1.2 - The nuclear atom Flashcards
16FEB25
What are elements?
Substances that cannot be broken down into simpler components by chemical reactions
What is an atom?
The smallest unit of an element
Modern idea of atoms created by John Dalton?
- All matter is composed of tiny indivisible particles called atoms
- Atoms can’t be created or destroyed
- Atoms of the same element of alike in every way
- Atoms of different elements are different
- Atoms can combine together in small numbers to form molecules
What did the British scientist J.J Thompson discover?
That different metals produce a stream of negatively charged particles when a high voltage is applied across two electrodes
What was Ernest Rutherford’s experiment?
Tested Thompson’s model by firing alpha particles at a piece of gold foil
- Most of alpha particles passed but a small number were repelled
Mass of proton?
1amu
Mass of neutron?
1amu
Mass of electron?
0.0005amu (negligible)
Why is the existence of neutrally charged neutrons so crucial?
Its crucial for the stability of nuclei of elements that have more than one proton
What would happened to an atom of there was no neutrons?
The positively charged protons would mutually repel each other and the nucleus would fall apart
Why must the positive charge of the proton be balanced by the negative charge of electrons?
Because an atom has no overall charge
What does the mass of an atom depend on?
On the number of protons and neutrons only
What symbol is the mass number given?
A
What symbol is the atomic number given?
Z
What symbol is the element given?
X
What is a cation and how is it formed?
A positive ion formed when an atom loses electrons
What is an anion and how is it formed?
A negative ion formed when an atom gains electrons
What are isotopes?
Atoms of the same element with different mass numbers
What are radioisotopes?
Isotopes that can be used as tracers to follow the movement of elements or compounds in complex processes like living systems
How can radioisotopes be used as tracers?
When they behave chemically the same way as nonradioactive isotopes
What does the stability of a nucleus depend on?
The balance between the number of protons and neutrons
When is a nucleus radioactive?
When it contains too many or too few neutrons to be stable
How does a radioactive nucleus change into a more stable one?
By giving out radiation
What does the mass spectrometer measure?
Mass/ charge ratio of deflected particles
