physical chemistry AS

Question 1

what is an isotope

Answer 1

elements with the same number of protons but different number of neutrons

Question 2

what is the history of the atom

Answer 2

-John Dalton- Atoms are spheres and each element is made of different spheres
-JJ Thompson- discovery of electrons and plum pudding model
-Rutherford- discovery of nucleus that was positively charged, atom is mostly empty space and alpha scattering experiment.
-Bohr- electron orbit the nucleus at specific distances.
-Discovery of protons
-Chadwick- discovery of neutrons

Question 3

what is electron impact in mass spectrometry

Answer 3

vaporised sample is injected at a low pressure with an electron gun firing high energy electrons at the sample, knocking the outer electron forming a positive ion
(Used for low Mr)

Question 4

what is electro spray ionisation

Answer 4

sample is dissolved in a volatile, polar solvent and injected through I fine hyperdermic needle giving a fine mist. The tip of the needle has a high voltage and the sample gains a proton (used for larger molecules)

Question 5

why can’t high mr molecules use electron impact

Answer 5

it can cause organic molecules to fragment whereas in electro spray ionisation, the softer conditions mean fragmentation doesn’t occur

Question 6

what is the process of mass spectrometry

Answer 6

-ionization ( electron impact or electrospray)
- acceleration
-ion drift
- detection

Question 7

what is the process of acceleration

Answer 7

positive ions are passed through an electric field, particles with lower mass/charge ratio will accelerate quicker

Question 8

what is the process of ion drift

Answer 8

particles travel through with constant speed and kinetic energy

Question 9

what is the process of detection

Answer 9

ions are detected as electrical current. particles with lower m/z ratio will hit the negatively charged plate first as they travel faster. the relative abundance is proportional to the size of the current produced by the ion.

Question 10

what are the conditions needed for mass spec

Answer 10

the sample needs to be vaporized ( turned into a gas) and process needs to happen in a vacuum ( low pressure) to remove the possibility of air molecules interfering with the flight of ions

Question 11

what is the relative atomic mass

Answer 11

the average mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12

Question 12

what is the relative molecular mass

Answer 12

average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12

Question 13

what is ionization energy

Answer 13

the minimum amount of energy required to remove 1 mole of electrons from one mole of atoms in the gases state

Question 14

what is the relative molecular isotopic mass

Answer 14

mass of the isotope relative to 1/12 of the mass of a carbon-12 atom

Question 15

is ionization energy endothermic or exothermic? why?

Answer 15

it is endothermic as it requires energy to overcome the attraction between the positive nucleus and the outer electron, in order to remove the outer electron.

Question 16

what are the factors affecting ionization energy and how do they affect it?

Answer 16

• atomic radius- the further away the outer electron is from the
  positive nucleus, it means less attraction between
  them so less energy is required to remove this
  electron.
  -nuclear charge- the more protons in the nucleus of an atom, the
  stronger the attraction is between the positive
  nucleus and the outer electron, requiring more
  energy to overcome these attraction
  -shielding- as the number of shells increase, the outer electrons get
  further away from the positive nucleus, so there is less
  attraction between positive nucleus and negative
  electrons. therefore, there is less energy needed to
  remove the outer electrons.

Question 17

does IE increase or decrease as you do down a group? why?

Answer 17

IE decreases as you go down a group as there is more shielding and increase atomic radius, making it easier to lose outer electrons, therefore decreasing IE.

Question 18

does IE increase or decrease as you go across a period? why?

Answer 18

IE increases at the atomic radius and shielding stays the same, as all elements on the same period have the same number of shells, but nuclear charge increases, so there is more positive charge in the nucleus and therefore the attraction will increase, resulting in a higher IE.

Question 19

why does repulsion often cause a drop in the IE?

Answer 19

when electrons didn’t used to share an orbital, and then gains another electron and one electron pair is forced to share the same orbital, it causes repulsion, resulting in less energy required to remove one of the electrons from the outer shell, decreasing IE.

Question 20

what is ionic bonding and what structure do they have?

Answer 20

transfer of electrons between metal and a non-metal in which the metal loses its outer electrons to form a positive ion and the non-metal gains the electrons to form negative ions. they always exist in a giant lattice structure.

Question 21

what are the properties of ionic compounds?

Answer 21

-they are solids at room temperature.
-the giant structures mean they have high melting and boiling points due
to strong electrostatic forces that require a lot of energy to overcome.
-only conducts electricity when molten or dissolved in water (aq) as the
ions that carry current are now free to move in its liquid state not solid
state.

Question 22

what is covalent bonding?

Answer 22

sharing of outer electrons in order for atoms to obtain a full outer shell. there is electrostatic attraction between the shared electrons and the positive nucleus.

Question 23

what is dative covalent/ co-ordinate bonding?

Answer 23

when 1 atom donates 2 electrons from an atom or ion to form a bond.

Question 24

what is successive ionisation

Answer 24

removal of more than 1 electron from the same atom

Question 25

what is the symbol and charge for hydroxide

Answer 25

OH-

Question 26

what is the symbol and charge for nitrate

Answer 26

NO3-

Question 27

what is the symbol and charge for ammonium

Answer 27

NH+

Question 28

what is the symbol and charge for sulfate

Answer 28

SO4 2-

Question 29

what is the symbol and charge for carbonate

Answer 29

CO3 2-

Question 30

what is the symbol and charge for phosphate

Answer 30

PO4 3-

Question 31

what is the symbol and charge for hydrogen carbonate

Answer 31

HCO3 -

Question 32

what is the symbol and charge for hydride

Answer 32

H-

Question 33

what is metallic bonding

Answer 33

attraction between delocalised electrons and the positive ions arranged in a lattice. the metals consist of a lattice of positive ions and a sea of delocalised electrons.

Question 34

what are macromolecules

Answer 34

giant structures that are covalently bonded into a giant lattice, each atom has many covalent bonds which cause it to have strong and high melting points.

Question 35

why do molecules have specific shapes with specific bond angles

Answer 35

the bonds repel each other equally and want to be as far away from each other as possible.

Question 36

what happens if the atom has lone pairs

Answer 36

lone pairs repel more than bonding pairs and reduce the bond angle by 2.5 degrees.

Question 37

what is electronegativity

Answer 37

the power of an atom to attract the pair of electrons in a covalent bond

Question 38

what are the factors affecting electronegativity

Answer 38

-atomic radius -> as this increases, electronegativity decreases
- nuclear charge -> as this increases, electronegativity increases
-shielding -> as this increase, electronegativity decreases.

Question 39

what is the general pattern of electronegativity across a period and a group

Answer 39

period -> general increase
group -> general decrease

Question 40

what does polar mean

Answer 40

in a covalent bond, there is a big difference in electronegativity, causing the unsymmetrical sharing of electrons.

Question 41

what does non-polar mean

Answer 41

in covalent bond, there isn’t a big difference in electronegativity so the electrons are shared equally and molecule is symmetrical.

Question 42

how can a molecule have polar bonds, but be non-polar overall

Answer 42

the dipoles are symmetrical so the dipoles cancel out.

Question 43

what are dipole-dipole forces

Answer 43

exist in molecules with polarity (big difference in electronegativity).
stronger than van der Waals forces

Question 43

explain what van der Waals are as an intermolecular force

Answer 43

occurs as electron charge cloud move from one end of a molecule to another randomly, so the charge could be more on one side than the other causing a temporary dipole. if the 2 molecules are moved away, the dipole interaction is destroyed. the bigger the atom, the more van der Waals forces (stronger) are as there are more electron charge clouds

Question 44

what are hydrogen bonds

Answer 44

the strongest intermolecular forces and occurs with very electronegative molecules -> between hydrogen and nitrogen, oxygen or fluorine.

Question 45

what is rate of reaction ( the equation and meaning )

Answer 45

the amount of reactants used or products made per unit time
rate=amount of reactants used or products made/ time

Question 46

what is the meaning of activation energy

Answer 46

the minimum amount of energy required for a reaction to occur.

Question 46

what must happen for a reaction to occur

Answer 46

particles need to collide with sufficient energy ( equal to or more than that activation energy)