atomic structure Flashcards
what was discovered in 1661 about the atom?
Robert Boyle- substances that couldn’t be made simpler which are chemical elements
what was discovered in 1803 about the atom?
John Dalton- elements were composed of invisible atoms. All atoms of a particular element had different masses. Atoms couldn’t be broken down.
what was discovered in 1893 about the atom?
Henri Becquerel- discovered radioactivity. particles came from inside the atom. Following year JJ Thomsan discovered the electron which showed that electrons were negatively charged and electrons from all elements were the same . All electrons had negative charge. Electrons were located located within the atom in circular arrays like plum pudding.
what was discovered in 1911 about the atom?
Ernest Rutherford- most of the mass and all positive charge of atom was in tiny central nucleus.
The sub-atomic particles
Atoms are made of - protons, electrons, neutrons.
Protons and neutrons form the nucleus.
Electrons surround the nucleus.
arrangement of sub-atomic particles
Protons and neutrons are in centre of the atom held together by a force called strong nuclear force. This is much stronger than the electrostatic forces of attraction that hold electrons and protons together in the atom, so it overcomes the repulsion between protons in the nucleus.
Nucleus is surrounded by electrons. Electrons are found in a series of levels - called orbits or shells which get further and further away from the nucleus.
atomic number (z) ?
number of electrons in an atom (atomic number) is equal to proton number. Atomic number defines the chemical properties of an element.
Atomic number (z) = protons
mass number (A)?
nucleons responsible for almost all of the mass of an atom.
Mass number (A) = number of protons + number of neutrons.
isotopes?
atoms with the same number of protons but different number of neutrons.
Different isotopes of same element react chemically in the same way as they have the same electron configuration.
what was discovered in 1913 about the arrangement of the electrons?
Niels Bohr out forward the idea that the atom consists of tiny positive nucleus orbited by negatively charged electrons to form an atom. Electrons orbit in shells of fixed size and movement of electrons from one shell to the net explained how atoms absorbed and gave out light. This was the beginning of quantum theory.
what was discovered in 1926 about the arrangement of electrons?
Erwin Schrodinger worked out an equation that used the idea that electrons had some of the properties of waves as well as those of particles. This led to a theory called quantum mechanics which is used to predict behaviour of sub-atomic particles.
What was discovered in 1932 about the arrangement of the electrons?
James Chadwick discovered the neutron.
One important contributor was Gilbert Lewis and he put forward the ideas that:
The inertness of noble gases were related to their having full outer shell pf 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 pouter shells.
Relative atomic mass Ar
1/12 mass of an atom of an element compared to 1/12 of the mass carbon-12.
Steps of time of flight mass spectrometer
1) Vacuum- whole apparatus kept under a high vacuum to prevent ions colliding with molecules.
2) ionisation- Two types.
1- electrospray ionisation- sample dissolved in volatile solvent and forced through a fine hollow needle . This produces tiny positively charged droplets that have gained a proton from the solvent. The solvent evaporates from the droplets onto vacuum and droplets get smaller until they contain no more than a single positively charged ion.
2- Electron impact sample is vaporised and high energy electrons are fired at it from an electron gun which is a hot wire filament with a current running through it that emits beam of high energy electrons. This usually knocks off one electron from each particle forming a 1+ ion-
x(g) + e- → x+(g) + 2e-
3) acceleration- positive ions are attracted towards a negatively charged plate and accelerates towards it. Lighter ions and more highly charged achieve a higher speed.
4) ion drift- ions pass through a hole in the negatively charged plate forming a beam and travel along a tube called flight tube to detector.
5) detection - Flight times are recorded. Positive ions pick up an electron from detector which causes current to flow.
6) data analysis- the signal from detector is passed to a computer which generates a mass spectrum.
Atomic orbitals (s,p,d,f)
s block- hold up to 2 electrons
p block- hold up to 6 electrons
d block- hold up to 10 electrons
f block- hold up to 14 electrons
ionisation energy (IE)
when electrons can be removed from atoms and the energy it takes to remove them can be measured.
ionisation energy is the energy required to remove a mole of electrons from a mole of atoms in gaseous state.
successive ionisation energies
1) first electron needs the least ionisation energy because its being removed from a neutral atom → eg- Na(g) → Na+(g) +e-
2) second electron needs more energy than first because its being removed from a 1+ ion.
eg- Na+(g) → Na2+(g)+e-
etc…
