topic 1: physical chemistry

What is all matter composed of?

Atoms

What is an atom?

The basic building block of all substances and it is the smallest part of an element that takes place in a chemical reaction

What are atoms made up of?

Mostly made up of space around a very small dense nucleus that contains protons and neutrons

What are protons and neutrons referred to?

Nucleons because they are found in the nucleus

What charge does the nucleus have and why?

It has a positive charge because protons are positive and neutrons are neutral

Where are negative electrons found?

They are found in orbitals in the space around the nucleus and they create a cloud of negative charge

What does the nucleus contain?

Protons and neutrons where most of the mass is concentrated

What are sub atomic particles?

Particles that an element is made up of; protons, neutrons and electrons

What is the charge of a proton?

+1

What is the charge of a neutron?

0\ neutral

What is the charge of an electron?

-1

What is the relative mass of a proton?

1

What is the relative mass of a neutron?

1

What is the relative mass of an electron?

1/1836

Define mass number

The number of protons and neutrons

Define atomic number

It is the number of protons which is also equal to the number of electrons

What holds the atom together?

The electrostatic attraction between the positive nucleus and the negatively charged electrons orbiting around it

What is the difference between atoms and ions?

Atoms are neutral and have no overall charge whereas ions are formed when atoms gain or lose electrons causing them to become charged

What is the same for all atoms and ions of the same element?

They all have the same number of protons in their nucleus/ atomic number

How does the number of electrons in an ion compare with its atomic number?

An ion has a different number of electrons from its atomic number depending on its charge

How is a positively charged ion formed?

Formed when its lost electrons

Goes a positively charged ion have more protons or electrons?

More protons

How is a negatively charged ion formed?

Formed when an atom gains electrons

Does a negatively charged ion have more protons or electrons?

More electrons than protons

Define isotope

Atoms of the same element that contain the same number of protons and electrons but different number of neutrons and therefore has a different mass number

Why do isotopes have the same chemical properties but different physical properties?

Isotopes have the same number of electrons on their outer shell. Electrons take part in chemical reactions and therefore determine the chemistry of an atom. However isotopes have a different number of neutrons which add mass and density

How do you calculate the relative atomic mass for the abundance of an isotope?

RAM=(% x mass number)+(% x mass number)/100

What is time of flight (TOF) mass spectrometry?

It is a powerful analytical technique used to determine the relative atomic mass of an element and relative molecular mass of a molecule

What is produced as the sample passes through the mass spectrometer?

A spectrum is produced which plots abundance of ions against their mass to charge ratio (m/z)

What is often the molecular ion peak?

The peak at the highest m/z value

What is the tallest peak called?

The base peak

Why is the entire apparatus kept under a high vacuum?

To prevent ions from colliding with each other

What are the 4 key stages of TOF mass spectrometry?

Ionisation, acceleration, ion drift and detection

What happens during ionisation?

→ the sample is converted into positive ions

→ the 2 main methods are electron impact and electrospray ionisation

What is electron impact?

This is used for elements and low mass compounds. High energy electrons bombard the vaporised sample from an electron gun. The high energy electrons knock an electron off each particle to form a 1+ ion.

X(g)→X+(g)+e-

The 1+ ion formed are called molecular ions (M+) this high energy process can also cause the M+ ions to break into smaller pieces known as fragments. Fragment ions also pass through a TOF mass spectrometer and appear on the final mass spectrum

What is electrospray ionisation ESI?

This is used for higher mass compounds like proteins to prevent fragmentation. This is a soft ionisation technique where the sample is dissolved in a volatile solvent and injected through a high voltage needle. This causes the particles to gain a proton (H+) from the solvent.

M(g)+H+ →MH+(g)

What occurs during acceleration?

The positive ions are:

. Attracted towards a negatively charged plate

. Accelerated by an electric field

The key principle is that all ions are accelerated to have the same KE since KE=1/2mv2 so ions with a lower mass have a higher velocity and vice versa

What occurs during ion drift?

The accelerated ions pass through a hole in the negatively charged plate and travel down a flight tube at a constant speed and KE

The flight tube is a region with no electric field

The time it takes for an ion to travel this distance is its time of flight

Ions with a lower mass to charge ratio (M/Z) travel faster and have a shorter time of flight

What occurs during detection?

When ions arrive at the detector and hit it, it gains an electron which generates a small electric current

The size of this current is directly proportional to the abundance of that specific ion

A computer records the time flight and relative abundance for each ion to produce the mass spectrum

What are the key equations?

How do you calculate the mass of a single ion?

1. Divide the relative isotopic mass by the avogadro constant (L) 6.022X10{23}

2. Divide result by 1000 to convert from g to kg

Define relative atomic mass

The average mass of an atom of an element when measured on scale on which the mass of an atom of C12 is exactly 12

Define relative isotopic mass

The mass of an atom of an isotope of an element measured on scale on which the mass of an atom of C12 is exactly 12

Define relative molecular mass

The average mass of a molecule when measured on scale on which the mass of an atom of C12 is exactly 12

Define electron configuration

Arrangement of electrons in an atom in the shells, sub shells and orbitals

How are electrons arranged around the nucleus?

In principle quantum shells/ principle energy levels

What are principle quantum numbers used for?

Used to number the energy levels or quantum shells

He lower the principal quantum number the further the shell is to the nucleus. True or false?

False. The lower the principal quantum number the closer the shell is to the nucleus

What is the first shell which is closes to the nucleus?

N=1

If the principal quantum number is larger is the energy of the shell higher or lower?

Higher

What is the fixed number of electrons can n=1 hold?

Up to 2 electrons

What is the fixed number of electrons can n=2 hold?

Up to 8 electrons

What is the fixed number of electrons can n=3 hold?

Up to 18 electrons

What is the fixed number of electrons n=4 hold?

Up to 32 electrons

What are the principal quantum shells split into?

Sub shells

What letters are the subshells given?

S, p and d

What do elements with more that 5 electrons have?

An f shell

What order does the energy of the electrons in the subshells increase?

S<p<d<f

What are orbitals?

The region of space around the nucleus of an atom where up to 2 electrons with opposite spins can be found

What do subshells contain?

One or more atomic orbitals

Where do orbitals exist?

They exist at specific energy levels

Can electrons be found in between the energy levels?

No the can only be found at these specific energy levels

How many electrons can occupy each atomic orbital?

A maximum of 2 electrons

How many orbitals in the s subshell?

One

How many electrons in the s orbital?

A total of 2 electrons

How many orbitals in the p subshell?

Three

How many electrons in the p subshell?

A total of 6 electrons

How many orbitals are there in the d subshell?

Five

How many electrons occupy the d subshell?

A total of 10 electrons

How many orbitals in the f subshell?

Seven orbitals

How many electrons occupy the f orbital?

A total of 14 electrons

Do the orbitals which make up the subshells have the same or different energies?

They have the same energy and are described as degenerate

Describe the shape of the s orbital.

It has a spherical shape, the size increases with increasing shell number e.g. the s orbital of the 3rd quantum shell n=3 is bigger than the s orbital of the first quantum shell n=1

Describe the shape of the p orbital

It has a dumbbell shape. Every shell has 3 orbitals except for the first one. The p orbitals occupy the x, y and z axes and point at 3 right angles to each other so are orientated perpendicular to one another, the lobes of the p orbitals become larger and larger with increasing shell number

What is the ground state?

This is the most stable electronic configuration of an atom which has the lowest amount of energy

How is ground state achieved?

It’s achieved by filling the subshells of energy with the lowest energy first

At which subshell does the order of increasing energy not follow a regular pattern?

At n=3 and higher

What are the 4 blocks that the periodic table is divided into?

S, p, d or f block

What is the purpose of these blocks?

It tells us the orbital which contains their outer most valence electron. E.g. s block elements have their valence electron in an s orbital

What is the purpose of these blocks?

It tells us the orbital which contains their outer most valence electron. E.g. s block elements have their valence electron in an s orbital

The 3d orbital is higher in energy than the 4s. True or false?

True. As a result the 4s orbital is filled before the 3d

What are the 2 ways that electronic configuration can be written in?

Full or shorthand

What is the full way of writing electronic configuration?

Shows the arrangement of electrons starting from the 1s subshell e.g. potassium has 19 electrons so the EC is 1s(2) 2s(2) 2p(6)3s(2) 3p(6)4s(1)

What is the shorthand way of writing electronic configuration?

It uses the symbol of the nearest proceding noble gas to represent the electrons in filled inner shells e.g. potassium=19 electrons

Nearest noble gas= argon this accounts for 18 of potassium 19 electrons so [Ar] 4s(1)

Do negative ions add or remove electrons from the outer shell?

Add

Do positive ions add or remove electrons from the outer shell?

They remove

Once ions are formed which subshell are they lost from?

The 4s subshell rather than the 3d because the 4s subshell is higher in energy once the 3d subshell contains electrons

What property of electrons can be represented as either up or down?

Electron spin

Do electrons with the same spin attract or repel each other?

They repel; this is known as spin pair repulsion

What do electrons do to minimise spin pair repulsion?

Electrons occupy separate orbitals within the same subshell before pairing up and they do with the same spin direction

When do electrons only pair up?

When no empty orbitals are remaining within a subshell

When pairing occurs do electrons have the same or opposite spins?

They have the opposite spins to minimise repulsion

Define ionisation energy

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions

Why is ionisation energy needed?

To overcome the electrostatic attraction between the electrons and the nucleus

What factors affect ionisation energy?

→ nuclear charge

→ atomic/ionic radius

→ electron shielding

How does nuclear charge affect ionisation energy?

More protons= greater nuclear attraction for electron removed

How does atomic radius affect ionisation energy?

Larger atomic radius= weaker nuclear attraction

How does electron shielding affect ionisation energy?

More shells= weaker nuclear attraction

Define first ionisation energy

Energy required to remove one mole of electrons from one mole of atoms of an element to form one mole of 1+ ions

Why do successive ionisation energies always increase?

This is due to the increasing positive charge of the ion- remaining electrons are more strongly attracted to the nucleus

Removing an electron from a positive ion is more difficult than from a neutral atom

The decreasing radius- as electrons are removed remaining electrons are pulled closer to the nucleus

Nuclear attraction for remaining electrons acts over a shorter distance each time.attractive forces increase due to the decreasing shielding and an increase in the proton to electron ratio