Radioactivity Flashcards
Describe Bohr’s atomic model
In this model, the nucleus is orbited by electrons, which are in different energy levels.
Describe Democritus’ atomic model
Was a giant ball as he claimed they were indivisible
Describe Dalton’s atomic model
Was the same as Democritus’s model
Describe Thomson’s atomic model
He proposed that electrons were embedded into a positively charged-soup hence the name plum-pudding model.
Describe Rutherford’s atomic model
The atom had a tiny positively charged core named the nucleus while the electrons circulated the nucleus like planets in the solar system.
Describe Schrodinger’s atomic model
He treated electrons as matter waves with the nucleus being in the centre of the waves.
Who proposed the name for atom?
Democritus named it atomos
What does atomos mean?
Not to be cut
Why was Democritus theory rejected?
Aristotle and Plato favoured the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers.
Who caused the acceptance of the existence of atoms?
John Dalton
What was Dalton’s theory?
He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles.
Atoms of the same element are exactly alike.
Atoms of different elements are different.
Compounds are formed by the joining of atoms of two or more elements.
Who provided the idea of something being smaller than atoms?
J.J. Thomson
What was Thomson’s theory?
Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.
What was Rutherford’s theory?
Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”
He called the centre of the atom the “nucleus”
The nucleus is tiny compared to the atom as a whole.
Name of Thomson’s model
Plum pudding model
What was Bohr’s theory?
According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.
Who invented the wave model?
Ernest Schrodinger
What was Schrodinger’s theory?
Electrons do not move about an atom in a definite path, like the planets around the sun.
In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has.
According to the modern atomic model, an atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.
Why do we change models?
We (scientists) change to using a new model, mainly because the old model has been shown not to work well enough.
This is usually because of new evidence that doesn’t fit the old model.
And this is usually because new technology has been invented that can do better (more accurate, more detailed or just different) experiments. This ‘new technology’ can even include new mathematics.
Define nuclear radiation
When the atom’s nucleus falls apart or decays resulting in the large production of energy often along with particles emitted from the nucleus. The radiating or spreading out of the particles from the nucleus is known as nuclear radiation.
Are atoms stable?
Not all are stable?
3 types of radiation
Alpha and Beta particles radiation and Gamma rays radiation
What are alpha particles?
2 protons and neutrons (helium particle)
Mass of alpha particles
4 AMU
Alpha particles penetration
Penetration: Not much (blocked by paper or 5-10cm air)
Alpha particles charge
+2
What is beta radiation?
An electron
Charge of beta radiation?
-1
Beta particles penetration
Penetration: (Blocked by sheet of wood, metal, some plastics)
Mass of Beta particles
very little
Symbol for 3 types of radiation
Alpha: α
Beta:β
Gamma:γ
What is gamma radiation?
An electromagnetic wave with a very short wavelength (high energy, above x-rays)/ photon emission
Mass and charge of gamma radiation
None
Gamma radiation penetration
Penetration: Very! (blocked by lead sheets, concrete, metres of material)
Device to measure and detect radiation
The main tool is a Geiger Muller tube, connected to a counter. This is better known as a Geiger counter.
How does a Geiger counter work?
Radiation ionises (knocks electrons off) a gas inside the tube. This movement of electrons creates a current, that an electric circuit detects and counts.
Provide 3 examples of how radiation is used
To locate certain cancers
Smoke detectors
Detecting leaks underground
Who began the studies of quantum theory?
Ernest Schrodinger
How did Democritus discover the atom?
He conducted a simple experiment where he took a seashell and broke it half and continued doing this until he theorised that he would get to the indivisible atom.
How did Thomson discover electrons?
He directed the cathode rays between two parallel aluminum plates to the end of a tube. When the top aluminum plate was negative, the rays moved down; when the upper plate was positive, the rays moved up.
How did Rutherford discover the nucleus?
Rutherford’s experiment involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)
Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.
Some of the positively charged “bullets,” however, bounced away from the gold sheet as if they had hit something solid.
This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material.
Rutherford concluded that an atom had a small, dense, positively charged centre that repelled his positively charged “bullets
How did Dalton discover compounds?
He carefully examined the experiments of others (and repeated a few) and realised that elements seemed to join in very fixed ratios, as if 1 ‘part’ of an element always connected to 2 (or 3 or 4) parts of another element.
