Chapter 2 Flashcards
What are ions?
Positively or negatively charged atoms
When are ion formed?
When electrons are transferred from one atom to another
What are cations?
Positively charged ions
What are anions?
Negatively charged ions
Generally, what is the charge on a metal ion equal to?
Its group number
Generally, what is the charge on a non-metal ion equal to?
Its group - 8
What does electrostatic attraction do?
It holds positive and negative ions together
What is an ionic bond?
The strong electrostatic attraction between 2 appositely charged ions
When does an ionic compound form?
When oppositely charged ions for an ionic bond
What 2 things affect the strength of an ionic bond?
The ionic charges and the ionic radii
How do ionic charges affect the strength of the ionic bond?
The greater the charge on an ion, the stronger the ionic bond
What is the relationship between the charge dennsity of an ion and the strength of an ionic bond?
The higher the charge density, the stronger the ionic bond
What is the relationship between the ionic radii and the strength of an ionic bond?
Smaller ions pack together closer together than large ions, so small packed ions have stronger ionic bonding than larger ions, which sit further apart
What happens to the ionic radius as you go down a group?
It decreases
What are isoelectronic ions?
Ions with different atoms with the same number of electrons
What happens to the ionic radius of isoelectronic ions as the atomic number increases?
The ionic radius decreases
What do dot-and-cross diagrams show?
The arrangement of electrons in an atom or a bond, and which atom the electrons in a bond originally came from
What structures do ionic compounds form?
Giant ionic lattice structures
What structure are ionic crystals?
Giant lattices of ions
What is a lattice?
A regular structure
What is a giant lattice?
A structure made up of the same basic unit repeated over and over again
Why does a giant lattice form?
Because each ion is electrostatically attracted in all directions to ions of the opposite charge
As ionic compounds have high melting points, what does this tell you?
The ions are held together by strong attraction
Why is an ionic compound soluble in water, but not in non-polar solvents?
The ions are pulled apart by polar molecules as they are charged
Why can ionic compounds conduct when molten, but not when solid?
Because their ions are fixed when solid, but free to move when molten
Why can’t ionic compounds be shaped?
Because the repulsion between ions would be very strong, so ionic compounds are brittle
When you electrolyse a green solution of copper chromate on a piece of wet filter paper, what colour does the filter paper turn at the cathode and anode?
Blue at the cathode and yellow at the anode
What does isoelectronic mean?
Having the same number of electrons
When are molecules formed?
When 2 or more atoms bond together, that are held by covalent bonds
What is a covalent bond?
A covalent bond is when atoms share electrons
How many electrons make up a covalent bond?
2 electrons
Why is 8 electrons (a full outer shell) good for the atom?
It is very stable
In covalent bonds, what is the positive nuclei attracted to?
The area where the shared electrons are
What is the bond length?
The distance between the 2 nuclei is the distance where the attractive and repulsive forces balance each other (bond length)
What is the relationship between the electron density and the bond length?
The higher the electron density between the atoms, the stronger the attraction between the atoms and the shorter the bond length
What is the relationship between bond enthalpy and bond length?
The shorter the bond length, the higher the bond enthalpy is
What is dative covalent bonding?
Where both electrons come from 1 atom. One atom donates 2 electrons to a bond
How is the ammonium ion NH4 + formed?
When the nitrogen atoms in an ammonia molecule donates a pair of electrons to a proton H+.
How is dative covalent bonding shown in a diagram?
By an arrow pointing away from the donor atom
What does the molecular shape depend on?
The number of pairs of electrons in the outer shell of an atom
Why do electron pairs repel each other?
Because electrons are all negatively charged, so electron pairs will repel.
What repel more, lone pairs of electrons or bonding pairs of electrons?
Lone pairs of electrons
Why are lone pair/lone pair angles the biggest in molecules?
Because they repel each other the most
Why are the bonding pair/bonding pair angles the smallest in molecules?
They repel each other the least
In methane (CH4) where there are no lone pairs of electrons, what are all the bond angles?
109.5 degrees
In ammonia, where there is 1 lone pair of electrons, what are all the bond angles?
107 degrees
In water, where there are 2 lone pairs of electrons, what is the bond angle?
104.5
When there are 2 electron pairs around a central atom, what are the bond angles?
180 degrees
What are linear molecules?
When the bond angle around an atom is 180 degrees
When there are 3 electron pairs around a central atom and no lone pairs, what are the bond angles?
120 degrees
What is a trigonal planar?
When there are 3 electron pairs around a central atom and no lone pairs
When there are 3 electrons pairs around a central atom, one of which is a lone pair, what is it referred to and what is the bond angle?
It is referred to non-linear, and the bond angle is 119 degrees
What is a tetrahedral?
When there is 4 electron pairs around a central atom, and no lone pairs
What is a trigonal pyramidal?
When the is 4 electron pairs around a central atom, one of which is a lone pair
What is a trigonal bipyramidal?
When there is 5 electron pairs around a central atom (no lone pairs).
What is a seesaw?
When there is 5 electron pairs around an atom, one of which is a lone pair
What is a distorted T?
When there are 5 electron pairs around an atom, 2 of which are lone pairs
What is the bond angle of a distorted T?
87.5 degrees
What is an octahedral?
When there are 6 electron pairs around a central atom
What is a square pyramidal?
When there are 6 electron pairs around a central atom , one of which is a lone pair
What is a square planar?
When there are 6 electrons pairs around a central atom, 2 of which are lone pairs.
How many atoms can great lattices often contain?
Billions and billions of atoms
Why are huge great lattices much stronger than simple covalent molecules?
The electrostatic attraction holding the molecules together is much stronger
Why can carbon and silicon form giant lattices?
They each form 4 strong covalent bonds
What are the 5 main properties of giant structures?
- High melting points
- Hard
- Good thermal conductors
- Insoluble
- Can’t conduct electricity
Why can’t giant structures conduct?
No charged electrons(all are in covalent bonds)
Why are giant structures good thermal conductors?
Vibrations travel easily through stiff lattices
Why are giant lattices insoluble?
They don’t contain ions
Why can graphene conduct electricity?
Each carbon atom shares 3 electrons with other carbons, which one left to move freely, allowing it to conduct.
How are the carbon sheets in graphene held together?
By relatively weak forces
What are the positive metal ions attracted to?
The delocalised negative electrons
What is metallic bonding?
When postive metal ions are attracted to negative electrons
Why are metals insoluble?
Becuase of the strength of the metallic bonds
Why are metals malleable?
There are no bonds holding specific ions together
Why are metals good conductors?
Their electrons are free to move around and carry a charge
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond.
What element is the most electronegative element?
Fluorine
Does electronegatvity increase or decrease up a group?
It increases, as electronegative elements have small atomic radii
Does electronegativty increase or decrease along a period?
It increases, as electronegative elements have high nuclear charges
In a covalent bond, how do the bonding electrons between 2 nuclei sit when the atoms have similar electronegativities?
Roughly in the middle, so the bond will be non-polar
Why are the covalent bonds in diatomic gases non-polar?
Because the atoms have the same electronegativity value
In a polar bond, what does the electronegativity between the atoms cause?
A dipole
What is a dipole?
A difference in charge between 2 atoms caused by a shift in electron density
What does a ‘Pauling Scale’ allow you to predict?
The % ionic character in a bond
What is a polar molecule?
When the polar bond gives the whole molecule a permanent dipole
Does a molecules having polar bonds mean that the molecule is a polar molecule?
Not always
Give an example when a molecule is not a polar molecule, but has polar bonds:
C02. The delta- signs on the oxygen atoms face in opposite directions, and therefore cancel out
What are intermolecular forces?
The forces between molecules
Are intermolecular forces stronger or weaker than covalent, ionic or metallic bonds?
They are much weaker
What are London Forces?
Instantaneous dipole-induced dipole bonds, which cause all atoms and molecules to be bonded to each other
How does a temporary dipole come about?
At any particular moment electrons in an atom are more likely to be on one side than the other. This dipole can then induce another temporary dipole in the opposite direction. The dipoles are then attracted to each other
What is a simple molecular structure?
When atoms are held in pairs by strong covalent bonds, which are then held together in a molecular lattice arrangement by London Forces
Are London Forces stronger in smaller or larger atoms?
They are stronger in larger atoms, as larger atoms have larger electron clouds, making the forces stronger.
What are the alkane molecules held together by?
London forces
What is the relationship between the length of the carbon chain and the strength of the London forces?
The longer the carbon chain, the stronger the forces as there is more molecular surfaace contact and more electrons to interact
What causes permanent dipole-permanent dipole bonds?
The S+ and S- charges on molecules cause weak forces of attraction between molecules
Can a molecule have permanent dipole-permanent dipole forces as well as London forces?
Yes
What is the strongest type of intermolecular force?
Hydrogen bonding
When is the only time that hydrogen bonding occurs?
When hydrogen is bonded to either fluoring, nitrogen or oxygen, as they are very electronegative, which draws the bonding electrons away from the hydrogen atom
How does hydrogen bonding work?
The bond is so polarised that the hydrogen atoms form weak bonds with the lone pair of electrons on the oxygen, fluorine or nitrogen atom
How are hydrogen bonds represented on a diagram?
As dotted lines
Why is the boiling point of HF much greater than the boiling points of HCl and HBr?
Because only hydrogen flouride contains hydrogen bonds, which require a large amount of energy to overcome
Why does hydrogen iodide have a higher boiling point than hydrogen bromide?
The number of electrons increases, so the strength of the London forces increases.
Why does water have an extremely high boiling point compared to the other group 6 hydrides?
Because water contains hydrogen bonds.
Explain why ice floats:
- In ice the molecules are arranged so that there is a maximum number of hydrogen bonds (wastes a lot of space)
- As the ice melts, some of the hydrogen bonds are broken allowing molecules to fill the spaces.
- This makes ice much less dense than water
Why do alcohols have low volatilities?
Hydrogen bonding due to their polar groups
For a substance to dissolve in another, what 3 things have to happen?
- Bonds in substance and solvent have to break
- New bonds have to form between the substance and the solvent
What are polar solvents?
Solvents made up of polar molecules, such as water
When an ionic substance is mixed with water, where are the ionic substances attracted to?
Oppositely charged ends of the water molecules. The ions are pulled away from the ionic lattice by the water molecules.
What is hydration?
When ions are pulled away from an ionic lattice by water molecules
Why don’t some ionic substances dissolve?
Because the bonding between their ions is too strong
How do alcohols dissolve in water?
The polar O-H bond in alcohols is attracted to the polar O-H bond in water, causing hydrogen bonds to form
What is the relationship between the length of the carbon chain and how soluble the alcohol is?
The longer the carbon chain, the less soluble the alcohol as the carbon part of the alcohol is not attracted to water
Why don’t all molecules with polar bonds dissolve in water(halogenoalkanes)?
The hydrogen bonding between water molecules is stronger than the bonds that would for with halogenoalkanes, so halogenoalkanes don’t dissolve
Why do non-polar substances dissolve best in non-polar solvents?
They form similar bonds, so tend to dissolve in them
Why don’t non-polar substances dissolve well in water?
Water molecules are attracted to each other more strongly than they are to non-polar molecules such as iodinge
What is the most popular non-polar solvent?
Hexane
How are hexane molecules bonded to each other?
By London forces
What are the melting and boiling points of a substance determined by?
The strength of the attraction between its particles (the intermolecular forces)
When will a substance conduct electricity?
When it contains charged particles that are free to move
What are the main properties of ionic bonding?
- High melting point
- Doesn’t conduct when solid
- Conducts when liquid
- Soluble in water
What are the main properties of simple covalent bonding?
- Low melting point
- Usually liquid or gas
- Doesn’t conduct at all
- Only soluble when it contains hydrogen bonds
What are the main properties of giant covalent bonding?
- High melting point
- Not soluble
- Only graphite conducts
What are the main properties of metallic bonding?
- High melting point
- Conducts when solid and liquid
- Is not soluble in water
