chapter two atoms & the periodic table general, organic & biological chemistry janice...

Chapter TwoChapter TwoAtoms & the

Periodic Table

General, Organic & Biological General, Organic & Biological Chemistry Chemistry

Janice Gorzynski SmithJanice Gorzynski Smith2010 McGraw-Hill2010 McGraw-Hill

CHE120 Chapter Two 2

Classification of MatterClassification of Matter

H o m o g eneo usa ir

sa lt w a te rb ra ss

H etero g eneo ussa nd & g rav e l

m e ta m u c illa w n fo od

M ixtu re

E lem enth yd ro gen

su lfu riron

C o m p ou ndw ater

p rop aneb a kin g so da

P u re S ub stan ce

M atter


Atomic TheoryAtomic 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.


Atoms are composed of tiny Atoms are composed of tiny subatomic particlessubatomic particles called called protonsprotons, , neutronsneutrons, and , and electronselectrons. .

The masses of atoms and their subatomic particles The masses of atoms and their subatomic particles are extremely small when measured in grams. are extremely small when measured in grams. These masses are expressed on a These masses are expressed on a relative mass relative mass scalescale. That is, one atom is assigned a mass, and all . That is, one atom is assigned a mass, and all others are measured relative to it. 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).).


Protons and a neutrons have a mass of 1 amu. Protons and a neutrons have a mass of 1 amu. Hydrogen atoms have mass of 1 amu, oxygen Hydrogen atoms have mass of 1 amu, oxygen atoms have mass of 16 amu, etc.atoms have mass of 16 amu, etc.

Subatomic particles are not distributed randomly Subatomic particles are not distributed randomly throughout an atom.throughout an atom.

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, mostly empty volume of rapidly through a large, mostly empty volume of space.space.


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

Fig 3.1 The structure of an atomFig 3.1 The structure of an atom


The structure of the atom is determined by an The structure of the atom is determined by an interplay of different attractive and repulsive interplay of different attractive and repulsive forces.forces.

Unlike charges attract - the negatively charged Unlike charges attract - the negatively charged electrons are held close to the nucleus due to this electrons are held close to the nucleus due to this attraction.attraction.


Like charges repel each other - electrons try to get Like charges repel each other - electrons try to get as far away from each other as possible thereby as far away from each other as possible thereby occupying a large volume in space. The positively occupying a large volume in space. The positively charged protons in the nucleus also repel each other, charged protons in the nucleus also repel each other, however, they are held together by a unique however, they are held together by a unique attraction called the attraction called the nuclear strong forcenuclear strong force..


Element and Atomic NumberElement and Atomic Number

Atomic Number Atomic Number (Z):(Z): Number of protons in the Number of protons in the nucleus of an atom. The number Z is unique to each nucleus of an atom. The number Z is unique to each element. We can identify the element if we know the element. We can identify the element if we know the number of protons in the nucleus.number of protons in the nucleus.

Mass Number (A):Mass Number (A): The total number of protons and The total number of protons and neutrons in an atom.neutrons in an atom.

The electrical charge on an atom is neutral because The electrical charge on an atom is neutral because the number of positively charged protons and the the number of positively charged protons and the number of negatively charged electrons are the same.number of negatively charged electrons are the same.


Isotopes and Atomic WeightIsotopes and Atomic Weight

IsotopesIsotopes: 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. Hydrogen, deuterium, and tritium are three isotopes Hydrogen, deuterium, and tritium are three isotopes of hydrogen. of hydrogen.

-- Most abundant hydrogen isotope has one Most abundant hydrogen isotope has one proton and no neutron (A=1); proton and no neutron (A=1);

-- deuterium isotope has one proton and one deuterium isotope has one proton and one neutron (A=2), and neutron (A=2), and

-- tritium isotope has one proton and two tritium isotope has one proton and two neutrons (A=3). neutrons (A=3).


Isotopes of hydrogen Isotopes of hydrogen


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


The Periodic TableThe 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 table, elements are arranged by increasing atomic number into seven horizontal rows, atomic number into seven horizontal rows, called 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 have similar and other elements in group 1A have similar properties. Likewise, chlorine, bromine, iodine, properties. Likewise, chlorine, bromine, iodine, and other elements in group 7A behave and other elements in group 7A behave similarly.similarly.


Fig 3.2 The periodic tableFig 3.2 The periodic table


The Periodic TableThe Periodic Table


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


Some Characteristics of Different Some Characteristics of Different GroupsGroups

Various elements in a given group of the periodic Various elements in a given group of the periodic table show remarkable similarities in their table show remarkable similarities in their properties. For example, The Alkali Metals (1A)properties. For example, The Alkali Metals (1A)

Lithium(Li), Lithium(Li), Sodium(Na), Potassium(K), Sodium(Na), Potassium(K), Rubidium(Rb), Rubidium(Rb), Cesium(Cs) and Francium(Fr) are Cesium(Cs) and Francium(Fr) are shiny and soft shiny and soft and and have low melting points. All have low melting points. All react rapidly with react rapidly with water to form products that are water to form products that are highly alkaline - hence the name alkali metals.highly alkaline - hence the name alkali metals.


Group 2A – Alkaline Earth metals: Beryllium(Be), Group 2A – Alkaline Earth metals: Beryllium(Be), Magnesium(Mg), Calcium(Ca), Strontium(Sr), Magnesium(Mg), Calcium(Ca), Strontium(Sr), Barium(Ba), and Radium(Ra) are lustrous,, silvery Barium(Ba), and Radium(Ra) are lustrous,, silvery metals. They are less reactive than the Alkali metals. They are less reactive than the Alkali group.group.

Group 7A - Halogens: Fluorine(F), Chlorine(Cl), Group 7A - Halogens: Fluorine(F), Chlorine(Cl), Bromine(Br), Iodine(I), and Astatine(At) are Bromine(Br), Iodine(I), and Astatine(At) are colorful and corrosive nonmetals. All are found in colorful and corrosive nonmetals. All are found in nature in combination with other nature in combination with other elements, elements, such as sodium in sodium chloride (NaCl)such as sodium in sodium chloride (NaCl)


Group 8A-Noble gases: Helium (He), Neon Group 8A-Noble gases: Helium (He), Neon (Ne), (Ne), Argon (Ar), Krypton (Kr), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon Xenon (Xe), and Radon (Rn) are (Rn) are colorless gases of very low chemical colorless gases of very low chemical reactivity. reactivity.


Transition Between Atomic Nucleus Transition Between Atomic Nucleus & Outside the Nucleus& Outside the Nucleus

Nothing stronger known in the universe Nothing stronger known in the universe than nuclear forces – that holding protons than nuclear forces – that holding protons and neutrons together.and neutrons together.

But the action is outside the nucleus, where But the action is outside the nucleus, where the electrons are spinning and moving.the electrons are spinning and moving.

They don’t have much mass but they make They don’t have much mass but they make up for it with the amount of energy involved up for it with the amount of energy involved in their movement.in their movement.


Electronic Structure of AtomsElectronic Structure of Atoms

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

Electrons are not perfectly free to move Electrons are not perfectly free to move about in an atom.about in an atom.

Each electron is restricted to moving about Each electron is restricted to moving about only in a certain region of space within the only in a certain region of space within the atom, atom, depending on the amount of depending on the amount of energy the electron has.energy the electron has.


Different electrons have different amounts Different electrons have different amounts of energy and thus occupy different regions of energy and thus occupy different regions within the atom.within the atom.

The energies of electrons are quantized, or The energies of electrons are quantized, or restricted to having only certain values.restricted to having only certain values.

The electron energy levels in an atom are The electron energy levels in an atom are grouped around the nucleus into shells.grouped around the nucleus into shells.

Within the shells, electrons are further Within the shells, electrons are further grouped into grouped into subshellssubshells of four different of four different types, identified as types, identified as ss, , pp, , dd, and , and ff in order of in order of increasing energy. increasing energy.


- - The first shell has only an The first shell has only an ss subshell subshell

- - The second shell has an The second shell has an ss and a and a pp subshell subshell

- - The third shell has an The third shell has an ss, , pp, and a , and a dd subshell.subshell.

- - The fourth shell has an The fourth shell has an ss, , pp, , dd, and an , and an f f subshell.subshell.


The number of subshells in a given shell is equal to The number of subshells in a given shell is equal to the shell number. For example, shell number 3 has the shell number. For example, shell number 3 has 3 subshells.3 subshells.

Within each subshell, electrons are further grouped Within each subshell, electrons are further grouped into into orbitalsorbitals, regions of space within an atom where , 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.

There are different numbers of orbitals within the There are different numbers of orbitals within the different kinds of subshells.different kinds of subshells.


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


The first shell (nearest to the nucleus) can hold The first shell (nearest to the nucleus) can hold only 2 electrons. They are in a single 1s only 2 electrons. They are in a single 1s orbital.orbital.

The second shell can hold 8 electrons – 2 in the The second shell can hold 8 electrons – 2 in the 2s orbital and 6 in the 2p orbitals.2s orbital and 6 in the 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 the 3p orbitals, and 10 in the 3d orbital, 6 in the 3p orbitals, and 10 in the 3d orbitals.orbitals.

The fourth shell can hold 32 electrons – 2 in a The fourth shell can hold 32 electrons – 2 in a 4s orbital, 6 in the 4p orbitals, 10 in the 4d 4s orbital, 6 in the 4p orbitals, 10 in the 4d orbitals, and 14 in the 4f orbitals. orbitals, and 14 in the 4f orbitals.


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


Electron ConfigurationElectron ConfigurationElectron ConfigurationElectron 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, beginning with 1s and continuing in available, beginning with 1s and continuing in order shown in the fig. 3.5. order shown in the fig. 3.5.

2.2. Each orbital can hold only two electrons, which Each orbital can hold only two electrons, which must have opposite spins.must have opposite spins.

3.3. Two or more orbitals with the same energy – each Two or more orbitals with the same energy – each orbital gets one electron before any orbital gets orbital gets one electron before any orbital gets two.two.


Electrons fill orbitals in ascending order, from the lowest-energy Electrons fill orbitals in ascending order, from the lowest-energy orbitals upward. Generally, this means that lower-numbered orbitals upward. Generally, this means that lower-numbered shells fill before higher-numbered shells. However, some overlap shells fill before higher-numbered shells. However, some overlap in energy levels occurs starting in the third energy level. in energy levels occurs starting in the third energy level.

Fig 3.5 order of orbital Fig 3.5 order of orbital

energy levelsenergy levels


Electronic configuration of a few elements are Electronic configuration of a few elements are shown below:shown below:


Electron Configuration and the Electron Configuration and the Periodic tablePeriodic table

The periodic table can be divided into four The periodic table can be divided into four regions or blocks, of elements according to regions or blocks, of elements according to the shells and subshells as shown in Fig 3.6.the shells and subshells as shown in Fig 3.6.Valence ShellValence Shell : Outermost shell of an atom.: Outermost shell of an atom.Valence electronValence electron: Electron in the outermost : Electron in the outermost shell of an atom. These electrons are loosely shell of an atom. These electrons are loosely held and are most important in determining held and are most important in determining an element’s chemical properties.an element’s chemical properties.


Fig 3.6 electron configurations and the periodic tableFig 3.6 electron configurations and the periodic table


Chapter SummaryChapter Summary All matter is composed of All matter is composed of atomsatoms.. An atom is the smallest and simplest unit into An atom is the smallest and simplest unit into which an element can be divided while which an element can be divided while maintaining the properties of the element.maintaining the properties of the element. Atoms are made up of Atoms are made up of subatomic particlessubatomic particles called called

protons, neutrons and electrons.protons, neutrons and electrons. Protons have Protons have a +1 charge, electrons have a −1 charge, and a +1 charge, electrons have a −1 charge, and

neutrons have no electrical charge.neutrons have no electrical charge. ElementsElements differ from each other according to the differ from each other according to the

number of protons their atoms contain (Atomic number of protons their atoms contain (Atomic number, Z)number, Z)


Chapter Summary Contd.Chapter Summary Contd. Mass number (A):Mass number (A): Total number of protons and Total number of protons and

neutrons in an atom.neutrons in an atom. Isotopes:Isotopes: Atoms with identical number of protons Atoms with identical number of protons

but different numbers of neutrons.but different numbers of neutrons. Periodic table:Periodic table: Tabular arrangement of elements Tabular arrangement of elements

according to their valence shells.according to their valence shells. The electrons surrounding an atom are grouped The electrons surrounding an atom are grouped into into shellsshells. Within each shell, electrons are grouped . Within each shell, electrons are grouped

into into subshellssubshells, and within subshells into , and within subshells into orbitalsorbitals (regions of space where electrons are most (regions of space where electrons are most

likely to be found). likely to be found).


Chapter Summary Contd.Chapter Summary Contd. ss orbitals are spherical and orbitals are spherical and pp orbitals are orbitals are dumbbell dumbbell shaped.shaped. Each orbital and each shell can hold a specific Each orbital and each shell can hold a specific number of electrons. number of electrons. -- The first shell can hold only two electrons. 2 The first shell can hold only two electrons. 2 electrons in an s orbital (1Selectrons in an s orbital (1S22). ). -- The second shell can hold 8 electrons. The second shell can hold 8 electrons.

2 electrons in an 2 electrons in an ss orbital and 6 electrons in 3 orbital and 6 electrons in 3 pp orbitals. (2Sorbitals. (2S2 2 2p2p66).).

-- The third shell can hold 18 electrons. 2 electrons The third shell can hold 18 electrons. 2 electrons in an in an ss orbital, 6 electrons in 3 orbital, 6 electrons in 3 pp orbitals, and 10 orbitals, and 10 electrons in 5 electrons in 5 d d orbitals (3S orbitals (3S2 2 3p3p6 6 3d3d1010); and so on.); and so on.


End of Chapter 2End of Chapter 2

chapter two atoms & the periodic table general, organic & biological chemistry janice...

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