Atomic structure Flashcards
Energy levels in an atom
Shells (energy levels) further from the nucleus have a higher energy
Shells (energy levels) closer to the nucleus have a lower energy
When do electrons change energy levels?
If an atom absorbs electromagnetic radiation (energy)
An electron moves from the lower energy level (inner shell) to the higher energy level (outer shell)
The electron now emits radiation
It returns back to the lower energy level (inner shell)
Atomic number
The smaller number in an element
Equals the number of protons
All atoms of an element have the same number of protons, if the number of protons is different then the element is different
How to find the number of electrons in an atom?
It is equal to the number of protons as an atoms overall charge is 0
Mass number
The large number
Total number of protons and neutrons as electrons don’t weigh anything
How to find the number of neutrons?
Mass number (protons and neutrons) — atomic number (protons) gives us just the number of neutrons
Eg sodium:
23 - 11 = 12 neutrons
Isotopes
When atoms of the same element have different numbers of neutrons, so the mass number changes
Many isotopes are radioactive
What is the radius of an atom?
1x10⁻¹⁰m
Radius of the nucleus in an atom?
Less than 1/10000 of the radius of the atom
What did the alpha scattering experiment tell us about atomic structure?
Most particles went straight through = particles are mostly empty space
Some particles changed direction = centre of an atom has a + charge causing them to repel
Some particles bounced back = the mass of an atom is concentrated at the centre (nucleus)
Plum Pudding model
Ball of positive charge with electrons floating around inside
Rutherford’s first model
Ball of positive charge in the centre, however electrons are randomly inside not in shells nor at specific distances
Rutherford’s nuclear model
Contained shells however they weren’t at specific distance
Had a positive nucleus
