Unit 6: Classification of Matter, Periodic Table and Atomic Theory

Matter

Particles

Pure substance

• 1 type of particle

• Can’t be physically separated

Element

• 1 type of particle

• 1 type of atom

• Diatomic element

Compound

• 1 type of particle

• More than 1 type of atom bonded to another atom

Mixture

• 2 or more different types of particles

• Cab be physically separated

Heterogeneous

• Unevenly mixed

• Can identify different particles

Homogeneous

• Evenly mixed

• Can’t identify difference particles

Atomic number

Number of protons

Atomic mass

Average of atomic mass exiting

Protons + neutrons

Democritus

First to suggest the existence of atom

Invisible

Dalton’s Model

• All elements are composed of tiny indivisible and indestructible particles called atoms

  Atoms of the same element are identical.  

  Atoms cannot be created or destroyed.

  Atoms of different elements can combine in whole number ratios to form compounds.

What is wrong with Dalton’s Model?

Atoms of the same elements are identical is wrong because there are isotopes

Cathode Ray tube experiment

Evidence: When a magnetic field was brought near the cathode ray tube, the beam was deflected

Conclusion: The subatomic particles making up the beam must be negatively charged

The cathode ray tube experiment involved a sealed glass tube with a vacuum, where high voltage was applied across two metal electrodes. This produced a beam of cathode rays traveling from the negative electrode to the positive electrode (anode). Thomson observed that the rays were deflected by electric and magnetic fields, proving they were negatively charged particles.

Ernest Rutherford

Predicted that if Thomson’s model was correct the a particle would go straight through atoms

Conducted gold foil experiment

Rutherford’ Gold Foil Experiment

a beam of positively charged alpha particles was directed at a thin sheet of gold foil. Surrounding the foil was a photographic film, which would emit light when struck by the particles. By observing the flashes of light, Rutherford’s team tracked the paths of the alpha particles, noting whether they passed straight through, deflected at small angles, or bounced back. It showed atoms have a small, dense, positively charged nucleus, as most alpha particles passed through the foil while some were deflected at large angles.

James Chadwick’s Model of Nucleus

Model: discovered the neutrally charged neutronlocated in the nucleus

Mass Spectroscopy

Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It works by ionizing chemical compounds, separating the ions based on their mass and charge using electric and magnetic fields, and detecting them.

alpha decay