Atoms and Isotopes

Question 1

describe the basic structure of an atom

Answer 1

a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons

most of the mass of an atom is concentrated in the nucleus

Question 2

what is the atomic number

Answer 2

the number of protons in an element

Question 3

what is the mass number

Answer 3

the total number of protons and neutrons in an atom

Question 4

what are isotopes

Answer 4

atoms of the same element that have different numbers of neutrons

Question 5

state how atoms can turn into ions

Answer 5

if they gain or lose electrons to have a full outer energy levels

Question 6

describe the sphere model

Answer 6

before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided

Question 7

describe the plum pudding model

Answer 7

the discovery of the electron led to the plum pudding model of the atom which suggested that the atom is a ball of positive charge with negative electrons embedded in it

Question 8

describe the alpha particle scattering experiment

Answer 8

this experiment led to the conclusion that the mass of the atom was concentrated at the centre (nucleus) and that the nucleus was charged. this replaced the plum pudding model

Question 9

explain why the evidence from the scattering experiment led to a change in the atomic model.

Answer 9

• a few alpha particles are deflected by a positive nucleus
• most of the alpha particles pass straight through the gold foil unaffected by its presence.
• a tiny number of alpha particles reflected because they collide with the nucleus of the gold atoms