atomic structure Flashcards
describe Dalton’s atomic theory
-atoms=tiny particles made of elements
-atoms cannot be divided
-all atoms in an element are the same
-atoms of one element are different to those of other elements
what did Thompson discover about electrons
-negative charge
-can be deflected by electromagnetic fields
-very small mass
explain current model of the atom
-protons & neutrons found in nucleus
-electrons orbit nucleus in shell
-nucleus=tiny compared to total vol of atom
-most of atom’s mass is in the nucleus
-most of atom=empty space beween nucleus and electrons
charge of proton and electron
electron= -1
proton= +1
which particle has the same mass as a proton
neutron
which particles make up most of atom’s mass
protons and neutrons
what does atomic number tell us about element
number of protons in an atom
how is mass number calculated
mass number= protons + neutrons
isotope definition
atoms of the same element with different number of neutrons (and mass number) but same number of protons (atomic number)
why do different isotopes of the same element react in the same way.
-neutrons have no impact on chemical activity
-reactions involve electrons, isotopes have the same electronic configeration
why do different isotopes of the same element react in the same way.
-neutrons have no impact on chemical activity
-reactions involve electrons, isotopes have the same electronic configuration
define relative atomic mass
weighted mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12
define relative isotopic mass
mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12.
relative isotopic mass is the same as which number
mass number
what 2 assumptions are made when calculating mass number
-contribution of electron is neglected
-mass of both proton and neutron is taken as 1.0 u
3 uses of mass spectrometry
-identify unknown compounds
-find relative abundance of each isotope of an element
-determine structural information
what does the principal quantum number indicate
shell occupied by the electrons
shell definition
group of orbitals with the same principal quantum number
how many electrons can the 1st shell hold
2
how many electrons can the 2nd shell hold
8
how many electrons can the 3rd shell hold
18
how many electrons can the 4th shell hold
32
what is equation for number of electrons in a shell
2n²
what is an orbital
a region around the nucleus that can hold up to 2 electrons with opposite spins
how many electrons can an orbital hold
2
what are the 4 types of orbital
S P D F
shape of S and P orbital
S=spherical
P=dumbell/8 and rotates on axis
how many orbitals are found in a S subshell
1
how many electrons can be held in a S subshell
2
how many orbitals does P subshell have
3
how many electrons can be held in a P subshell
6
how many orbitals are present in a D subshell
5
how many electrons can be held in a D subshell
10
how many orbitals are present in a F subshell
7
how many electrons can fill F subshell
14
when using ‘electrons in box’ representation, what shape is used to represent electrons
arrow
what letter is used to represent shell number
n
from which shell onwards is S orbital present
n=1
from which shell onwards is P orbital present
n=2
from which shell onwards is D orbital present
n=3
from which shell onwards is F orbital present
n=4
what are the 5 rules by which electrons are arranged in the shell
-electrons are added one at a time
-lowest available energy level filled first
-each energy level must be filled before next can be
-each orbital is filled singly before pairing
-4s is filled before 3d
why does 4s orbital fill before 3d orbital
4s orbital has a lower energy than 3d before it is filled
electronic configuration of krypton (Ar=36)
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
how can the electron configuration be written in short
the noble gas before the element is used to abbreviate
E.g. Li→1s2 2s1 ; Li→(He) 2s1
how is the group number related to the number of electrons
group number= number of electrons in the outer shell
how are elements of the periodic table arranged
in order of increasing atomic numbers
what is meant by periodicity
the repeating trends in chemical and physical properties
define first ionisation energy
energy required to remove one electron from each atom in one mole of gaseous atoms which become one mole of gaseous ions
write an equation for the first ionisation energy of magnesium
Mg(g)→Mg+(g) + e-
factors affecting ionisation energy
-atomic radius
-nuclear charger
-electron shielding
why does first ionisation energy decrease between group 2 to 3
-in group 3 the outermost electrons are in P orbitals
-in group 2 the outermost electrons are in S orbitals so the electrons are more easily removed
why does first ionisation energy decrease between group 5 to 6
-group 5 electrons in P orbital which are single electrons
-group 6 the outermost electrons are spin paired
why does first ionisation energy decrease between group 5 to 6
-group 5 electrons in P orbital which are single electrons
-group 6 the outermost electrons are spin paired
does first ionisation increase or decrease between end of one period and start of the next
decrease
increase in atomic radius=increase in electron shielding
does first ionisation increase or decrease down a group
-decrease
-shielding increases → weaker attraction
-atomic radius increases → distance between the outer electrons and nucleus increases → weaker attraction
-increase in n. protons is outweighed by increase in distance and shielding
describe the structure, forces and bonding in every element across period 2
- Li & Be→ giant metallic; strong attraction between positive ions and delocalised electrons ; metallic bonding
-B & C → gaint 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
