L2.5: Atoms, Molecules, and Ions

• Dalton’s Atomic Theory (1808)

  ● All elements are composed of atoms.

  ● Each element has its own atoms. All of these atoms are identical to one another but different from the atoms of another element.

  ○ Ex: Uranium 235 and 234 have the same atoms. But uranium and iron do not have the same atoms.
• Dalton’s Atomic Theory (1808)

  ● Compounds are made of 2 or more elements. Each element is made of atoms. The ratio of atoms on each element in the compound will be proportional with the ratio of atoms in an element that is not in a compound.

  ○ Ex: Water or H2O is composed of 2 hydrogens and 1 oxygen. If 1 hydrogen has 2 atoms, the hydrogen in H2O will have 4 atoms. 2 and 4 can be further simplified, thus they are proportional to one another.

  ● Atoms cannot be created nor destroyed. Thus, in any chemical reaction, combination, separation, and rearrangement of atoms only occurs.
• Law of Mass Conservation

  ● When 2 elements are combined, its individual mass does not decrease or increase. It just adds to one another.

  ○ Ex: Calcium oxide, that has a mass of 56.08g, is chemically combined with carbon dioxide that has 44.00g. Abiding with the law of mass conservation, the mass of the two elements will be combined resulting in a total mass of 100.8g, which is the mass for calcium carbonate, the resulting compound of calcium oxide and carbon dioxide.
• Law of Definite (or Constant) Composition

  ● No matter where the compound is found, its elements will stay the same.

  ○ Ex: Water from Australia is the same as the water in the Philippines. Both water is composed of H2O
• Law of Multiple Proportion

  ● The Law of Multiple Proportions states that when two elements combine to form more than one compound, the ratio of their masses can be expressed in small whole numbers.

  ○ Ex: Carbon and oxygen can make carbon oxide I and carbon oxide II. When we calculate the ratio of carbon and oxygen for each compound, the resulting number can form a ratio that illustrates their differences in the proportion of its elements.
• Ions

  ● Atoms that have a charge because it either gave an electron or received an electron.

  ● Formed from the combination of metal and nonmetal.
• Polyatomic Ion

  ● Ions that contain more than one atom.

  ● Has a fixed formula.

  ● Can either be anion or a cation.
• Cation

  ● Ion that has a positive (+) charge

  ● If an ion has a positive charge, meaning it loses one or more electrons.

  ● OIL - Oxidation is Loss
• Anion

  ● Ion that has a negative (-) charge

  ● If an ion has a positive charge, meaning it gains one or more electrons.

  ● RIG - Reduction is Gain
• Ionic Compounds

  ● Formed between metal and nonmetal elements.
• Metal

  ● Found on the left side of the periodic table.

  ● Forms cations.
• Covalent Compounds

  ● Formed between metal and nonmetal elements,

  or metal to a metalloid.
• Molecules

  ● Group of atoms that share electrons.
• Isotopes

  ● These are atoms of the same element that have different mass numbers.
• The mass number of elements found in the periodic table is the averages of all isotopes of that element.

  ○ Ex: Uranium 235 and Uranium 234 are both isotopes of uranium. They are the same elements that just have different mass numbers because they have different number of neutrons

  ○ If we get the average mass number of Uranium 235, Uranium 234, and the

  other isotopes, we will find the average atomic mass number of Uranium.
• Binary Acids

  ● Solutions that form when certain gaseous compounds dissolve in water.

  ● Hint: Most acids have hydrogen on it.
• Oxoacids

  ● Acids that have oxygen on it.