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2 Elements and Compounds

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Chapter Goals1. Metals, Nonmetals, and Metalloids.2. Monoatomic, Diatomic and Polyatomic Elements3. Physical States of Elements4. Luster, Malleability, Ductility, and Hardness of Elements5. Groups, Rows, and Section Names6. Ions7. Ionic and Covalent Compounds8. Repeating Units of Elements and Compounds9. Chemical Formulas10. Subatomic Particles11. Atomic Number and Mass Number12. Isotopes13. Radioactivity14. Atomic Mass

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Metals, Nonmetals, and Metalloids

• Elements to the left of the bold staircase on the periodic table are metals while thiose to the right are non-metals. Any elements on either side of the staircase are metalloids. Note that Al is considered a metal and not a metalloid and H is considered a non metal.

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Metals, Nonmetals, and Metalloids

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Chemical Particles

• An atom is the smallest particle of an element that maintains its chemical identity through all chemical and physical changes.

• Fundamental particles are the basic building blocks of atoms, they consist of electrons, protons, and neutrons.

• A molecule is the smallest particle of a diatomic or polyatomic element or a compound that can have a stable independent existence.

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Monoatomic, Diatomic, and Polyatomic Elements• Most elements exist as

single atoms. These are mono atomic elements.

• Only a few elements are made up of two or more atoms, so they consist of molecules.

• Diatomic elements consist of 2 atoms. Polyatomic elements are made up of more than 2 atoms.

VA VIA VIIAH2

N2 O2 F2

P4 S8 Cl2Br2

I2At2

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Fig. 1-3, p. 7

Monoatomic, Diatomic, and Polyatomic Elements

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Fig. 1-4, p. 7

Monoatomic, Diatomic, and Polyatomic Elements

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Physical State of Elements

• All elements are solids at room temperature except:

a.) those that are liquids

(Hg and Br2)

b.) those that are gases

VA VIA VIIA VIIIAH2 He

N2 O2 F2 Ne

Cl2 ArKrXeRn

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Luster, Malleability, Ductility and Hardness of Elements• Metals have luster. Nonmetals do not have

luster, so they are dull.• Most metals are malleable (they can be rolled or

hammered into shape).• Most metals are ductile (they can be drawn into

wires).• Most metals are hard.• Nonmetals are neither malleable nor ductile.• Nonmetals are soft.

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Group, Row, and Section Name of Certain Elements

• In the periodic table, horizontal rows are referred to as periods.• Vertical columns are referred to as families.• Elements that are in certain groups, rows, and sections have

specific names:

Group IA are the alkali metals. Group IIA are the alkaline earth metals. Group VIA are the chalcogens. Group VIIA are the halogens. Group VIIA are the noble gases. The “B” group elements are the transition metals. The two rows at the bottom of the periodic table are the lanthanides,

or rare earth elements, and the actinides. Together they are called the inner transition metals.

Hydrogen is neither an alkali metal nor a halogen.

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Group, Row, and Section Name of Certain Elements

IA IIA IIIA IVA VA VIA VIIA VIIIA1 H H234567

alka

li m

etal

s

ActinidesLanthanides

alka

lin

e ea

rth

m

etal

s

chal

cog

ens

hal

og

ens

no

ble

gas

es

"B" Groups

Transition Metals

(Inner Transition Metals)

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Ions

• Elements can gain or lose electrons and become ions.

• An ion is an atom or a group of atoms that carries and electrical charge.

• A cation possesses a positive charge. e.g. Na+, Mg2+

• An anion possesses a negative charge. e.g. Cl- , S2- .

• A polyatomic ion is a group of atoms that bear an electrical charge. e.g. NH4

+ (the only cation), SO4

2-, PO43-, OH-, NO3

-.

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Chemical Formulas

• Chemical formula shows the chemical composition of the substance.– ratio of the elements present in the molecule or

compound

• He, Au, Na – monatomic elements• O2, H2, Cl2 – diatomic elements• O3, S8, P4 - more complex elements• H2O, C12H22O11 – compounds

• Substance consists of two or more elements

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Chemical Formulas

Compound 1 Molecule ContainsHCl 1 H atom & 1 Cl atom

H2O 2 H atoms & 1 O atom

NH3 1 N atom & 3 H atoms

C3H8 3 C atoms & 8 H atoms

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Ions and Ionic Compounds

• Ions are atoms or groups of atoms that possess an electric charge.

• Two basic types of ions:• Positive ions or cations

– one or more electrons less than neutral– Na+, Ca2+, Al3+

– NH4+ - polyatomic cation

• Negative ions or anions– one or more electrons more than neutral– F-, O2-, N3-

– SO42-, PO4

3- - polyatomic anions

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Ions and Ionic Compounds

• Sodium chloride– table salt is an ionic compound

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Types and Basic Repeating Unit of Elements and Compounds• An atom is the smallest particle of an element that

maintains its chemical identity through all chemical and physical changes.

• Fundamental particles are the basic building blocks of atoms, they consist of electrons, protons, and neutrons.

• A molecule is the smallest particle of an element or compound that can have a stable independent existence. It is incorrect to say a molecule of NaCl. The correct way is to indicate a formula unit of NaCl. It is also incorrect to say a molecule of He. You must say an atom of He. Examples of molecules include H2, S8, H2O, C6H12O6.

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Types and Basic Repeating Unit of Elements and Compounds

Covalent

Atoms

Elements Compounds

Monoatomic Diatomic Polyatomic

Molecules Molecules

Ionic

Molecule FormulaUnit

Type

BasicRepeatingUnit

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Allotropes

• Allotropes are different forms of the same element in the same physical state.

• Examples: graphite and diamond are both C.

oxygen, O2, and ozone, O3, are

both O.

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p. 48

Allotropes

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Hydrates

• A hydrate is a solid compound containing a definite percentage of bound water.

• For example: CuF2 .2H2O

• The heating of a hydrate results in the loss of bound H2O:

CuF2 .2H2O CuF2 + 2H2O

This is considered a chemical change.

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Subatomic Particles

• Atoms are made up of even smaller particles called subatomic particles.

• These subatomic particles are: electrons, protons, and neutrons.

• There are other subatomic particles, but from a chemical perspective they are unimportant.

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Subatomic Particles

Particle Symbol Electrical

Charge

Approx. Mass

Proton p+ +1 1 amu

Neutron no 0 1 amu

Electron e- -1 0 amu

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Subatomic Particles

10-15 m

10-10 m

Nucleus

proton (p+)

neutron (no)

Electron (e-) Cloud

The following diagram depicts the arrangement of subatomic particles.The nucleus, made up of protons and neutrons, is tiny in diameter (approx. 10-5 Angstroms), yet heavy.

1 Angstrom (A) = 1 x 10-10 m = 1 x 10-8 cm.

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Subatomic Particles

• Electrons are found outside the nucleus in certain energy levels.

• In these levels the electrons are dispersed at a relatively great distance from the nucleus.

• The diameter of an entire atom is in the range of 1-5 Angstroms.

• The electrons are dispersed at distances that extend up to 105 times the diameter of the nucleus.

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Subatomic Particles

• Since like charges repel each other, that is why electrons are so far away from each other.

• The nucleus, which contains protons (that have like charges) is very compact, however. The neutrons are said to be the glue that hold the protons together.

Like Charges Repel Each Other Opposite Charges Attract each other

+ + +- - -

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Atomic Number (Z) and Mass Number (M)• The atomic number, Z, is what determines the atom’s

identity.

Z = # of protons in an atom.• The atomic number for each element is found in the

periodic table. Depending on the periodic table, the atomic number is either written below or above the element’s symbol.

18 Ar39.95

39.95 Ar 18

Atomic Number

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Atomic Number (Z) and Mass Number (M)• For atoms, # protons=# electrons. Therefore, atoms are

electrically neutral.• For ions, # protons = # electrons.• Cations with a charge of c+ have c less electrons (but

the same # of protons and neutrons) than its corresponding neutral atom.

• Anions with a charge of (c-) have c more electrons (but the same # of protons and neutrons) than its corresponding neutral atom.

• Being that electrons hardly weigh anything, the number of protons and neutrons that are present in a given atom is what essentially determines the mass of an atom.

• Mass Number = # protons + # neutrons

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Atomic Number (Z) and Mass Number (M)• What is the mass number, atomic number,

and how many protons, neutrons, and electrons, that are present in the following species?

a.) mass number = 40, atomic number = 18

# protons = 18 = # electrons, # neutrons = 40-18 = 22

b.)

c.) H+

4018

Ar

3216

S2-mass number = 32, atomic number = 16 # protons = 16, # electrons=18 # neutrons = 32-16=16

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mass number = 1, atomic number = 1# protons = 1, # electrons=0 # neutrons = 1-1 = 0

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Isotopes

• Isotopes are any two or more forms of an element having the same atomic number and the same chemical properties but different mass number and slightly different physical properties.

• Isotopes of a given element have the same number of protons but different number of neutrons.

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Isotopes

• To distinguish between different isotopes of the same element we write an isotope symbol that indicates the mass number and the atomic number of the atom. The isotope symbol for one isotope of argon is:

Ar4018

Mass Number (M)

Atomic Number (A)

Symbol of Element

M = # of p+ + # no

Z = # of p+

M-Z = [(#p+ + # no) - #p+) - #p+] = # of no

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Isotopes

• The following represents the arrangement of subatomic particles in an atom of Argon-40 (40 stands for the mass number):

Ar4018

Mass number = 40# of p+ = 18# of e- = 18# of no = 40-18 = 22

18p+

22 no

18 e-

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Isotopes

• Examples:

and are isotopes of the same element-Chlorine. ( atomic # = 17)

, (deuterium=D), and (tritium = T) are all isotopes.

Uranium-238 and Uranium-235 have different atomic masses (due to the different amount of neutrons) but chemically both would behave similarly.

X3517 X3717

H11 H21 H31

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Isotopes

• Example Problem:

Which of the following are isotopes of boron-12?

X135 X126 X125

Only is an isotope.

X135

X125Is boron-12, the identical atom.

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Radioactivity

• Elements with Z>83 are unstable (i.e., are radioactive).• Radioactivity is the spontaneous emission of high energy

particles and/or radiation.• Radiation is the emission and transmission of energy

through space in the form of waves.• Radioactive Substance is a substance that decays, or

breaks down, spontaneously. They can decay by emitting one or more of the following: a) alpha particle, b) beta particle, c) gamma radiation.

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Radioactivity

• Particles and Rays Frequently Encountered in Radiation:

Particle or ray

Name of radiation

Symbol Charge Biological Effects

Energetic Radiation

Gamma Ray

X RayX-ray

0

0

Most penetrating, most damaging; can’t be stopped by shielding materials as easily as and particles.

Electron Beta Particle or -1 Less penetrating than rays; not as harmful unless injested or inhaled.

Helium Nucleus

Alpha Particle or +2 least penetrating, not as harmful unless ingested or inhaled.

01 e01

He42

42

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Atomic Mass (Weight) Scale• The atomic mass scale is based on the mass of the carbon-12

isotope. By definition all masses are determined relative to defining the mass of carbon-12 as exactly 12 amu.

• Atomic masses (weights), found in the periodic table are not whole numbers because the weighted average of the masses of all the naturally occurring isotopes of the particular element is taken into account.

• Since the mass of the electron is negligible compared to the mass of the nucleus, the atomic mass of an isotope is approximately equal to its mass number:

AW(average) = (f1 x AW1) + (f2 x AW2) + …. where f1 = fraction of isotope #1 AW1 = atomic weight of isotope #1 f2 = fraction of isotope #2 AW2 = atomic weight of isotope #2

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Atomic Mass Calculation

• Calculate the average atomic mass of copper given the following information:

Isotope %Abundance Atomic Mass (amu) 63Cu 69.1 62.9 65Cu 30.9 64.9AW(average) = (f1 x AW1) + (f2 + AW2)f1 = 69.1 = .691 f2 = 30.9 = .309 100 100AW1 = 62.9 AW2 = 64.9AW(average) = (.691 x 62.9) + (0.309 x 64.9) = 63.6

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Atomic Mass Calculation

• Antimony has two common isotopes. If one of the isotopes is antimony-121 with an atomic mass of 120.9038 amu and an abundance in nature of 57.25%, what is the atomic mass (to 4 significant figures) of the other isotope?

• From the periodic table we see that the average atomic mass for Sb is 121.75 amu.

• Since there are only two common isotopes, the % abundance of the second isotope is 100%-57.25% = 42.75%

AW(average) = (f1 x AW1) + (f2 + AW2)121.75 = (0.5725 x 120.9083) + (0.4275 x AW2)AW2 = 121.75 – (0.5725 x 120.9083) = 122.9 amu .4275

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Atomic Weight Calculation• The atomic weight of fictitious element X is 251.7 amu. If element X consists

of two isotopes that have mass numbers of 250 and 253, what is the approximate % natural abundance of each isotope?

• Since the mass of the electron is negligible compared to the mass of the nucleus, the atomic weight of an isotope is approximately equal to its mass number.

• Since there are only two isotopes, if one has an abundance of X the other isotope must have an abundance of 100%-X or in fractions 1-X.

• Let X be the “fractional” abundance of 250X and (1-X) be the “fractional” abundance of 253X.

AW(average) = (f1 x AW1) + (f2 + AW2) 251.7 = [X x 250] + [(1-X) x 253] 251.7 = 250X + 253 – 253X 251.7 = -3X + 253 251.7 – 253 = X 0.43 (Fraction of 250X) -3Approx. abundance of 250X=43% and approximate abundance of 253X = 57%.