Atomic structure Flashcards
Describe the structure of an atom.
An atom is made u of mostly empty space with most of its mass concentrated in a tiny positive central nucleus
State the 3 subatomic particles, their relative masses and relative charges.
- Proton, Charge +1, Mass 1
- Neutron, Charge 0, Mass 1
- Electron, Charge -1, Mass 1/1840
What is the charge of an atom?
Explain your answer.
An atom has an overall charge of 0.
Because the charges on the protons and electrons cancel each other out.
An elements nuclear notation is shown below:
A
X
Z
State what each letter represents.
X- Element symbol
A- Mass number/RAM/Ar
Number of protons and neutrons
Z- Atomic Number
Number of protons in the nucleusHow is an ion formed?
An ion is formed when an atom gains or loses electrons
What type of ions have…
No. of electrons< No. of protons
Positive ions
What is an isotope?
Isotopes are atoms of the same element with the same atomic number but different mass number due to different number of neutrons.
State and explain, if any, a difference between the chemical properties of the isotopes of an element.
No differences.
Chemical properties of an element depend on the number and arrangement of electrons in an atom.
Describe John Dalton’s perception of the structure of the atom
J.D. described atoms as solid spheres and said that different spheres make up different elements
What did J. J. Thompson discover about the atom and what did it show?
He discovered atoms contain electrons
It proved atoms weren’t solid and invisible
What was the name of J. J. Thompson’s model of the atom, and what did it suggest?
He proposed the plum pudding model (where an atom was made up of a positive “dough” with negatively charged electrons, the “plums”, scattered across it.
Describe the experiment Rutherford carried out and the conclusion he arrived at about the structure of the atom.
Rutherford carried out the gold foil experiment in which he fired alpha particles at a thin sheet of gold. He expected most of the particles to be deflected by the positive “pudding” that made up most of the atom. Instead, he found that most passed straight through with very few bouncing back. He concluded that an atom was made up of mostly empty space with a tiny positively charged nucleus at its centre surrounded by a cloud of electrons.
State a fault Bohr found with Rutherford’s model and what he suggested
Bohr discovered that the clouds of negatively charged electrons Would be attracted to the positive nucleus and would spiral towards it causing the atom to collapse
He suggested:
- Electrons only exist in fixed shells with fixed energies
- when an electron moves between shells electromagnetic radiation is emitted slash absorbed and because the energy of the shells is fixed the radiation will have a fixed frequency
Give the discoveries made about the atomic structure more recently
Scientists found that not all electrons in a shell had the same amount of energy so they introduced subshells
Give a reason why the older less accurate atomic models are still used today
The older models are more simpler and easy to understand then newer ones and yet are still able to explain many observations
What can mass spectrometry be used to find out about an element?
Abundance of each isotope of an element
Their masses
And hence the elements RAM
List the four stages in Mass Spectrometry
- Electrospray Ionisation
- Acceleration
- Ion Drift
- Detection
There are two ways in which a sample can be ionised. State and describe each method.
-Electron impact
The sample is vaporised and then high energy electrons are fired at it using a hot electron gun. This knocks 1 electron off each atom forming +1 ions.
-Electrospray ionisation
The sample is dissolved in a volatile solvent and is then injected through a fine hypodermic needle to form a fine mist. The tip of the needle is attached to the positive terminal of a power supply. As the sample leaves the needle the particles are ionised by gaining a proton (H+ - so their mass number increases by 1 )
Explain why it is necessary to ionise the atoms
Only ions can be accelerated using an electric field and only ions will create a current when hitting the detector.
Explain how the ions can be accelerated
all the ions are now positive so they can be accelerated using an electric field. This gives all the particles the same kinetic energy. However, the lighter irons will experience a greater acceleration than the heavier ones.
Describe what happens in ion drift
Particles enter the flight tube where they are able to spread out. This is because ions with lower masses travel through the flight tube quicker than heavier ions and so move ahead of them.
Describe how detection occurs
Because lighter ions travel faster, they hit the detector first causing a current flow. The size of the current can be used to work out the abundance of each isotope (the bigger the current the more of the isotope present).
How can you use mass spectrometry to identify an element
Compare the pattern on the mass spectrum, of the sample, with the patterns formed by other known elements.
Give the formula needed to calculate the relative atomic mass of an element
Abundance one times mass one plus abundance two times mass 2 divided by total abundance
