The Evolution of the Atomic Model

Question 1

What did the atomic model look like in 400BC?

Answer 1

like a billiard ball

Question 2

What was Democritus’s theory about the atom?

Answer 2

Matter cannot be divided into smaller pieces forever. Eventually the smallest piece would be obtained, which would be indivisisble.

Atoms have different sizes, are in constant motion, and separated by empty space.

Question 3

Democritus named the smallest piece of matter ________ meaning ______________

Answer 3

atomos, not to be cut

Question 4

What did Aristotle propose?

Answer 4

that all matter is composed of four essential substances

Question 5

What are the four essential substances Aristotle proposed?

Answer 5

Earth
Air
Water
Fire

Question 6

What was John Dalton’s theory?

Answer 6

• All matter is made up of tiny particles called atoms.
• An atom cannot be created, destroyed or divided into smaller particles
• The atoms of one element cannot be converted into the atoms of any other element
• All the atoms of one element have the same properties, such as mass and size. These properties are different from the properties of the atoms of any other element
• Atoms of different elements combine in specific proportions to form compounds

Question 7

What was the experimental proof for Dalton’s Model?

Answer 7

Lavoisier - Law of conservation of mass
Proust - Law of constant composition

Question 8

What is the law of conservation of mass?

Answer 8

mass of reactants must equal the mass of products - balanced equations

Question 9

What is Proust’s Law of constant composition.

Answer 9

each atom has a particular combining capacity

Question 10

Dalton believed atoms are not indivisiable

Answer 10

false

Question 11

When were the series of experiments that demonstrated the atoms is made of smaller components performed?

Answer 11

betwee the 1850s to 1900

Question 12

What were the three atom components discovered between the 1850s to 1900s?

Answer 12

• electrons
• protons
• neutrons

Question 13

What did J.J THomson study? What did he discover?

Answer 13

the passage of an electric current through a gas. As the current passed through the gas, it gave off rays of negatively charged particles.

Question 14

Who discovered electrons? What were they called at the time?

Answer 14

J.H Thomson, they were called corpuscles.

Question 15

What did J.J Thomson conclude from his experiments?

Answer 15

that negative charges come from within the atom so a smaller particle than the atom had to exist. The gas was also known to be neutral so there had to be something positive balancing out the negative particles.

Question 16

What was Thomson’s model? And what year was it presented in?

Answer 16

“plum pudding” model in 1897

Question 17

Describe the structure of the plum pudding model.

Answer 17

atoms were made of a positively charged substance with negatively charged electrons scattered about like raising in a pudding

Question 18

What was Ernest Rutherford’s experiment? What was it’s purpose?

Answer 18

The Gold Foil Experiment - to test Thomson’s model

Question 19

Describe the Gold Foil Experiment.

Answer 19

alpha particle was shot through a small hole in lead at gold foil.
- measured how much the gold foil deflected the alpha particles. The surrounding screens glowed where the alpha particles hit.

Question 20

What were the expectations of the gold foil experiment?

Answer 20

• If electrons were equally distributed throughout the atom, the positively charged alpha particles should pass straight through the gold foil
• there would be little to no deflection

Question 21

What were the experimental findings of the gold foil experiment?

Answer 21

• Most of the positively charged ‘bullets’ passed right through the gold foi without changing course at all
• sme of the alpha particles bounced away from the gold sheet as if they had hit something solid.
• Rutherford knew that positive charges repel positive charges

Question 22

What were the conclusions of the gold foil experiment?

Answer 22

• glod atoms in the sheet were mostly open space
• an atom had a small, dense, positively charged center that repelled positively charged alpha particles
• center of the atom is the ‘nucleus’
• the nucleus is tiny compared to the rest of the atom
• the nuclear model/planetary model - 1920

Question 23

What are the limitations of Rutherford’s model?

Answer 23

• an atomic nucleus composed entirely of positive charges should break apart as a result of electrostatic forces of repulsion
• could not adequately explain the total mass of the atom (neutrons hadn’t been discovered yet)
• accodring to scientific laws and understandings of the time an electron in motion around a central body must conticously emit radiation (as the electron loses energy it should sprial into obliterate the nucleus)

Question 24

What was James Chadwick experiment?

Answer 24

• he bombarded beryllium with fast mocing alpha particles, a beam of particles was given off
• the beam was not affected by magnest or charged objects. It must have been made of uncharged particles - neutrons

Question 25

What did Neils Bohr propose?

Answer 25

- electrons exist in circular orbits with electrostatic force from the nucleus holding them in place - electrons can exist in only a series of allowed orbits (energy levels) that can hold a certain number of electrons. Therefore the energy of electrons are quantized - while an electron is in one orbit it does not radiate energy - electrons can "jump" between energy evels by absorbing and emmitting photons (packets of energy) carrying an amount of energy that equals the difference in energy levels of electrons

Question 26

How many ways can an atom absorbe energy and become excited in one of two ways?

Answer 26

2

Question 27

What are the ways an atom can absorb energy and become excited in?

Answer 27

1. atom can collide with a highly energit particle (e.g. electron) in an electric current passing through a gas) 2. Atom can absorb a phton that has an amount of energy equal to the difference betweent he energy of the orbit it occupies and energy of a higher orbit

Question 28

How does the Atomic LIne (Emission) Spectrum exist?

Answer 28

- electrons excited to higher enrgy levels emit light when they fall back down - when passed through a prism, the pattern of light emitted is shown to be unique for each element

Question 29

What colour has the most energy?

Answer 29

violet

Question 30

What colour was the least energy?

Answer 30

red

Question 31

What happens when it is a hot gas that goes through the prism?

Answer 31

you get mostly black with the colours involved visible

Question 32

What happens when the high density hot matter goes through cold gas?

Answer 32

the absorption spectrum is the entire rainbow with the involved colours blacked out.

Question 33

When is the absoprtion spectra produced?

Answer 33

when atoms absorbe energy

Question 34

What is the absorption spectra comprised of?

Answer 34

dark lines or gaps in the line spectrum

Question 35

When is the emission spectra produced?

Answer 35

when atoms release energy

Question 36

What does the emission spectra comprise?

Answer 36

coloured lines in the spectrum

Question 37

How can the emission spectra be helpful?

Answer 37

in figuring out the composition of certain matter and the type of photoms emitted is helpful in figuring out the kind of elements the substance is made of as each element radiates a different amount of energy and has a unique emission level

Question 38

How can the absorption spectra be used?

Answer 38

to figure out the ability of certain objects to retain heat and its absorption level and in figuring out the number os substances in the sample

Question 39

How are emission and absorption spectra used in the real world?

Answer 39

- anywhere where there are coloured lights - fireworks - neon signs - street lights

Question 40

What is the modern atomic theory?

Answer 40

- all matter is made up of tiny particles called atoms, which are made up of smaller subatomic particles: protons, neutrons and electrons - the atoms of one element cannot be converted into the atoms of any other element by a chemical reaction (*doesn't include nuclear reactions*) - atoms of one element have the same properties which are different from other elements - different isotopes of an element have different numbers of neutrons and thus different masses. - atoms of different elements combine in specific proportions to form compounds

Question 41

although an atom is divisble, it is still the smallest particle of an element that has the properties and indentity of the element