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Science - Physics - GCSE > P1 - Atomic Structure > Flashcards

P1 - Atomic Structure Flashcards

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1
Q

What happened to the theory of the atom in 1804 ?

A

John Dalton theorised that atoms were tiny spheres, that couldn’t be broken, specific to different elements.

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2
Q

What happened to the model nearly 100 years after 1804 ?

A

JJ Thompson discovered removable electrons, and suggested atoms were balls of positive charge with electrons stuck in them. The plum pudding model.

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3
Q

What happened to the model in 1909 ?

A

Scientists in Rutherford’s lab fired alpha particles at thin gold foil - alpha scattering experiment.

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4
Q

What happened in the alpha scattering experiment ?

A

They were expecting the majority of alpha particles to pass straight through, however a larger than expected portion were deflected at greater angles than expected.

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5
Q

What happened as a result of the alpha scattering experiment ?

A

They realised most of the mass of an atom was concentrated at the centre in a positive nucleus, and also that the atom was mostly empty space - the nuclear model.

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6
Q

What did Niels Bohr refine in the nuclear model ?

A

He theorised electrons orbited the nucleus at fixed distances (energy levels), which matched experimental data.

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7
Q

How was the nucleus adapted after the discovery of electron shells ?

A

The proton was discovered through further experimentation.

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8
Q

Who discovered the neutron ?

A

In 1932 James Chadwick proved the existence of neutrons - explaining the imbalance between the atomic and mass numbers.

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9
Q

What does today’s model of the atom look like ?

A

Nucleus 10000 times smaller than the radius of the atom, it contains protons and neutrons; the rest is mostly empty space with negative electrons orbiting in shells. Radius of an atom is around 1 × 10^-10m.

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10
Q

What does the number of protons determine ?

A

The element that an atoms is, all atoms of an element have the same number of protons - this is the atomic number.

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11
Q

What is the mass number of an atom ?

A

Signifies the relative mass of the nucleus, number of protons + number of neutrons.

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12
Q

What is an isotope ?

A

Atoms of an element with the same number of protons but a different number of neutrons.

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13
Q

How many isotopes do atoms have ?

A

All atoms have different isotopes but there are usually only one or two stable ones.

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14
Q

What happens to unstable isotopes ?

A

They decay into other elements by giving out radiation to become more stable - radioactive decay.

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15
Q

What is ionising radiation ?

A

Radiation that knocks electrons off atoms creating positive ions, ionising power relates to how easily radiation can do this.

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16
Q

What do radioactive substances release ?

A

Ionising radiation (alpha,beta,gamma), and also sometimes neutrons when they decay.

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17
Q

What is an alpha particle ?

A

Comprised of two neutrons and two protons (helium nucleus).

18
Q

What are the characteristics of alpha particles ?

A

Low penetration depth (few cm in air and absorbed by sheet of paper), large size means they’re highly ionising.

19
Q

What are beta particles ?

A

A high speed electron, no mass and a charge of -1. And for every beta particle emitted a neutron in the nucleus turns into a proton.

20
Q

What are the characteristics of beta particles ?

A

Moderately ionising, and moderate penetration depth (few meters in air and stopped by sheet of aluminium - 5mm)

21
Q

What are gamma rays ?

A

They are EM waves with short wave lengths released by the nucleus.

22
Q

What are the characteristics of gamma rays ?

A

Long penetration depth (stopped by thick lead or meters of concrete), weakly ionising as they can pass through rather than collide with atoms.

23
Q

What are nuclear equations ?

A

A way of showing radioactive decay, written in the form: atom before decay –> atom after decay + radiation

24
Q

How are alpha particles written in nuclear equations ?

A

Can be written as a helium nucleus.

25
Q

How does emitting an alpha particle affect the original atom ?

A

Its atomic number is reduced by 2, and the mass number reduced by 4.

26
Q

How does an emitted beta particle affect the original atom ?

A

The mass of the nucleus doesn’t change (1 neutron lost, 1 proton gained) and atomic number increased by 1.

27
Q

How does emitting a gamma ray affect the original atom ?

A

They don’t change anything, they’re a way of getting rid of excess energy from a nucleus.

28
Q

How can radiation be measured ?

A

With a geiger-muller tube and counter, which records the count rate.

29
Q

What is count rate ?

A

The number of radiation counts per second.

30
Q

What is a half-life ?

A

The time it takes for the amount of radiation emitted by a source to halve or the number of radioactive nuclei in an isotope to halve.

31
Q

What is activity ?

A

The rate at which a source decays, measured in becquerels, Bq (1 Bq is 1 decay per second)

32
Q

What does having a short half-life mean ?

A

Activity falls quickly - unstable nuclei rapidly decay, this is dangerous because of the high amount of radiation emitted at the start.

33
Q

What does having a long half-life mean ?

A

Activity falls more slowly - releasing small amounts of radiation over a long time.

34
Q

What is background radiation ?

A

The low-level radiation around us all the time.

35
Q

Where can background radiation come from ?

A

Naturally occurring unstable isotopes, radiation from space (cosmic rays) mostly from the sun, and due to human activity (i.e nuclear waste).

36
Q

What is the radiation dose ?

A

Tells you the risk of harm to body tissues due to exposure to radiation. Measured in Sieverts (Sv)

37
Q

What affects your radiation dose ?

A

Where you live, if your jobs involves radiation, and other factors such as x-rays.

38
Q

What is irradiation ?

A

Exposure to radiation, objects near to a radioactive source are irradiated. Irradiating something doesn’t make it radioactive.

39
Q

How can you reduce irradiation ?

A

Keeping sources in lead lined boxes, standing behind barriers or handling sources remotely.

40
Q

What is contamination ?

A

Where radioactive particles get onto the object

41
Q

P

A

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Science - Physics - GCSE (9 decks)

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