Chemistry Chapter 4- Atomic Theory

Properties of Subatomic Particles

Electron: e-, relative charge -1, relative mass 0, actual mass 9.11 x 10^-28 Proton: p+, relative charge +1, relative mass 1, actual mass 1.67x10^-24 Neutron: n^o, relative charge 0, relative mass 1, actual mass 1.67x10^-24

Sir Crooke and the Crookes Tube

*This proved how atoms are made up of other things. Hypothesized that the glow was caused by a stream of particles, and they called the stream of particles "cathode rays".

Learning outcomes of Crookes Tube

1) All atoms were made up of negatively charged particles 2) All elements have atoms that are made up of the negatively charged particles

What were the two other fundamental ideas that were investigated and who investigated them?

1) Law of Definite Proportions: when atoms combine to form compounds, they combine in whole number ratios. This was for all elements and was created by Joseph Proust. 2) Law of Multiple Proportions: Created by John Dalton, this stated that atoms can combine in different proportions and thus would create different compounds.

Learning outcomes of Rutherford's experiment

1) there is empty space between atoms 2) alpha particles which are positive are repelled by positive protons, therefore there was a deflection 3) some alpha particles hit the positive protons straight on. IN ORDER FOR THIS TO HAPPEN, the idea that protons are grouped rather than individually floating arose, thus hypothesizing about a nucleus. 4) more empty space than there are protons 5) electrons have no influence on the direction of alpha particles.

Who was Antoine Lavoisier and what did he do?

Antoine Lavoisier was a French chemist, known as the "Father of Modern Chemistry." He observed how matter behaves before and after of reaction. His experiments lead him to establish the Law of Conservation of Matter, which stated that the total mass of reactions equals the total mass of products.

Who was Aristotle and what did he do?

Aristotle was a popular Greek scientist and philosopher. He believed that matter was continuous and opposed the idea of atoms, and his lack of interest in the microscopic world made chemistry die for 1400 years.

Summary thus far

Atoms are divisible (Crookes) Electrons are present in all atoms and are identical from atom to atom and have a negative charge (Thompson) Next hypothesized ideas: Atoms are electrically neutral, and thus must have a positive particle to balance the negative particle (Thompson) Because electrons are basically massless, there must be something else that accounts for an atom's mass (Millikan)

John Dalton

Dalton came up with on of the first atomic theories. He summed it up in 5 statements: 1) All matter is composed of extremely small particles called atoms, which are indivisible (NOT ENTIRELY TRUE)--Dalton also came up with the Cue Ball Model to represent how atoms were indivisible 2) Atoms of a given element are identical in size, mass, and other properties; vice versa for different elements (PARTIALLY TRUE) 3) Atoms cannot be subdivided, created, nor destroyed (NOT ENTIRELY TRUE-- atoms can be subdivided, but cannot be created nor destroyed) 4) Atoms of different elements combine in simple whole number ratios to form chemical compounds, aka Law of Multiple Proportions (100% TRUE) 5) In chemical reactions, atoms are combined, separated, or rearranged (100% TRUE)

Who was Democritus and what did he do?

Democritus was an ancient greek scientist that developed the idea of atoms. He thought that atoms were the smallest particle in existence. He also proposed that all matter in the universe is composed of tiny, indivisible particles of atoms. However, he had no proof and was not very popular thanks to Aristotle, so his theory was not believed.

What happened in the late 1800s?

Experiments were made in which electronic currents passed through various gases at low pressure-- simplest was the Crookes Tube

Goldstein

Goldstein observed a cathode ray tube and found rays traveling in the opposite direction of that of the cathode rays. He called the rays canal rays and concluded they were composed of positive particles. It was soon discovered that the positive particle was about 2000 times the mass of an electron. Thompson revised his Plum Pudding Model based off of Goldstein's discovery

Ernest Rutherford

He tested Thompson's model of an atom using massive radioactive alpha-particles: Roentgen (now used in x-rays), Becquerel (used for radioactivity), and Curies (used a lot in modern chem practices). Rutherford directed a narrow beam of alpha particles at a very thin sheet of gold foil. Results: 1) most alpha particles went straight through the gold foil, 2) some alpha particles deflected, and 3) some alpha particles reflected.

James Chadwick

In 1932, James Chadwick confirmed the existence of another subatomic particle-- the neutron, which is a particle with no charge, and its mass nearly equaled that of a proton. THEREFORE, the subatomic particles are the electron, proton, and neutron.

JJ Thompson

JJ Thompson proved the particles within cathode rays are negatively charged because when a positively charged magnet was moved close to the rays, the rays were attracted to the magnet. This also allowed Thompson to calculate the e/m ratio. He found that the ratio was the same regardless of the metal used as the cathode, thus proving that all metals have negatively charged particles. He then went on to conclude that all atoms have negatively charged particles.

Robert Millikan

Millikan performed an experiment to calculate the mass of an electron. The mass of an electron = 1/2000 the mass of the simplest atom (hydrogen). He also performed the oil drop experiment, which proved that if an electron existed in all substances, all electrons are identical. He also found the mass of an electron to be 9.109x10^-31 kg, and for all practical purposes, the mass is 0.

What is amazing about the four categories of matter the Greeks discovered?

The Greeks' theory about air, water, earth, and fire being the only four categories of matter still holds some truth today, except air--> gas, water--> liquid, earth--> solid, and fire--> plasma/energy.

What was the significance of the early Greeks to chemistry?

The early Greeks discovered the correlation between air, water, earth, and fire.

What happened in 1790?

The study of matter was revolutionized by a new emphasis on quantitative analysis because of the inventions of more improved balances.

Plum Pudding Model

Thompson made the Plum Pudding Model, nicknamed the chocolate chip cookie model or blueberry muffin model by Americans, which assumed that there were some positive particles to balance out negative charges