Focus 3 Flashcards
(3 cards)
Describe the relationship between electron arrangement and the organisation of the periodic table.
The periodic table is arranged into vertical groups and horizontal periods which reflect the electron configuration of atoms.
The group number is related to the number of valence electrons of an element
e.g. Group 1 (alkaline metals) have 1 valence electron which makes them highly reactive
e.g. Group 8 or 18 (noble gases) have 0 valence electrons, meaning that they have full electron shells and therefore are highly unreactive
The period number is related to an element’s first ionisation energy
The atomic number is the number of protons in the nucleus and determines the order of elements on the periodic table.
The standard atomic weight or mass number is the relative average atomic mass (sum of mass of protons and neutrons) of the element’s naturally occurring isotopes
Isotopes of an element have the same number of protons but a different number of neutrons, resulting in different atomic masses.
Analyse how the trend in first ionisation energy is related to the reactivity of metals and their position on the periodic table
Ionisation energy is a measure of the amount of energy required for atoms of a specific element to lose an electron from its outer shell
The first ionisation energy is the amount of energy required to remove the most loosely held electron from 1 mole (6.02 x 1023) of gaseous atoms to produce 1 mole of gaseous ions, each with a charge of 1+
X(g) → X+ + e-
X(g) = 1 mole of element X gas
X+ = 1 mole of element X+ gaseous ions
e- = electrons
Ionisation energy is measured in kJ mol-1 (kilojoules per mole)
e.g. 381 kJ mol-1 (low value), 2370 kJ mol-1 (very high value)
All elements have a first ionisation energy – even atoms which do not form positive ions still have a first ionisation energy, however they require incredibly large amounts of energy to remove one of their electrons (e.g. helium)
In the periodic table, the ionisation energy increases from the left to right of the periods and decreases when you move down a group
In Group 1, the ionisation energy decreases as you move down the group because the valence electron is further away from the nucleus and therefore requires less energy to remove, meaning that the reactivity of elements in Group 1 increases as you move down the group
In Group 7, the ionisation energy decreases as you move down the group because the outer shell is further away from the nucleus and therefore electrons require less energy to remove. However, Group 7 has a valency of -1, meaning that it needs to gain 1 electron to become stable. Therefore, it’s reactivity decreases as you move down the group, because an electron’s attraction to the nucleus decreases the further away the outer shell is
Construct balanced chemical equations for the displacement reactions used to determine reactivity
Single displacement reactions AB + C → AC + B
1 element is displaced from a compound by another (more reactive) element (metals replace metals and/or non-metals replace non-metals)
If C is more reactive than B, a reaction occurs
If C is less reactive than B, no reaction occurs
Generally compounds involved in single displacement reactions are ionic and occur in solution (aq)
Acid + carbonate → salt + CO2 + H2O
Acid + metal → salt + H
