Radioactivity + Atomic Structure Flashcards
Define an alpha particle
A particle made of 2 protons and 2 neutrons
Emitting ionising radiation
Helium Nucleus
Define an ion
Charged particles that form when an atom either gains or loses electrons
When are negative ions created?
When an atom gains electrons
What is the overall charge of an atom?
Neutral
What is the charge of a positron?
+1
What is the relative mass of a positron?
1/2000
(negligable)
Name the antiparticle of an electron
Positron
When can positrons be produced?
During nuclear beta plus decay
when a proton spontaneously changes into a neutron and a positron
In normal conditions (not in a vacuum), how long do positrons last?
A fraction of a second before they react with electrons and are destroyed
Why does the atom have a neutral charge?
The number of negative elctrons is equal to the number of positive protons
What is meant by atomic number?
Number of protons in an atom
What does proton number determine?
Which element an atom is
What is the atomic number of Hydrogen?
1
What is meant by mass number?
And what can it also be called?
The total number of particles within an atom’s nucleus
(protons and neutrons)
Nucleon number
Define Isotope
Atoms of the same element with an equal number of protons but a different number of neutrons
Name the 3 isotopes of hydrogen in order from fewest to most neutrons
Protium
Deuterium
Tritium
True or false:
A paritcular element’s nucleus always has the same charge
True
What makes some isotopes unstable?
An imbalance of protons and neutrons
State an alternative name for shells
Energy Levels
The higher the energy level…
the further the distance of the electron from the nucleus
What happens to electrons when they absorb electromagnetic radiation?
They move to a higher energy level
and are exited
What does it mean for an elctron to be exited?
It has moved up an energy level
What happens as an exited electron returns to its original energy level?
Emits a wave of EM radiation
Where do light waves come from?
Electrons moving down energy levels and emitting EM radiation
State 3 ways in which electrons in an atom’s outer energy level can be knocked out
Friction when objects are rubbed together
Absorbing EM radiation so gaining enough energy to leave the atom
Chemical reactions
Who discovered electrons?
JJ Thomson
Which model did JJ Thomson propose?
Plum Pudding Model
Describe Thomson’s Plum Pudding Model
The atom was a positvely charged mass (dough) with embedded negatively charged electrons (plums)
Name Rutherford’s experiment that helped him form his nuclear model
Gold Foil Experiment
Describe the Gold Foil Experiment
inc. their expectations
Rutherford directed a beam of Alpha particles at a thin gold foil
They expected the Alpha particles to travel straight through and maybe change direction a small amount
State Rutherford’s observations from the Gold Foil experiment
Most Alpha Particles passed straight through the thin gold foil (like they had predicted)
Some alpha particles changed direction but continued through the foil
A few alpha particles bounced back off the gold foil
What did Rutherford discover the Plum Pudding model could not explain?
Why some of the alpha particles bounced back from the gold foil
State Rutherford’s 3 conclusions from his Gold Foil experiment
Atoms are mostly empty space
The nucleus has a strong positive charge
Atoms contain a small, dense nucleus
Name Rutherford’s model
Nuclear Model
State features of Rutherford’s nuclear model
Nearly all of an atoms mass is concentrated in the centre of the atom (in the nucleus)
The nucleus is positively charged
Negatively charged electrons orbit the nucleus at a distance
State the additions Niels Bohr added to his model of the atom
Electrons orbit the nucleus at different distances
Different orbit distances are called energy levels
2 electrons orbit in the first energy level
8 electrons orbit in the second and third energy levels
Why was the Bohr model accepted?
It could explain findings from other experiments better than the Nuclear Model
It could explain the processes of absorption and emission of EM radiation
What is the radius of an atom?
1 x 10 ^ -10 m
