P4 - Atomic Structure Flashcards
Who replaced the plum pudding model with the nuclear model?
Rutherford
When is the earliest known thought about atoms?
Democritus in 5th Century BC Greece thought all matter was made of identical lumps called atomos
Who discovered, (and rearrange them in chronological order):
a) Protons
b) Neutrons
c) Electrons
c) J J Thompson, round 1900
b) Rutherford
a) James Chadwick
What was John Dalton’s theory about atoms? 1804
He agreed with the Greek Democritus that matter was made of tiny spheres (atoms) that couldn’t be broken up, but he thought each element was made up of a different type of atom
What were J J Thompson’s conclusion about atoms? Early 1900’s
He discovered particles called electrons that could be removed from atoms, so Dalton wasn’t quite right. Thompson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding - this is the plum pudding model
What was Rutherford’s experiment? 1909
Scientists tried firing alpha particles at thin gold foil, expecting them to pass straight through the gold sheet, or only get slightly deflected.
However, most did go straight through, but others were deflected in all sorts of directions. The plum pudding model couldn’t explain this.
After Rutherford’s experiment, what did he conclude? 1909
Because alpha particles were deflected back, they realised that most of the mass of the atom must be concentrated at the centre, in a tiny nucleus. It must also be positively charged, as it repelled the positive alpha particles.
They also realised - as most alpha particles passed through fine - that most of the atom is empty space.
He concluded an early version of the nuclear model of the atom, where there was a TINY positive ball of charge at the centre, then a cloud of electrons around it
What did Niels Bohr discover and how did he develop the atomic model?
He discovered that electrons all orbited at certain distances from the nucleus called energy levels (or shells)
How did James Chadwick develop the atomic model? 1932
He proved the existence of the neutron, explaining the imbalance between the atomic and mass numbers.
This led to the current model of the atom, with electrons orbiting in shells, then protons and neutrons in the tiny nucleus at the centre
Complete the sentence:
The number of protons =
The number of electrons. (as protons and electrons have an equal but opposite charge, and atoms have no overall charge, so they must cancel out)
How many times smaller in the radius of the nucleus compared to the rest of the atom?
10,000
In case I phrased it wrong, “The nucleus… its radius is abut 10,000 times smaller than the radius of the atom)
What is the radius of an atom roughly?
1 x 10^-10 (to the power of -10)
Fill the blanks:
Electrons in energy levels can ____ within (or sometimes _____) the atom. If they gain energy by absorbing __ _________, they move to a ______ energy level, further from the nucleus. If they release this same type of energy, they move to a _____ energy level, ______ to the nucleus. If one or more outer electrons leave the atom, the atom becomes a __________ _______ ___
Move Leave EM radiation (electromagnetic I think) Higher Lower Closer Positively charged ion
What are isotopes?
Isotopes are different forms of the same element.
OR they are atoms with the same number of protons (the atomic number is the same, so the same charge is on the nucleus), but a different number of neutrons (a different mass number)
What subatomic particle defines the element?
Protons - the atomic number
What subatomic particle determines if it is an isotope?
Neutrons - the mass number
All elements have different isotopes, but none of them are stable. True or false?
False - normally only one or two stable ones
What is the mass number?
The sum of protons and neutrons, as they are they only too that have a clear mass of 1 (electrons are relative to 0)
What do unstable isotopes tend to do?
Decay into other elements and give out radiation as they try and be more stable.
They try and balance the number of protons and neutrons in the nucleus or get rid of excess energy.
This process is radioactive decay
What is radioactive decay?
The process of an unstable isotope decaying into other elements and give out radiation as they try and become more stable.
They try and balance the number of protons and neutrons in the nucleus or get rid of excess energy.
What do radioactive substances release?
Ionising radiation - alpha, beta or gamma (and more that we don’t need to know)
They can also release neutrons when they decay ro rebalance the number of protons and neutrons
What is ionising radiation?
The type that knocks electrons off other atoms, creating positive ions
What determines how easily ionising radiation will be able to knock off the electrons from ther atoms?
Its ionising power
What are these radiation types?
a) β
b) γ
c) α
a) Beta radiation
b) Gamma radiation
c) Alpha radiation
Give a use for each ionising radiation
Alpha particles - used in smoke detectors (it ionises air particles, causing a current to flow. If smoke is in the air, it binds to the ions - meaning the current stop and the alarm sounds)
Beta particles - Tests the thickness of sheets of metal & paper (as the particles aren’t immediately absorbed by the material like alpha radiation is, and don’t penetrate as far as gamma rays)
Gamma rays - As a medical tracer (a gamma-emitting source is injected into the patients body, and its progess is followed)
