon atom is assigned a mass of exactly 12 atomic mass units (exactly 12 atomic mass units (amuamu).).

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► Both protons and neutrons have a mass close to one Both protons and neutrons have a mass close to one amu.amu.

► Electrons are 1836 times lighter than protons and Electrons are 1836 times lighter than protons and neutrons.neutrons.

► Protons and electrons have electrical charges that are Protons and electrons have electrical charges that are equal in magnitude but opposite in sign. equal in magnitude but opposite in sign.

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► The protons and neutrons are packed closely The protons and neutrons are packed closely together in a dense core called the together in a dense core called the nucleusnucleus. . Surrounding the nucleus, the electrons move about Surrounding the nucleus, the electrons move about rapidly through a large volume of space.rapidly through a large volume of space.

► The relative size The relative size of a nucleus in of a nucleus in an atom is the an atom is the same as that of a same as that of a pea in the pea in the middle of this middle of this stadium.stadium.

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► Diameter of a nucleus is only about 10Diameter of a nucleus is only about 10-15-15 m. m.► Diameter of an atom is only about 10Diameter of an atom is only about 10-10-10 m. m.

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► The structure of the atom is determined by The structure of the atom is determined by interplay of different forces.interplay of different forces.

► Opposite electrical charges attract each other, Opposite electrical charges attract each other, like charges repel each other.like charges repel each other.

► Protons and neutrons in the nucleus are held Protons and neutrons in the nucleus are held together by the nuclear strong force.together by the nuclear strong force.

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3.2 Element and Atomic Number3.2 Element and Atomic Number►Atomic NumberAtomic Number (Z):(Z): The number of protons in The number of protons in each atom of an element. All atoms of a particular each atom of an element. All atoms of a particular element have the same number of protons in the element have the same number of protons in the nucleus.nucleus.►Atoms are neutral overall and have no net charge Atoms are neutral overall and have no net charge because the number of positively charged protons and because the number of positively charged protons and the number of negatively charged electrons are the the number of negatively charged electrons are the same in each atom.same in each atom.►Mass NumberMass Number (A):(A): The total number of protons The total number of protons and neutrons in an atom.and neutrons in an atom.

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3.3 Isotopes and Atomic Weight3.3 Isotopes and Atomic Weight

Isotopes:Isotopes: Atoms with identical atomic numbers (Z) Atoms with identical atomic numbers (Z) but different mass numbers (A) are called isotopes. but different mass numbers (A) are called isotopes. Protium, deuterium, and tritium are three isotopes of Protium, deuterium, and tritium are three isotopes of the element hydrogen. the element hydrogen. ► H, most abundant hydrogen isotope has one H, most abundant hydrogen isotope has one

proton and no neutrons (Z=1, A=1) proton and no neutrons (Z=1, A=1) ► D, this heavy hydrogen isotope has one proton D, this heavy hydrogen isotope has one proton

and one neutron (Z=1, A=2), and one neutron (Z=1, A=2), ► T, this radioactive hydrogen isotope has one T, this radioactive hydrogen isotope has one

proton and two neutrons (Z=1, A=3).proton and two neutrons (Z=1, A=3).

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Isotopes of HydrogenIsotopes of Hydrogen

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A specific isotope is represented by showing its mass A specific isotope is represented by showing its mass number (A) as a superscript and its atomic number number (A) as a superscript and its atomic number (Z) as a subscript in front of the atomic symbol. For(Z) as a subscript in front of the atomic symbol. For

example, the symbol for tritium is:example, the symbol for tritium is:

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Atomic Weight:Atomic Weight: The weighted average mass of an The weighted average mass of an element’s atoms in a large sample that includes all the element’s atoms in a large sample that includes all the naturally occurring isotopes of that atom.naturally occurring isotopes of that atom.

To calculate the atomic weight of an element, the To calculate the atomic weight of an element, the individual mass and the percent abundance of each individual mass and the percent abundance of each naturally occurring isotope must be known.naturally occurring isotope must be known.

Atomic weight= (isotope abundance)*(isotope mass)

The Greek symbol, The Greek symbol, , indicates the summation of , indicates the summation of terms over all naturally occurring isotopes. terms over all naturally occurring isotopes.

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3.4 The Periodic Table3.4 The Periodic Table

► Beginning at the upper left corner of the periodic Beginning at the upper left corner of the periodic table, elements are arranged by increasing atomic table, elements are arranged by increasing atomic number into seven horizontal rows, called number into seven horizontal rows, called periodsperiods, , and 18 vertical columns, called and 18 vertical columns, called groupsgroups. .

► The elements in a given group have similar The elements in a given group have similar chemical properties. Lithium, sodium, potassium chemical properties. Lithium, sodium, potassium and other elements in group 1A (or 1) have similar and other elements in group 1A (or 1) have similar properties. Similarly, chlorine, bromine, iodine, and properties. Similarly, chlorine, bromine, iodine, and other elements in group 7A (or 17) behave other elements in group 7A (or 17) behave similarly.similarly.

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The Periodic TableThe Periodic Table

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The table has 114 boxes, each of which tells the symbol, The table has 114 boxes, each of which tells the symbol, atomic number, and atomic weight of an element.atomic number, and atomic weight of an element.

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All seven periods do not contain the same number All seven periods do not contain the same number of elements.of elements.

► The first period contains only 2 elements.The first period contains only 2 elements.► The second and third periods each contains 8 The second and third periods each contains 8

elements.elements.► The fourth and fifth periods each contain 18 The fourth and fifth periods each contain 18

elements.elements.► The sixth period contains 32 elements.The sixth period contains 32 elements.► The seventh period, still incomplete, contains 27 The seventh period, still incomplete, contains 27

elements.elements.

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The groups on the periodic table are divided into three The groups on the periodic table are divided into three main categories.main categories.

►Main Groups:Main Groups: The two groups on the far left (1-2) The two groups on the far left (1-2) and the six on the far right (13-18) are the main groups.and the six on the far right (13-18) are the main groups.

►Transition Metal Groups:Transition Metal Groups: Elements in the groups Elements in the groups numbered 3 through 12.numbered 3 through 12. ►Inner Transition Metal Groups:Inner Transition Metal Groups: The 14 groups The 14 groups shown at the bottom of the table that are not numbered shown at the bottom of the table that are not numbered containing the Lanthanides and the Actinides.containing the Lanthanides and the Actinides.

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3.5 Characteristics of Different Groups3.5 Characteristics of Different Groups

Group 1A or 1 Group 1A or 1 Alkali metals:Alkali metals:► Li, Na, K, Rb, Cs, and Li, Na, K, Rb, Cs, and

FrFr► Shiny, soft, and Shiny, soft, and low low

melting point metalsmelting point metals► All react rapidly with water All react rapidly with water

to form flammable Hto form flammable H22 gas gas

and alkaline or basic and alkaline or basic solutionssolutions

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► Group 2A or 2 Group 2A or 2 Alkaline Alkaline earth metals:earth metals:

► Be, Mg, Ca, Sr, Ba, and Be, Mg, Ca, Sr, Ba, and RaRa

► Lustrous, silvery metalsLustrous, silvery metals► React with OReact with O22

► They are less reactive to They are less reactive to water than the alkali water than the alkali metalsmetals

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Group 7A or 17 Group 7A or 17 Halogens:Halogens:► F, Cl, Br, I, and AtF, Cl, Br, I, and At► Colorful and corrosive Colorful and corrosive

nonmetalsnonmetals► All are found in nature in All are found in nature in

combination with other combination with other elements, such as with elements, such as with sodium in sodium sodium in sodium chloride (NaCl)chloride (NaCl)

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Group 8A or 18 Group 8A or 18 Noble gases:Noble gases:

► He, Ne, Ar, Kr, Xe, and RnHe, Ne, Ar, Kr, Xe, and Rn

► Colorless gasesColorless gases

► Very low chemical Very low chemical reactivity reactivity

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A graph of atomic size versus atomic number shows a A graph of atomic size versus atomic number shows a periodic rise-and-fall pattern. The maxima occur for periodic rise-and-fall pattern. The maxima occur for atoms of the group 1A elements the minima occur for atoms of the group 1A elements the minima occur for atoms of the group 7A elements. atoms of the group 7A elements.

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3. 6 Electronic Structure of Atoms3. 6 Electronic Structure of Atoms

Quantum mechanical model of atomic structure:Quantum mechanical model of atomic structure:

► The electrons in an atom are grouped around the The electrons in an atom are grouped around the nucleus into shells, roughly like the layers in an nucleus into shells, roughly like the layers in an onion.onion.

► The farther a shell is from the nucleus, the larger it The farther a shell is from the nucleus, the larger it is, the more electrons it can hold, and the higher the is, the more electrons it can hold, and the higher the energies of those electrons.energies of those electrons.

► The smallest shell closest to the nucleus is labeled The smallest shell closest to the nucleus is labeled shell 1,the next one is shell 2, and so on.shell 1,the next one is shell 2, and so on.

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► Within the shells, electrons are further grouped Within the shells, electrons are further grouped into subshells of four different types, identified as into subshells of four different types, identified as s, p, d, and f in order of increasing energy.s, p, d, and f in order of increasing energy.

► A shell has a number of subshells equal to its A shell has a number of subshells equal to its shell numbershell number..

► The first shell has only an s subshell; the second The first shell has only an s subshell; the second shell has an s and a p subshell; the third shell has shell has an s and a p subshell; the third shell has an s, a p, and a d subshell, and so on.an s, a p, and a d subshell, and so on.

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► Within each subshell, electrons are further grouped Within each subshell, electrons are further grouped into orbitals, regions of space within an atom where into orbitals, regions of space within an atom where the specific electrons are more likely to be found. the specific electrons are more likely to be found.

► The number of orbitals within a subshell increases The number of orbitals within a subshell increases as the odd numbers.as the odd numbers.

► An s subshell has 1 orbital, a p has 3, a d has 5 and An s subshell has 1 orbital, a p has 3, a d has 5 and so on.so on.

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Different orbitals have different shapes. Orbitals in Different orbitals have different shapes. Orbitals in s s subshells are spherical (a), while orbitals in subshells are spherical (a), while orbitals in pp subshells are roughly dumbbell shaped (b).subshells are roughly dumbbell shaped (b).

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► Any orbital can hold a maximum of 2 electrons.Any orbital can hold a maximum of 2 electrons.

► The first shell has one 1s orbital and holds 2 The first shell has one 1s orbital and holds 2 electrons.electrons.

► The second shell can hold 8 electrons, 2 in a 2s The second shell can hold 8 electrons, 2 in a 2s orbital and 6 in three 2p orbitals.orbital and 6 in three 2p orbitals.

► The third shell can hold 18 electrons, 2 in a 3s The third shell can hold 18 electrons, 2 in a 3s orbital, 6 in three 3p orbitals, and 10 in five 3d orbital, 6 in three 3p orbitals, and 10 in five 3d orbitals, and so on.orbitals, and so on.

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The overall electron distribution within an atom is The overall electron distribution within an atom is summarized in table 3.2 below.summarized in table 3.2 below.

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3.7 Electron Configurations3.7 Electron Configurations

Electron Configuration: Electron Configuration: The exact arrangement The exact arrangement of electrons in atom’s shells and subshells. Rules of electrons in atom’s shells and subshells. Rules to predict electron configuration:to predict electron configuration:

1.1. Electrons occupy the lowest energy orbitals Electrons occupy the lowest energy orbitals available first. available first.

2.2. Each orbital can hold only two electrons, which Each orbital can hold only two electrons, which must be of opposite spin.must be of opposite spin.

3.3. If two or more orbitals have the same energy, each If two or more orbitals have the same energy, each orbital gets one electron before any orbital gets orbital gets one electron before any orbital gets two.two.

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Order of orbital energy Order of orbital energy levels:levels:►Electrons fill orbitals Electrons fill orbitals from the lowest-energy from the lowest-energy orbitals upward.orbitals upward.► Lower numbered shells Lower numbered shells fill before higher numbered fill before higher numbered shells at first. shells at first. ►Some overlap in energy Some overlap in energy levels occurs starting with levels occurs starting with shell 3 and 4.shell 3 and 4.

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Below is a mnemonic device for remembering the Below is a mnemonic device for remembering the order of the energy levels in an atom.order of the energy levels in an atom.

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►Electron configurations are described by writing the Electron configurations are described by writing the shell number and subshell letter in order of increasing shell number and subshell letter in order of increasing energy. The number of electrons actually occupying energy. The number of electrons actually occupying each subshell is indicated by a superscript.each subshell is indicated by a superscript.►A graphic representation can be made by indicating A graphic representation can be made by indicating each orbital as a line and each electron as an arrow. each orbital as a line and each electron as an arrow. The head of the arrow indicates the electron spin.The head of the arrow indicates the electron spin.►A shorthand using noble gas configurations is very A shorthand using noble gas configurations is very useful for large atoms.useful for large atoms.

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These are the electron configurations for B - NThese are the electron configurations for B - N

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These are the electron configurations for O - NeThese are the electron configurations for O - Ne

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3.8 Electron Configuration and the 3.8 Electron Configuration and the Periodic tablePeriodic table

Valence ShellValence Shell :: Outermost, highest energy shell of an Outermost, highest energy shell of an atom.atom.

Valence electrons:Valence electrons: An electron in an outermost shell An electron in an outermost shell of an atom. These electrons are loosely held, they are of an atom. These electrons are loosely held, they are most important in determining an element’s properties.most important in determining an element’s properties.

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► The periodic table can be divided into four regions or The periodic table can be divided into four regions or blocks, of elements according to the subshells that are blocks, of elements according to the subshells that are last to fill, s, p, d, or f.last to fill, s, p, d, or f.

► Beginning at the top left corner of the periodic table, Beginning at the top left corner of the periodic table, the first row contains only two elements H and He. the first row contains only two elements H and He. The 1s subshell is being filled here.The 1s subshell is being filled here.

► The second row begins with two s-block elements (Li The second row begins with two s-block elements (Li and Be) and continues with six p-block elements (B and Be) and continues with six p-block elements (B through Ne), so electrons fill the next available s through Ne), so electrons fill the next available s orbital (2s) and then the first available p orbitals (2p). orbital (2s) and then the first available p orbitals (2p).

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► The third row is similar to the second row, so The third row is similar to the second row, so the 3s and 3p orbitals are filled next. the 3s and 3p orbitals are filled next.

► The fourth row again starts with two s-block The fourth row again starts with two s-block elements (K and Ca) but is then followed by elements (K and Ca) but is then followed by ten d-block elements (Sc through Zn) and six ten d-block elements (Sc through Zn) and six p-block elements (Ga through Kr). Thus, the p-block elements (Ga through Kr). Thus, the order of orbital filling is 4s followed by the order of orbital filling is 4s followed by the first available d orbitals (3d) followed by 4p.first available d orbitals (3d) followed by 4p.

► Continuing through Continuing through successivesuccessive rows of the rows of the periodic table provides a visual method to periodic table provides a visual method to recall the entire filling order.recall the entire filling order.

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Visual method to recall the order of orbital filling.Visual method to recall the order of orbital filling.

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3.9 Electron-Dot Symbols

►Electron-dot symbol: An atomic symbol with dots placed around it to indicate the number of valence electrons.

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Chapter SummaryChapter Summary►An atom is the smallest unit of an element that An atom is the smallest unit of an element that maintains the properties of the element.maintains the properties of the element.► Atoms are made up of protons, neutrons, and Atoms are made up of protons, neutrons, and electrons. Protons have a positive charge, neutrons are electrons. Protons have a positive charge, neutrons are neutral, and electrons have a negative charge.neutral, and electrons have a negative charge.► Protons and neutrons are present in a dense, Protons and neutrons are present in a dense, positively charged region called the nucleus. Electrons positively charged region called the nucleus. Electrons are a relatively large distance away from the nucleus.are a relatively large distance away from the nucleus.►The number of protons an element contains is called The number of protons an element contains is called the atomic number (Z). The total number of protons the atomic number (Z). The total number of protons plus neutrons in an atom is called the mass number (A).plus neutrons in an atom is called the mass number (A).

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Chapter Summary Contd.Chapter Summary Contd.►Atoms with identical numbers of protons and Atoms with identical numbers of protons and electrons but different numbers of neutrons are called electrons but different numbers of neutrons are called isotopes. isotopes. ►The atomic weight of an element is the weighted The atomic weight of an element is the weighted average mass of the element’s naturally occurring average mass of the element’s naturally occurring isotopes measured in atomic mass units (amu).isotopes measured in atomic mass units (amu).►Elements are organized into the periodic table, Elements are organized into the periodic table, consisting of 7 rows, or periods, and 18 columns, or consisting of 7 rows, or periods, and 18 columns, or groups.groups.►Elements in the same group have the same number of Elements in the same group have the same number of valence electrons in their outermost shell.valence electrons in their outermost shell.

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Chapter Summary ContdChapter Summary Contd..►Electrons in an atom are grouped into layers, or shells. Electrons in an atom are grouped into layers, or shells. In each shell, electrons are grouped into subshells, and In each shell, electrons are grouped into subshells, and each subshell into orbitals.each subshell into orbitals.►S orbitals are spherical, and p orbitals are dumbbell S orbitals are spherical, and p orbitals are dumbbell shaped.shaped.►Each orbital can hold 2 electrons. Each shell can hold Each orbital can hold 2 electrons. Each shell can hold a number of electrons equal to 2 times the shell number a number of electrons equal to 2 times the shell number squared. The first shell can hold 2, the second shell can squared. The first shell can hold 2, the second shell can hold 8, the third shell can hold 18, and so on. hold 8, the third shell can hold 18, and so on. ►The electron configuration of an element is predicted The electron configuration of an element is predicted by assigning the element’s electrons into orbitals, by assigning the element’s electrons into orbitals, beginning with the lowest-energy orbital.beginning with the lowest-energy orbital.

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Key WordsKey Words

►Alkali metalAlkali metal►Alkaline earth metalAlkaline earth metal►AtomAtom►Atomic mass unit Atomic mass unit (amu)(amu)►Atomic number (Atomic number (ZZ))►Atomic theoryAtomic theory►Atomic weightAtomic weight►dd-Block element-Block element

►ElectronElectron►Electron configurationElectron configuration►Electron-dot symbolElectron-dot symbol►ff-Block element-Block element►GroupGroup►HalogenHalogen►Inner transition metal Inner transition metal elementelement►IsotopeIsotope

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Key Words Contd.Key Words Contd.

►Main group elementMain group element►Mass number (Mass number (AA))►NeutronNeutron►Noble gasNoble gas►NucleusNucleus►OrbitalOrbital►pp-Block element-Block element►PeriodPeriod

►ProtonProton►ss-Block element-Block element►Shell (electron)Shell (electron)►Subatomic particleSubatomic particle►Subshell (electron)Subshell (electron)►Transition metal Transition metal elementelement►Valence electronValence electron►Valence shellValence shell