Atomic Structure Flashcards
What did Robert Boyle propose?
That there were some substances that could not be made simpler- the chemical elements
What did John Dalton propose?
That elements were composed of invisible atoms. All the atoms of a particular element had the same mass and atoms of different elements had different masses. Atoms could not be broken down
What did Henry Becquerel discover in 1896?
Radioactivity which showed that particles could come from inside the atom and therefore the atom was not invisible
In 1897, what did J J Thomson discover?
The electron. He showed that electrons were negatively charged and electrons from all elements were the same
What did Ernest Rutherford discover?
That most of the mass and all the positive charge of the atom was in a tiny central nucleus
What are protons and neutrons sometimes called?
Nucleons because they’re found in the nucleus
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/1840
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What force holds protons and neutrons together in the centre of the atom?
The strong nuclear force which is much stronger than electrostatic forces of attraction that hold electrons and protons together in the atom
What does the number of electrons in the outer shell of an atom determine?
The atom’s chemical properties and what sort of element it is
What makes up the mass number (A) of an atom?
The total number of protons and neutrons in the nucleus
What is an isotope?
An atom with the same number of protons but different numbers of neutrons
Why do isotopes of the same element react chemically in exactly the same way?
Because they have the same electronic configuration
Why do isotopes of the same element vary in mass?
Because they have different numbers of neutrons in their nuclei
What did Niels Bohr propose in 1913?
That the atom consisted of a tiny positive nucleus orbited by negatively-charged electrons. The electrons orbited in shells of fixed size and the movement of electrons from one shell to the next explained how atoms absorbed and gave out light
Who discovered the neutron in 1932?
James Chadwick
What ideas did Gilbert Lewis put forward about how electrons allowed atoms to bond together?
- the inertness of noble gases was related to their having full outer shells of electrons
- ions were formed by atoms losing or gaining electrons to attain full outer shells
- atoms could also bond by sharing electrons to form full outer shells
How many electrons can the first electron shell hold?
Up to 2 electrons
How many electrons can the second shell?
Up to 8 electrons
How many electrons can the third shell hold up to?
Up to 18 electrons
What is the mass spectrometer used for?
It is used to determine relative atomic masses (Ar)
What are relative atomic masses measured on a scale of?
They’re measured on a scale on which the mass of an atom of Carbon-12 is defined as exactly 12
How do you work out the Ar?
Average mass of 1 atom / 1/12th mass of 1 atom of Carbon-12
How are mass spectrometers used by forensics scientists?
To identify substances such as illegal drugs
Why is the TOF apparatus kept under a high vacuum?
To prevent ions that are produced colliding with molecules from the air
How are ions formed in TOF spectrometry?
The sample to be investigated is dissolved in a volatile solvent and forced through a fine hollow needle that is connected to the positive terminal of a high voltage supply. This produces tiny positively charged droplets which have lost electrons to the positive charge of the supply. The solvent evaporates from the droplets into the vacuum until only a single positively charged ion is left behind
Describe the acceleration stage of TOF spectrometry:
The positive ions are attracted towards a negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve a higher speed
Describe the ion drift stage of TOF spectrometry
The ions pass through a hole in the negatively charged plate, forming a beam and travel along a tube, called the flight tube, to a detector
How are ions detected in TOF spectrometry?
When ions with the same charge arrive at the detector, the lighter ones are first as they have higher velocities. The flight times are recorded. The positive ions pick up an electron from the detector which causes a current to flow
How are the flight times analysed in TOF spectrometry?
The signal from the detector is passed to a computer which generates a mass spectrum
What can the mass spectrometer be used to identify?
Different isotopes that make up an element
How does a mass spectrometer detect different isotopes separately?
It detects individual ions so different isotopes are detected because they have different masses
What do the solutions to the Schrödinger equation give?
The probability of finding an electron in a given volume of space called an atomic orbital
What is the definition of ionisation energy?
Ionisation energy is the energy required to remove a mole of electrons from a mole of gaseous atoms
What is the general trend in ionisation energies across a period?
Ionisation energies generally increase across a period because the nuclear charge is increasing which makes it more difficult to remove an electron
Why is there a decrease in First IE between magnesium and aluminium?
Because the outer electron in aluminium is in a 3P orbital which is of a slightly higher energy than the 3S orbital. It therefore needs less energy to remove it
Why is there a decrease in First IE values between phosphorus and sulfur?
In phosphorus, each of the three 3P orbitals contains just one electron whereas in sulfur, one of the 3P orbitals contains 2 electrons. The repulsion between these paired electrons makes it easier to remove one of them despite the increase in nuclear charge
What is the general trend in First ionisation energies down group 2?
There is a general decrease down group 2 because the outer electron is in a main level that gets further from the nucleus in each case and increased shielding of nuclear charge
