development of the atom

Question 1

what did Ancient Greeks believe all matter was made from

Answer 1

indivisible particles

Question 2

what did Dalton believe

Answer 2

he described atoms as solid spheres and said that different sphere made up the different elements

Question 3

what did Thompson believe about atoms

Answer 3

they weren’t solid and indivisible

Question 4

what was Thompsons experiment

Answer 4

he placed 2 oppositely charged electric plates around the cathode ray. the cathode ray deflected away from the negative plate towards the positive plate

Question 5

what did Thompsons experiment show

Answer 5

the cathode ray has negative particles

Question 6

apart from the cathode rays what else did Thompson do

Answer 6

he placed 2 magnets on either side of the tube and observed this magnetic field also deflected the cathode ray

Question 7

what did the use of the magnets help Thompson determine

Answer 7

the mass to charge ratio of cathode ray particles. this showed the mass of the particles were much smaller than any atom

Question 8

what did Thompson to ensure the validity of his results

Answer 8

he repeated experiments using different metals as electrode materials and found properties of cathode rays remained constant no matter what material

Question 9

what were the conclusions of Thompsons experiment

Answer 9

cathode rays are composed of negative particles which he called electrons. these must exist as part of the atom.

Question 10

what was J.J Thompsons model called

Answer 10

the plum pudding model

Question 11

what did the plum pudding model show

Answer 11

the atom as a ball of positive charge with negative electrons embedded in it

Question 12

where did Thompson believe all subatomic particles were found

Answer 12

within all atoms of all elements

Question 13

what did Rutherford conduct

Answer 13

alpha scattering experiment

Question 14

what was the setup of the alpha scattering experiment

Answer 14

consisted of alpha particles fired at thin gold foil and a detector on the other side to detect how many particles deflected at different angles

Question 15

what is the charge of alpha particles

Answer 15

positive

Question 16

what theoretically happens when you throw alpha particles at gold foil

Answer 16

most of them go straight through but a small number bounce back

Question 17

majority of the particles went through, this meant…

Answer 17

…the atom is mostly empty space

Question 18

some particles deflected through small angles, which meant..

Answer 18

…there is a positive nucleus at the centre

Question 19

only a small number deflected through large angles (more than 90°) which meant…

Answer 19

…the nucleus is extremely small and is where the mass and charge of an atom is concentrated

Question 20

what did Rutherford conclude about atoms

Answer 20

• they consist of small dense positively charged nuclei
• the atom is mostly empty space
• the nucleus is surrounded by a cloud of freely orbiting negative electrons

Question 21

what did Henry Mosely discover

Answer 21

the charge of the nucleus increased from one element to another in units of one

Question 22

how did Mosely use X ray spectroscopy

Answer 22

to establish mathematical study between atomic number of elements and the wavelength of the X rays.

Question 23

what did Mosely discover about atomic numbers

Answer 23

the atomic number refers to the exact number of positive charges in the nucleus of an atom. they can be used to order the elements in the periodic table

Question 24

what did Rutherford discover further after Mosely discovered atomic numbers

Answer 24

the nucleus contained positively charged atoms that he called protons.

Question 25

how did Rutherford explain the charges of the nuclei of different atoms

Answer 25

the atoms of different elements have a different number of protons in their nucleus

Question 26

what did scientists realise about the electrons being in a “cloud” around the nucleus

Answer 26

the electrons would spiral down into the nucleus causing the atom to collapse

Question 27

how did Neils Bohr propose his model

Answer 27

he incorporated the idea of quantum physics that light energy is emitted or absorbed in discrete amounts known as quata

Question 28

what did Bohr suggest about electrons

Answer 28

they follow certain paths around the nucleus with discrete energy. the electrons in “shells” could not lose energy and can only jump from one energy level to another

Question 29

what are the basic principles of Bohrs model

Answer 29

• electrons can only exist in fixed shells and not anywhere in between
• each shell has a fixed energy
• when an electron moves between shells em raditation is absorbed or emitted
• because the energy of shells is fixed, the radiation will have a fixed frequency

Question 30

what happened when electrons jumped from one energy level to another

Answer 30

light was emitted or absorbed at a frequency proportional to the energy difference between shells

Question 31

what did Bohrs model help explain

Answer 31

some periodic properties such as spectral lines seen in emission spectra and energy of electrons at different distances from the nucleus

Question 32

how did the Bohr model explain why some elements are inert

Answer 32

the shells of an atom can only hold a fixed number of electrons and that an elements reactivity is due to its electrons. when an atom has full shells of electrons, it is stable and does not react

Question 33

what was the problem with Rutherfords model even after discovering the proton

Answer 33

the mass of the nuclei of atoms was greater than the protons it contained

Question 34

what did rutherford end up predicting about the nucleus (after proton)

Answer 34

there were other particles in the nucleus that had mass but no charge

Question 35

who discovered the neutron

Answer 35

james chadwick

Question 36

how did Chadwick discover the neutron

Answer 36

he bombarded high energy alpha particles to beryllium and observed the mysterious highly penetrating and electrically neutral radiation

Question 37

what did chadwick demonstrate about the netural radiation

Answer 37

they had a similar mass to a proton and cant be weight less gamma rays

Question 38

what is the modern atomic model

Answer 38

The modern atomic model maintains the ideas of a dense nucleus surrounded by electrons.
However, electrons are now understood to be in ‘clouds’, or orbitals, instead of fixed rings.
These orbitals are regions of space where an electron is most likely to be found.