Chemistry 2nd Quarter SCIENTISTS

Antoine-Laurent de Lavoisier 

• The Father of Modern Chemistry

• He discovered the role of oxygen in combustion; he recognized and named oxygen in 1778 and hydrogen in 1783. This debunked the prominent phlogiston theory, which posited that there is a fire-like element called phlogiston in combustible objects and they are released during combustion.

• Combustion requires fuel, heat, and oxygen. Combustion reaction: CxHy + O2 = CO2 + H2O (and heat and light) 

• He established the Law of Conservation of Mass: Mass cannot be created nor destroyed.

Law of Conservation of Mass

• Mass cannot be created nor destroyed.

by Antoine-Laurent de Lavoisier 

Leucippus and Democritus 

• In the 5th century BC, they stated that all matter was composed of small indivisible particles called “atomos,” meaning uncuttable. 

• They and other ancient Greek atomists theorized that nature consists of two fundamental principles: atom and void. 

Epicurus of Samos

• A Greek philosopher known for his school of thought (Epicureanism) to attain ataraxia. (state of calmness)

• He contributed to atomism by proposing that different types of atoms have different weights and that all atoms have the same speed regardless of size.

Ernest Rutherford, 1st Baron Rutherford of Nelson

• The Father of Nuclear Physics

• He studied under J. J. Thomson (discovered the electron).

• He discovered the concept of half-life (coined the term “half-life”), as he worked with radioactive elements.

• Most notably, however, he differentiated and named alpha and beta radiation. 

• Alpha radiation

• On the other hand, beta radiation is produced in beta decay, where a beta particle (an electron or positron) is emitted out of an atom. The beta decay of a neutron transforms it into a proton by emitting an electron and an antineutrino, or conversely, a proton transforms into a neutron and emits a positron and a neutrino. In the first case, that is called beta-minus decay, which increases the atomic number by one; for the latter, it is called beta-plus decay, which decreases the atomic number. In both cases, the atomic weight of the atom is maintained, only becoming an isobar (atoms of different elements with the same mass number) of that nuclide. This decay is the consequence of the weak force.

Ernest Rutherford

• He was awarded the Nobel Prize in Chemistry in 1908, “for his investigations into the disintegration of the elements, and the chemistry of radioactive substances.”

• Alpha radiation

• is produced in the process of alpha decay, where a particle consisting of 2 protons and 2 neutrons (similar to the nucleus of a helium-4 atom)  is emitted by a nucleus of a very heavy nuclide; this reduces the element’s mass number by 4 and atomic number by 2.

Ernest Rutherford

• He also discovered the element radon, along with Robert B. Owens in 1899.

• After receiving the Nobel in 1908, he carried out the gold foil experiment with Geiger and Marsden; this led to the discovery of the atomic nucleus and prompted Rutherford to devise a new model of the atom, displacing Thomson’s plum pudding model. 

• In 1912, Rutherford was joined by Niels Bohr to create their model of the atom. 

• The element rutherfordium (104) was named after him.

Hans Geiger and Ernest Marsden 

• Under the direction of Rutherford, they performed a landmark series of experiments called the Geiger-Marsden experiments (Rutherford gold foil experiment). 

• The prevailing theory then was that every atom was a sphere of positive charge where electrons are distributed, this was the plum pudding model devised by J.J. Thomson.

• In these series of experiments, they learned that every atom has a nucleus where all of its positive charge and most of its mass is concentrated. 

• They deduced this after seeing some positively charged alpha particles bouncing off the gold foil.

• Following Thomson’s model, all alpha particles would have passed through with minimal scattering as the electric fields in an atom are too weak to affect these particles as the negative and particle charges within the model are spread out and not concentrated.

• After the experiment, they concluded that there is a nucleus (where its positive charge was concentrated) within atoms that can scatter positively-charged alpha particles.

• For ______, the Geiger counter (a widely-used device used to detect ionizing radiation) is named after him.

• BASICALLY UNDER RUTHERFORD’S ALPHA GOLD EXP

Michael Faraday

• Michael Faraday was a protege of Humphry Davy and became one of his successors as Professor of Chemistry at the Royal Institution of Great Britain.

• He established the concept of the electromagnetic field in physics by his research on the magnetic field around a conductor carrying a direct current. 

• His inventions utilizing this concept, the electromagnetic rotary devices became the foundation of electric motor technology. 

• Faraday’s law (or law of induction) states how a magnetic field will interact with an electric circuit to produce an electromotive force – a phenomenon known as electromagnetic induction, the fundamental operating principle of transformers, inductors, and electric motors.

• He is also known for the discovery of the ion which he termed the then-unknown species that goes from one electrode to the other through an aqueous medium.

• In his honor, the SI unit of capacitance (capability of a material to store electric charge) is called farad. 

He also discovered:

• Benzene (named it bicarburet of hydrogen), which he isolated from the oily residue derived from the production of illuminating gas.

• Laws of electrolysis

• Popularized the terms anode, cathode, and electrode (conductor used to make contact with a nonmetallic part of a circuit). 

• Diamagnetism (property of materials that are repelled by a magnetic field)

Humphry Davy

• He invented the Davy lamp which is created for use in coal mines to reduce the risk of explosions due to methane and other gasses.

• He is remembered for isolating (with electricity) the following elements for the first time: potassium, sodium, calcium, strontium, barium, magnesium, and boron.

• He also experimented with nitrous oxide and nicknamed it “laughing gas” and took note of its potential anesthetic properties. 

Henri Becquerel 

• He is known to be the first person to discover radioactivity. Along with Marie and Pierre Curie, he received the 1903 Nobel Prize in Physics for its discovery. 

• Becquerel was interested in phosphorescence (when exposed to radiation of a shorter wavelength, that substance will glow, absorbing the light and remitting it at a longer wavelength) and by that time, Röntgen just discovered X-rays. 

• He soon began looking for a connection between phosphorescence and x-rays. 

• After experimentation with potassium uranyl sulfate, he surmised that the penetrating radiation came from the uranium itself, without any need for excitation by an external energy source. 

• He also made the discovery that radioactivity could be used for medicine which led to the development of radiotherapy, now used to treat cancer. 

• The SI unit for radioactivity, the becquerel (Bq), is named after him.

Henry Moseley

• He developed the concept of the atomic number. 

• He is known for Moseley’s law. Through X-ray diffraction experiments, it led to organizing the periodic table by proton count. 

• Through this discovery, it showed that atomic numbers are not arbitrarily assigned, but have a physical basis as each successive element has a nuclear charge exactly one unit greater than its predecessor. 

WW1 broke out and was killed by a sniper in the Battle of Gallipoli.

John Dalton

• He is best known for introducing the atomic theory. 

Atomic Theory:

1. Elements are made of atoms (extremely small particles).

2. Atoms of a given element are identical while those of different elements differ.

3. Atoms cannot be subdivided, created, or destroyed.

4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

5. In chemical reactions, atoms are combined, separated, or rearranged.

• For his research into color blindness (which he also had), Daltonism is another term for color blindness in several languages.

• Also known as Dalton’s law, the Law of Multiple Proportions states that if two elements form more than one compound, then the ratios of the masses of the second element which combine with a fixed mass of the first element will always be ratios of small whole numbers. 

• His model of the atom is a solid sphere, also known as the Billiard Ball Model of the Atom.

Joseph John Thomson

• He is credited with the discovery of the electron, the first subatomic particle to be found.

• He was also a teacher and seven of his students went on to be Nobel laureates. 

• By experimenting with Crookes tubes (cathode ray tubes),  it showed that all atoms contain negatively charged electrons. 

• He fired a cathode ray in between two magnets with opposing poles. He saw that the ray deviated from the negative pole and oriented towards the positive pole, which shows that there is a negative charge present in the ray.

• He then presented his model of the atom which was the Plum-Pudding model. It shows that electrons are embedded within a positively-charged “soup.”

Joseph-Louis Proust

• He is best known for his discovery of the law of definite proportions, also known as the law of constant composition.

• It states that a given chemical compound always contains its component elements in fixed ratio and does not depend on its source and method of preparation.

• That means, for example, the mass ratio of hydrogen in water is 1:8, regardless of the quantity of water. 

Marie Curie

• She was the first woman to win a Nobel Prize, the first person to win the Nobel twice, and the only person to win a Nobel Prize in two scientific fields.

• She, together with her husband Pierre, and Henri Becquerel, pioneered the field of radioactivity and received the 1903 Nobel Prize in Physics. She coined the word “radioactivity.”

• She also discovered radium and polonium which garnered her another Nobel Prize, this time in Chemistry.

• In World War I, she developed mobile radiography units, known as Little Curies, so wounded soldiers can be immediately operated upon. 

• The element curium (96) was named after her and her husband. 

Niels Bohr 

• He developed the Bohr model of the atom, where he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but they can jump from one energy level to another. 

• It is also known as the Solar System Model as it is akin to the solar system with electrons orbiting the nucleus like how planets orbit the sun. 

• The element bohrium (107) was named after him. 

Paul Villard 

• He discovered gamma rays, which have the shortest wavelength electromagnetic waves and have the highest photon energy.

• While studying radiation emitted by radium, he discovered that the radiation was more powerful than both alpha and beta rays and is more penetrating. However, out of modesty, he did not consider naming them as a different fundamental type.

• Ernest Rutherford instead named them, as gamma rays. 

Gamma rays occur through the radioactive decay of atomic nuclei such as nuclear fission in nuclear reactors and weapons. It also comes from cosmic ray particles (particularly gamma-ray bursts).

Alpha radiation

Radiation, most ionizing; paper can stop it.

Beta radiation

• second most ionizing radiation; passes through paper, thin aluminum stops it. 

Gamma radiation

least ionizing radiation; passes through paper and aluminum; thick lead stops it.

Wilhelm Röntgen 

• He first produced and detected X-rays which earned him the Nobel Prize in Physics.

• He was testing whether cathode rays could pass through glass when he noticed a glow coming from a nearby chemically coated screen. 

• Since he did not know what the rays were, he called them X-rays, meaning “unknown” rays. 

• The element roentgenium (111) is named after him. Same can be said for the unit of measurement roentgen, used to measure the exposure of X-rays and gamma rays. 

Robert Millikan 

• He is notable for measuring the (elementary electric charge) electron’s charge and for his work on the photoelectric effect.

• Famous for his oil drop experiment he conducted together with his student Harvey Fletcher. 

• He sprayed charged tiny oil droplets with an atomiser to pass through a hole into an electric field. By varying the strength of the electric field the charge over an oil droplet was calculated, it always came as an integral value of ‘e’. 

• The charge of an electron was then determined to be 1.602 x 10^-19. 

• Meanwhile, the photoelectric effect is the emission of electrons when electromagnetic radiation such as light hits a material. 

Robert Boyle

• He is best known for Boyle’s law, the inversely proportional relationship between the absolute pressure and volume of a gas (with temperature constant).

• P1V1 = P2V2

• He also wrote the Sceptical Chymist, a cornerstone of modern chemistry. He presented his hypothesis that matter consisted of corpuscles that are in motion and that every phenomenon was the result of collisions of particles in motion. 

James Chadwick

• He is mainly known for his discovery of the neutron that got him the Nobel Prize in Physics in 1935. 

• He detected neutrons by bombarding beryllium with alpha radiation from polonium. This released an unknown radiation scientists believed to be gamma rays. However, the energy released was far too small for that. He then noticed that it ejected protons off the paraffin wax panel (which was full of protons). Chadwick reasoned out that a neutral particle could eject a proton from the paraffin, and surmised it must have similar mass with a proton.

• In other ventures, he wrote the final draft of the MAUD Committee Report, which was tasked to perform the research to determine if an atomic bomb was feasible. (The name MAUD comes from a strange line in a telegram from Niels Bohr, referring to his housekeeper, Maud Ray.)

• In WW2, he was part of the Tube Alloys Project, the R&D program authorized by the UK (with participation of Canada) to develop nuclear weapons. It started before the Manhattan Project in the US.

• When the Quebec Agreement merged his project with the Manhattan Project, he was part of the British mission and became head of the British team. They worked at the Los Alamos Laboratory.

• For his efforts, he was knighted in 1945. 

Eugen Goldstein

• He is known for the discovery of the proton. However, that honor is still debatable.

• He did discover canal rays (anode rays) consisting of positively charged particles produced from gases. The ray consisted of hydrogen gas, which was made of H+ ions (basically protons).  

• However, it was Wilhelm Wien who identified the hydrogen ion as the particle with the highest charge-to-mass ratio in ionized gas. Furthermore, Ernest Rutherford proved that the hydrogen nucleus is present in other nuclei (meaning that there were protons present in other nuclei), so Goldstein’s contribution is still debated. 

• He also did his own investigations of discharge tubes and named the light emissions studied by others as Kathodenstrahlen or cathode rays. As he discovered another ray that travels in the opposite direction, he called them Kanalstrahlen or canal rays. 

Joseph Priestly

• He is credited with the discovery of oxygen and nine other important gasses (however, he gave them different names at the time):

• Nitric oxide (nitrous air), nitrogen dioxide (red nitrous vapor), nitrous oxide (inflammable nitrous air; laughing gas), hydrogen chloride (marine acid air), ammonia (alkaline air), sulfur dioxide (vitriolic acid air), silicon tetrafluoride (fluor acid air), nitrogen (phlogisticated air), oxygen (dephlogisticated air), and carbon monoxide (unknown gas).

• He discovered oxygen by directing sunlight through a burning lens to heat a sample of mercuric oxide. He saw that the gas isolated kept candles burning longer and brighter, and made rats in a sealed container live longer.

• He called it dephlogisticated gas because it was not saturated with phlogiston, so it can carry more phlogiston and allow substances to combust.

• However, his determination to defend phlogiston theory eventually left him ostracized within the scientific community, culminating in the Priestley Riots, prompting him to leave England and move to the US.

• He is also known for the discovery of carbonated water, the main ingredient of today’s soft drinks. Through infusing water with carbon dioxide by pouring water back and forth above a beer vat at a local brewery, he found water that had a pleasant taste and offered it to his friends as a cool and refreshing drink. 

Democritus and Leucippus

•  concluded the smallest unit particle and named this smallest unit particle as “atomos”.

Epicurus

• proposed that different types of atoms have the same speed regardless of size.

Robert Boyle,

•  the founder of chemistry, defined element as the simplest composition of matter that cannot be broken down further by any chemical means. He suggested that atoms of elements combine to form different compounds. 

Joseph Priestly

• studied more on the concepts of elements and compounds. He isolated gas which he called “dephologisticed air” by heating mercury oxide.

Antoine Laurent Lavoisier,

• the father of modern chemistry, discovered oxygen that was involved in the process of combustion and respiration.

Joseph-Louis Proust

• established the law of definite proportion, stating that different samples of any pure compound contain the same proportions by mass.

John Dalton,

, the father of chemical theory, proposed the law of multiple proportions.

Law of multiple proportions

• According to John Dalton’s model of the atom, atoms are seen as solid, indestructible, spheres. According to John Dalton, matter is made up of extremely small indivisible particles called atom, atoms of the same element are identical and are different from those of other elements, compounds are formed when atoms of different elements combine in certain whole-number ratios, and atoms rearrange only during a chemical reaction to form new compound.

Joseph John Thomson

• discovered the electron, a negatively charged particle in the atom, and described the atom as a plum pudding model.

Robert Millikan

• determined the electric charge carried by a single electron using the oil drop experiment.

Ernest Rutherford

• investigated the alpha and beta rays and used the alpha particles to discover a very dense, positive charged nucleus surrounded primarily by empty space using the gold foil alpha scattering experiment.

Eugen Goldstein

•  was an early investigator of discharge tubes, the discoverer of anode rays, and is credited with the discovery of the proton.

James Chadwick

•  was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932.

Niels Bohr

•  theorized that electrons had several possible orbits at different distance from the nucleus, and this energy of electrons are quantized.

Henry Moseley

• demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight by correlating the frequencies of the x-rays to a series of whole numbers that assigned to each element.

Humphry Davy and Michael Faraday

• were the first to demonstrate the electrical nature of matter.

Henry Becquerel

•  proposed that x-rays coming from within the potassium uranyl sulfate exposed the film introducing the rays to magnetic field.

Marie Curie,

• the first woman to receive a Nobel Prize in Physics, discovered the radioactivity that explained the rays deflected when exposed to magnetic field.

Wilhelm Roentgen

• discovered penetrating rays that could travel through walls emitted from a vacuum discharged tube.

Paul Ulrich Villard

• discovered the rays similar to x-ray emitted from radioactive materials but even more penetrating and have neither mass not change.