atomic structure p1 Flashcards
explain the current model of the atom
- protons and neutrons are found in the nucleus
- electrons orbit the nucleus in shells
- the nucleus is tiny compared to the total volume of atom
- most of atom’s mass is in the nucleus
- most of the atom is empty space between the nucleus and the electrons
what is the charge of a proton and an electron?
proton = +1
electron = -1
which particle has the same mass as proton?
neutron
which two particles make up most of atom’s mass?
protons and neutrons
what does the atomic number show about an element?
atomic number = number of protons in an atom
how is the mass number calculated?
mass number = number of protons + number of neutrons
isotope
atoms of the same element with different number of neutrons and therefore different mass number
why do different isotopes of the same element react in the same way?
- neutrons have no impact on the chemical reactivity
- reactions involve electrons, isotopes have the same number of electrons in the same arrangement
relative atomic mass
weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12
relative isotopic mass
the mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12
the relative isotopic mass is same as which number?
mass number
what two assumptions are made when calculating mass number?
- contribution of the electron is neglected
- mass of both proton and neutron is taken as 1.0
how to calculate the relative molecular mass and relative formula mass?
both can be calculated by adding the relative atomic masses of each of the atom making up the molecule or the formula
what are the uses of mass spectrometry?
- identify unknown compounds
- find relative abundance of each isotope of an element
- determine structural information
what is the m/z value of the M+ ion from a graph??
last peak
what does the principal quantum number indicate?
the shell occupied by the electrons
what is a shell?
a group of orbitals with the same principal quantum number
how many electrons can each shell hold?
1st - 2
2nd - 8
3rd - 18
4th - 32
what is an orbital?
a region around the nucleus that can hold up to two electrons with opposite spin
95% (?) chance of finding an electron
what are the four types of orbitals?
s, p, d, f
what shape are the orbitals?
s - spherical
p - dumb bell
how many orbitals are present in each sub shell?
s - 1, 2 electrons
p - 3, 6 electrons
d - 5, 10 electrons
f - 7, 14 electrons
what rules are electrons arranged in a shell by?
- electrons are added one at a time
- lowest available energy level is filled first
- each energy level must be filled before the next one can fill
- each orbital is filled singly before pairing
- 4s is filled before 3d
why does 4s orbital fill before 3d orbital?
4s has a lower energy than 3d before it is filled
how can the electron configuration be written in short?
the noble gas before the element used to abbreviate
(often [Ar])
how are the elements arranged in a periodic table?
they are arranged in the order of increasing atomic numbers
what is a period on a periodic table?
horizontal rows
what is a group on a periodic table?
vertical columns
how is the group number related to the number of electrons?
group number = number of electrons in outer shell
what is meant by periodicity?
the repeating trends in chemical and physical properties
first ionisation energy
the energy required to remove a mole of electrons from a mole of gaseous atoms to form one mole of gaseous 1+ ion under standard conditions
first ionisation energy equation of Mg
Mg(g) –> Mg+(g) + e-
what are the factors that affect ionisation energy?
- atomic radius
- nuclear charge
- electron shielding or screening
why does ionisation energy increase across a period?
increased nuclear charge, decreased atomic radius, same electron shielding
more energy needed to remove first electron
why does first ionisation energy decrease between group 2 to 3?
decreases between 2 to 3 because in group 3 the outermost electrons are in p orbitals
whereas in group 2 they are in the s orbital so the electrons are easier to remove from p as it is further from the nucleus
why does first ionisation energy decrease between groups 5 and 6?
decrease due to the group 5 electrons in p orbital which are single electrons
in group 6 the outermost electrons are spin paired, with some repulsion
therefore the electrons are slightly easier to remove
does first ionisation increase or decrease between the end of one period and the start of the next? why?
decrease
there is increase in atomic radius
increase in electron shielding
does first ionisation increase or decrease down a group? why?
decrease
shielding increases, atomic radius increases, nuclear charge increases however outweighed by radius and shielding
describe the structure, forces and bonding in every element across period 2? (Li, Be, B, C, N, O, F, Ne)
Li & Be –> giant metallic; strong attraction between positive ions and delocalised electrons; metallic bonding
B & C –> giant covalent; strong forces between atoms; covalent
N2, O2, F2, Ne –> simple molecular; weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules
describe the structure, forces and bonding in every element across period 3: Na, Mg, Al, Si, P, S, Cl, Ar
Na, Mg, Al –> giant metallic; strong attraction between positive ions and delocalised electrons; metallic bonding
Si –> giant covalent; strong forces between atoms; covalent
P4, S8, Cl2, Ar –> simple molecular; weak intermolecular forces between molecules and intermolecular forces between molecules
what are the 4 stages of mass spec?
1 - ionisation - element is vaporised and injected into the mass spec where a high voltage is passed over the chamber causing electrons to be removed leaving +1 charged ions
2 - acceleration
3 - ion drift - ions deflected by a magnetic field into a curved path
4 - detection - positive ions hit negatively charged detection plate, gaining an electron and producing a flow of charge - the greater the abundance the greater the current produced
5 - analysis
