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Chapter 2: Atoms, Molecules, and Ions

The Atom

  • Atoms are mostly empty space.

Subatomic Particles

  • Protons have a positive charge.

  • Neutrons have a neutral charge.

  • Electrons have a negative charge.

  • Protons and neutrons are found in the nucleus and essentially have the same mass.

  • Electrons travel around the nucleus.

Atomic Number

  • Atomic number: the number of protons in the nucleus of an atom; it also provides the number of electrons an atom has.

  • The number of protons equals the number of electrons in an atom.

Atoms of an Element

  • Elements are represented by a one or two letter symbol.

  • All atoms of the same element have the same number of protons, which is the atomic number. It is the subscript before the symbol.

  • The mass number is the total number of protons and neutrons in the nucleus of an atom. It is the superscript before the symbol.

Isotopes

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

  • Isotopes have different numbers of neutrons, but the same number of protons.

  • Example: Isotopes of Carbon

Symbol

Number of Protons

Number of Electrons

Number of Neutrons

11C

6

6

5

12C

6

6

6

13C

6

6

7

14C

6

6

8

Atomic Mass Unit (amu)

  • Atoms have extremely small masses.

  • A mass scale on the atomic level is used, where an atomic mass unit (amu) is the base unit.

    • 1 amu = 1.66054 × 1024- g

Atomic Weight

  • Atomic weight: an average mass is found using all isotopes of an element weighted by their relative abundances.

  • Atomic Weight Formula:

    • \sum [(isotope mass)x(fractional natural abundance)] for ALL isotopes (add same equation for all isotopes).

The Periodic Table

  • The periodic table is a systematic organization of the elements.

  • Elements are arranged in order of atomic number.

  • Organized into groups and periods.

Reading the Periodic Table

  • The atomic number is above the symbol.

  • The atomic weight is below the symbol.

  • Atomic number = amount of protons and electrons.

  • Atomic weight = protons + neutrons

Organization of the Periodic Table

  • The rows on the periodic table are called periods.

  • Columns are called groups.

    • Elements in the same groups have similar chemical properties.

Group Names

  • 1A are Alkali metals (Li, Na, K, Rb, Cs, Fr)

  • 2A are Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)

  • 3-12 are Transition metals

  • 6A are Chalcogens (O, S, Se, Te, Po)

  • 7A are Halogens (F, Cl, Br, I, At)

  • 8A are Noble gases (He, Ne, Ar, Kr, Xe, Rn)

Metals, Nonmetals, and Metalloids

  • Metals are on the left side of the periodic table.

    • Properties include shiny luster, conducting heat and electricity, and solids (except Hg).

  • Nonmetals are on the right side of the periodic table (they include Hydrogen, H).

    • They are mostly gases, but can be solid (Carbon), liquid (Bromine), or gas (Neon) at room temperature.

  • Metalloids occur at a “stair step”.

    • They include Boron, Silicon, Germanium, Arsenic, Antimony, and Tellurium.

    • Their properties are sometimes like metals and sometimes like nonmetals.

Chemical Formulas

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

  • Molecular compounds are composed of molecules and almost always contain only nonmetals.

Diatomic Molecules

  • These seven elements occur naturally as molecules containing two atoms:

    • Hydrogen (H2)

    • Nitrogen (N2)

    • Oxygen (O2)

    • Fluorine (F2)

    • Chlorine (Cl2)

    • Bromine (B2)

    • Iodine (I2)

  • They can never exist alone, they must be paired with something else.

Types of Formulas

  • Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound; simplest formula.

  • Molecular formulas give the exact number of atoms of each element in a compound; actual formula.

  • If we know the molecular formula of a compound, we can create its empirical formula.

Ions

  • When an atom of a group of atoms loses or gains electrons, it becomes an ion.

  • Ion - a charged atom.

  • Cations are formed when at least one electron is lost.

    • Monoatomic cations are formed by metals.

    • Group 1A (1+) and 2A (+2)

      • Trick: Cation = paw-sitive

  • Anions are formed when at least one electron is gained.

    • Monoatomic anions are formed by nonmetals, except the noble gases.

    • Groups 5A (3-), 6A (2-), and 7A (1-)

Polyatomic Ions

  • Sometimes a group of atoms will gain or lose electrons.

  • Polyatomic ions - many atoms grouped together.

  • Polyatomic cation example: Ammonium is NH_{4}^{+}

  • Polyatomic anion example: Sulfate is SO_{4}^{2-}

Ionic Compounds

  • Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

  • Metal + Nonmetal

  • Cation written first then anion.

  • Electrons are transferred from the metal to the nonmetal. The oppositely charged ions attract each other. Only empirical formulas are written.

Writing Formulas

  • When writing formulas, the charge of the cation becomes the subscript for the anion.

  • The charge for the anion becomes the subscript for the cation.

  • If they are not the lowest whole-number ratio, divide them by the greatest common factor.

Chemical Nomenclature

  • The system of naming compounds is called chemical nomenclature.

  • Inorganic nomenclature

    • Write the name of the cation. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. If it is a polyatomic cation, it will end in -ium.

    • 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.

  • Nomenclature of Binary Molecular Compounds

    • The name of the element farther to the left in the periodic table or lower in the same group is usually written first.

    • A prefix is used to denote the number of atoms of each element in the compound.

    • The prefix mono is not used on the first element listed.

    • Prefixes:

      Prefix

      Meaning

      mono-

      1

      di-

      2

      tri-

      3

      tetra-

      4

      penta-

      5

      hexa-

      6

      hepta-

      7

      octa-

      8

      nona-

      9

      deca-

      10

  • The ending of the second element is changed to -ide.

    • CO2: Carbon dioxide

    • CCl4: Carbon tetrachloride

Acid Nomenclature

Three Rules

  • 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

  • If the anion ends in -ite, change the ending to -ous acid.

    • HClO: hypochlorous acid

    • HClO2: chlorous acid

  • If the anion ends in -ate, change the ending to -ic acid.

    • HClO3: chloric acid

    • HClO4: perchloric acid

  • Helpful mnemonic device for naming acids:

    • My ride has hydrolics (-ide changes to hydro____ic acid)

    • I ate something icky (-ate changes to -ic acid)

    • Sprite is delicious (-ite changes to -ous acid)

S

Chapter 2: Atoms, Molecules, and Ions

The Atom

  • Atoms are mostly empty space.

Subatomic Particles

  • Protons have a positive charge.

  • Neutrons have a neutral charge.

  • Electrons have a negative charge.

  • Protons and neutrons are found in the nucleus and essentially have the same mass.

  • Electrons travel around the nucleus.

Atomic Number

  • Atomic number: the number of protons in the nucleus of an atom; it also provides the number of electrons an atom has.

  • The number of protons equals the number of electrons in an atom.

Atoms of an Element

  • Elements are represented by a one or two letter symbol.

  • All atoms of the same element have the same number of protons, which is the atomic number. It is the subscript before the symbol.

  • The mass number is the total number of protons and neutrons in the nucleus of an atom. It is the superscript before the symbol.

Isotopes

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

  • Isotopes have different numbers of neutrons, but the same number of protons.

  • Example: Isotopes of Carbon

Symbol

Number of Protons

Number of Electrons

Number of Neutrons

11C

6

6

5

12C

6

6

6

13C

6

6

7

14C

6

6

8

Atomic Mass Unit (amu)

  • Atoms have extremely small masses.

  • A mass scale on the atomic level is used, where an atomic mass unit (amu) is the base unit.

    • 1 amu = 1.66054 × 1024- g

Atomic Weight

  • Atomic weight: an average mass is found using all isotopes of an element weighted by their relative abundances.

  • Atomic Weight Formula:

    • \sum [(isotope mass)x(fractional natural abundance)] for ALL isotopes (add same equation for all isotopes).

The Periodic Table

  • The periodic table is a systematic organization of the elements.

  • Elements are arranged in order of atomic number.

  • Organized into groups and periods.

Reading the Periodic Table

  • The atomic number is above the symbol.

  • The atomic weight is below the symbol.

  • Atomic number = amount of protons and electrons.

  • Atomic weight = protons + neutrons

Organization of the Periodic Table

  • The rows on the periodic table are called periods.

  • Columns are called groups.

    • Elements in the same groups have similar chemical properties.

Group Names

  • 1A are Alkali metals (Li, Na, K, Rb, Cs, Fr)

  • 2A are Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)

  • 3-12 are Transition metals

  • 6A are Chalcogens (O, S, Se, Te, Po)

  • 7A are Halogens (F, Cl, Br, I, At)

  • 8A are Noble gases (He, Ne, Ar, Kr, Xe, Rn)

Metals, Nonmetals, and Metalloids

  • Metals are on the left side of the periodic table.

    • Properties include shiny luster, conducting heat and electricity, and solids (except Hg).

  • Nonmetals are on the right side of the periodic table (they include Hydrogen, H).

    • They are mostly gases, but can be solid (Carbon), liquid (Bromine), or gas (Neon) at room temperature.

  • Metalloids occur at a “stair step”.

    • They include Boron, Silicon, Germanium, Arsenic, Antimony, and Tellurium.

    • Their properties are sometimes like metals and sometimes like nonmetals.

Chemical Formulas

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

  • Molecular compounds are composed of molecules and almost always contain only nonmetals.

Diatomic Molecules

  • These seven elements occur naturally as molecules containing two atoms:

    • Hydrogen (H2)

    • Nitrogen (N2)

    • Oxygen (O2)

    • Fluorine (F2)

    • Chlorine (Cl2)

    • Bromine (B2)

    • Iodine (I2)

  • They can never exist alone, they must be paired with something else.

Types of Formulas

  • Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound; simplest formula.

  • Molecular formulas give the exact number of atoms of each element in a compound; actual formula.

  • If we know the molecular formula of a compound, we can create its empirical formula.

Ions

  • When an atom of a group of atoms loses or gains electrons, it becomes an ion.

  • Ion - a charged atom.

  • Cations are formed when at least one electron is lost.

    • Monoatomic cations are formed by metals.

    • Group 1A (1+) and 2A (+2)

      • Trick: Cation = paw-sitive

  • Anions are formed when at least one electron is gained.

    • Monoatomic anions are formed by nonmetals, except the noble gases.

    • Groups 5A (3-), 6A (2-), and 7A (1-)

Polyatomic Ions

  • Sometimes a group of atoms will gain or lose electrons.

  • Polyatomic ions - many atoms grouped together.

  • Polyatomic cation example: Ammonium is NH_{4}^{+}

  • Polyatomic anion example: Sulfate is SO_{4}^{2-}

Ionic Compounds

  • Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.

  • Metal + Nonmetal

  • Cation written first then anion.

  • Electrons are transferred from the metal to the nonmetal. The oppositely charged ions attract each other. Only empirical formulas are written.

Writing Formulas

  • When writing formulas, the charge of the cation becomes the subscript for the anion.

  • The charge for the anion becomes the subscript for the cation.

  • If they are not the lowest whole-number ratio, divide them by the greatest common factor.

Chemical Nomenclature

  • The system of naming compounds is called chemical nomenclature.

  • Inorganic nomenclature

    • Write the name of the cation. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. If it is a polyatomic cation, it will end in -ium.

    • 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.

  • Nomenclature of Binary Molecular Compounds

    • The name of the element farther to the left in the periodic table or lower in the same group is usually written first.

    • A prefix is used to denote the number of atoms of each element in the compound.

    • The prefix mono is not used on the first element listed.

    • Prefixes:

      Prefix

      Meaning

      mono-

      1

      di-

      2

      tri-

      3

      tetra-

      4

      penta-

      5

      hexa-

      6

      hepta-

      7

      octa-

      8

      nona-

      9

      deca-

      10

  • The ending of the second element is changed to -ide.

    • CO2: Carbon dioxide

    • CCl4: Carbon tetrachloride

Acid Nomenclature

Three Rules

  • 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

  • If the anion ends in -ite, change the ending to -ous acid.

    • HClO: hypochlorous acid

    • HClO2: chlorous acid

  • If the anion ends in -ate, change the ending to -ic acid.

    • HClO3: chloric acid

    • HClO4: perchloric acid

  • Helpful mnemonic device for naming acids:

    • My ride has hydrolics (-ide changes to hydro____ic acid)

    • I ate something icky (-ate changes to -ic acid)

    • Sprite is delicious (-ite changes to -ous acid)

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