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Atomic Structure and Compounds: Hypotheses, Theories, and Subatomic Particles, Lecture notes of Chemistry

Iowa State University (ISU)Chemistry

An overview of scientific methods, atomic theory, and the investigation of atomic structure through experiments by Millikan, Thomson, and Rutherford. It covers the subatomic particles electrons, protons, and neutrons, isotopes, atomic mass, and the naming of molecular and ionic compounds.

Typology: Lecture notes

2020/2021

Uploaded on 02/02/2021

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Scientific Methods:
โ€ขWhat is a hypothesis?
โ€“A tentative and testable
explanation for an observation.
Example: Studentsโ€™ performance.
โ€ขDefine a scientific theory.
โ€“A set of tested hypotheses that
explain a widely observed natural
phenomena.
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Atoms, Molecules, and Ions
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Download Atomic Structure and Compounds: Hypotheses, Theories, and Subatomic Particles and more Lecture notes Chemistry in PDF only on Docsity!

Scientific Methods:

โ€ข What is a hypothesis?

  • A tentative and testable

explanation for an observation.

Example: Studentsโ€™ performance.

โ€ข Define a scientific theory.

  • A set of tested hypotheses that

explain a widely observed natural

phenomena.

Atoms, Molecules, and Ions

The Atom

  • What are the four outlines of Daltonโ€™s Atomic Theory?

1. An atom in the smallest indivisible particle of an element.

2. All atoms of the same element are identical but different from

those of other elements.

3. Atoms combine in simple whole number ratios to form

compounds.

4. Atoms can be rearranged in a chemical reaction but can neither

be created nor destroyed.

The Atomic Structure

  • Identify and describe the subatomic particles
  • Electrons - negatively charged cloud.
  • Nucleus - contains two types of particles:
    • Protons - positively charged subatomic particles.
    • Neutrons - electrically neutral subatomic particles.
  • The nucleus is approximately 1/10,000 the size of the atom. Sodium atom

Atomic Symbols

  • How is an atomic symbol represented?
  • Mass number (A) โ€“ total number of protons + neutrons.
  • Atomic number (Z) โ€“ # protons (Atomic # = Protons # = Electrons #).
  • The symbol for phosphorus, Na, having 11 protons and 12 neutrons

can be written as

X

A

Z

Elemental symbol

Atomic Mass: Weighted Average

Mass spectrometer representative peaks for natural neon.

A mass spectrometer measures the masses of atoms.

  • Given that natural neon consists of three isotopes as shown below,

what is the average atomic mass of neon?

Atomic Mass: Weighted Average ๐‘€๐‘Ž๐‘ ๐‘  = { 90 .4838% ๐‘œ๐‘“ 19. 9924 + 0 .2696% ๐‘œ๐‘“ 20. 9940 + 9 .2465% ๐‘œ๐‘“ 21. 9914 } ๐‘Ž๐‘š๐‘ข = { 0. 904838 19. 9924 +. 002696 20. 9940 + 0. 092465 21. 9914 }๐‘Ž๐‘š๐‘ข = 20. 1799 ๐‘Ž๐‘š๐‘ข

The Modern Periodic Table

  • Metals
    • shiny solids; conduct heat and electricity; are malleable and ductile.
  • Nonmetals
    • solids, liquids, and gases; nonconductors; solids are brittle.
  • Metalloids
    • Shiny solids (like metals); brittle (like nonmetals); semiconductors.

Molecular Compounds

  • What are molecular compounds?
  • They are compounds held together by covalent bonds ; bonds

created by sharing one or more pairs of electrons.

  • What are the 4 ways by which a molecule can be represented?

โ€’ Chemical formula (such as CH 4 for methane)

โ€’ Structural formula

โ€’ Space-filling model

โ€’ Ball-and-stick model

Structural formula Space-filling model Ball-and-stick model

Ionic Compounds

e.g., NaCl

  • How are ionic compounds different from

molecular compounds?

  • They are held together by electrostatic

forces (ionic charges); electrons NOT shared.

  • Formed from a reaction between a metal

and a nonmetal.

  • Cations
  • Anions
  • Charges depend on the location of the atom

in the periodic table.

  • Group 1 metals = +
  • Group 2 metals = +
  • Halogens = โ€“ 1

Naming Ionic Compounds

  • What would be a convenient name for MgCl 2?
  • Cation named first using name of element. Example, Mg = magnesium
  • Anion named by adding the - ide suffix to the name of the element.

Example, Cl = chlorine, which becomes chlor ide.

  • Formulas for ionic compounds must always be neutral. Mg2+^ + (Clโ€“) x 2 MgCl 2

Polyatomic Ions

Oxyanions:

  • Are polyatomic anions containing oxygen in combination with one or more other elements.
  • Named based on the element that appears first in the formula, with its ending changed to either - ite or - ate.
  • Some elements form more than two oxyanions: - ate implies one more oxygen than โ€“ ite ; prefix hypo implies one less oxygen; prefix per - means one more oxygen.
  • Are charged

group of two or

more atoms

joined together

by covalent

bonds.

Naming Acids

  • What are binary acids? Can you provide a convenient name for a

common binary acid such as HCl?

  • Contain hydrogen and a monoatomic anion (e.g., Cl

, Br

  • Common examples include HCl and HBr.

  • Acid names: HCl is hydrochloric acid; HBr is hydrobromic acid

  • Oxyanions and Corresponding Acids

  • If oxyanion name ends in:

    • ite, the corresponding acids ends in - ous
    • ate, the corresponding acids ends in - ic Oxyanions of Bromine and Their Corresponding Acids Ions Acids