Thermochemistry

shielding

inner shell e-e repulsion

Electronegativity

a measure of an atom's ability to attract shared electrons to itself

If the ΔH is positive

Heat energy has increased so the reaction is endothermic

If ΔH is negative

heat energy has decreased so the process is exothermic

Atomic radius

The distance from the nucleus to the outermost electron.

In atomic radius what happens across a period?

The number of electron shells remains the same AND more protons will increase which increases the nuclear charge OVERALL the attraction between the nucleus and the outer electron increases. L —> R.

In atomic radius what happens down a group?

The number of electron shells increases despite the number of protons increasing (nuclear charge). OVERALL the attraction between the nucleus and the outer electron decreases. TOP —> BOT

Ionisation energy

The energy required to remove 1 mol of the least tightly held electron from 1 mol of gaseous atoms.

In ionisation energy what happens across a period?

Ionisation energy increases due to increasing attraction between nucleus and valence electron

In ionisation energy what happens down a group?

Ionisation energy decreases due to decreased attraction between nucleus and valence electron.

Is an endothermic reaction spontaneous or not?

No, it is not spontaneous

Is exothermic spontaneous or not?

yes, it is spontaneous

Temporary dipoles

Weakest intermolecular forces caused by temporary dipoles that occur when electrons in two adjacent atoms occupy positions that form temporary dipoles.

Permanent Dipole - Permanent dipole (PD-PD)

occur between molecules that have permanent dipole moments, aligning in such a way that the positive end of one molecule is near the negative end of another.

a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (such as fluorine, oxygen, or nitrogen) and is attracted to a lone pair of electrons on another electronegative atom.

Hydrogen bonding

Intermolecular forces

Forces of attraction or repulsion between neighbouring molecules

London dispersion forces (td-td)

weakest intermolecular forces caused by temporary dipoles that occur when electrons in two adjacent atoms occupy positions that form temporary dipoles.

List types of molecules that are held together by temporary dipole forces


All molecules no matter the size

Why temporary dipoles get stronger as the molecular size increases

As the number of electrons increase, the positive and negative charges can be stronger and uneven electron distribution happens more frequently.

How non polar molecules, or uncharged molecules, can be attracted to one another

Nonpolar or uncharged molecules are able to attract each other as it induces neighbouring molecules to also have charged ends, it does this through electron-electron repulsion. All these molecules have positively charged and negatively charged regions and can interact with each other through attraction of opposite charges.

What are temporary dipole electrons like?

These electrons are constantly moving around, meaning at any point electrons won't be evenly distributed throughout the whole molecule.

Do polar molecules always have charged ends?

yes

The main idea of permanent dipoles is...

the positively charged regions are attracted to the negatively charged regions of a neighbouring molecule.

Are temporary dipoles stronger than permanent dipoles?

No. Permanent dipoles also have higher MP and BP than temporary dipoles.

For a hydrogen bond, a hydrogen atom must attach to

F, O, or N because these atoms are the most electronegative

Do hydrogen bonds share with atoms who are less electronegative when a covalent bond is formed?

No

What happens when F, O, N covalently bond with H?

The electronegative atom hogs the electrons so that the H is pretty much a proton.

When does hydrogen bonding occur?

when this proton bonds to negatively charged regions of neighbouring molecules sue to attractiveness of unlike charges.

What are the forces of hydrogen bonds like?

The strongest out of the three, and have a high MP and BP

What type of dipoles do polar molecules have?

td-td, pd-pd

If the molecule has an H atom bonded to an electronegative atom, it forms ...

Hydrogen bonds, pd-pd, and td-td

Why might td-td forces be greater?

• If both molecules have similar sized electron clouds

• more electrons are present, which means uneven electron distribution happens more

• Leads to more positive and negative charges to be stronger

• Large molecules

Trigonal Bipyramid MS

• Parent shape: Trigonal Bipyramid

• 5 bonding 0 lone pairs

• 90 degree bond angle (axial equatorial)

• 120 degree bond angle (equatorial)

• Symmetrical

Seesaw MS


• Parent shape: trigonal bipyramid

• 4 bonding 1 lone pair

• 90, 120, and 180 bond angle

• Asymmetrical

T-shape MS

• Parent shape: trigonal bipyramid

• 3 bonding, 2 lone pairs

• 180 and 90 bond angle

• Asymmetrical

Linear MS

• Parent shape: trigonal bipyramid

• 2 bonding, 3 lone pairs

• 180 bond angle

• symmetrical

Octahedral MS

• Parent shape: octahedral

• 6 bonding, 0 lone pairs

• 90 bond angle

• symmetrical

Square pyramid MS

• Parent shape: Octahedral

• 5 bonding, 1 lone pair

• 90 bond angle

• Asymmetrical

Square planar MS

• Parent shape: Octahedral

• 4 bonding 2 lone pair

• 90 bond angle

• symmetrical

Ssurr is exothermic

Energy is being released, meaning more Ek particles which leads to faster particle movement. Therefore there is more disordered, which is more favourable for a spontaneous reaction.

Ssurr is endothermic

Energy is being absorbed, therefore less particles of Ek, which means slower particle movement. Therefore is less disordered and is less favourable for a spontaneous reaction.

STot needs to be what for spontaineity?

>0

When will products be more disordered?

If the products have more moles

what happens if Ssurr is <0?

Ssys must outweigh the magnitude of Ssurr such that Stot is positive

When does Electronegativity increase?

across a period

When does electronegativity decrease?

down a period