Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Chapter 5 and 6: Atomic Structure and Chemical Names and Formulas

Atoms,Molecules,

and Ions

© 2009, Prentice-Hall, Inc.

Chapter 5 and 6:Atomic Structure and Chemical Names and

Formulas

Atoms,Molecules,

and Ions


Atoms/Elements

Atoms,Molecules,

and Ions


Subatomic Particles

• Protons and electrons are the only particles in an atom that have a charge.

• Protons and neutrons have essentially the same mass (1 unit each).

• The mass of an electron is so small we ignore it.

Atoms,Molecules,

and Ions


Symbols of Elements

Elements are symbolized by one or two letters.

Atoms,Molecules,

and Ions


Atomic Number

All atoms of the same element have the same number of protons:

The atomic number (Z)

Atoms,Molecules,

and Ions


Atomic Mass

The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

Atoms,Molecules,

and Ions


Isotopes

• Isotopes are atoms of the same element with different masses.

• Isotopes have different numbers of neutrons.

116C

126C

136C

146C

Atoms,Molecules,

and Ions


Atomic Mass

Atomic and molecular masses can be measured with great accuracy with a mass spectrometer.

Atoms,Molecules,

and Ions


Average Mass

• Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations.

• Average mass is calculated from the isotopes of an element weighted by their relative abundances.

Atoms,Molecules,

and Ions


Periodic Table

• It is a systematic catalog of the elements.

• Elements are arranged in order of atomic number.

Atoms,Molecules,

and Ions


Periodicity

When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

Atoms,Molecules,

and Ions


Periodic Table

• The rows on the periodic chart are periods.

• Columns are groups.• Elements in the same

group have similar chemical properties.

Atoms,Molecules,

and Ions


Groups

These five groups are known by their names.

Atoms,Molecules,

and Ions


Periodic Table

Nonmetals are on the right side of the periodic table (with the exception of H).

Atoms,Molecules,

and Ions


Periodic Table

Metalloids border the stair-step line (with the exception of Al, Po, and At).

Atoms,Molecules,

and Ions


Periodic Table

Metals are on the left side of the chart.

Atoms,Molecules,

and Ions


Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms.

Atoms,Molecules,

and Ions


Compounds/Molecules/Ions

Atoms,Molecules,

and Ions


Chemical Formulas for Compounds

The subscript to the right of the symbol of an element tells the number of atoms of that element in one unit of the compound.

Atoms,Molecules,

and Ions


Law of Constant CompositionJoseph Proust (1754–1826)

• This is also known as the law of definite proportions.• It states that the elemental composition of a pure

substance never varies, whether it is a single element or a combination of elements in a compound.

• For example, H2O (water) is always made of two hydrogen for every one oxygen.

Atoms,Molecules,

and Ions


Chemical Formulas of Molecules

Molecular compounds are composed of molecules and almost always contain only nonmetals. They are joined by covalent bonds, which means they share electrons.

Atoms,Molecules,

and Ions


Types of Formulas for Molecules

• Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound. Ex: CH2O

• Molecular formulas give the exact number of atoms of each element in a compound.Ex: C6H12O6 or C3H6O3

Atoms,Molecules,

and Ions


Ways Formulas can be Visually Represented

• Structural formulas show the order in which atoms are bonded.

• Perspective drawings also show the three-dimensional array of atoms in a compound.

• Ball and Stick drawings show 3D shape and relative sizes and organization of atoms in molecule.

• Space Filling Models more accurately shows what the molecule looks like…

Atoms,Molecules,

and Ions


Nomenclature of Binary Molecules

• The less electronegative atom is usually listed first (furthest to the left or lowest down on the periodic table).

• A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however) .

Atoms,Molecules,

and Ions



• The ending on the more element written second is changed to -ide.

– CO2: carbon dioxide– CCl4: carbon tetrachloride

Atoms,Molecules,

and Ions



• If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one.

N2O5: dinitrogen pentoxide

Practice Problems # 37, 38 on pg 159.

Atoms,Molecules,

and Ions


Ions

• Some atoms gain or lose electrons to bond. When atoms lose or gain electrons, they become ions.– Cations are positive and are formed by elements on the left side of

the periodic chart (metals).– Anions are negative and are formed by elements on the right side

of the periodic chart (non-metals).– Ionic charge can be predicted by determining how many electrons

an atom has to lose or gain to become like the nearest stably arranged noble gas.

– Practice Problems 1 and 2 on pg 136 and 16 and 17 on pg 145.

Atoms,Molecules,

and Ions


Ionic BondsIonic compounds (such as NaCl) are generally formed between metals and nonmetals. After the atoms lose or gain electrons they have a charge. The opposite charges attract to each other creating the bond.

Atoms,Molecules,

and Ions


Writing Formulas for Ionic Compounds

• Because all compounds are electrically neutral, one can determine the formula of an ionic compound this way:– The charge on the cation becomes the subscript

on the anion.– The charge on the anion becomes the subscript

on the cation.– If these subscripts are not in the lowest whole-

number ratio, divide them by the greatest common factor.

– Practice Problems #24, 25 on pg 151.

Atoms,Molecules,

and Ions


Common Cations

Atoms,Molecules,

and Ions


Common Anions

Atoms,Molecules,

and Ions


Nomenclature for Ionic Compounds

• Write the name of the cation.• If the anion is an element, change its ending to -

ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. (No prefixes are used)

• If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses.

• Do Practice Problems # 26-29 on pgs 153-156.

Atoms,Molecules,

and Ions


Nomenclature of Acids

• If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- .– HCl: hydrochloric acid– HBr: hydrobromic acid– HI: hydroiodic acid

Atoms,Molecules,

and Ions


Acid Nomenclature

• If the anion in the acid ends in -ate, change the ending to -ic acid.– HClO3: chloric acid

– HClO4: perchloric acid

Atoms,Molecules,

and Ions


Acid Nomenclature

• If the anion in the acid ends in -ite, change the ending to -ous acid.– HClO: hypochlorous

acid

– HClO2: chlorous acid

Practice Problem #40 on pg 160.

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Atoms, Molecules, and Ions © 2009, Prentice-Hall, Inc. Chapter 5 and 6: Atomic Structure and Chemical Names and Formulas