Atomic Structure Flashcards
what are the four atomic models?
- daltons billiard ball”
- Thomson “plum pudding “model
- rutherford model
- Bohr model
What did dalton believe about the atom?
- all matter is proposed of atoms that are indivisible and indestructible
- different elements had atoms of differing size and mass.
What did Thomson believe about the atom?
- the atoms are indivisible but contain negatively charged particles.
- plum pudding model
What did Rutherford believe about the atom?
- the gold foil experiment proved the plum pudding model to be wrong.
-alpha particles passed through and some were deflected back - the atoms are mostly empty space with a dense positive nucleus.
what did Bohr believe about the atom?
- if electrons were in a cloud around the nucleus then it would spiral down into the nucleus causing it to collapse. due to forces of attraction
- electrons can only exist in fixed orbits or shells
- each shell has a fixed energy.
What happened after the Bohr model? How was it refined?
- not all electrons in the same shell had the same energy
- Subshells are added
- explains why some elements are inert
- an element’s reactivity is due to its electrons.
What are the properties of a proton?
- weighs 1
- charge + 1
- in the nucleus
What are the properties of a neutron?
- weights 1
- charge = 0
- in the nucleus
what are the properties of an electron?
- weighs 1/1840
- charge -1
What does PEN stand for?
P - protons
E- neutrons
N - Electrons
what is the mass number (a)
Total number of protons and neutrons
what is the atomic number? (Z)
the total number of protons?
what is an isotope?
- isotopes are atoms of the same element that contain different numbers of neutrons
- only slightly changes the physical properties.
How much of chlorine 35 is in naturally occurring chlorine?
- about 75%
- the rest is chlorine 37.
What is the relative atomic mass of an element?
- the average mass of its atoms compared to 1/12th the mass of carbon 12
How do you calculate the relative atomic mass?
- Total mass of atoms / total number of atoms. (abundance percentages)
what does the mass spectrum help us to indicate?
- the mass and abundance of each isotope present in an element
- these numbers can be plugged into the equation to find the RAM
how do isotopes react in the mass spectrum?
- ions with different isotopes produce different signals
What happens in stage 1 of time of flight mass spectrometry? (electron impact)
- ionisation
- the sample is vaporised and then high energy electrons are fired at it. these come from an electron gun which is a hot wire filament with a current running through it.
- this forms a +1 ion
- the ions are then attracted towards a negative electric plate where they are accelerated.
what is the equation from electron impact?
- X(g) + e- -> X+(g) + e-
why is electron impact used?
- it is used for elements and substances with a low formula mass.
What happens in electrospray ionisation?
- the sample is dissolved in a volatile solvent e.g. water or ethanol and I injected through a fine hypodermic needle to give a fine mist (aerosol)
- the tip of the needle is attached to the positive terminal of a high-voltage power supply.
-this gives the particles a proton (H+) so they are ionised as they leave the needle producing XH+ ions - the solvent evaporates away while the XH+ ions are attracted towards a negative plate where they are accelerated.
what is the equation in electrospray ionisation?
X(g) + H+ -> XH+(g)
Why is electrospray ionisation used?
- used for substances with higher molecular mass.
What happens in stage 2 of ToF mass spectrometry (acceleration)?
- the positive ions are accelerated using an electric field so that they all have the same kinetic energy.
- because all particles have the same kinetic energy, the velocity of each particle depends on its mass.
What equation is used to find the velocity of particles in the acceleration tube?
- KE = 1/2 mv^2
- KE (j)
- m (kg)
- m/s
What happens in stage 3 of ToF mass spectrometry (flight tube?)?
- the positive ions travel through a hole in the negatively charged plate into a tube the time of flight of the particles depends on their velocity.
what are the equations used to find the time of flight of the particles?
- T = D/v
- t = d x (sqrt m/2ke)
what is the time of flight proportional to?
time of flight is proportional to the square toot of the mass of the ions.
What happens in stage 4 of ToF mass spectrometry (detection)?
- the positive ions hit a negatively charged plate. when they hit the detector plate, the positive ions are discharged by gaining electrons from the plate
which generates a movement of electrons and hence an electric current is measured. the size of the current gives a measure of the the number of ions hitting the plate.
what are the four blocks of the periodic table?
- S, D , P , F
- s block element have their valence electrons in an s orbital
- p block elements have their valence electrons in p orbitals etc..
where are electrons found in the modern model of the atom?
- in specific energy levels known as shells surrounding the nucleus.
what subshells are electrons split into?
- s - has 1 orbital and can hold 1 e (spherical)
- p- has 3 orbitals and can hold 2x3 = 6 electrons
- d has 5 orbitals and can hold 10 electrons
- f has 7 orbitals and can hold 14 electrons
why can 4s go before 3d in the electron config of an element?
- because 4s has a lower energy level than 3d
Where do you remove or add the electrons in the electron configuration of an ion?
- from the highest energy level first.
why do the electron configurations of chromium and copper behave differently?
- an electron from the 4s subshell moves into the 3d orbital to create a more stable half-full or full 3d subshell.
what is the electron configuration of chromium?
- 1s2 2s2 2p6 3s2 3p6 3d5 4s1
what is the electron configuration of copper?
- 3d 10 4s 1
what is the difference in electron configuration for transition metals?
- in an ion you remove the electron from the 4s subshell first because they are lower in erergy than
