Introduction to Elements & the Periodic Table

1. Introduction to Elements & the Periodic Table

2. Introduction to Atoms • The first known culture to think about the nature of matter were the Greeks. • Around 430 B.C., a Greek philosopher named Democritus proposed the idea that matter was formed from smaller pieces called “atomos” or “uncuttable”. • Unfortunately, Democritus was unable to prove this idea. • Later, philosophers like Aristotle would advocate the idea that all matter was made up of a combination of only four elements: Fire, Water, Earth, & Air. • It was this false idea that would be taught until modern times.

3. Early Chemistry: Alchemy • During the Middle Ages, there were several people that practiced that art of Alchemy. • Alchemy - • Alchemist were often treated more as magicians than scientists. • Many believed it was possible to turn lead (Pb) into gold (Au) • Some believed it was possible to create an elixir that could stop aging or grant immortality • Even though alchemist didn’t always practice good science, they did make several scientific discoveries. • They discovered the elements mercury, sulfur, and antimony • They discovered several properties of common elements • They learned how to prepare acids • They learned how to create alloys • They developed new glassware for experimentation

4. Development of the Atomic Model • In modern times, scientists returned to the idea that matter was made up of smaller units called atoms, but they still couldn’t describe what atoms looked like. • Several scientists from the 1600s to the 1900s proposed different models to explain how atoms behaved and what they looked like. Dalton’s Model Thomson’s Model Rutherford’s Model Bohr’s Model

5. Modern Atomic Model • In the 1930s the current atomic model was designed. • Atoms are composed of a tiny nucleus at the center of the atom that contain protons and neutrons. • The nucleus is surrounded by an electron cloud that contains electrons. These electrons occupy certain areas of the electron cloud, but are in constant, random movement.

6. Atomic Particles • Even though atoms are considered the smallest form of matter, they are actually composed of smaller particles; each with unique properties that give the element its characteristics. • An element’s overall characteristics are determined by the number of atomic particles found in each atom. • Protons & Neutrons make up the majority of the mass in each atom. Electrons also have mass, but are generally not considered in when calculating the total mass of each atom.

7. Atomic Number & Mass • Every element has a specific atomic number that is unique to that element. • Atomic Number – The number of protons in the nucleus of an atom. • Examples: • Hydrogen always has an atomic number of 1 • Carbon always has an atomic number of 6 • Uranium always has an atomic number of 92 • Although all atoms of an element have the same number of protons, their number of neutrons can vary. • Atoms with the same number of protons, but a different number of neutrons are called isotopes. • Isotope – Atoms with the same atomic number, but different atomic masses. • Atomic Mass - The total number of protons and neutrons in the nucleus of an atom. • Examples: • Carbon has three common isotopes: Carbon-12, Carbon-13, & Carbon-14 • Carbon-12 has 6 protons and 6 neutrons (Atomic Number 6, Atomic Mass 12) • Carbon-13 has 6 protons and 7 neutrons (Atomic Number 6, Atomic Mass 13) • Carbon-14 has 6 protons and 8 neutrons (Atomic Number 6, Atomic Mass 14)

8. Reading Elemental Squares • To help scientists study elemental information, their atomic number, mass, symbol, and name are listed on Elemental Squares. • Atomic/Chemical/Elemental Symbol – The universally accepted abbreviation of the element’s name. • Abbreviations can be 1-2 letters, only the first letter is ever capitalized to avoid confusion. (Hypothetical elements yet to be created have three letter abbreviations until they are “discovered”.) • Most chemical symbols are abbreviated from the element’s name in English, but some are also Latin. • Examples: • Iron, or Ferrum in Latin, has the chemical symbol: Fe • Lead, or Plumbum in Latin, has the chemical symbol: Pb • Note that the Atomic Mass/Weight sometimes is not a nice whole number. That number represents the calculated average of all of that element’s isotopes found in nature.