2.04 Video: Crash Course Chemistry #37

Around 400 BC, Greek philosopher Democritus proposed that matter is made of indivisible particles called:

• Plum pudding

• Atomos

• Electrons

Answer explanation

Democritus believed the indivisible atomos of every material had the properties of the material.

Lavoisier proposed the idea that even if matter changes shape or form, its mass stays the same. This idea is:

• The Law of Conservation of Mass

• Unsupported by experiments

Answer explanation

Lavoisier is considered the father of modern chemistry for the Law of Conservation of Mass. He also identified the role of oxygen in combustion, named oxygen and hydrogen, and helped construct the metric system.

In the 1800s, John Dalton determined that:

• The positive charge of an atom is concentrated in the nucleus

• Electrons are more likely to be found in orbitals

• Elements exist as discrete packets of matter. Matter is made of solid, indivisible atoms and atoms of an element are identical.

Answer explanation

Dalton's theory is sometimes called the "Billiard Ball Model" for the solid atoms. He also found that atoms combine in fixed, whole number ratios to form compounds.

Thomson's experiments indicated cathode rays were actually small, negatively charged particles. He called them corpuscles. What did Thomson discover?

• The proton

• The neutron

• The electron

Answer explanation

Thomson imagined negatively charged electrons distributed randomly in a positively charged matrix, like the English dessert plum pudding.

Which atomic model is depicted in this picture?

• Billiard Ball Model

• Plum Pudding Model

• Quantum Model

Answer explanation

Because plum pudding is not as popular outside England, this model is sometimes referred to as a "chocolate chip cookie" model.

Rutherford's gold foil experiment led to:

• The discovery of a positively-charged nucleus

• The discovery of the electron

Answer explanation

Rutherford is considered to be the father of nuclear physics as he discovered the positively-charged nucleus of the atom.

Most alpha particles passed through the atoms undeflected, which indicated to Rutherford that:

• Most of the atom is empty space

• The billiard ball model was correct

Answer explanation

Rutherford also bombarded nitrogen with alpha particles, which resulted in hydrogen ions. He recognized that these positive ions were protons.

Bohr applied mathematical principles to Rutherford's atomic model and predicted the most likely positions of electrons within the atom based on energy levels. This resulted in what model of the atom?

• 
• 
• 

Answer explanation

The planetary model represents electrons in orbits around a small central nucleus. Each orbit can have a specific number of electrons, which correlates to the energy levels and orbitals in the current quantum model.

Heisenberg discovered that learning more about the momentum of any subatomic particle makes it difficult to measure its position, so:

• Electrons cannot be said to be neatly aligned in circular orbits

• He proposed that electrons are particles

Answer explanation

Electrons behave like both particles and waves, and their position and momentum cannot both be determined with certainty. This is Heisenberg's Uncertainty Principle and it turns up in comics.

Schrodinger's quantum model of the atom has electrons arranged around the nucleus in probability clouds called orbitals because

• Electrons behave like particles and waves and their position cannot be determined with certainty

• The nucleus is bigger than expected

Answer explanation

Quantum model orbitals have different shapes by energy level.