chem midterm #2

mono

1

di

2

tri

3

terta

4

5

penta

hexa

6

hepta

7

8

octa

9

nona

deca

10

IV

4

V

5

VI

6

explain how the presence of one or more lone pairs in a molecule or ion will change the bond angles.

• Lone pairs repel more strongly than bonding pairs, so they push the bonds closer together and make the bond angles smaller than the ideal angle. The more lone pairs there are, the smaller the angles get.

explain, using valence bond theory, how bonds form.

A bond forms when two half-filled orbitals from two atoms overlap. The two electrons pair up with opposite spins and are shared between both nuclei, which lowers the energy and holds the atoms together.

what is the exception to writing electron configurations when the configuration involves a transition metal? what if its a main heavy group metal?

SD PS

Cation

electrons removed, and gain energy (K+)

Anion

electrons added, and lose energy (S-)

Explain the trend in ionization energy (IE) moving from left to right on the periodic table, then moving up to down. explain why this happens

moving left to right — increases: the stronger pull holds the electrons tighter, and the atom gets smaller. so it’s harder to remove an electron

moving up to down— decreases: outermost electrons are further away from the nucleus making it easier to remove

Electron affinity

amount of energy released when 1 mol of gas phase atoms accepts 1 mole of electrons to become 1 mole of gas phase anions. usually negative because energy is being released

what is a chemical bond + why does it form

Chemical bond: a force of attraction that holds two atoms together.

Why a bond forms: the bonded atoms have lower energy (they’re more stable) than the separate atoms. Atoms lose, gain, or share electrons to reach a full outer shell like a noble gas (the octet).

Electronegativity

measures the attraction for the electrons in a chemical bond

• the higher the attraction is the greater the atoms attraction for the bonding electrons

• the greater the difference, the more polar it is.

what does a greater negativity difference mean for an atom?

the more polar it is

ionization energy

amount of energy that must be added to 1 mole of gas phase atoms to yeild 1 mole of gas phase cations and 1 mole of electrons

Be able to explain why some of the first ionization energies do not follow the trends (i.e. be able to explain the exceptions).

Across a period, first ionization energy usually increases from left to right, but there are two exceptions where it drops.

The first exception is between groups 2 and 13, like Be to B or Mg to Al. In boron, the electron being removed is in a 2p orbital, while in beryllium it comes from a 2s orbital. A p electron is higher in energy, sits slightly farther from the nucleus, and is shielded by the filled s orbital beneath it. This makes it easier to remove, so boron has a lower ionization energy than beryllium.

The second exception is between groups 15 and 16, like N to O or P to S. Nitrogen has three p electrons, one in each p orbital, which is a stable half-filled arrangement. Oxygen has four p electrons, so two of them have to share an orbital. Those paired electrons repel each other, which makes one of them easier to remove, so oxygen has a lower ionization energy than nitrogen.

when writing a lewis structure, where should the negative charge

on the most electronegative atom (best FC)

what is it called when bonds share unequally due to one atom being more electronegative? what elements are these usually? why does this happen?

polar covalent

it happens because one atom is pulls the electrons harder , so it becomes δ− and the other becomes δ+

what is it called when bonds share equally?

non polar covalent (same atoms)

why is the periodic trend the way it is?

As the distance between the nucleus and outermost electron increases, the force of attraction decreases. This means that as you go down a periodic table, the outermost electrons are farther from the nucleus and easier to remove.

Be able to explain why successive ionization energies always increase for a given element. [Sections 3.6 & 3.7] 

whenever you take away an electron, more energy is being used since its harder to take away an electron as you get closer to the center.

exception of electron affinity?

usually the elements at the top right (higher nuclear charge) have the highest EA values. but if they have a full or half filled shell they tend to have lower EA values (also meaning they dont want the electron as much)

Effective nuclear charge:

Z-effective = # protons - # core electrons

find core by atomic #- valence electrons

how do dipoles and electronegtivity go hand in hand?

to find the bond type, you can use electronegtivity scale/ difference to predict the bond type (non polar covalent, polar covalent, ionic) from there, to find the polarity of a molecule (aka if a molecule is polar) you can use dipoles. Dipoles occur when there are polar bonds between a molecule (polar: shared unequally, points toward more electronegtive) if the dipoles cancel its non polar. if they dont then its polar

for bonds: list the electronegtivity values and their predicted metals for

1. non polar/pure (same elements)

2. polar covalent (non metal only)

3. ionic (non metal and metals)

less than 0.4

between 0.4-2.0

more than 2.0

what type of covalent bonds when electrons are shared equally?

non polar

what type of covalent bond when electrons are shared unequally?

polar covalent (atoms are different, so one has higher electronegativity and pulls the shared electrons closer. δ⁻ and δ⁺.

in a polar molecule, whats the trend with dipoles and the overall shape?

dont cancel- dipoles go the same direction

unsymmetric

LP in the central

outer atoms are diff

in a nonpolar molecule, whats the trend with dipoles and the overall shape?

cancel- dipoles go opposite ways

symmetric

no LP in the center

outer atoms the same