Elements, Compounds and States of Matter

History of the Periodic Table• ~400 BCE - Socrates initiates Socratic thinking in Athenian

Greece and is credited for modern Western democratic thinking.

• Approximately 2000 years ago in Greece, Plato and his student, Aristotle, proposes all matter is made up of Fire, Earth, Air, Water and Aether

History of the Periodic Table

• 460 – 470 BCE. - Democritus (father of modern science) suggested that all matter is made up of small particles too small to be seen and lead to the creation of particle theory and ‘atomist’ theory

• In 1829, a German scientist Johann Wolfgang Dobereiner begins to foreshadow the Periodic table using periodic triad patterns with respect to atomic masses

History of the Periodic Table

• In 1862, a French geologist and mineralologist named Alexandre-Emile Beguyer de Chancourtois, arranged the elements in order of their atomic weights. As it was written for the geological community, it went unrecognized.

History of the Periodic Table• Dmitri Mendeleyev’s table, published in 1869 became the

most recognized version of the periodic table.

The Periodic Table• 92 naturally occurring elements• Each element has a distinct atomic number that describes the

number of protons and electrons a neutral atom• The atomic weights represent the number of protons and

neutrons in the nucleus of the atom.• Since atoms of the same element may have different masses

due to a difference in the number of neutrons, atomic masses are expressed in decimal

averages.• These different forms of the same element are called isotopes.

Certain atomic isotopes are unstable and give off radioactive energy

The Atom• Electrons are found in energy levels surrounding the proton/neutron filled

nucleus• These electrons do not follow traditional paths. Their location can be

described in terms of probability.

The Atom• Electrons found in the

outer most energy levels are called valence electrons

• The number of valence electrons of an element is a strong predictor of its chemical properties

Elements in the Universe and on Earth

• Astronomers have identified hydrogen and helium as the most abundant elements in the Universe

• The most abundant elements on Earth are oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium

• Does this make sense? Why, or why not?

CompoundsCovalent compounds make up molecules• Molecular compounds SHARE electrons and usually

occur between non-metals• Molecular compounds may be polar (unequal

electron sharing) or nonpolar (equal electron sharing)

Ionic compounds make up ionic compounds• Ionic compounds transfer electrons and stay bonded

through electronegative force

Metallic bonds• Extremely organized and structured lattice of

positive metal ions in a ‘sea of electrons’

Acids and Bases• Acids produce H+ ions in solution• Bases produce OH- ions in solution

States of Matter• Solids -> crystalline structure• Liquids -> vibrations in any material begin to occur at 0 K (−

273.15°C). Upon reaching a melting point, the vibrations break forces holding the solid structure together

• Gases-> when more energy is introduced liquids may change into gases through evaporation. Particles in this states are far away from each other and travel randomly.

• Plasma -> matter existing at temperatures greater than 5000 degrees Celsius experience collisions that knock electrons away from nuclei. This produces a hot, ionized, electrically conductive gas

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