Bonding Flashcards
Main two types of bonding
Ionic and covalent
When are ions formed?
When one or more electrons are transferred from one atom to another
What is ionic bonding
When ions are held together by electrostatic attraction
What are the simplest ions?
Single atoms which have lost or gained electrons do they’re got a full outer shell
What do elements in the same group have?
The same number of outer electrons they want so form ions with same charges
What’s electrostatic attraction?
The thing that holds positive and negative ions together. It’s very strong
What are a lot of ions made of?
Groups of atoms with no overall charge (compound ions).
Sulfate
SO4 3-
Hydroxide
OH-
Nitrate
NO3 -
Carbonate
CO3 2-
Ammonium
NH4+
Ionic compounds are made up of?
Positively charged parts and negatively charged parts
Overall charge of any compound is?
Zero
What must negative charges in a compound do ?
Balance all the positive charges
What can you use charges on individual ions present to work out?
The formula of an ionic compound
Sodium chloride structure
Giant ionic lattice
What are ionic crystals?
Giant lattices of ions
What’s a lattice?
Just a regular structure
Why’s giant ionic lattice called giant?
Because it’s made up of same basic unit repeated over and over again
Sodium chloride describe
Na+ and Cl- ions packed together
Sodium chloride lattice is cube shaped- different ionic compounds have different shaped structure
What does the structure of an ionic compound determine?
Their physical properties
Ionic compounds properties
Conduct electricity when molten or dissolved but not when solid
Have high melting points
Tend to dissolve in water
Why do ionic compounds Conduct electricity when molten or dissolved but not when solid?
Ions in a liquid are free to move and carry a charge
In a solid the ions are fixed in position by strong ionic bonds
Why do ionic compounds Have high melting points?
Giant ionic lattice held together by strong electrostatic forces. Takes loads of energy to overcome forces so melting points are very high
Ionic compounds Tend to dissolve in water why?
Water molecules are polar- part of molecules has a small negative charge and other bit have small positive charges. Charged parts pull ions away from lattice causing it to dissolve
When do molecules form?
When two or more atoms bond together. Doesn’t matter if atoms are same or different
Molecules held together by?
Strong covalent bonds
What does covalent bond happen between?
Non-metals
What’s a single covalent bond?
A shared pair of electrons
In covalent bonding what happens?
Two atoms share electrons so both full outer shells of electrons. Both positive nuclei are attracted electrostatically to shared electrons
Types of bonds atoms form?
Single bonds
Double bonds
Triple covalent bonds
What do multiple bonds contain
Multiple pairs of electrons
Describe giant covalent structure
Have huge network of covalently bonded atoms
Macromolecular structures
Why can carbon form giant covalent structure?
Can form 4 strong, covalent bonds
Graphite structure explains what?
It’s properties
What do the weak bonds in graphite do?
Weak bonds between layers in graphite are easily broken so sheets can slide over each other.
Graphite feels slippery and is used as a dry lubricant and in pencils
Delocalised electrons graphite?
The delocalised electrons in graphite aren’t attached to any particular carbon atoms and are free to move along the sheets carrying a charge. Graphite is an electrical conductor
Layers of graphite?
Far apart compared to covalent bonds so graphite is low density and is used to make strong, lightweight sports equipment
Why does graphite have a high melting point?
Strong covalent bonds in hexagon sheets.
Graphite very high melting point (sublimes at over 3900K)
Graphite with any solvent?
Insoluble
Covalent bonds in sheet are too strong to break
Graphite structure
Carbon stone arranged in flat hexagon covalently bonded sheets with three bonds each. Four outer electron of each carbon atom is delocalised
Diamond is the?
Hardest known substance
Made if carbon atoms
Diamond structure
Each carbon atom is covalently bonded to four other carbon atoms. Atoms arrange in tetrahedral
Because of diamonds strong covalent bonds it?
Has very high melting point Extremely hard Good thermal conductor Can't conduct electricity Won't dissolve in any solvent You can cut diamonds to form gemstones
When does diamond sublime?
sublimes at over 3900K
What’s diamond used in?
used in diamond-tipped drills and saws
Why’s diamond a Good thermal conductor?
Vibrations travel easily through stuff lattice
Why can’t diamond conduct electricity?
All outer electrons held together in localised bonds
Why does diamond sparkle?
It refracts light a lot
What is dative covalent bonding?
Where both electrons come from one atom
Describe ammonium ion?
Classic example of dative covalent or coordinate bonding
Forms when nitrogen in an ammonia molecule donates a pair of electron to a proton
Molecules and ions come in
Loads of different shapes
What does the shape depend on?
Electrons in outer shell of central atom
Bonding pairs and lone pairs exist as?
Charge clouds
What’s a charge cloud
An area where you have a big chance of finding an electron pair. Electrons whizz around inside charge cloud.
When do you get a compound?
When different elements or bonds join together
E.g. Elements hydrogen and oxygen make water
What are all what charged and what do the charge clouds do?
Negatively charged and so charge clouds will repeal each other as much as they can so pairs of electrons in outer shell of atom sit as far apart from each other as they possibly can
What does the shape of the charge cloud affect?
How much it repels other charge cloud. Lone pair clouds repel more then bonding-pair charge clouds
What are the greatest angles between?
Lone pairs of electrons and bond angles between bonding pairs are often reduced because they are pushed together by lone-pair repulsion
What are the biggest angle?
Lone pairs
What are the second biggest angle?
Lone pair/ bonding pair
What are the smallest angles?
Bonding-pairs
Explain what is used to display bonds
Wedge shows bonds sticking out of page
Broken lines show bonds that go into page
What’s this theory called?
Valence-shell electron-pair repulsion theory
What do you need to predict a shape of molecule?
You need to know how many bonding and lone pairs on central atom of the molecule
How to predict shape of molecule
First work out central atom (one others are bonded to)
Use periodic table to work out number of electrons in outer shell of central atom
Add 1 to number for every atom that central atom is bonded to
Divide by 2 to find number of electron pairs on central atom
Compare number of electron pairs to number of bonds to find number of lone pairs and number of bonding pairs on central atom
What happens if dealing with an ion?
You need to take its charge into account
After step 3, add 1 for each negative charge on the ion
2 electron pairs?
180 degrees
Linear- no lone pairs
Cl-Be-Cl
3 electrons pairs
120
No lone pairs
trigonal planar
Tetrahedral
No lone pairs
4 electron pairs
109.5
Trigonal pyramidal
4 electron pairs
1 lone pair
107
Bent
2 lone pairs
4 electron pairs
105
Trigonal bipyramidal
No lone pairs
5 electron pairs
90 in corner
120 side
Seesaw
1 lone pair
5 electron pairs
87
102
T-shaped
2 lone pairs
5 electrons
88
Octahedral
No lone pairs
6 electron pairs
90 in corner right
90 on middle right
Square planar
2 lone pairs
6 electron pairs
90 degrees
Molecules with 5 electrons and 1 lone pair?
Pretty rare like octahedral but with bottom Element replaced by a lone pair
Example:predicting shape of molecule H2S
Central atom is sulfur
Sulfur’s group 6 so has 6 electrons in outer shell
Sulfur atom bonded to 2 hydrogen atoms so had 8 electrons in outer shell in H2S
Sulfur atom has 4 electron pairs and has made 2 bonds so has 2 bonding pairs and 2 lone pair
H2S will have bent shape
What’s electro negativity?
An atom’s ability to attract electron pairs in a covalent bond
What’s the most electronegative element?
Fluorine
Oxygen, nitrogen and chlorine also strongly electronegative
What makes a bond polar?
In a covalent bond two atoms of different electronegatives the bonding electron will be pulled towards the more electronegative atom making the bond polar
Why in a covalent bond between 2 atoms of the same element is it non-polar?
The atoms have equal electronegativites so ejection are equally attracted to both nuclei
What are some elements like carbon and hydrogen?
Have pretty similar electronegative so bonds between them are essentially non-polar
What happens in a polar bond?
The difference in electron in electronegativity between 2 atoms causes a permanent dipole.
What’s a dipole?
A difference in charge between 2 atoms caused by shift in electron density in the bond
Delta means?
Slightly
Delta + means slightly positive
Why do chlorine and hydrogen form a permanent dipole?
Chlorine is much more electronegative than hydrogen
Correlation between electronegativity of atoms and polarity?
The greater difference in electronegativity between the atoms the more polar the bond
What happens if a molecule contains polar bonds?
You can end up with an uneven distribution of charge across the whole molecule. When this happens, the molecule is polar
Do all molecules that contain polar bonds be polar?
No. If polar bonds are arranged symmetrically in the molecule then the charges cancel out and there is no dipole
In a substance made up of molecules with permanent dipoles?
There will be weak electrostatic forces of attraction between delta + and delta - on neighbouring molecules
If you put a charged rod next to a jet of polar liquid e.g. Water what happens
The liquid will move towards the rod because polar liquid contains molecule with permanent dipole.
Doesn’t matter if rod is positively or negatively charged. Polar molecules in liquid can turn around so opposite charged end attracted towards the rod
What are intermolecular forces?
Forces between molecules
Much weaker than covalent, ionic or metallic bonds
Weakest intermolecular force
Induced dipole-dipole
van der Waals
Middle intermolecular force strength
Permanent dipole-dipole forces
Ones caused by polar molecules
Strongest electrostatic intermolecular forces?
Hydrogen bonding
Why are intermolecular force important?
Affect physical properties of a compound
Van der Waals forces found
Between all atoms and molecules
Cause all atoms and molecules to be attracted to each other
What are electrons in a charge cloud always doing?
Moving very quickly
At any moment, the electrons in an atom are likely to be more to one side than other. At this moment the atom would have a temporary dipole
What do dipole cause
Another temporary dipole in the opposite direction on a neighbouring atom. The two dipoles are attracted to each other
What can the second dipole cause?
A third dipole in a third atom
Like domino effect
What happens because electrons are constantly moving?
Dipoles being created and destroyed all the time. Even though dipoles keep changing overall effect is for atoms to be attracted to each other
Why is iodine a solid at room temperature?
Van der Waals forces between iodine molecules that are responsible for holding them together in a lattice
Forces and bonds of solid iodine
Iodine atoms are held together in pairs by strong covalent bonds to form I2 molecules
Molecules held together by molecular lattice arrangement by weak van der Waals
Strengths of Van der Waals?
Aren’t all same strength
Larger molecules have larger electron clouds meaning stronger van der Waals forces
What does shape of molecules have to do with van der Waals?
Shape of molecule affects strength of Van der Waal forces
Long, straight molecules lie closer together than branched ones
The closer together 2 molecules get the stronger the forces between them are
What happens as you boil a liquid?
You need to overcome intermolecular forces so particles can escape from liquid surface. Stands to reason you need more energy to overcome stronger intermolecular forces so liquids with stronger van der Waals forces will have high boiling points
As alkane chains get longer
The number of electrons in the molecules increases
Meaning stronger van der Waals so boiling point increases
What else does Van der Waals affect?
Other physical properties e.g. Melting point and viscosity
When does hydrogen bonding happen?
Only when hydrogen is covalently bonded to fluorine, nitrogen or oxygen
Why does hydrogen bonding happen with fluorine, nitrogen and oxygen?
They are very electronegative so draw bonding electrons away from hydrogen atoms. Bond is polarised and hydrogen has such a high charge density (so small) that hydrogen the hydrogen atoms form weak bonds with lone pairs of electrons on fluorine, nitrogen or oxygen atoms of other molecules
What two groups do hydrogen bonding usually contain?
-OH or -NH groups
Water and ammonia both have?
Hydrogen bonding
Substances with hydrogen bonding melting and boiling points?
Higher then other similar molecules because extra energy is needed to break the hydrogen bonds
Water and hydrogen fluoride has a much higher boiling point than other hydrogen halides
What happens as water cools to form ice?
Molecules make more hydrogen bonds and arrange themselves in a regular lattice structure
In regular structure H2O molecules are further apart on average than molecules in liquid water so ice is less dense than liquid water
Metal elements exist as?
Giant metallic lattice structure
Giant metallic lattice describe
Outermost shell of metal atom electrons are delocalised- electrons move about metal leaving positive ion e.g. Na+…
Positive metal ions attracted to delocalised negative electrons form lattice of closely packed positive ions in sea of delocalised electrons (metallic bonding)
Why do metals have high melting point?
Strong electrostatic attraction between positive ions and delocalised sea of electrons
What also affects melting point of metals?
Number of delocalised electrons per atom. The more there are the stronger the bonding will be and the higher the melting point. E.g.?Mg2+ has 2 delocalised electrons per atom got a higher melting point than Na+ which has 1
What are metals good thermal conductors
Delocalised electrons can pass kinetic energy to each other
What makes metal a good electrical conductor?
Delocalised electrons can move and carry a current
Why are metals insoluble except liquid metals?
Because of strength of metallic bonds
Typical solid
Particles are very close together
Give a high density and make it incompressible. Particles vibrate about a fixed point and can’t move about freely
Typical liquid
Similar density to a solid
Virtually incompressible. The particles move about freely and randomly within the liquid allowing it to flow
Gases
Particles have loads more energy and much further apart
Density generally pretty low and very incompressible. The particles move about freely with not a lot of attraction between them so they’ll quickly diffuse to fill container
What do you need to do to change from a solid to a liquid or a liquid to gas?
You need to break forces that are holding the particles together. To do this you need to give the particles more every by hearing them
To melt or boil a simple covalent compound?
You only have to overcome the intermolecular forces that hold the molecules together
Don’t need to break stronger Covalent bonds that hold atom together in molecules. Causes simple covalent compounds to have a low melting and boiling point.
Water boiled
Stream
Describe chlorine
Cl2 Simple covalent substance Melting point of -101 oC Boiling point of -34oC Gas at room temperature and pressure
Describe pentane
C5H12 Simple covalent compound Melting point of -130 oC Boiling point of 36oC Liquid at room temperature and pressure
Diamond contrast describe
Giant covalent substance
Have to break covalent bonds between atoms to turn to liquid or gas
Never really melts
Sublimes at over 3600oC
Melting point and boiling point determined by?
Strength of attraction between particles
When will a substance conduct electricity
If it has charged particles that are free to move
How soluble a substance is water depends on?
Type of particles it contains
Water polar solvent so substances that are polar or charged will dissolve in it well whereas non-polar or uncharged substances won’t
Ionic bonding
Examples
NaCl
MgCl2
Ionic bonding
Melting and boiling?
High
Typical state at room temperature and pressure
Ionic bonding
Solid
Ionic bonding
Liquid and solid conductivity
Solid doesn’t because ions held in place
Liquid does ions are free to move
Ionic bonding
Water solubility
Yes
Simple covalent
Molecular
Examples
CO2
I2
H2O
Melting point and boiling point of simple covalent molecular molecules?
Low because it involves breaking intermolecular forces but not covalent bonds
Typical state at room temperature and pressure
simple covalent molecular molecules
May be solid like I2 but usually liquid or gas
simple covalent molecular molecules
Does solid conduct electricity?
No
simple covalent molecular molecules
Does liquid conduct electricity?
No
simple covalent molecular molecules
Is it soluble in water?
Depends how polarised the molecule is
Giant covalent macromolecular examples
Diamond
Graphite
SiO2
Giant covalent macromolecular
Melting and boiling points?
High
Giant covalent macromolecular
Typical state at room temperature and pressure?
Solid
Giant covalent macromolecular
Does it conduct electricity?
No except graphite
Giant covalent macromolecular
Does the liquid conduct electricity?
N/A
Sublimes rather than melting
Giant covalent macromolecular
Is it soluble in water?
No
Metallic examples
Fe
Mg
Al
Metallic melting and boiling point?
High
Metallic typical state at room temperature and pressure?
Solid
Metallic does it conduct electricity when solid?
Yes delocalised electrons
Metallic does it conduct electricity when liquid?
Yes delocalised electrons
Is metallic soluble in water?
No
What can you predict using a materials properties?
It’s structure
Substance X has a melting point of 1045K. When solid, it is an insulator, but once melted it conducts electricity. Identify the type of structure present in substance X
Workings
1) substance X doesn’t conduct electricity when solid but does conduct electricity once melted so looks ionic. Fits with high melting point
2) isn’t simple covalent because of high melting point. Isn’t metallic because doesn’t conduct electricity when solid isn’t giant covalent as conducts electricity when melted
Substance X has a melting point of 1045K. When solid, it is an insulator, but once melted it conducts electricity. Identify the type of structure present in substance X
Answer
Substance X must be ionic
