periodic table and hydrogen

What is the metallic radius?

Half the distance between the centre of the atoms in the solid state of an element

What is the covalent radius?

Half the internuclear distance of neighbouring atoms of the same element in a molecule

• half the distance between the nuclei

What does ‘atomic radii’ consist of?

Metallic and covalent radius

How does atomic radii change across a group and period?

• increases in size down a group

• decreases in size along a period

What is the first ionisation energy of an element?

The change associated with the removal of the first valence electron at 0K and 1atm from a gaseous atom

What is the difference between ionisation energy and enthalpy?

Ionisation energy is at 0K and 1atm

Ionisation enthalpy ΔH_ion is at 298K

What is electron pairing energy?

Electron-electron repulsion causes lower than expected ionisation energy

What are the lowest and highest IE values?

Highest = noble gases as filled shells

Lowest = alkali metals - single electrons outside a full shell

What is the first electron affinity EA₁?

What is the equation?

The internal energy released when an electron is added to a neutral gas phase atom

X (g) + e^- → X^- (g)

What is electronegativity?

What is it an indicator of?

The ability of an atom to attract electrons to itself in a molecule

It is an indicator of:

1. general chemical behaviour

2. electron distribution in a bond

3. whether a compound will be ionic or covalent

What does the Ketelaar triangle look like?

Do metals conduct electricity when:

• solid?

• molten?

Yes and yes

Are metals soluble in water?

No

What does melting point and strength depend on in metals?

What does strength of metallic bonding depend on?

Depends on strength of underlying metallic bonding

• depends on how many electrons are delocalised or given up into the electron sea

Why is H₂ relatively unreactive?

It is non labile, and has high activation energy

3 examples of H₂ reacting rapidly?

1. free radical chain reactions

2. homolytic dissociation at a metal surface

3. heterolytic dissociation at a metal surface

3 main electronic processes of hydrogen reactions

1. losing electron to make H⁺

2. gaining electron to make H^-

3. sharing electrons to make covalent molecules

Why is hydrogen able to penetrate metals?

What does it form?

It is able to penetrate metals due to small size of H atom

Forms metallic hydrides

Why do LiH and BeH₂ have high melting points?

They have extended lattice structures

Why does diborane and methane have very low melting points?

They are molecular with London dispersion forces

Why do NH₃, H₂O and HF have fairly low melting points?

They have LDFs and hydrogen bonds

Where in the periodic table are saline hydrides?

How are they formed?

What are the partially positive charges?

Formed by the electropositive elements of groups 1 and 2 (s block)

E^𝛿+-H^𝛿-

Saline hydrides

• Ionic or covalent?

• What colour?

• High or low melting point?

Ionic

Colourless

High melting points

What is the structure of group 1 MH?

What is the structure of group 2 MH₂?

MH = rock salt structure

MH₂ = range of structures

Where in the periodic table are the metallic hydrides?

Which elements form them i.e. which block?

Formed by the d and f block elements

Where in the periodic table are the intermediate hydrides?

What are their properties?

Intermediate between the ionic and molecular hydrides

Be, Mg, Cu, Zn, Al

Where in the periodic table are the covalent molecular hydrides?

Which elements form them (which block)?

What are the three types?

Formed by electronegative elements from groups 13-18 (p block)

• electron deficient

• electron precise

• electron rich

What happens to the bond when an H atom is covalently bonded to an electronegative element?

The bond is polarised

Evidence for hydrogen bonds

Anomalously high boiling points of HF, NH₃, and H₂O

• they can form H bonds in the liquid state

What causes dipole-dipole forces?

Electrostatic attraction between the dipoles

• there must be an overall dipole on the molecule

What causes London dispersion forces?

Instantaneous dipoles which induce dipoles in neighbouring molecules