3. Periodicity Flashcards
What is the nuclear charge of an atom?
The atomic number.
What is the effective nuclear charge of an atom?
The attractive positive charge of protons acting on valence electrons.
(The effective nuclear charge is always less than the total number of protons present in a nucleus due to the shielding effect).
Periodic Trends: Effective Nuclear Charge
Across a period: increases.
(electron shielding remains constant).
Down a group: constant.
(increase in additional shells balanced by the increase in the number of protons).
What is atomic radius?
Distance from the centre of the nucleus to outermost electron of an atom.
Periodic Trends: Atomic Radius?
Across the period: decreases.
(greater attraction to the nucleus)
Down a group: increases.
(increased number of shells).
Periodic Trends: Ionic Radius?
Across the period: decreases.
(greater attraction to the nucleus as more protons are added but the valence shell number remains constant).
Down a group: increases.
(increased number of shells).
What is the difference between ionic radius and atomic radius?
The ionic radius is the distance from the nucleus to the outermost electrons in an ion.
The atomic radius is the distance from the center of the nucleus to the outermost shell of an atom.
What is a cation?
A positively charged ion.
What is an anion?
A negatively charged ion.
What is ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms in their ground state.
Periodic Trends: Ionisation Energy?
Across a period: increases.
(closer to a full shell configuration).
Down a group: decreases.
(greater shielding effect, less attraction).
Why are groups 2 and 3 as well as 15 and 16 exceptions to the increasing IE trend?
Ex: Its easier to remove from group 3/16 than from group 2/15 because group 2/15 would have a filled sub-shell.
What is electron affinity?
The energy charge when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions.
Periodic Trends: Electron Affinity?
Across a period: increases.
(the electrons added to energy levels become closer to the nucleus).
Down a group: decreases.
(increased shielding effect, weaker bonds).
What groups are an exception to the EA trends and why?
Group 2: elements already have a full valence s shell and the addition of a new electron would move to the higher energy p shell that is otherwise left empty in the neutral atom.
Group 15: Due to increased electron-electron repulsion when adding electrons into a half-full orbital.
What is electronegativity?
The measure of the ability of an element’s atoms to attract electrons in a covalent bond.
Periodic Trends: Electronegativity?
Across a period: increases.
(nuclear charge increases, attracting bonding pairs of electrons strongly).
Down a group: decreases.
(the radius of the atom increases and the number of protons increases + shielding).
What are some trends in chemical and physical properties of metals?
Chemical:
- easily donates electrons
- reactivity increases down a group
Physical:
- good conductors of electricity
- low density
- grey shiny surface (when cut)
Periodic Trends: Oxides?
Across the period:
basic - amphoteric - acidic
What group 3 oxides are ionic?
Ionic compounds are formed between a metal and a nonmetal so the oxides of Na, Mg, and Al have giant ionic structures.
What group 3 oxides are covalent?
Covalent compounds are formed between non-metals so the oxides of P, S, and Cl are molecular covalent.
What is electrical conductivity?
A measure of ionic character and can only be measured in the molten state when electrons are free to move.
Of the period 3 oxides, which elements are basic?
Na -> Na2O
Mg -> MgO
Of the period 3 oxides, which elements are amphoteric?
Al -> Al2O3
Si -> SiO2
What does it mean for an oxide to be amphoteric?
It can react to neutralise base or acid - they show acidic and basic properties.
Of the period 3 oxides, which elements are acidic?
P -> P4O6 and P4O10
S -> SO3 and SO2
Cl -> Cl2O7 and Cl2O
What is the reaction of a metallic oxide (basic)?
Basic oxides dissolve in water to form a basic or alkaline solution due to the presence of hydroxide ions.
The solution produced has pH>7.
ex: Na2O+H2O⟶2NaOH
MgO+H2O⟶Mg(OH)2
What is the reaction of a non-metallic oxide (acidic)?
Non-metallic oxides react readily with water to produce acidic solutions with pH<7.
ex: P4O10+6H2O⟶4H3(PO4)
P4O6+6H2O⟶4H3(PO3)
ex.2: SO3+H2O⟶H2(SO4)
SO2+H2O⟶H2(SO3)
What is a exception to amphoteric oxides?
Silicon dioxide does not react with water, but reacts with concentrated alkalis to for silicates:
ex: SiO2 + 2OH(-) -> SiO3 (2-) + H20
What is a mettalloid?
A chemical element whose physical and chemical properties fall in between the metal and non-metal categories.
