Atomic Structure and the Periodic Table

What is the relative mass and relative charge of the three subatomic particles?

Proton- 1. +1. Neutron- 1. 0. Electron- 1/1837. -1.

What are ions?

an atom or molecule with an overall charge due to the loss or gain of one or more electrons.

What are isotopes?

Atoms of the same element with different numbers of neutrons

Why do isotopes tend to have the same chemical properties?

It is the number and arrangement of electrons that generally decide the chemical properties of an element, and isotopes have the same electronic configuration.

What type of properties may isotopes have slightly different?

Physical properties such as density and rate of diffusion as these depend on mass.

What is relative atomic mass?

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

What is relative isotopic mass?

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

Which of relative atomic mass and relative isotopic mass is usually a whole number and why?

Relative isotopic mass as relative atomic mass is an average of the relative isotopic masses.

What is relative molecular mass?

The average mass of a molecule or formula unit, compared to 1/12th of the mass of an atom of carbon-12

Find the relative atomic mass of boron, given that 20% of the boron atoms found on Earth have a relative isotopic mass of 10.0, while 80% have a relative isotopic mass of 11.0.

(0.2 x 10) + (0.8 x 11) = 10.8

What is mass spectrometry used for?

to measure the masses of the components of a substance to determine what a sample is made up of.

What do mass spectrometers produce and what can these tell us?

Mass spectra- these can tell us about the relative isotopic masses and abundances of different elements.

What is on the axes of a mass spectrum?

y-axis- abundance of ions as a percentage x-axis- m/z value, or mass/charge ratio. As the charge on the ions is mostly +1, you can often assume that this is just the relative isotopic mass.

What are the steps to work out the relative atomic mass from a mass spectrum?

1- multiply each relative isotopic mass by its relative isotopic abundance and add up the results. 2- Divide by the sum of the isotopic abundances.

The mass spectrum of neon has three peaks- one at 20 for 114%, one at 21 for 0.2% and one at 22 for 11.2%. What is the relative atomic mass of neon?

(20x 114) + (21 x 0.2) + (22 x 11.2) = 2530.6 2530.6/(114+0.2+11.2) = 20.2

Silicon exists in three isotopes. 92.23% of silicon is 28Si and 4.67% of silicon is 29Si. The relative atomic mass of silicon is 28.1 . Calculate the abundance and isotopic mass of the third isotope.

100% - 92.23 - 4.67 = 3.1%- the abundance. (28 x 0.9223) + (29 x 0.0467) +0.031x = 28.1 x= 29.719 The mass of the third isotope is 30.

Chlorine has two isotopes. 35Cl has an abundance of 75% and 37Cl has an abundance of 25%. Predict the mass spectrum of Cl2.

1. Make a table showing all the different Cl2 molecules and multiply the abundances to get the relative abundance of each one.

What are the stages of mass spectrometry?

1- vaporisation 2- ionisation 3- acceleration 4- deflection 5- detection

How do you use a mass spectrum to find the relative molecular mass of a compound?

Look at the molecular ion peak- the peak with the highest m/z value, ignoring any small M+1 peaks. The m/z value of this peak is the molecular mass.

What are electron shells made up of, and what is bigger?

subshells and orbitals, orbitals form part of subshells.

What do electrons move around the nucleus in? What numbers are these given?

quantum shells, principle quantum numbers.

Which shells have a higher energy level- closer of further from the nucleus?

further

What is a subshell?

A group of orbitals of the same type within a shell

What is an orbital?

A region of space around the nucleus where an electron is likely to be found. They hold up to 2 electrons each in opposite spins.

What are the types of subshell and how many orbitals and electrons can each contain?

s - 1 orbital - 2 electrons p- 3 orbitals - 6 electrons d- 5 orbitals - 10 electrons f- 7 orbitals- 14 electrons

What shape are s-orbitals?

spherical

What shape are p-orbitals?

dumbbell

What is the electronic configuration of magnesium (atomic number 12)?

1s22s22p63s2

What is the electronic configuration of titanium (atomic number 22)?

1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d2

What is the electronic configuration of chromium (atomic number 24)

1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5

What is the electronic configuration of Cu2+ (Cu has atomic number 29)?

1s2, 2s2, 2p6, 3s2, 3p6, 3d9

Why do chromium and copper donate one of their 4s electrons to the 3d subshell?

They are more stable with a full or half-full d-subshell.

What is the electromagnetic spectrum?

The range of electromagnetic radiation

What is electromagnetic radiation?

Energy transmitted as waves with a spectrum of different frequencies.

What happens to the radiation along the electromagnetic spectrum?

It increases in frequency and decreases in wavelength.

What is ground state?

The lowest energy position of an electron. An electron's natural position.

What happens if an atom's electrons take in energy from the surroundings?

They can move to higher energy levels and are said to be excited.

How do electrons release energy?

By dropping to a lower energy level from a higher one.

Why is the spectrum for each element unique?

Each element has a different electron arrangement, so the frequencies of radiation absorbed and emitted are different.

What does it mean that the energy levels are discrete?

They all have certain fixed values.

What is a line spectrum?

Coloured lines, representing frequencies of light emitted when electrons drop down energy levels, on a dark background

Describe an emission spectrum.

• lots of sets of lines, each one representing electrons moving to a different energy level. Eg. One set of lines when electrons fall to the n=1 level, one set when electrons fall to the n=2 level, etc.

• each set of lines gets closer together, making the lines converge, because the energy levels get closer as the frequency increases. The image is the emission spectrum of hydrogen

What are the four principles of electron shells?

• electrons can only exist in fixed orbits or shells, and not anywhere in between.

• each shell has a fixed orbit.

• when an electron moves between shells electromagnetic radiation is emitted or absorbed.

• because the energy of the shells is fixed, the radiation will have a fixed frequency.

How do emission spectra support the idea of quantum shells?

The emission spectrum of an atom has clear lines for different energy levels , supporting the idea that energy levels are discrete as the electrons must 'jump' between them with no in-between stage.

What is ionisation?

The removal of one or more electrons

What is the first ionisation energy?

The energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form one mole of gaseous 1+ ions.

What is the equation for the first ionisation of oxygen?

What happens to first ionisation energies down a group?

What three factors affect ionisation energy?

• nuclear charge

• electron shell/atomic radius

• shielding

How does nuclear charge affect ionisation energy?

The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons. Therefore the higher the nuclear charge, the higher the ionisation energy.

How does the electron shell/atomic radius affect ionisation energy?

As attraction decreases rapidly with distance, the further the shell of the outer electon from the nucleus, the less attracted the electron is to the nucleus. Therefore as atomic radius increases, ionisation energy decreases.

How does shielding affect the ionisation energy?

As the number of electons between the outer electrons and the nucleus increases, the outer electrons experience less attraction towards the nuclear charge. Therefore as shielding increases, ionisation energy decreases.

Ionisation energies fall because:

• elements further down a group have extra electron shells compared to ones above, so the outer electrons are further from the nucleus, greatly reducing their attraction.

• the additional inner electrons shield the outer electrons from the attraction of the nucleus.

What does the decrease in ionisation energies down a group provide existence for?

Electron shells

What is the definition for the second ionisation energy?

The energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.

How does a graph of successive ionisation energies provide evidence for the shell structure of atoms?

• within each shell, successive ionisation energies increase because electrons are being removed from an incerasingly positive ion and there is therefore less repulsion amongst the remaining electrons.

• the big jumps in ionisation energy happen when a new shell is broken into and an electron is being removed from a shell closer to the nucleus.

How can a graph of the successive ionisation energies of an element tell you which group the element belongs to?

Count how many electrons are removed before the first big jump.

How can a graph of the successive ionisation energies of an element tell you the electronic structure of an element?

Working right to left, count the points before each big jump to find out how many electrons there are in each shell beginning with the first.

How does the modern periodic table arrange elements?

By proton number.

What is periodicity?

Repeating trends in physical and chemical properties of the elements across a period due to all elements in a period having the same number of electron shells.

How does electronic configuration decide the chemical properties of an element?

It changes how easily electrons can be lost or gained to form an inert gas configuration, ions or covalent bonds.

What happens to atomic radius across a period?

It decreases because as the number of protons increases, the positive charge of the nucleus increases, attracting the electrons and decreasing the atomic radius. Shielding is unaffected.

What happens to ionisation energy across a period?

It increases because as the number of protons increases, so does nuclear attraction. Atomic radius and shielding are ineffective.

Why is aluminium's ionisation energy lower than magnesium?

Aluminium's outer electron is in a 3p orbital rather than a 3s. The 3p orbital has a slightly higher energy than 3s, and so is on average further from the nucleus. There is also additional electron shielding from the 3s2 electrons. Both of these factors override the effect of increased nuclear charge.

Why is phosphorus's ionisation energy higher than sulfur's?

In sulfur, the electron is being removed from an orbital occupied by 2 electrons rather than 1 like in phosphorus. The repulsion between two electrons in an orbital means that an electron is slightly easier to remove.

How does bond strength affect melting and boiling points across a period?

For metals, meltong and boiling points increase because the metallic bonds get stronger (increasing number of delocalised electrons and decreasing radius= stronger attraction). The elements with giant covalent lattice structures have strong covalent bonds linking all the atoms together. The elements with simple molecular structures have lower boiling points as the boiling points depend on the strength of the weak london forces between molecules. The noble gases have the lowest melting point as they are monatomic, resulting in only very weak london forces that need to be broken.

How might the difference in rates of reaction of strontium and barium with water be due to the difference of the sum of their first and second ionisation energies? (6) (PMT)

• the sum of the first two ionisation energies of Ba is lower.

• Ba is a bigger atom

• Ba has more shielding

• These outweigh the greater proton charge of Ba.

• Ba therefore reacts faster and is more explosive.