Module 2: section 1 The atom/atomic models Flashcards Preview

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What are the 3 subatomic particles of an atom?

protons, neutrons and electrons


Where is most of the mass of an atom located?

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


What subatomic particles does the nucleus contain?

protons and neutrons


What is the relative mass of:

proton = 1
neutron = 1
electron = 1/2000 (mass of an electron is negligible compared to a proton or neutron)


What is the relative charge of:

proton = +1
neutron = 0
electron = -1


What is the mass (nucleon) number?

mass number tells you the number of protons and neutrons in the nucleus (top number)


What is the atomic number?

atomic (proton) number tells you the number of protons in the nucleus (bottom number)


What are isotopes?

isotopes are atoms of the same element with different numbers of neutrons


What decides the chemical properties of an element?

the number and arrangement of electrons decides the chemical properties of an element


Why do isotopes have the same chemical properties?

isotopes have the same electron configurations, so they've got the same chemical properties


Why do isotopes have slightly different physical properties?

isotopes of an element have slightly different physical properties (e.g. different densities and rates of diffusion) because physical properties tend to depend more on the mass of an atom


What was the theory of the ancient Greeks about atoms?

some ancient Greeks thought that all matter was made from indivisible particles


At the start of the 19th century, what was John Dalton's theory?

John Dalton described atoms as solid spheres, and said that different types of sphere made up different elements


In 1897, what was JJ Thompson's theory?

JJ Thompson proved atoms weren't solid and indivisible.
The 'plum pudding model' was a positively charged sphere with negative electrons embedded in it


In 1909, what was Ernest Rutherford's theory?

Ernest Rutherford, with his students Hans Geiger and Ernest Marsden, conducted the alpha particle scattering experiment. They fired positively charged alpha particles at an extremely thin sheet of gold.
From the plum pudding model, they expected most of the alpha particles to be deflected very slightly by the positive 'pudding' that made up most of the atom. But, most of the alpha particles passed straight through the gold atoms, and a very small number were deflected backwards (through more than 90°). This showed that the plum pudding model couldn't be right and it was replaced by the nuclear model of the atom.


Describe the Nuclear model of the atom.

-there is a tiny, positively charged nucleus at the centre of the atom, where most of the atom's mass is concentrated
-the nucleus is surrounded by a 'cloud' of negative electrons
-most of the atom is empty space


In what order were the subatomic particles discovered?

electron (JJ Thompson)
proton (Rutherford)
neutron (James Chadwick)


Describe the Bohr Model of the atom.

Niels Bohr proposed a new model (Bohr model) with 4 principles:
-electrons can only exist in fixed shells and not anywhere in between
-each shell has a fixed energy
-when an electron moves between shells, electromagnetic radiation is emitted or absorbed
-because the energy of the shells is fixed, the radiation will have a fixed frequency


Why was the Bohr Model accepted?

the frequencies of radiation emitted and absorbed by atoms were already known from experiments. The Bohr Model fitted these observations.


How does the Bohr Model explain why some elements (noble gases) are inert?

Bohr Model states that shells of an atom can only hold fixed numbers of electrons, and that an element's reactivity is due to its electrons. Atoms react in order to gain full shells of electrons. When an atom has full shells of electrons it is stable and does not react.


What is the most accurate model of the atom we have today?

The quantum model of the atom:
-you can never know where an electron is or which direction its going in at any moment, but you can say how likely it is to be at any particular point in the atom.
-electrons can act as waves as well as particles


Which model is used today?

The Bohr Model is still widely used because its simple and explains many observations (bonding, ionisation energy trends). The quantum model is more accurate and explains some observations the the Bohr model cannot but it's a lot harder to get your head round and visualise. So scientists use whichever model is most relevant to whatever they're investigating.


Why was the Nuclear model of the atom replaced by the Bohr Model?

scientists realised that electrons in a 'cloud' around the nucleus of an atom would spiral down into the nucleus, causing the atom to collapse. So Niels Bohr proposed the Bohr Model.