Periodicity and group 2 Flashcards
What does the atomic number tell us about an element?
Number of protons in an atom
How is mass number calculated?
Number of protons + number of neutrons
Define relative atomic mass
Average mass of all isotopes of an element compared to 1/12 the mass of am atom of carbon12
What is an isotope of an element?
Different forms of the same element, containing the same number of protons but different numbers of neutrons. They still have the same chemical properties.
Name the number of orbitals
1s2 2s2 2p6 3s2 3p6 4s2 3d10
Does 3D or 4s have a higher energy?
3D
What is an orbital?
A region around the nucleus that can hold up to two electrons
What would be the relationship between 2 electrons in the same orbital in terms of their spin?
Have opposite spin as repel each other as both negative
Explain why chromium does not fit the trend for electronic configuration
It only has one electron in its 4s orbital before filling 3D
Explain why cooper does not follow the trend for electronic configuration
It only has one electron in its 4s orbital before 3d
What are the two types of ionisation for a mass spectrometer? How do they differ?
1) electron impact- electron gun knocks odd one electron from each particle to form each 1+ ion
2) electron spray- sample dissolved in volatile solvent and injected through a fine needle which is attached to a high voltage, it gains a proton producing XH+ ions
When would you use the different types of ionisation in a mass spec?
Electron impact is used for substances with a low formula mass
Electron spray is used for substances with a high molecular mass
Describe how a time of flight mass spec works
Acceleration- positive ions attracted towards a negatively charged plate
Ion drift- ions pass through hole in plate, form a beam with constant kinetic energy, travel along tube to detector. Time of flight is therefore directly proportional to the square root of mass
Detection- positive ions pick up electrons, current flows m/z value and time of flight recorded. Largest current from most abundant ions
Define first Ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Explain the graph of first ionisation energy of group 3
Increases across group 3 because of increase in nuclear charge, decreased atomic radius and same electron shielding means more energy is needed to remove first electron.
Dips at Al because outer electron is in a 3p orbital which has a higher energy than 3s
Dips at S because one 3p orbital contains two electrons and there is a repulsion between the paired electrons
Describes ionisation energy down group 2
Decreases because number of filled electron shells increases down the group so increased shielding so increases atomic radius so weaker force between electrons and nucleus
How does reactivity with water change as you go down group 2?
Mg least
Ba most
Because outer electrons are further away from nucleus and more electron shielding so electrons are lost more easily
Write an equation for the reaction of Ba and water
Ba + 2H2O -> Ba(OH)2 + H2
Equation between Mg and steam
Mg + H2O -> MgO + H2
What is the trend in hydroxide solubility down group 2?
Increases down the group
Mg(OH)2 is almost insoluble
Ba(OH)2 creates a strong alkaline solution
What is the trend in sulphate solubility down group 2?
Decreases down group
MgSO4 is soluble
BaSO4 is insoluble
Trend in melting point down group 2
Decreases because sea of delocalised electrons is further away from nucleus so weaker metallic bonds
What is the trend in atomic radius down group 2
Increases as there are more occupied shells
What is Ca(OH)2 used for
Neutralise soil
What is Mg(OH)2 used for
Antacid to treat indigestion
What is a use of BaSO4
Barium meals to outline gut in X-rays
