The Atom

Question 1

What is the theory of the universe

Answer 1

• There is an empty space between atoms
• atoms have no internal structure
• atoms are completely solid
• each atom (of a different substance) is different in size, weight and shape.

Question 2

Who is democritus

Answer 2

A Greek philosopher who developed the initial idea of an atom in 420 bc

Question 3

Who is John Dalton

Answer 3

The first person to adapt Democritus’ theory into the first modern atomic model in 1800s

Question 4

What is John daltons atomic model

Answer 4

1. All matter consists of tiny particles called atoms
2. Atoms are indestructible and unchangeable
3. Elements are characterised by the weight of their atoms
4. When elements react, it is their atoms that have combined to form new compounds

Question 5

What was the downfall of daltons billiard ball model of the atom

Answer 5

It offers no explanation of the forces that hold the atoms together in compounds. Offers no explanation for the electrical nature of matter.

Question 6

Who indicated the electrical nature of atoms

Answer 6

English chemists Davey and his assistant Micheal Faraday and Swedish chemist Berzelius. They found out that chemical compounds broke up when an electrical current was sent through. Later another scientist Stoney, predicted that electricity consisted of separate units or particles, he proposed the name electron for the unit of electrical charge

Question 7

Who is J.J Thompson

Answer 7

He is an English scientist who discovered in 1897 that electrical charge is composed of small negatively charged particles. These particles were identified as electrons predicted by Stoney. Thompson also did accurate calculations that showed electrons of all substances have the same mass and charge, which brought him to the conclusion that electrons of all matter are identical. This he came to the conclusion that substances differ not because of their electrons but because they are arranged differently inside the atom (later proved wrong)

Question 8

What was the downfall of J.J Thompson’s raisin cake model/ plum pudding model of the atom

Answer 8

• it does not predict the movement of the electrons
• it suggested atoms are filled with a positively charged mass which was later proved incorrect after the discovery of the atomic nucleus by Rutherford

Question 9

What was the bright side of J.J Thompson’s raison cake/ plum pudding model of the atom

Answer 9

• It correctly predicted that there are positive and negative charges which are present in an atom

Question 10

What was the bright side of Daltons billiard ball model of the atom

Answer 10

It correctly predicted That atoms have a spherical shape

Question 11

What are other names for Thompson’s model of the atom

Answer 11

Raisin cake model and plum pudding model

Question 12

What did Thompson’s raisin cake/ plum pudding model of the atom entail

Answer 12

That each atom is a sphere filled with a positively charged mass. This mass resembles the sticky part of a pudding. Also that electrons are negatively charged particles suspended in the positive mass. This resembles the plums in the pudding. Hence the name plum pudding model

Question 13

Who is Ernest Rutherford

Answer 13

A New Zealander who in 1911 was not convinced about the model of the atom proposed by Thompson thus he set up his now famous gold foil experiment with radioactive particles with his two collaborators Geiger and Marsden

Question 14

What type of ions do metals form

Answer 14

Positive ions

Question 15

What type of ions do non-metals form

Answer 15

Negative ions

Question 16

What was Rutherford gold foil experiment

Answer 16

1. He fired alpha particles from the radioactive source (positively charged) at gold foil surrounded by a fluorescent zinc sulphide screen
2. He measured how the alpha particles moved through the atom
3. Most of the particles showed no deviation, some deflected and some reflected

Question 17

What is the explanation behind the observations of the gold foil experiment

Answer 17

1. The particles that went straight through passed through an empty space (missed nucleus and didn’t touch an electron)
2. The particles that were deflected hit an electron
3. The particles which were reflected hit the nucleus

Question 18

What did Rutherfords experiment reveal

Answer 18

• positively charged particles of an atom are concentrated in a very small volume (the nucleus)
• nucleus is surrounded by an “empty”space consisting of negatively charged electrons of very small mass that occur at relatively large distances around the nucleus.
• the volume of an atom is mainly created by the rapidly moving electrons
  -the mass of an atom is mainly located in the core

Question 19

What was Rutherfords atomic model called

Answer 19

The planetary model

Question 20

What was the downfall of Rutherfords planetary model of the atom

Answer 20

It wrongly predicted the movement of electrons

Question 21

Who is neils bohr

Answer 21

A danish scientist who developed a theory that not only explained the existence of light spectra but also presented an explanation for the fact that moving electrons do not collapse. He predicted the total energy of an electron in an atom is quantised thus this energy can only have certain values

Question 22

What is Bohrs theory

Answer 22

1. Electrons move around the nucleus of an atom in one of several concentric circles (shells) or energy levels
2. Electrons with the same energy move in the same energy level
3. The energy levels further from the nucleus have a higher energy than energy levels closer to the nucleus
4. Energy levels closer to the nucleus are filled first with electrons
5. Each energy level is indicated by the letters KLMNOPQ or by the numbers 1234567
6. Each energy level can only take a certain number of electrons (2n^2 where n is the energy level)
7. Electrons in orbits close to the nucleus are in lower energy levels than orbits away from the nucleus
8. If electrons are in the lowest available energy level, then the atom is in a state of the lowest possible energy or in the ground state
9. When electrons absorb energy they move to a higher energy level. The electron is then in the excited state
10. The excited state is unstable and electrons fall back to lower energy levels when they release energy

Question 23

What is the downfall of bohrs theory

Answer 23

Electrons do no travel on a specific orbit or path

Question 24

What is the modern model of the atom called

Answer 24

The wave mechanical atomic model/ the orbital model

Question 25

Who discovered the neutron

Answer 25

James chadwick in 1932

Question 26

Who is Erwin Schrödinger

Answer 26

An Australian who in 1925 proposed a wave mechanical atomic model where the moving electrons forms a special wave (three dimensional) around the nucleus of the atom called an orbital

Question 27

What is used to measure the atomic mass of elements

Answer 27

A spectrometer