atomic structure history

Question 1

Plato and Aristotle

Answer 1

Greek philosophers who thought matter consisted of the 4 elements: fire, water, air and earth, which were infinitely divisible

Question 2

What did Democritus propose about matter

Answer 2

matter consisted of tiny indivisible particles with nothing in between them but empty space.

Question 3

What did Democritus call the particles that made up matter. what does it mean

Answer 3

atomos; meaning uncuttable or indivisible

Question 4

Name of the chemist who discovered the ‘law of conservation of mass’

Answer 4

Antoine-Laurent Lavoisier

Question 5

What kind of experiments did Antoine-Laurent Lavoisier typically perform

Answer 5

combustion reactions in sealed containers of air

Question 6

What did Antoine-Laurent Lavoisier conclude from his combustion experiments

Answer 6

there was no change in mass during chemical reactions.

Question 7

who proposed the atomic theory

Answer 7

john dalton

Question 8

atomic theory 1: elements are composed of … which are

Answer 8

elements are composed of extremely small particles called atoms, which were indivisible

Question 9

atomic theory 2: all atoms of a given element are … , having the same … Atoms of different elements have different…

Answer 9

all atoms of a given element are identical, having the same size, mass and chemical properties. Atoms of different elements have different size, mass and chemical properties.

Question 10

atomic theory 3: atoms are not …nor…or…

Answer 10

Atoms are not created nor destroyed or changed into different types during a chemical reaction

Question 11

atomic theory 4: a chemical reaction only involves …

Answer 11

a chemical reaction only involve separation, combination or rearrangement of atoms

Question 12

atomic theory 5: compounds are formed when atoms of … combine …

Answer 12

compounds are formed when atoms of more than one element combine in specific ratios

Question 13

what did john dalton typically experiment with

Answer 13

gas and ratios

Question 14

what did j.j. thomson discover

Answer 14

the electron

Question 15

what is the name of jj thomsons’s model and describe it. explain the reason why it is the way it is

Answer 15

plum pudding model. It illustrates numerous negatively charged electrons embedded within a larger positively charged sphere. Through his experiment, he knew that electrons were negatively charged and since the overall charge of an atom is neutral, there had to be something of positive charge to counterbalance it; so he included that large sphere

Question 16

what did ernest rutherford discover and how

Answer 16

the nucleus.

Question 17

describe how rutherford’s experiment was set out

Answer 17

he targetted a beam of alpha particles at a thin sheet of gold foil. Alpha particles have a +2 charge and they are given off during radioactive decay processes. He put a bit of radium (a radioactive metal) inside a lead box with a small opening. The lead absorbs most of the radiation but a thin beam of alpha particles would escape through the hole and shoot towards the gold foil. Those particles could be detected since the foil was surrounded with a fluorescent screen coated with ZnS that will would flash when alpha particles hit it.

Question 18

what did rutherford propose about the atom after his experiment

Answer 18

the atom consists of a mostly empty space occupied by electrons. The low-mass electrons orbit around a tiny, positively charged central region called the nucleus that contains most of the atom’s mass.

Question 19

what were Aristotle, Plato and Democritus’s proposals based on

Answer 19

philosophies and beliefs

Question 20

why were Lavoisier’s findings such a major breakthrough?

Answer 20

because there was a lot of confusion as to what happens to mass during a chemical reaction. People were unaware of the role that gasses like carbon dioxide and oxygen had in combustion reactions.

Question 21

how can Lavoisier’s law apply to a burning log? When you burn a piece of wood, the remaining ashes would obviously be lighter than what it originally was. doesn’t this violate the law?

Answer 21

no. The rest of the mass is actually in the form of carbon dioxide and water (water vapour), which escaped into the atmosphere. If you burned wood in a closed system, the mass of the remains after will be the same as its original mass.

Question 22

describe the experiment that Lavoisier performed.

Answer 22

He strongly heated substances like tin or mercury in sealed containers of air to form various “calxes” (aka metal oxide). After he weighed the container again, it remained the same mass as it was before the chemical reaction.

Question 23

what did robert boyle think elements were made up of

Answer 23

he thinks that elements are made up of ‘unmingled bodies’ what we now know as atoms.

Question 24

what did boyle define an element as

Answer 24

an element is a substance that could not be decomposed into simpler substances.

Question 25

what law did joseph proust discover and what does it state

Answer 25

law of definite proportions

states that a chemical compound always contains its constituent elements in a fixed mass ratio.

Question 26

how did proust discover that law. what compound did he experiment with

Answer 26

he experimented with copper carbonate (CuCO3). whenever he breaks off a piece of it, it always showed that it had copper, oxygen and carbon in a fixed mass ratio of 5:4:1.

Question 27

whose laws did Dalton built his discoveries on

Answer 27

proust’s law of definite proportions

lavoisier’s law of conservation of mass

Question 28

other than his atomic theory, what law did dalton propose. what did it state and what did it state in simpler terms

Answer 28

law of multiple proportions. whenever two elements form more than one compound, the different masses of one element that combines with the fixed mass of the other element will always be in a whole number ratio.

aka. elements can combine in different ratios to form different compounds

Question 29

what couldn’t dalton find out about the atom

Answer 29

its structure

Question 30

what did thomson experiment with. describe what the instrument is consisted of and how the experiment was set up

Answer 30

cathode-ray tube (CRT). It consists of an evacuated glass tube with electrodes attached to both ends. When high voltage is applied to the negative cathode and the positive anode electrodes, the energy causes a beam of cathode rays to be produced from the cathode and flow straight towards the anode. The ray, although invisible, can be detected as the screen is coated with ZnS; a phosphor that glows when energised.

Question 31

what did thomsons first add to his crt experiment to test the charge of the cathode ray and what did he conclude from that

Answer 31

he put 2 charged metal plates on both side of the crt and observed that the ray would bend towards the positively-charged plate, instead of flowing straight. He concluded that the ray must consists of negatively-charged particles since opposite charges attract.

Question 32

other than charged metal plates, what did thomson use to test the charge of the cathode ray and what did he observe

Answer 32

as another test, thomson put magnets on either side of the crt. A charged particle would be deflected by the magnetic field and as expected, it did.

Question 33

what were the 3 conclusions about the cathode ray’s particles that thomson came up with after the experiments.

Answer 33

1. a cathode ray consisted of negatively-charged particles
2. those particles must exists as part of an atom because its mass is much smaller than that of an atom. It was 1/2000th the mass of a hydrogen atom; the lightest atom there is.
3. the particles are subatomic particles which can be found in all elements.

Question 34

how did thomson know that the particles in the cathode ray are subatomic particles which can be found in all elements.

Answer 34

because he tested using different metals for the cathode and anode but the results remained the same

Question 35

what did rutherford expect to see happen in his experiment

Answer 35

he expected for most of the alpha particles to pass straight through the gold foil unaffected because according to Thomson’s model, the positive charge of an atom is spread through the entire atom.

Question 36

what did rutherford actually observe in his experiment that shocked him.

Answer 36

As expected, most of the alpha particles went through the gold foil unaffected but a small few significantly deflected; even going back in the direction where they were shot out from.

Question 37

how did the significant deflections allude Rutherford to thinking that there was a nucleus.

Answer 37

Rutherford thought the mass and charge of the atom isn’t evenly spread through the atom; like what Thomsons proposed, because of those significant deflections. Instead, there has to be a tiny but dense part of the atom that accounts for most of its mass and positive charge.

Question 38

why did rutherford conclude that the atom was made up of mostly empty space which is occupied by electrons

Answer 38

because most of the alpha particles passed through undeflected

Question 39

what did scientists find to be wrong with rutherford’s model

Answer 39

The atom he modelled was unstable, according to classical physics. if electrons are orbiting the nucleus, it would lose energy and speed, and eventually falling into the nucleus and make the atom collapse.

Question 40

what did the bohr model propose that built upon the mistakes of the rutherford model.

Answer 40

proposed that electrons move around the central nucleus in circular orbits (just like what Rutherford said) but only in certain fixed radii. Each discrete distance corresponds to the energy level of the electron, meaning that the electron in the lowest possible radii had the lowest amount of energy (at its ground state). Therefore, electrons couldn’t simply lose energy and fall into the nucleus.

Question 41

what did bohr experiment with. explain the setup and process

Answer 41

used a gas discharge tube to see the emission/line spectrum of hydrogen atom. He filled the tube with hydrogen gas and applied high voltage to its attached electrodes. That energy makes the gas electrically excited and it emits energy, which passes through a triangular glass prism and produces hydrogen’s emission spectrun.

Question 42

what did bohr see in his experiment with hydrogen’s emission spectrum. how did he account for it using his model.

Answer 42

he observed 4 distinct lines in the gas’s electromagnetic spectrum; violet, blue, cyan and red. Those lines show when an excited electron released a photon in order to get to a lower energy level; concluding that electrons are in specific orbits classified by energy. The energy levels of hydrogen he calculated from his model matches with the wavelengths of light seen in hydrogen’s line spectrum

Question 43

what did bohr propose about the energy levels of an atom that is occupied by electrons

Answer 43

an excited electron (one with excess energy) can move from a higher energy orbit to a lower one by emitting a photon that has the energy exactly equal to the difference between the two energy levels.

Question 44

what did james chadwick discover

Answer 44

neutron

Question 45

go through the experiment that chadwick performed to discover the neutron

Answer 45

Chadwick shot a beam of alpha particles towards atoms of beryllium and observed that highly-penetrating rays were released from it. Trying to identify it, he put a block of paraffin (wax) in front of the rays and protons were detecting being shot out of the paraffin rapidly; almost as though the particles in the radiation are pushing them out. He initially thought that the rays were gamma rays but decided that it wasn’t since its had insufficient energy. Therefore, he proposes that the unknown particle in the radiation must be something of similar size and mass as the proton.

Question 46

what is the current atomic model like

Answer 46

central nucleus of protons and neutrons. Instead of having electrons orbitting around it in energy levels, the electrons orbit within orbitals: regions of characteristic electron distribution.

Question 47

list the name of each scientist in order of their discoveries.

Answer 47

aristotle and plato
democritus
robert boyle - elements
antoine-laurnet lavoisier - law of conservation of mass
joseph proust - law of definite proportions
john dalton - atomic theory and law of multiple proportions
jj thomson - plum pudding + crt + electrons
ernest rutherford - gold foil + nucleus
neils bohr - hydrogen emission spectrum + energy levels
james chadwick - paraffin & beryllium & alpha + neutron
louis de broglie - wave nature of electrons
schrodinger and heisenberg - electrons are in orbitals

Question 48

who discovered the wave nature of electrons which accounted for the reason why it had to be in quantised orbits

Answer 48

Louis de broglie

Question 49

who discovered that electrons were in orbitals.

Answer 49

heisenberg and schrodinger

Question 50

do particles smaller than an atom’s subatomic particles exist

Answer 50

yes, protons and neutrons are made up of even smaller particles called quarks.