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

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 × 10^24- 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 for Acid Nomenclature

• 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)

Reference: Chemistry The Central Science (14th Edition)