C4 Flashcards
(151 cards)
What are atoms?
Tiny particles of matter that make up everything in the universe
At the start of the 19th century what did John Dalton describe atoms as?
Solid spheres and the different spheres made up the different elements
In 1897 what did J J Thomson conclude from his experiment?
That atoms weren’t solid spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons.
This was known at the plumb pudding model.
Who showed that the ‘plumb pudding model’ was wrong?
Ernest Rutherford, and his students Hans Geiger and Ernest Marsden.
They conducted the famous gold foil experiment.
What is the famous gold foil experiment?
They fired positively charged particles at an extremely thin sheet of gold. From the plumb pudding model, they were expecting most of the particles to be deflected by the positive ‘pudding’ that made up most of the atom. In fact, most of the particles passed straight through the gold atoms, and a very small number were deflected backwards. so the plumb pudding model couldn’t be right.
What new theory did Rutherford come up with?
The theory of the nuclear atom.
In this there’s a tiny, positively charged nucleus at the centre, surrounded by a ‘cloud’ of negative electrons - most of the atom is empty space.
Most scientists realised that the ‘cloud’ around the atom would be attracted to the nucleus causing the atom to collapse. What did Bohr decide instead?
That the electrons can only exist in fixed orbits, or shells, and not anywhere between. Each shell had a fixed energy.
It contained a nucleus in the middle and was pretty close to the structure we have today.
Give 4 facts about the nucleus
It’s in the middle of the atom
It contains protons and neutrons
It has a positive charge because of the protons
Almost the whole mass of the atom is concentrated in the nucleus
Give 5 facts about electrons
They move around the nucleus in electron shells
They’re negatively charged
They’re tiny, but they cover a lot of space
The volume of their orbits determines the size of the atom
Electrons have virtually no mass
What are protons?
Heavy and positively charged
What are neutrons?
They are heavy and neutral
What are electrons?
Tiny and negatively charged
What is the number of protons equal to in an atom?
Electrons
What charge do neutral atoms have?
No charge
Wanna hear a joke…? :P
A neutron walks into a bar and asks how much for a drink.
The bar man says, “For you, no charge.”
Why are atoms neutral?
The charge on the electrons is the same size as the charge on the protons but opposite - so the charges cancel out
What is ‘The Mass Number’?
The top number next to the symbol on the periodic table.
It is the total number of protons and neutrons in the atom
What is ‘The Atomic Number’?
The bottom number next to the symbol on the periodic table.
It is the number of protons in the atom
How can you get the number of neutrons in an atom?
By subtracting the atomic number from the mass number
Which number is always the biggest number when looking at an atom on the periodic table?
The mass number
What is the ‘relative atomic mass’?
The mass number, the top number when looking at an atom on the periodic table
What are elements?
Substances made up of only one type of atom.
How many elements are there?
100 ish, more are still being discovered
What does the modern periodic table show the elements in order of?
Ascending atomic number