atomic structure

Question 1

what does an atom consist of?

Answer 1

a nucleus containing protons, neutrons surrounded by electrons

Question 2

what did Democritus discover?

Answer 2

atom is the smallest and its indivisible

Question 3

what did John Dalton discover?

Answer 3

all matter was composed of atoms, indivisible and indestructible building blocks, each element has different size atoms and masses

Question 4

what did j.j Thompson discover?

Answer 4

the plum pudding model : atoms are a ball of positive charge with negative electrons embedded in it

Question 5

what did Rutherford discover

Answer 5

did the alpha particle scattering experiment with gold foil which proved that the plum pudding model was wrong. he fired positively charged alpha particles at the gold foil. the results showed most passed straight through and some were deflected back, proving that the plum pudding model couldn’t be right

Question 6

what did Niels Bohr discover?

Answer 6

the nuclear model, that electrons can only exist in fixed orbits or shells so each shell has a fixed energy

Question 7

why was the nuclear model not accurate?

Answer 7

not all electrons in the same shell had the same energy so this model is wrong. its refined to be right by adding more subshells. this explains why some elements are inert. Elements reactivity is due to its electrons, so when the shell is full its inert and does not react.

Question 8

what did James Chadwick discover?

Answer 8

provided the evidence to show the existence of neutrons within the nucleus and has a mass

Question 9

what are the relative mass for electrons, protons and neutrons?

Answer 9

1. electrons: 1/1840 - negligible
   2.neutrons: 1
2. protons: 1

Question 10

what are the relative charges for protons, neutrons and electrons?

Answer 10

1. electrons: -1
2. protons: +1
3. neutrons 0

Question 11

what is the atomic number

Answer 11

number of protons in the nucleus

Question 12

what is the mass number

Answer 12

total number of protons and neutrons in the atom

Question 13

what are isotopes?

Answer 13

-Isotopes are atoms with the same number of protons, but different numbers of neutrons.
-Isotopes have similar chemical properties because they have the same electronic structure.
They may have slightly varying physical properties because they have different masses.

Question 14

what is the relative atomic mass?

Answer 14

the relative atomic mass of an element is the average mass of an atom, compared to 1/12th the mass of a carbon-12 atom

Question 15

how do you calculate the relative atomic mass of an element?

Answer 15

if percentage abundance is used: R.A.M = (isotopic mass x % abundance) divide 100
if relative abundance is used: R.A.M = (isotopic mass x relative abundance) divide
total relative abundance

Question 16

what is the time of flight spectrometer used for

Answer 16

-The mass spectrometer can be used to determine all the isotopes present in a sample of an element and to therefore identify elements and used to determine relative molecular mass
- It needs to be under a vacuum otherwise air particles would ionise and register on the detector

Question 17

what are the two ways that a sample can be ionised?

Answer 17

Two of these techniques are electron impact and electrospray ionisation

Question 18

what happens in electron impact?

Answer 18

-A vaporised sample is injected at low pressure
-An electron gun fires high energy electrons at the sample
-This knocks out an outer electron
-Forming positive ions with different charges
e.g. Ti (g)– Ti+(g)+ e–
- Electron impact is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment.

Question 19

what happens in the electrospray ionisation?

Answer 19

-The sample is dissolved in a volatile, polar solvent
-injected through a hypodermic needle giving a fine mist or aerosol ( because its all positive so it repels)
-the tip of needle has high voltage
-at the tip of the needle the sample molecule, M, gains a proton, H+, from the
solvent forming MH+
-M(g) + H+ – MH+(g)
-The solvent evaporates away while the MH+
ions move towards a negative plate
-Electro spray ionisation is used preferably for larger organic molecules. The ‘softer’ conditions of this technique mean fragmentation does not occur

Question 20

what happens in stage 2 of acceleration in the TOF?

Answer 20

-Positive ions are accelerated by an electric field
-To a constant kinetic energy through attraction to a negative charged plate KE = ½MV^2
KE = kinetic energy of particle (J)
m = mass of the particle (kg)
v = velocity of the particle (ms–1)
-Given that all the particles have the same kinetic energy, the velocity of each particle depends on its mass. Lighter particles
have a faster velocity, and heavier particles have a slower velocity.

Question 21

what happens in stage 3 of flight tube?

Answer 21

*The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move
faster.
*The heavier particles take longer to move through the drift area.
*The ions are distinguished by different flight times
-t= d/v
t = time of flight (s)
d = length of flight tube (m)
v= velocity of the particle (m s–1)

Question 22

what happens in stage 4 of detection in TOF?

Answer 22

• positive ions hit a negative metal plate and is detected as they gain electrons
• the electrons move from the plate to the ion because of force of attraction
• this produces an electric current (movement of electrons)
• the size of current is proportional to abundance of each isotope

Question 23

what’s the definition of the first ionisation energy change?

Answer 23

the energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to form one mole of 1+ ions (also in their gaseous state)
- removes one electron only in the outer shell and requires energy to overcome the force of attraction

Question 24

what is the definition of the second ionisation energy?

Answer 24

The second ionisation energy is the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge

Question 25

what are the factors that affect ionisation?

Answer 25

1.The attraction of the nucleus (The more protons in the nucleus the greater the attraction but not always as distance and force of attraction take in account too. protons are not as important when it comes to ionisation down the group)
2. The distance of the electrons from the nucleus - the further the outer electron is the weaker the force of attraction
3. Shielding of the attraction of the nucleus
(An electron in an outer shell is repelled by electrons in complete inner shells, weakening the attraction of the nucleus)

Question 26

what is the pattern when the elements are ionised down the group?

Answer 26

• less force of attraction between the nucleus and outer electron
• decrease in ionisation energy
• more distance/ bigger atomic radius + shielding

Question 27

what is the trend across a period during ionisation?

Answer 27

• more proton/ higher nuclear charge ( cant have more protons in the same period, only if its at a different energy level)
• same shell/ same shielding
• closes to nucleus/ smaller atomic radius
• stronger force of attraction between nucleus + outer electron
• higher ionisation energy

Question 28

Why do first ionisation energies decrease down a group?

Answer 28

As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 29

Why is there a general increase in first ionisation energy across a period?

Answer 29

As one goes across a period the electrons are being added to the same
shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective
attraction of the nucleus greater.

Question 30

Why is there a small drop from Mg to Al?

Answer 30

Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s
sub shell. The electrons in the 3p subshell are slightly easier to remove because
the 3p electrons are at higher energy level so there’s less force of attraction between the nucleus and its outer electrons so there will be a dip in a graph

Question 31

Why is there a small drop from P to S?

Answer 31

With sulfur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove

Question 32

Why are successive ionisation energies always larger?

Answer 32

-The second ionisation energy of an element is always bigger than the first ionisation energy.
-When the first electron is removed a positive ion is formed.
-The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger.

Question 33

what are the trends in successive ionisation energy?

Answer 33

• successive ionisation energies are always greater than the previous one as the electron is being pulled away from a more positive species
• large increase occur when there is a change of shell as there is a big decrease in shielding
• large increase can be used to predict the group of an unknown element

Question 34

what are the % for the two isotopes of chlorine and bromine?

Answer 34

chlorine:
- Cl35 = 75%
- Cl 37= 25%
bromine:
- Br 79 = 50%
- Br 81= 50%