Topic 1 - Atomic Structure and Periodic Table

Question 1

Sturcture of the Atom

Answer 1

Nucleus = (contains protons and neutrons) and most of the mass of an atom is found here
Electrons orbit the nucleus in shells and take most of the space of the atom

Question 2

Relative mass and relative charge of protons, neutrons and electrons

Answer 2

• Protons have a charge of +1 and a relative mass of 1
• Neutrons have no overall charge but a relative mass of 1
• Electrons have a charge of -1 with a relative mass of 1/1850

Question 3

atomic (proton) number and mass number

Answer 3

• Atomic proton number tells us the number of orotons in the nucleus and is equal to the electron number in an atom
• Mass number tells is the number of oprotons and neutrons in the nucleus (bigger number)

Question 4

Isotopes

Answer 4

Isotopes are atoms of the same element with the same atomic number, but different mass number (same number of protons but different number of neutrons)
–> Isotopes have similar chemical properties because they have the same electronic structure, but have slightly varying physical properties because they have different masses

Question 5

Relative isotopic mass

Answer 5

The average mass of an atom of an isotope relative to 1/12th of the mass of one atom of carbon-12

Question 6

Relative atomic mass

Answer 6

The weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of Carbon-12

Question 7

relative molecular mass and relative formula mass
and calculating these values from relative atomic masses

The term ‘relative formula mass’ should be used for compounds with giant
structures.

Answer 7

relative formula mass should be used for compounds with giant
structures
relative molecular mass is the mean mass of a molecule, whereas formula mass is the is the average mass of one formula unit relative to the mass of 1/12 of a carbon12 unit

Question 8

Mass Spectrometry

Answer 8

m/z is the mass of an isotope divided by the charge (found on x axis)
% abundance is always shown on y axid and is the % of isotopes and must add to give 100%

Question 9

Working out Relative atomic mass via a mass spectrometer

Answer 9

relative atomic mass can be calculated by

(abundace of a X m/z of a) + (abundance of b X m/z of b) divided by total abundance

Question 10

Predict the mass spectra, including relative peak heights, for diatomic
molecules, including chlorine

Answer 10

1. Write the percentages as decimals
2. Create a table showing the isotope combinations in a single molecule - multily the decimal abundances of each isotope to get the relative abundance for each molecule
3. Any moleculeds which are the same, add the abundances together
4. Divide all relative abundances by the smallest value - will give a whole number ratio which can be used to predict the spectra

Question 11

Mass spectrometry can be used to determine the relative
molecular mass of a molecule

Limited to the m/z value for the molecular ion, M+, giving the relative molecular
mass of the molecule.

Answer 11

peaks show fragments of the original molecule - the last peak is the M+1 peak or the molecular ion peak - is the same as the relative molecular mass of the molecule

Question 12

First ionisation energy

Answer 12

The amount of energy required to remove one mole of electrons from one mole of gaseous atoms (to form 1 mole of gaseous positive ions)
(endothermic process - energy is put in to ionise atom)
e.g. Na (g) –> Na+ (g) + e- (must be atom)

Question 13

Successive ionisation
energies

Answer 13

Atoms with more than one electron can be successively removed)
The energy required to remove one mole of electrons from one mole of gaseous unipositive +1 ions (to form one mole of gaseous dipositive +2 Ions)
e.g. Na+ (g) –> Na2+ (g) + e-

Successive ionisation energies are always greater than the previous one. 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 14

Ionisation energies are influenced by the number of protons, the
electron shielding and the electron sub-shell from which the electron is removed

Answer 14

Factors affecting ionisation energy:
* Nuclear charge – The more protons in the nucleus, the greater the charge and the stronger the attraction to the negatively charged electrons – greater IE energy required
* Shielding – The more electron shells between the nuclei and the outer electron, means that the the outer electrons feel less attraction towards the nuclear charge. And less energy is required to remove the outer electron
* Atomic size – The bigger the atom, the further the outer electrons from the nucleus and the weaker the attraction of the nucleus and the outer electron

Question 15

Reasons for the decrease in first ionisation energy down a group

Answer 15

Decreases down a group – Despite an increased nuclear charge, the extra shells shielding means that the atomic radius is greater, so the outer electrons are further away from the nucleus, which reduces the attraction to the nucleus and so less energy is required to remove the electrons ++ A decrease in ionisation energy going down a group provides evidence that electron shells really exist

Question 16

Reasons for the general increase in first ionisation energy across a
period

Answer 16

Increases across a period – The number of protons increases, and therefore so does the nuclear charge. All the electrons are in the same energy level and therefore electron shielding remains the same

Question 17

Electronic Configuration

Answer 17

electron shells are split into 4 subshells

s - has 1 orbital and can hold 2 electrons - spherical in shape - electrons can move anywhere within the shape ]

p - has 3 orbitals and can hold 6 electrons - px,py,pz orbitals (all 90degree from eachother) - combine to make full p subshell - there are 3p orbitals in the shape of dumbbells each can hold up to 2 electrons and can move anywhere within the shape

d - has 5 orbitals and can hold 10 electrons
f - has 7 orbitals and can hold 14 electrons

Question 18

Spin pairing

Answer 18

when 2 electrons occupy 1 orbital, they spin in opposite directions