Module 2 (chapter 5 and 6) - bonding and intermolecular forces Flashcards
What is the general electron configuration
2.8.18.32
What does the number in front of sub shells mean?
The principle quantum level (shells)
This can be found from the row of that element on the periodic table
What are the rules when filling electron orbitals?
- fill form bottom up with arrows going up then down
- when there is move than one box fill along before pairing up as like charges repel
- fill up 4d before 3P as they have very similar energy levels but loose from 4D before 3P
- Group principle quantum levels together
How do you use Nobel gas configurations when filling shells?
Choose the previous novel gas and pit it in square brackets
-list the remaining sub shells until all electrons in the element are used
How is the periodic table classed into S,D,P and F blocks?
Based off their highest energy electrons
E.g. first two columns have their highest energy electrons in an S sub shell so they are in the S block
What is the general order of sub shells?
1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2
What is an ion?
Positively or negatively charged atoms (covalently bonded) or groups of atoms (a molecule ion)
-they have an imbalance of protons and electrons leading to an overall charge on the particle
(E.g. atomic ions like Li+ and covalently bonded ions like Co3 2-]
What is relative isotopic mass?
(RIM) The mass of an atom of an isotope compared with 1/12 of the mass of carbon-12
What is relative atomic mass?
The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12
What is the relative molecular mass?
The weighted mean mass of a molecule compared with 1/12 of the mass of an atom of c-12
Only applies to simple covenant molecules
What is relative formula mass?
The weighed mean mass of a formula unit compared to 1/12 of the mass of an atom of carbon-12
-can apply to iconic substances as these occur as giant lattices
What does a full stop in an equation mean?
Hydrated
-makes up structure but isn’t chemically bonded
Atomic number
Number of protons in the nucleus of the atom
Z
Mass number
The number of particles (protons and neutrons) un the nucleus of an atom
(A)
Isotopes
Atoms of the same element with the same number of protons but different number of neutrons
What are properties of isotopes?
- sometimes extra neutrons make the nucleus unstable so it’s radioactive
- different isotopes of the same element can have different physical properties
- always have the same chemical properties as reactions depend on the electron structure
In mass spectrometry why can’t you join the peaks?
As there are no isotopes in between
In mass spectrometry why are there two clusters of peaks?
As some elements have more than one atom per molecule
- when passed through an electron is knocked of the molecule giving a molecular iron
- these can be unstable and fall apart leading to fragmentation so the two sets account for both fragmented and un-fragmented ions
What value to you approximate the tallest peak
100
Why can’t you predict the relative heights f the two clusters only approximate?
Because it is dependent on what proportion of molecular ions break up into fragments
In mass spectrometry what do the different lines mean?
They are different isotopes in proportion of their varying charges and masses
What the calculation to work out atomic contribution and RAM from mass spectrometry?
Amount/total amount x mass
Add all of these together from different isotopes for RAM
ionic bond
an electrostatic force of attraction between oppositely
charged ions. they are non directional in three dimensions
-there is a transfer of electrons
ion
an electrically charged particle formed by the loss or gain of one or more electrons from one atom or group of atoms
element
substance made of one type of atom
compound
substance made of two or more types of atoms chemically bonded together
molecule
particles made from two or more atoms chemically bonded together using covenant bonds
giant ionic lattice
structure resulting from oppositely charged ions strongly attracted in all directions
melting and boiling point of ionic compound
-high melting and boiling point due to strong electrostatic forces of attraction between oppositely charged ions which means a lot of energy needed to overcome these
solubility of ionic compounds
some are soluble in water (polar solvents) if the ionic lattice breaks down and if water molecules attract and surround ions
- this is because opposite charges of salt and water ion are attracted and as this happens atoms begin to separate was water molecules surround it dissolving it
- therefore solubility depends on the relative strength of the attractions as this has a greater effect, and solubility decreases as ionic charge increases
electrical conductivity of ionic compounds
conducts electricity when molten or dissolved
- in a solid state the ions are in a fixed position in the giant ionic lattice so there are no mobile charge carriers
- yet when the lattice is broken down ions are now free to move as mobile charge carriers
what is a covenant bond?
a strong electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms
occur in:
-nonmetallic elements
-compounds of non metallic elements
-polyatomic ions
it is an overlap of atomic orbitals each containing one electron
-the bonded atoms often have outer shells with the same electron structure as the nearest Nobel gas
what is a dative/coordinate covalent bond?
when both electrons come from the same atom
-the shared electron pair was originally a lone pair of electrons on one of the bonded atoms
what is the direction of the covalent bond?
- the attraction is localised acting solely between the shared pair of electrons and the nuclei of the two bonded atoms
- it is a directional force
what are multiple covenant bonds?
they exist when two atoms share more than one pair of electrons
double/triple covenant bonds is when there are two/three shared pairs of electrons between the nuclei of the bonding atoms
why do simple molecular have low melting and boiling points, whilst giant have high?
- due to weak intermolecular forces between molecules which require little energy to break apart
- yet in giant there are strong covalent bonds between atoms which require lots of energy to break apart
why don’t covenant substances conduct electricity?
- there are no free electrons to act as mobile charge carriers as they tend to be used in covalent bonds
- even in cases where electrons may be delocalised within a molecule there isn’t sufficient contact between the molecules to allow electrons to move through the whole solid or liquid
what is electron pair repulsion theory?
- the shape of a molecule is determined by the number of electron pairs surrounding the central atom
- as all electron pairs are negatively charged they repel one another until they’re as far apart as possible
- this holds the bonds in a definite shape
what did the different lines represent in terms of bonds?
- a solid line is a bond in the plane of the paper
- a solid wedge comes out of the plane of the paper
- a dotted wedge goes into the plane of the paper
what is significant about lone pairs in electron repulsion theory?
lone pairs sit slightly closer to the central atom and occupy more space than a bonded pair
- this means they repel more strongly slightly narrowing the bond angle
- for each lone pair the bond angle is reduced by 2.5 degrees
what is the linear shape?
2 electron pairs
-180 degree bond angles
what is the bent shape?
2 lone pairs and two bonding pairs
-bond angles of 104.5 degrees
what is the tetrahedral shape?
- 4 electron pairs
- 109.5 degree bond angles
what is the pyramidal shape?
- one lone pair and 3 bonding pairs
- bond angles of 107 degree
what is the trigonal planar shape?
- three bonded pairs
- 120 degree bond angles
what is the trigonal bipyramidal shape?
- 5 bonded pairs
- 90 degree bond angles for two
- 120 degree bond angles for three
what is the octahedral shape?
6 bonded pairs of electrons
-90 degree bond angles
what is the shape of the ammonium and sulphate ion?
- ammonium 4 bonding pairs around the central atom creating a tetrahedral shape
- sulphate has four regions of electron density
what is the shape of the carbonate and nitrate ion?
- they have three regions of electron density around the central atom
- this forms a trigonal planar shape
what is electronegativity?
the ability of an atom to attract the bonding electrons in a covenant bond
- this is shown on the Pauling scale, the more electronegative the atom the higher the number
- across the periodic table, the nuclear charge increases and the atomic radius decreases
how can electronegativity affect polarity?
- if the molecule is symmetrical the atoms will have the same electronegativity so electrons will be evenly spaced
- yet if the atoms have different electronegativities it means the electrons won’t be shared evenly forming a polar bond
how can polar bonds form non-polar molecules?
polar bonds occur when bonded atoms have different electronegativity values meaning electrons are unevenly distributed
-yet if the molecule is symmetrical they cancel forming a non polar molecule
what are inter and intra molecular forces?
- inter is between molecules
- intra is within molecules
what is the scale in strength of intermolecular forces?
hydrogen bonding is strongest then permanent then induced
50-10-1 times the strength
how do induced dipole dipole interactions work?
- movement of mobile electrons produces a changing dipole in a molecule
- at any instant, an instantaneous dipole will exist but its position is constantly shifting
- the instantaneous dipole induces a dipole on a neighbouring molecule
- the induced dipole induces further dipoles on neighbouring molecules which then attract one another
- these are only temporary and can disappear quickly
what are London dispersion forces?
weak intermolecular forces that exist between all molecules whether polar or non-polar
-they act between induced dipoles in different molecules
why can induced dipole dipole interactions work?
- in symmetrical molecules electrons aren’t static meaning they can be nearer one atom rather than another at anytime
- these oscillations create the instantaneous dipoles
what are permanent dipole-dipole interactions?
- weak attractive force that acts between the permanent dipoles in different polar molecules
- polar molecules have permeant dipoles
what is hydrogen bonding?
a type of intermolecular force which arises when:
- an electronegative element is attached to a hydrogen atom (H,N,F)
- the hydrogen forms an interaction with a lone pair of electrons on an electronegative atom
based off hydrogen bonding why is ice less dense than water?
- two lone pairs on the oxygen atom and two hydrogen atoms, each water molecule can form four hydrogen bonds
- these extend outwards holding water molecules slightly apart and forming an open tetrahedral lattice full of holes (bond angles around each hydrogen atom is close to 180)
- when it melts the structure collapses removing these holes meaning molecules move closer together forming a denser liquid
based off hydrogen bonding, why does water have a relatively high melting and boiling point?
as with all molecules water has London forces between molecules
- therefore hydrogen bonds are extra forces over and above the London forces
- a large amount of energy is needed to overcome these forces
based off hydrogen boning, why does water have high surface tension and viscosity?
hydrogen bonds means water molecules are relatively strongly attached to each other so water flows less easily than expected increasing viscosity
-strong properties can allow small objects/ insects to walk on surface
what determines the strength of induced dipole-dipole interactions?
- the more electrons in each molecule, the larger the instantaneous dipole, so the greater the induced dipole-dipole interactions increasing the attractive forces
- also the more electronegative element the greater the induced dipole
how do you predict the solubility of non polar substances ?
when a simple molecular compound is added to a non polar solvent intermolecular forces form between them
- these interactions weaken the intermolecular forces in the lattice allowing the compound to dissolve
- therefore non polar simple molecular substances tend to be soluble in non-polar solvents
- when a simple molecular compound is added to a polar solvent there is little interaction between molecules so the intermolecular bonding is often too strong to break so they tend to be insoluble in polar solvents
- some contain both polar and non polar parts of their structure so can dissolve in both polar and non-polar solvents
why is chlorine a gas but iodine a solid?
more electrons in iodine molecules
-this creates stronger dipoles in the molecule and therefore stronger induced dipole dipole interactions
orbital
a region within an atom that can hold up to two electrons (with opposite spin)
what causes stronger ionic bonds?
- compounds with a greater ionic charge as there is greater attraction between ions
- more energy required to break these bonds
isoelectronic
having the same number of electrons/ electronic structure
how do ionic compounds dissolve
- delta positive hydrogen attracts negative ions in ionic compound
- delta negative oxygen attracts positive ions in ionic compound
- pulls compound apart and it dissociates
