unit 3: atomic theory

Question 1

Democritus found and believed that

Answer 1

all matter is made up of small indivisible particles called “atomos”.

Question 2

Dalton’s atomic theory (4 parts + 1 bonus)

Answer 2

1. Elements are composed of extremely small particles called atoms.
2. All atoms of a given element are identical, having the same size, mass, and chemical properties. The atoms of one element are different from the atoms of all other elements.
3. Compounds are composed of atoms of more than one element. In any compound, the ratio of number of atoms of any two of the elements present is either an integer or a simple fraction.
4. A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
   Dalton made no attempt to describe the structure or composition of atoms.
   Bonus: he made no attempt to describe the structure of the atom.

Question 3

Proust’s law of definite proportions states

Answer 3

that different samples of the same compound always contain its constituent elements in the same proportion by mass.

Question 4

Law of multiple proportions (Dalton’s third hypothesis supports this)

Answer 4

if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Question 5

Law of conservation of mass (Dalton’s fourth hypothesis basically reiterates this)

Answer 5

matter can be neither created nor destroyed.

Question 6

Atom (definition)

Answer 6

the basic unit of an element that can enter into chemical combination.

Question 7

Subatomic particles (definition + examples)

Answer 7

smaller particles that atoms are made out of (protons, neutrons, and electrons).

Question 8

Radiation (definition)

Answer 8

the emission and transmission of energy through space in the form of waves.

Question 9

Cathode ray experiment (explain)

Answer 9

When two metal plates are connected to a high-voltage source, the negatively charged plate (the cathode) emits an invisible ray. A cathode ray is shot to a fluorescent screen. The cathode ray is drawn to the positively charged plate (the anode). Because it’s drawn to the positive plate and repels negativity, we know it has a negative charge, thus making it an electron.

Question 10

J.J. Thomson (explain experiment and findings)

Answer 10

used a cathode ray tube and his knowledge of the electromagnetic theory to determine the ratio of electric charge to the mass of an individual electron. He decided on -1.76 x 108 Coulomb/gram.

Question 11

R.A. Milikan (explain findings)

Answer 11

found the charge and mass of the electron:
charge: -1.6022 x 10-19 C.
used this and Thomson’s electron ratio of electric charge and mass: mass = 9.10 x 10^-28 g.

Question 12

Rontgen, Becquerel, Curie (explain findings)

Answer 12

Rontgen noticed that cathode rays caused glass and metal to emit very unusual rays that were highly energetic penetrated matter and could not be deflected by a magnet. He called them X-rays. Becquerel found something similar. His student, Marie Curie, suggested radioactivity.

Question 13

Radioactivity (definition)

Answer 13

spontaneously emission of particles and/or radiation.

Question 14

Decay (definition)

Answer 14

breakdown of radioactive substances. Produces three types of rays/particles.

Question 15

3 types of rays/particles produced in decay:

Answer 15

1. Alpha rays: consist of positively charged particles.
2. Beta rays: are electrons and are deflected by the negatively charged plate.
3. Gamma rays: high energy rays with no charge.

Question 16

Rutherford (experiment + findings)

Answer 16

Through the gold foil experiment understood positive charge + mass is concentrated in the nucleus with electrons on the outside of the nucleus. Rutherford shot alpha particles but most of them passed through. However, only a couple bounced back, which showed that the nucleus only occupied a small fraction of the volume of the atom. The nucleus is positive as alpha particles were deflected from it.

Question 17

Protons (definition + mass + charge)

Answer 17

Positively charged particles in the nucleus are called protons. It has the same magnitude of charge as an electron, but a mass of 1.67262 x 10-24.

Question 18

Atomic dimensions (unit)

Answer 18

typically picometers. A typical atomic radius is about 100 pm.

Question 19

Chadwick (experiment + findings)

Answer 19

He bombarded a beryllium sheet with alpha particles and found that very high energy radiation similar to gamma rays was emitted. He named these particles “neutrons”, which were electrically neutral particles with a mass slightly greater than protons.

Question 20

Atomic number (variable + definition)

Answer 20

(Z) the number of protons in an atom.

Question 21

Mass number (variable + definition)

Answer 21

(A) total number of protons and neutrons present in the nucleus of an atom.

Question 22

Planck (findings)

Answer 22

discovered that atoms and molecules could emit or absorb energy only in discrete quantities, like small bundles. He gave the name quantum to the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation.

Question 23

Wave (definition)

Answer 23

a vibrating disturbance by which energy is transmitted. The speed of the wave depends on the type of wave and the nature of the medium.

Question 24

Wavelength (definition)

Answer 24

distance between identical points on successive waves. typically in nanometers.

Question 25

Frequency (variable + defintion)

Answer 25

(v, nu) the number of waves that pass through a particular point in one second.

Question 26

Amplitude (definition)

Answer 26

the vertical distance from the midline of a wave to the peak or trough.

Question 27

Electromagnetic waves have two components

Answer 27

electric field component and magnetic field component. They have the same wavelength, frequency, and speed, but travel on mutually perpendicular planes.

Question 28

Electromagnetic radiation (definition)

Answer 28

the emission and transmission of energy in the form of electromagnetic waves

Question 29

Speed of light (variable + formula)

Answer 29

(c) 3.00 x 10^8 m/s (be careful; wavelengths are in nm!)

Question 30

Planck’s constant

Answer 30

6.63 x 10^-34

Question 31

Einstein’s photoelectric effect (description of the phenomenon, what he found, what he did not say)

Answer 31

a phenomenon in which electrons are ejected from the surface of certain metals exposed to the light of at least a certain minimum frequency (threshold frequency).
Said he found the dual nature of light; Everyone knew it was a wave, but he said it was also a stream of particles (photons). He DID NOT say that particles have a wave nature (deBroglie looked at Einstein’s work and said that).

Question 32

Emission spectra

Answer 32

either continuous or line spectra of radiation emitted by substances.
Can be seen with thermal energy or other form of energy.

Question 33

Line spectra

Answer 33

light emission only at specific wavelengths.
The emission spectra of atoms at a gas phase do not show a continuous spread of wavelengths instead, they produce bright lines at different parts of the visible spectrum.

Question 34

Ground state/ground level

Answer 34

lowest energy state of a system.

Question 35

Excited state/excited level

Answer 35

higher state of energy (unstable).

Question 36

How to move up energy levels

Answer 36

depends on the difference in energy levels between the initial and final states. (delta)E= E(sub)f = E(sub)I.