Periodic trends

What is the valence shell of an atom? 

-The valence shell of an atom is the outermost shell which is the furthest from the nucleus 

How does the valence shell affect the stability of atoms? 

-A full valence shell means an atom has maximum stability, so it is far less reactive 

What was it that made it so difficult to order the elements in a table in the 19^th century? 

-The thing that made this difficult was the fact that not all the elements have been discovered 

-Protons were also not discovered so there were no atomic numbers 

-They could only use atomic weights and observable characteristics 

 

What was unique about Mendeleev’s periodic table? 

-Mendeleev was able to predict the existence of many elements which were not discovered yet, and left gaps for them in his periodic table 

What group of elements were not on Mendeleev’s periodic table? 

-The noble gases were not included on Mendeleev’s periodic table 

-This was due to the fact that they have a stable octet, and they are hardly reactive 

-Due to their inertness, it was extremely difficult to get a reaction out of them with the technology they had back then 

Groups 

-Groups are the vertical columns on the periodic table 

-Elements in the same group have the same valence electrons and often share similar chemical properties 

Periods 

-Periods are the horizontal rows on the periodic table.  

-Elements in the same period contain the same number of occupied electron shells 

What is meant by core charge? 

-The core charge is the measure of attractive force experienced by a valence shell electron 

-It depends on the number of protons in the nucleus and number of electrons between the core and the valence shell 

What is the trend of the core charge from across periods? 

-The core charge increases from left to right across periods.  

-This is because the number of protons in the nucleus increase across periods but the number of inner shells remain constant 

 

What is the trend of the core charge down groups? 

-Core charge remains constant down groups  

-This is due to the amount of electron shells increasing proportionally to the amount of protons 

What is meant by Electronegativity? 

-Electronegativity refers to the tendency of an atom to attract another bonding pair when it is in a chemical bond. 

What is the trend of Electronegativity from across periods? 

-Electronegativity increases across periods 

-As the core charge increases there is a stronger force of attraction between bonding electrons and the nucleus 

What is the trend of Electronegativity down groups? 

-Electronegativity decreases down groups 

-This is because the atoms become larger as they go down the groups so the force of attraction from the nucleus and the valence shell weakens. 

What is meant by Atomic Radii? 

-Atomic radius is the distance between the nucleus and the valence shell 

What is the trend of Atomic radius across periods? 

-Atomic radius decreases across periods due to the increase of protons which means the attractive force will be greatly attracting the electrons strongly towards the nucleus decreasing the radius 

What is the trend of Atomic Radius down groups? 

-The Atomic radius increases down groups due to the number of shells increasing 

What is meant by ionisation energy? 

-Ionisation energy is the energy required to remove the first electron of the valence shell 

 

What is the trend of ionisation energy across periods? 

-First ionisation energy increases due to the core charge increasing. Since the protons in the nucleus will strongly attract the bonding electrons, the force to remove them will also be higher. 

What is the trend of ionisation energy down groups? 

-First ionisation decreases down groups due to the increase of the number of shells which means the attractive force will be weaker due to the electrons being further from the nucleus.