Chapter 2 - The Atom Flashcards
Matter
Scientific name for materials
The particulate nature of matter
The concept that all matter is made up of small particles
NH₃
ammonia
HCl
Hydrochloric acid
NH₄Cl
Ammonium chloride
Diffusion
Spreading of gases
What did Greek philosophers say about the atom?
- Matter is made of small particles
- Atoms are indivisible
- Only theory no experiments
What was Dalton’s Atomic Theory?
i) Matter is made of small particles called atoms
ii) Atoms are indivisible
iii) Atoms can neither be created nor destroyed
What did William Crookes do?
Passed electricity through a nearly vacuumed glass tube → noticed it was luminescent
What did William Crookes conclude from his experiments on Cathode rays?
- Cathode Rays travel in straight lines
- They cause glass to fluoresce
- Possess enough energy to move a paddle wheel
Who discovered whether electrons were positive or negative?
JJ. Thompson → negative
Who proposed the name ‘electron’?
George Stoney
What is the ratio of the charge of an electron to its mass?
charge of the electron
——————————– = 1.76 x 10¹¹ coulombs per kg
mass of the electron
Coulombs
Units in which quantity of charge is measured
Cathode rays
Streams of negatively charged particles called electrons. They travel in straight lines from the cathode to the anode, are deflected by electric and magnetic fields, and have sufficient energy to move a small object such as a paddle wheel.
What is the charge of an electron?
1.6 X 10⁻¹⁹ coulomb
What is the mass of an electron?
9.1 x 10⁻³¹ kg
Who proposed the plum pudding theory and when?
JJ Thompson in 1898
Describe the Plum Pudding Model of the atom
The atom was like a sphere of positive charge and electrons are embedded in the sphere at random
Who discovered the nucleus of an atom and when?
Ernest Rutherford in 1909
How was the nucleus of an atom discovered?
i) alpha particles passed through gold foil
ii) alpha particles are positively charged and have two neutrons and two protons
iii) it was found that some of the particles deflected at large angles when passed through the foil and some were deflected straight back
iv) concluded the atom was mostly made of space with a concentrated area of positive charge at the centre
Why, in Rutherford’s experiment, are some of the particles deflected straight back?
Positive alpha particles and the positive nucleus of the atom repelled each other
Who discovered the proton and when?
Ernest Rutherford in 1911
How were protons discovered?
It was found when lighter atoms such as oxygen or nitrogen were bombarded with alpha particles, positively charged particles were given out. This didn’t happen with the heavier atoms as their larger nucleus repels the alpha particles. The alpha particles broke up in nuclei of the lighter atoms releasing positively charged particles called protons
Who discovered the neutron and when?
James Chadwick in 1932
How was the neutron discovered?
Beryllium was bombarded with alpha particles. It was discovered that type of radiation consisting of neutral particle came from the beryllium. These particles have the same mass of a proton and they were called neutrons
