5.1.1 Atomic Structure Flashcards
What is a mixture?
A mixture is two or more elements or compounds put together but not chemically bonded.
The chemical properties of the elements or compounds are not changed.
How can mixtures be separated?
By physical processes e.g. filtration, crystallisation, distillation, fractional distillation, chromatography
(Could you name them all?)
How does filtration work?
Larger particles are trapped by the filter and particles smaller than the gaps in the filter can pass through.
Usually used to separate solid from liquid.
E.g. In a mixture of sand and water, sand would be trapped by filter paper and the water molecules can move through it.
How does crystallisation separate substances?
By evaporating the liquid (solvent), any dissolved substances (solutes) in the mixture (solution) are left behind.
How can distillation separate substances?
Distillation is where the liquid in a solution is boiled to become a gas. The gas is then cooled and condenses to become a liquid again.
Any dissolved substances (solutes) are left behind as solids.
How can fractional distillation separate substances?
Fractional distillation separates mixtures of liquids with different boiling points. In a fractional distillation column, substances with higher boiling points condense lower down the column, and the substances with lower boiling points condense towards the top.
How does chromatography separate substances?
By separating by solubility e.g. different dyes in pen ink.
More soluble dyes will travel further up the chromatography paper, and less soluble dyes will not travel as far.
Why did the discovery of the electron change our ideas about atoms?
Before electrons were discovered, we used to think atoms were tiny spheres (like a ball) that could not be divided.
What was the plum pudding model of the atom?
An atom is a sphere (ball) of positive charge with negative electrons embedded in it.
What did the alpha particle scattering experiment show us?
An atom’s mass is concentrated at its centre, telling us an atom has a nucleus. It also told us the nucleus was positively charged.
This is known as the nuclear model, which replaced the plum model.
What did Niels Bohr add to the nuclear model of the atom?
Electrons orbit the nucleus in electron shells.
What did James Chadwick prove?
The existence of neutrons within the nucleus
What is the relative charge of a proton?
+1
What is the relative mass of a proton?
1
What is the relative charge of a neutron?
0
What is the relative mass of a neutron?
1
What is the relative charge of an electron?
-1
What is the relative mass of an electron?
Very small (almost nothing)
What can you say about the number of protons and electrons in an atom?
They are always the same
What does atomic number tell us?
The number of protons in an atom (number of electrons is the same!)
Roughly how big is an atom?
0.1nm
What does an atom’s mass number tell us?
The number of protons + number of neutrons
Remember the mass is usually bigger than the atomic number!
Why are some mass numbers not whole numbers?
Because these are average values of the different masses of different isotopes of that element.
What is an isotope?
Different forms of the same atom with:
Same number of protons
Same number of electrons
Different numbers of neutrons
